Drawing Doom Chairs. Published by Fisher. Son & C° Caxton. London. June 23. 1827. THE CABINET M AKE R UPHOLSTERER, AND COMPLETE DECORATOR, WITH GEOMETRICAL SECTIONS, AND FURNITORE COLOURED ENGRAVINGS, AND A PERFECT GLOSSARY OF TECHNICAL TERMS USED IN CABINET MAKING , BY PETER NICHOLSON. fonbmt: EISHER & CAXTON. INTRODUCTION. The want of a complete treatise, by the aid of which all the various articles of Cabinet Furniture may be readily executed by the Mechanic with precision and tasteful elegance, and the designs made clearly intelligible to the Gentleman and the Amateur, has been long and sensibly felt as a serious inconvenience. Aware of this deficiency, the principal object of the Author, in the following Essay, is to supply the desideratum, by furnishing such a variety of designs as shall illustrate the principles upon which these articles are constructed, and afford every requisite information on this important and interesting subject. Before, however, he proceeds to enumerate the contents of this work, it may be necessary for him to prepare in some degree the mind of the reader for an advantageous perusal, by pointing out to him the nature and extent of his scientific researches. In the construction of objects, our first and chief consideration is utility * but when our actual wants are fully supplied^ we naturally seek further gratification in their varied forms and external ornaments ; yet in the choice of figure, we must' nevertheless, bo always governed by certain criteria, founded upon peculiar associations. It is one of the grand designs of this treatise to put the reader in possession of these principles, as they will prove eminently useful to him, both as an artisan and an amateur, by directing his attention to classic forms and tasteful embellishments. Every sensible object irwfche phenomena of surrounding nature, must necessarily be contained under some external form and appearance. But as it is desirable that the eye should be pleased, and the imagination gratified, the particular figure under which a thing presents itself can never be a matter of indifference; for it is a well-known fact, that while the contour of some VI INTRODUCTION. bodies communicate agreeable sensations, others are incapable of producing any ; while many again are wholly repugnant to every possible agreement with our feelings and ideas. But indeed, allowing, even in this instance, that we were satisfied, the illusion would not be lasting. The charm of novelty is gradually dissolved, and a repetition of the same object, however pleasing at first, soon loses its effect, and in the course of time ceases altogether to attract or delight. In order, therefore, to rouse the dormant spirit of curiosity, and rekindle the dying embers of exhausted pleasure, it becomes necessary to seek out fresh sources of intellectual gratification; and thus the powerful and inventive genius of man is called forth, and kept in constant and persevering exertion. It is a trite and oft-repeated observation, that “ there is nothing new under the sun;” hence many imagine that every possible variety has already been discovered ; that nature at length is completely exhausted ; and that nothing- further remains to be produced. This, however, is far from the truth; since although the number of forms may in some degree be said to be limited, their combinations are almost infinite. It is a knowledge of this interesting fact, that enables us to construct new figures, and to fashion them according to our desire; yet our taste must at all times be governed by certain principles, that are fixed upon as sure a foundation as are the sublime propositions contained in the Elements of Euclid. We shall therefore endeavour to establish some specific rule by which our judgment may invariably be directed, and which may serve both as a test of merit and as a standard of excellence. A judicious selection, then, of the beautiful forms and varieties of nature, and a strict adherence to curve lines produced by organical description, ought to constitute our elements of taste.* It was a knowledge of these principles that inspired the genius of the illustrious artisans of Greece, and enabled them to construct those sublime works, which remain, even to this day, the proud and lofty monuments of unrivalled excellence and universal admiration. The labours of remote antiquity would never have been held in such profound veneration, had not the scientific principles, which guided the hand of the artist, been clearly visible in those splendid examples that have been handed down to posterity, and have hitherto withstood the destroying hand of time. * The pleasing forms and wonderful variety of systems of curves, produced by Mr. Jopling’s ingenious contrivances, originally suggested by an article in the Imperial Magazine for 1822, are truly astonishing. INTRODUCTION. VII A caiefiil and an attentive study, therefore, of the works of the ancients, is most eminently useful to such as are desirous of improvement in the art of decoration ; and in older to furnish an example, we shall, in the present work, endeavour to construct our figures upon geometrical principles, drawing them fiom the purest classic models, selected from those precious remains of antiquity which were executed when the arts and sciences were in the very zenith of perfection. Mere language alone is insufficient to convey an adequate idea of those images that are conceived in the mind of one person, to the understanding of anothei . for since we know that even such simple terms as a point or an angle cannot be strictly or accurately defined, it may be easily inferred, that oui ideas of many forms and positions, though easily conceived, cannot be expressed intelligibly by words. From this acknowledged defect of written desciiption, we are, therefore, compelled to have recourse to some sensible mode of representation, by which the analogy, positions, and connexions of the separate parts of a body, may be clearly exhibited to the eye. Two distinct modes of representation have accordingly been invented, by which the forms, positions, and measures of the original parts of a complex object may be correctly ascertained. One is denominated Perspective, the other Orthographical Projection, and each possesses a peculiar advantage of its own. By the aid of perspective drawing, viewed from a certain point, the object is exhibited to the eye in such a manner as to produce the same image, and the same effect on the imagination, as the real object itself, when viewed from a corresponding point. By means of an orthographical projection* although the object be not so agreeably represented to the eye, the exact measures of all its parts can be asceitained with incomparably less trouble than by perspective repre- sentations. Orthographic projection, as applied to the representations of the circles of the sphere, has been long understood; but general representations are only of modern date. The French method of projection, by means of co-ordinate planes and traces, is very ingenious, and is in general use among them ; but a more commodious method, by means of an intersecting line, was first introduced into Rees’ Cyclopaedia by the author of this work, Mr. Peter Nicholson, in the year 1813. 3 his gentleman has been successful in applying his method to many architectural solids, floors, roofs, &c. (see his Builder’s Director.) Had Professor Farish been acquainted with these principles, he never would have given so imperfect a system, under the unmeaning name of Isometrical Perspective. — E d. VIII INTRODUCTION. A species of orthographical projection has been long understood and practised by Cabinet-makers, Carpenters, Joiners, Architects, and artisans concerned in Building, by means of plans, sections, and elevations. A Plan is a representation of all the horizontal and other lines in the height of the surface of an object upon a horizontal plane, by means of lines, drawn perpendicularly from all, or a sufficient number of points in these lines, to the said horizontal plane. A Section is a projection on a vertical plane, (dividing the object into two parts,) and is formed by lines falling perpendicularly from all the points in the horizontal and other lines of the object on one side of the plane of projection, upon the said plane; shewing, at the same time, those parts of the object that are really cut, or that coincide with the plane of projection. Lastly, an Elevation is a projection, upon a vertical plane, placed before the object by lines falling perpendicularly from all the points in the horizontal or other lines in the surface of the object to the plane of projection. Hence, the projecting rays in a section, and in an elevation, are parallel to the horizon; and hence, also, when the lines of the object are parallel to the • plane of projection, the lines of the projections are equal and similar to the corresponding lines of the object. Plans and elevations are eminently useful, for the purpose of enabling workmen to comprehend the designs of rectangular objects, especially where the object is simple, and all the faces of the three planes of projection are parallel to one or other of the faces of the object. The different forms in the three planes being represented by equal and similar figures, furnish an easy method of finding the dimensions. Yet, how useful soever this mode of representation may be to a tradesman, it does not convey to others, who are unacquainted with this species of drawing, any idea of the design; nor is it, after considerable study, that even proficients in new designs can connect all the different parts in their imagination, such as they would be in the original object. In complex, designs, many plans, sections, and elevations are required to explain them. Much labour and attention are therefore spared by an orthographical projection, which not only connects the several parts, but also gives their due proportions. As the construction of works, as well as every kind of delineation, requires the aid of mathematical principles, we have commenced our treatise with Practical Geometry, confining ourselves to such problems as may be found necessary, either to direct the mechanical execution, or to represent the object intended to be shewn. INTRODUCTION. IX In these two different species of projection, the art of perspective enables us to explain our designs in the most natural and in the most agreeable manner, both to the eye and to the understanding of others, and a sufficient number of its rudiments is given and illustrated, by their application to the subjects included in this treatise. In order, however, to proceed with the utmost certainty in explaining to workmen the forms and positions of all the parts of a complex object, which are intended to be executed in every part, agreeably to certain dimensions in feet and inches obtained from a scale ; we have deemed it requisite, without referring to more than one drawing, to explain as many of the principles of orthographic projection as may be required by the designer to communicate, and by the workman to understand, the complete intention of the design. After having explained the principles of representing objects, we shall next proceed to the construction of Furniture; in which, from certain given parts, the remaining parts are found. This is a branch of solid Geometry, the knowledge of which is indispensable. It is equally useful to the Cabinet- maker, the Carpenter, and the Joiner. The three grand branches which this work is designed to embrace, are, Cabinet-making, Upholstering, and Decorating. In these depart- ments it is not intended to direct the Artist in his mere mechanical operations, for with these it is presumed he is already fully acquainted; but to place before him various scientific principles, that on all occasions may become his guide. To the Cabinet-maker will be presented certain specific and permanent rules, equally applicable to dimensions and proportions in all their variety. These in their result will invariably ensure order, harmony, symmetry, and beauty, from which the eye receives gratification, and communicates pleasure to the mind. To the Upholsterer such directions will be given as will imprint on his work the footsteps of elegance and taste; so that while fancy dictates new modes of embellishment, an imperishable grandeur may associate with all his performances. The Decorator must always, in a certain degree, be exposed to the freaks of caprice, and the ever varying mutability of fashionable taste. With him, invention and genius are indispensable qualifications; and these, when combined, give perfection to his art. But, amidst this instability, there are certain principles, from which his lines, his curves, his festoons, his drapery, X INTRODUCTION. Vs ^ r t> his combinations, and his arrangements, must not depart. With these principles it is the design of the Author to furnish him. The Plates which embellish this volume, being entirely from original inventions and drawings, will have a particular claim upon public attention ; especially as they will be numerous, and executed in a superior style of elegance. But notwithstanding their originality, the explanations and references which accompany each, will render the whole perfectly intelligible; and their utility and advantage must be obvious to all who reflect upon their import and application. To furnish the reader with every possible information on the subjects of which this volume treats, being the primary and anxious design of the Author, he flatters himself, that, from the principles developed, and the incalculable variety of designs to which they may be applied, it will be found a useful instructor, even should a different taste prevail. Amidst the fluctuations of tasteful elegance, he will watch the kaleidoscope of fashion in all its movements, while this work is passing through the press, and avail himself of every appearance that may be deemed worthy of preservation. But whatever changes the progress of time may introduce, of this truth he has an indubitable assurance, that although fashions are fickle and capricious, yet the scientific principles, upon which alone these fashions are built, are imperishable and eternal. London, May 1st, 1826 THE CABINET-MAKER, UPHOLSTERER, AND COMPLETE DECORATOR. GEOMETRY. Geometry forming the basis on which our superstructure is to be raised, has the first claim on our attention. This exalted science appears to have been understood in some degree by the ancient Egyptians, as we are informed by Herodotus: and indeed, in a country like Egypt, subjected to the annual innundations of the river Nile, which destroyed all the landmarks either by the impetuosity of its waters, or by the deposition of mud or sand, a practical knowledge of Mensuration became necessary, in order to restore to the proprietors of the lands their proper portions, which had been blended into one undistinguishable surface. Hence, the word was originally limited to the science of Mensuration, for it is compounded of two Greek words, yv, earth , and /xerpew, to measure ; which, together, literally signify, measuring of the earth. But the Geometry of the Greeks is the science which treats of the properties of magnitudes, considered either as Lines, Angles, Surfaces, or Solids. 12 CABINET-MAKER, UPHOLSTERER, It is to this latter people that we are indebted for the perfection of this sublime branch of knowledge, and “ it is remarkable (says Professor Playfair) that the writings of Euclid, at the distance of two thousand years, continue to form the most approved introduction to the mathematical sciences.” Having thus given a brief sketch of the origin of Geometry, we shall now collect as many of its simple rules as will be useful to the Cabinet-maker in the formation of working drawings, and shall therefore proceed to PRACTICAL GEOMETRY. Practical Geometry treats of the methods of drawing lines in all manner of directions, and of the description of figures according to certain simple properties enumerated in words called Definitions. Def 1. Every material substance, in the language of Geometry, is termed a Solid. Def. 2. The external appearance (or outward face) of a solid is called a Surface. Def. 3. When a surface is divided, either in reality or in imagination, into two parts, the division is termed a Line. Def. 4. When two lines cross one another, the intersection is termed a Point. Surfaces are therefore merely the conceived divisions of a solid, lines are the divisions of a surface, and points are those of a line, into parts, but have no separate existence as substances. The lines and points of the diagrams of the practical Geometer are, however, real surfaces, because it is necessary that they should be visible ; but these are treated in the science as if they were metaphysically correct. Def 5. If while a line revolves round its two extreme points, every intermediate point remains in the same place, or point of space, the line is called a Straight Line. Cor . 1 . Hence, one straight line cannot meet another straight line in more than one point, unless they coincide in every point. AND COMPLETE DECORATOR. 13 Cor . 2. Hence, two straight lines cannot enclose a space. Cor. 3. Hence, if the position of two points in a straight line be determined, the position of the whole line is determined, for only one straight line can pass through these points. The definition of a straight line, in Euclid, as it Is translated from the Greek text, is obscure; a straight line, or right line, is defined to be a line which lies evenly between its extreme points, the word “ evenly” standing as much in need of an explanation, as the word straight or right, which it is intended to define. If the word equally had been used by the translator instead of “evenly,” the sense would have been quite as agreeable to the original text, and, though not explicit, would seem to imply the very idea of a straight line as we have defined it; viz. “a straight line is that which lies equally between its extreme points,” which means, that it is alike related on all sides of the surrounding space. Professor Playfair’s definition is excellent, it is as follows : If there he two lines which cannot coincide in two points without coinciding altogether , each of them is called a straight line. The objection to this is, that we are under the necessity of having recourse to lines instead of a line. This might have been avoided by supposing a line to be divided into any two parts, then if these parts could not coincide in two points without coinciding altogether, the line is a straight line; but the idea of cutting the line into two segments is not altogether agreeable. If there be any objection to the definition of a line which we have given, the same must apply to the definition of solids generated by revolving a plain figure about an axis, as a cone is generated by a right-angled triangle. Def. 6. A line, in which, if any two points be taken, and if the intercepted portion, however small, be not straight, such a line is called a Curve. Def. 7. A Mixed Line is that which is compounded of straight and curve lines. Def. 8. Linear Extension is the distance between one point and another, along a straight line between them, and this is also called the Distance of the Points. Def. 9. A Plane, or Plane Surface, is that which will every where coincide with a straight line. It is a curious fact, however, that though a surface may admit of two straight lines being drawn in that surface through any point in it, yet the surface may not be a plane, but if the surface admits of three straight lines being drawn upon it through any point, the surface is necessarily a plane. Two straight lines, which meet each other, are always in a plane. 14 CABINET-MAKER, UPHOLSTERER, Def 10. An Angle is the opening or space contained between two lines which meet each other. Def. 11. A Rectilinear Angle is that w ich is contained by two straight lines, which are not in the same straight line. All angles henceforth expressed are supposed to be rectilinear, unless the contrary is stated. Def. 12. The point where two straight lines, which form an angle, meet each other, is called the Vertex. Def. 13. If in two angles, in which, if the one be applied upon the other, so that when their vertices and one of their containing lines coincide, the two remaining lines coincide also, these Angles are said to be Equal. Hence the length of the lines, containing an angle, do not make the angle greater or less by being longer or shorter. Def. 14. If two equal angles have a common line of separation, and the other two containing lines in the same straight line, each of these angles is called a Right Angle; likewise the common line is called a Perpendicular to the straight line formed of the other two. Def. 15. If the contained space of an angle be applied upon that of a right angle, so that the two vertices and one of the containing lines of each may coincide, and the other containing line of the angle applied fall between the containing lines of the right angle, the angle thus applied is called an Acute Angle. Hence an acute angle is less than a right angle; for the right angle contains the acute angle and another angle besides. Def. 16. If the contained space of an angle be applied upon that of a right angle, so that the two vertices and one of the containing lines of each may coincide, while the other containing line of the angle applied falls without the space contained by the two lines of the right angle, the angle thus applied is called an Obtuse Angle. Hence an obtuse angle is greater than a right angle; for the obtuse angle contains not only the right angle, but likewise another angle besides the right angle. AND COMPLETE DECORATOR. 15 Def. 17. If two lines, in the same plane, are so situated that they cannot form an angle, however far they may be extended, these two lines are said to be Parallel. Def. 18. A Figure is that which is bounded by one or more lines, called the sides or edges of the figure. Def. 19. A Rectilineal Figure is that which is bounded by straight lines. Here we shall observe, that all boundaries are supposed to be rectilineal, unless a curve is expressed. » Def. 20. A Triangle is a figure, consisting of three sides, and consequently, of three angles; because an angle is opposite to every side. In respect to the Sides of a Triangle. Def 21. If a triangle has all its sides equal, it is called an Equilateral Triangle. It is easy to prove, and it is almost self-evident, that the angles, as well as the sides of an equilateral triangle, are equal. Def. 22. If a triangle have two of its sides equal, it is called an Isosceles Triangle. Def. 23. If a triangle have no two of its sides equal, it is called a Sealine Triangle In respect of the Angles of a Triangle. Def. 24. If a triangle have one right angle, it is called a Right-angled Triangle. Def 25. If a triangle have one obtuse angle, it is called an Obtuse-angled Triangle. Def. 26. If a triangle have its three angles acute, it is called an Acute- angled Triangle. Def. 27. A four-sided figure is called a Quadrangle, Quadrilateral, or Trapezium. 16 CABINET-MAKER, UPHOLSTERER, Def. 28. If a four-sided figure have one pair of its sides parallel, it is called a Trapezoid. j Def. 29. If a four-sided figure have both pairs of its sides parallel, it is called a Parallelogram. Def. 30. A parallelogram, of which neither the angles nor the sides are all equal, is called a Rhomboid. Def 31. A parallelogram, which has all its four sides equal, but not its angles, is called a Rhombus. Def. 32. A parallelogram, which has one of its angles a right angle, is called a Rectangle. It may be proved, and indeed it is in some measure evident, that all the angles of a parallelogram are equal, and that the opposite sides are equal. Def. 32. A rectangle, which has not all its sides equal, is called an Oblong. Def. 33. A rectangle, which has all its sides equal, is called a Square. Def. 34. Every figure, which has more than four sides, is called a Polygon. Def. 35. A polygon, which has all its sides equal, is said to be Equilateral. Def. 36. A “polygon, which has all its angles equal, is said to be Equiangular. Def 37. A polygon, which is both equilateral and equiangular, if such can be, is called a Regular Polygon. There may be some objections to this definition, which is that usually given, for it is easy to conceive, that all the sides of a figure may be equal, but not that the angles are equal at the same time. This coincidence of the equality of sides and angles requires demonstration, therefore, in order to qualify it, we have inserted the words, if such can be. Def. 38. A regular polygon, of three sides or angles, is called a Trigon. A trigon is, therefore, the same as an equilateral triangle, for an equilateral triangle may be proved to have its angles as well as its sides equal. Def. 39. A regular polygon of four sides, is called a Tetragon. A tetragon is, therefore, the same as a square, for it may easily be proved, that all the angles of a square are equal, as well as the sides. AND COMPLETE DECORATOR. 17 Def 40. A polygon of five, six, seven, eight, nine, ten, eleven, twelve, &c. sides, is called a Pentagon, Hexagon, Heptagon, Octagon, Enneagon, Decagon, Hendecagon, Dodecagon, &c. Def. 41. A Circle is a plane figure, contained by one line called the Circumference, and this line is every where equally distant from a point in the figure, called the Centre of the Circle. Def. 42. The Radius of a Circle is any straight line drawn from the centre of the circle to its circumference. Def. 43. The Diameter of a Circle is a straight line passing through the centre, and terminated at each extremity by the circumference. Corol. Hence the diameter of a circle is equal to twice the radius. Def. 44. A Chord is any straight line terminated at the two extremities by the circumference. Def. 45. An Arc of a Circle is any part of the circumference. Def. 46. A Segment of a Circle is a portion of a circle contained by an arc and a chord. Def. 47. A Sector of a Circle is a portion of the area contained by two radii, and the arc intercepted between them. E 18 ABINET-MAKER, UPHOLSTERER, PLATE I. Problem I. To bisect a given straight Line de, Figure 2, by a Perpendicular. From the points d and e, as centres, with any equal radii, describe the intersections f and g. Draw fg t intersecting de in the point f, and f is the middle of the line de; and the line fg, which passes through f, is at the same time perpendicular to de. Problem II. From a given Point c, in a given straight Line ab, Figure 1, to erect a Perpendicular. Mark the points c and d in the line ab, equally distant from c, and from each of the points c, d , with any equal radii, greater than cc or c d, describe the intersection d, and draw cd. cd is perpendicular to a b. Problem III. From a given Point g, Figure 3, in a given straight Line a b, to draiv a Perpendicular. From some convenient point i, above the line ab, asa centre, and with the distance ig, describe an arc fgh, meeting ab in h. Join hi; produce hi to f and draw fg, and fg is perpendicular to ab. Problem IV. From a given Point c, Figure 4, to draiv a Perpendicular to a given Line g h. From the point c, describe an arc de, so as to intersect gh in the points d and e. From each of the points d and e, as centres, with any equal radii greater than the half of de, describe arcs intersecting each other in f, and draw the line c f: cfis perpendicular to gh. / / ut \ tic y// ( reometr } y PISHES. SON, & C? LONDO.fr, 183* AND COMPLETE DECORATOR. 19 Problem Y. At a given Distance e f, Figure 5, to draw a straight Line parallel to a given straight Line ab. From any two convenient points e,f, in the line ab, with the radius e f, describe arcs at c and d , and draw the straight Line CD to touch the arcs at c and d. c d is parallel to a b, as required. Problem VI. At a given a, Figure 6, No. 1, in the straight Line Ab, to make an Angle equal to a given eDf, No. 2. From the point d, with any convenient radius, describe an arc ef and with the same radius, from the point a, describe the arc be. Make the arc be equal to ef and draw a c. b ac is the angle required. Problem YII. To bisect a given Angle abc, Figure v. that is, to divide it into two equal Parts. Let c be any point in bc; make ba equal to bc.; and from the points a and c, with any equal radii, describe two arcs so as to intersect in d, and draw the line dB. d b will divide the angle abc into two equal angles. This is called bisecting the angle. Problem YIII. To divide a straight Line a b, Figure 7, into any number of equal Parts. Draw any line ad, and through the point b draw bc parallel to ab. Run as many equal parts along the lines a d and b c, as the line a b is to contain equal parts. In this example it is required to divide the line a b into six equal parts. Join the point a to the last division c, and through the points 1, 2, 3, &c. in ad, draw lines parallel to ac, to intersect the line a b, and a b is divided, as required to be done. 20 CABINET-MAKER, UPHOLSTERER, Problem IX. Upon a given straight Line a b, Figure 8, to describe an Equilateral Triangle. From each of the points a and b, as centres, and with the radius ab, describe an intersection c on one side of the line. Join ca and cb, and abc is the equilateral triangle required. Problem X. In a given Triangle abc, Figure 9, to inscribe a Circle. Bisect any two of the angles a and b. From the point e, where the bisecting lines meet, draw e h perpendicular to bc, on any one of the sides. From the centre e, with the radius e h, describe the circle hik, and the circle hik will touch the three sides of the triangle abc, as required. Problem XL Upon a given straight Line bc, Figure 10, to describe a Pentagon . Bisect bc by the perpendicular Iiy. Draw c i parallel to hv, and make c i equal to ch. Join b *, and produce b« to l, making il equal to ic. From the centre c, with the distance cl, cut the line h f in f. From f, as a centre, with the radius fb or fc, describe the circle abcde; repeat bc within the circum- ference, so that the extremities of every two adjacent chords may meet, and the lines thus drawn will divide the circumference into five equal parts. If a pentagon be inscribed in a circle, it is very easy to inscribe a decagon, by bisecting the sides of the pentagon by perpendiculars, and mining the points where the perpendiculars cut the circumference to the extremities of the chords of the pentagon, as in the figure aA,bB,cc,dv>,eE,a. Problem XII. In a given Circle , Figure 11 ,to inscribe a Triangle, a Hexagon, or a Dodecagon. Apply the radius of a circle to the circumference as connected chords, and it will contain the radius six times, as ab, bc, cd, de, ef, fa. Bisect AND COMPLETE DECORATOR. 21 each of the Arcs in the points a, b y c , d, e,f and join these points to the extremities of the chords of the hexagon, and a dodecagon will be obtained. In this manner may the circle be divided into 24, 48, &c. parts, always doubling the number of sides. GENERAL OBSERVATION. Any regular polygon, inscribed in a circle, being once obtained, we may double the number of sides, and double this last number again, and so on, as often as we please; and thus, if we have a triangle inscribed in a circle, we may have the series of polygons, having 3, 6, 12, 24, 48, &c. sides. If we have a pentagon inscribed in a circle, we may have the following series of Polygons, having 5, 10, 20, 40, &c. sides. If we have an octagon inscribed in a circle, we may have the series of polygons, having 4,8, 16,32, &c. sides; and thus we have direct rules for dividing a circle into 3, 4, 5, 6 equal parts, or any polygon, of which the number of sides is expressed by any term of a geometrical progression, of which the [first term is 3, 4, 5, or 6, and the common multiplier 2. Rules for other polygons are neither easy to be described in words, nor to be given in figures of construction. Problem XIII. In a given Circle to inscribe any regular Polygon. Figures 12, 14, 15. Draw the diameter, and divide it into as many equal parts as the polygon is to have sides. Bisect the diameter by a perpendicular, cutting the opposite sides of the circumference. Produce the perpendicular, so that the part without the circle may be three-fourths of the radius. From the extreme point of the part produced, draw a straight line through the second point of division in the diameter to meet the circumference. Join the intersected point in the circumference to the extremity of the diameter, whence the equal parts commence, and the line thus joined will be a p 22 CABINET-MAKER, UPHOLSTERER, chord of the circumference in which it may be contained, as often as required, very nearly. Thus, in Figure 12, the intention is to inscribe in a circle a polygon of seven sides. The diameter gi is divided into seven equal parts. The perpendicular hd is drawn from the centre h, and the radius is divided into four parts, and three are set without the circle from four to seven. A line is drawn from d through the second point 2 in the diameter g i, to meet the circumference in a, and the line ag is the side of a polygon of seven sides; and by inspecting Figures 14 and 15, it will be seen that the same principle extends in all cases. Figure 12 is a heptagon; Figure 14 an enneagon; and Figure 15 an hendecagon. These methods are, however, only near approximations. Problem XIV. In a given Square A BCD, Figure 13, to cut out the largest regular Octagon . Draw the diagonals ad and cd, intersecting each other at i. From the points a, b, c, d, as centres, with the radius a i, equal to half one of the diagonals, cut the sides of the square in the points a , b, c , d, e,fg, h. Join ab, cd, ef, gh , and abcdefgh is the octagon required. Problem XV. To draw a Tangent to a given point c, Figure 16, in the Circumference of a Circle, of which the Centre is a. Join ac. Through the point c draw bd perpendicular to Ac, and bd is the tangent required. Problem XVI. Through three given Points b, a, c, Figure 17, not in a straight line , to draw the Circumference of a Circle. Join the two points b and c to the middle point a. Bisect each of the lines ab, ac, by perpendiculars meeting in h. From the point h, as a AND COMPLETE DECORATOR. 23 centre with the radius bh, ah, or ch, describe a circle bac, and the circumference will pass through the three points b, a, c, as required. Problem XVII. To describe the Arc of the Segment of a Circle , of which the Chord is ac, Figure 17, and the Rise of the Arc the Line d e. Bisect the chord a c by a perpendicular hf, intersecting A c in the point h. Make hb equal to de. Join ab, and bisect ab by a perpendicular hd. From the point h , where the two perpendiculars meet as a centre, with the distance Ab, describe the arc abc, which is that required. Another Method , Figure 19. Having set off the perpendicular from the middle of the chord to the point c in the circumference; fasten two laths, ae, ec, together, so as to intersect at c, and the edges to he on the points b and d. Brace these laths together by a cross-piece bd, so that the angle bcd may be immoveable. Bring the point c to b, and move the apparatus round, so that the leg a c may run upon the point or pin at b, and the leg c e upon the point or pin at d ; then a pencil held at c, in the act of moving, will describe the curve required. This method may be used where the radius would extend beyond the space upon which the operation is required to be performed. , Problem XVIII. To describe a Gothic Arch to any Width , ab, Figure 20, and Perpendicular Height i c in the middle of a b, so that the two Sides may meet in any given Angle in the Point c. Produce ci to g. Make the angle gcd equal to half of the vertical angle. Draw a d parallel to i c. In g c make g f equal to a d, and join a f. Divide af and ad each into the same number of equal parts, at the points 1, 2, 3, &c. From g, through the points 1, 2, 3, &c. in a f, draw lines to 24 CABINET-MAKER, UPHOLSTERER, intersect lines drawn from c to the corresponding points 1, 2, 3, &c. in a d, in the points «, b, c, d. Put pins in the points a, a, b,c, d, c, and bend a slip of wood round them, and draw a curve by the edge which touches the pins, and this curve will form one side of the Gothic Arch. In the same manner we may describe the other side. But when one side of a symmetrical figure is obtained by any method, the other side will be found by the following process. From the points a, b , c, d, draw lines parallel to a b, to terminate on the other side of cg, as double ordinates. From the points of intersection in ic, transfer the ordinates on the left of ig to the right hand side of it, and they will reach to h,g,f e. Put in nails as before in the points B,h,g,f, e, c, and bend the slip of wood to touch all the pins, and draw the curve as before. Problem XIX. To describe an Ellipse , to any Length and Breadth , by means of the Instrument called a Trammel , an Instrument well known to Workmen. Figure 21. Let three pins, «, b,\c, in a straight line, be fixed to three cross-pieces through which the rod passes; suppose one of the pieces which contains the pin c, to be fixed to the rod, and the pieces a and b , in which the other two pins are fixed, to be moveable, and the nearest point to the fixed point being of steel, and the other to be a pencil. Move tbe nearest sliding pin from the fixed pin, so that their distance may be equal to half the breadth of the ellipse, and move the pencil point from the fixed pin, so that their distance may be equal to half the length, or to half the longer axis. Place the arms of the trammel so that the grooves may coincide with the axis, the fixed point c of the rod in the groove which coincides with the conjugate axis, and the middle point in the groove over the transverse axis: then move the rod round from the extremity a of the longer axis, and the pencil at a will describe the curve. AND COMPLETE DECORATOR. 25 Figure 22, shews how points may be found in the curve upon the same principle. Let ghi be a slip of pasteboard, or a piece of ivory, straight on the edge gh i. Mark the three points i, h, g on the straight edge, so that i h may be equal to the semi-axis minor, and ig equal to the semi-axis major. Place the point i in the axis minor, and the point h in the axis major, and mark the point g upon the board or paper, which will give one point in the curve Repeat this operation till a sufficient number of points are found ; stick in pins or nails in all the points, bind a pliable slip of wood so as to coincide with all the pins or nails, and draw a curve by the edge of the slip which touches the pins, and it will be the ellipse required. If the points are found on paper, the curve may be drawn through the points with sufficient accuracy by hand. Problem XX. To find any number of continued Proportionals , or to divide ct given Line a c into a Series of continued Proportionals , the first cd being given. Draw a line a c, making any angle ca c, with ac. In a c, cut off a c equal to Ad , and join cc. Draw db parallel to c c , meeting ac in b . From ac cut off a a equal to a b , and draw ab parallel to db , and proceed in this manner, and the line will be divided as required to be done. PLATE II. Problem XXI. Upon a given straight Line to form a Polygon , similar to a given Polygon abcde, Figure 1. Make the straight line ae equal to ae. Find the point d by describing arcs with the radii ad, ed, from the centres a,e ; find the point b , by G 26 CABINET-MAKER, UPHOLSTERER, describing arcs with the radii ab, db, from the centres a,d,c, and find the point c, by describing arcs with the radii b c, dc, from the centres b and d. Join ab , be, cd, de , and abode will be the polygon required. i Problem XXII. To make a Square equal to the Sum of two' given Squares, h, f. Figure 2. Draw the straight line a e and e d perpendicular to ae. Make a e equal to the side of the square f, and e d equal to the side of the square h. Join A d. Draw a b perpendicular to a d, and make a b equal to a d. Find the point c, by describing arcs from b and d, with a radius, each equal to ad. Join bc, and cd; then abcd is the square required. Problem XXIII. Given three straight Lines ab, 6d, be, to find a fourth Proportional. Draw the two straight lines ba, bd, making any convenient angle with each other. Make bd equal to ab, bd equal to b d, cut ba in f so that bf may be equal to b f. Join ad. Cut bd in g, by drawing /g parallel to ad, an 1 bg is the fourth proportional required. Problem XXIV. To divide a given straight Line ab, Figure 4, in the same Proportion as another ca is divided. Draw the two straight lines ac, ab, making any convenient angle with each other. Make ac equal to ac, ab equal to a b, and join be. Cut the straight line ac in the points d, e,f,g, so that ad, ae, af ag be equal to the parts ad, ae, af, ag of the given line ac. Cut the line a b by drawing lines through the points d, e,fg in ac, parallel to cb, and ab will be divided in the same proportion as ac. AND COMPLETE DECORATOR. 27 Problem XXV. Two straight Lines ab, cd, Figure 5, being given , to find a mean Proportional. In the straight line da make db , ba, respectively equal to the lines cd, ab. On da, as a diameter, describe the semicircle dca. Draw be perpendicular to da, and be is the mean proportional required. Problem XXVI. To describe an Elliptic Arch, by finding Points in the Curvature to any Width bc, and Height fe, Figures 6 and 7. Find the point a in ef, produced by making fa equal to f e. Divide b f and b d each into the same number (5) of equal parts. Find the points a, c, e, g, by drawing lines from the points 1,2, 3, &c. in bd bE, to meet the corresponding lines drawn from a through the points 1, 2, 3, &c. in bf. Through the points b, a, c, e, g, e, draw a curve by the edge of a lath or slip of wood. The other half may be found in the same manner, or by transferring them upon the double ordinate. Another Method of finding Points in the Curve of an Ellipse is that exhibited in Figure 8. Let a b and cd be the two axes given in position and magnitude. Draw i n parallel to the greater axis. Find the points a, b, c in the curve, thus draw lines ad, bb', cc, &c. through the centre f. Cut the line in in a, b, c, &c.by producing Fa, eb, fc, &c. Find the point e, by producing fd, and making de equal to fa or fb. From e, with the radius e d, describe an arc. Find the points a, b,c in the arc, by joining g e, h e, i e. Draw aa,bb,cc, and through the points d, a, b, c, a draw a curve. Make Fa', f b', f c respectively equal to Fa, f b, f c, See. HQ CABINET-MAKER, UPHOLSTERER, Problem XXVII. To describe a Parabola , Figure 9, by finding Points a, c, e, g in the curve . Let a b be the base or double ordinate, and c d the height or abscissa. Draw ae and de parallel to cd and ab. Divide ae and de each into (5) the same number of equal parts. Find the points a,c,e,g, by drawing lines fiom 1,2,3, &c. in ae to d, to intersect lines drawn parallel to cd through 1, 2, 3, &c. in de. Draw the curve Aacegjy through the points, and the other side by transferring the ordinates to those on the other side of the abscissa. Problem XXVIII. To draw the Section of an Ovolo Moulding in the Form of a Parabolic Curve A, Figuie 10 being the Point of Projection , and d the Point where the End and Upper Edge of the Fillet below meet each other. Draw ac perpendicular to the length of the moulding, and draw dc at pleasure, depending on the form of the moulding. Divide ac and dc each into the same number of equal parts (5). Find the points a , b, c, &c. by drawing lines through the points 1 , 2, 3, &c. in dc to the point a, to intersect lines drawn parallel to cd through the points 1, 2, 3, &c. in a c, and draw the curve d a b c d Af Problem XXIX. To describe an Hyperbola , having an Ordinate bd, Figure 11, and the Abscissa b c. Draw df and cf parallel to bc and bd. Produce bc to a. Take the point a at a greater or less distance from c, as the curve is required to be flatter or quicker at the point c. Divide bd and fd each into the same number of equal parts (5). Draw lines from 1, 2, 3, &c. in b d to a, to intersect lines drawn through 1,2, 3, &c. in ed to c. Draw a curve through d and through the points a,c,e,g of intersection, and it will be one-half of the curve required. AND COMPLETE DECORATOR. 29 Figure 12, exhibits the application of the hyperbolic curve, in drawing the section of a moulding, bd being the ordinate, dc the abscissa, and the point d being the upper edge of the fillet at its projection. Problem XXX. To describe the Section of a Cima-recta or Ogee Moulding , a, Figure 13, being the Top of the Section , and b the Bottom. Join a b, and divide a b into two equal parts at the point c. Divide c b into six equal parts, and divide bc, ca, each by a perpendicular cf and gd. Cut the line cf by an arc described from b, with the radius of five equal parts. Make dg equal to cf. From the point f with the radius/B, describe the arc bc, and from the pointy, with the radius gc, describe the arc ca, and bca will be the moulding required Problem XXXI. To describe a Semi-reversa or Ogee Reverse , Figure 14, the Points a and b being the Ends of the Section of the Moulding. Divide ab into two equal parts in c, and bisect bc, ca, each by the perpendiculars cf, dg. From the middle points e and d make ef and dg, each equal to Be or ec. From f, with the radius^/B, describe the arc bc, and from g, with the radius gc, describe the arc ca; then bca is the semi- reversa required. Figures 15 and 16, shew the application of the method of describing an ellipse, by points to an ovolo moulding, db and da being semi-conjugate diameters, from which the curve may be described, similar to figures 6 and 7, from the axis. 30 CABINET-MAKER, UPHOLSTERER, PLATE III. Problem XXXII. To Draw the Section of aCima-recta , having theProjecture of its Extremities at a and d. Figure 1. Produce the upper edge of the lower fillet from a to c. Draw dc and a b perpendicular to ac. Bisect bd in f and draw fg parallel to ab; then fg will bisect ac as well as bd. Bisect fg, and through the point of bisection draw the straight line 4-4, meeting ab in 4, and dc in 4. Divide the distance between the point of bisection and each point at 4, into any number of equal parts, for example into 4, and mark the points of division 1, 2. 3 ; also, divide the distance between the point of bisection, and each of the points /and g, into the same number of equal parts, viz. four. From the points a, b, cl, c, draw r lines through the points of division 1, 2, 3, each line to intersect as in the figure, and through the points of intersection draw a curve, and the curve will be the cima-recta required. In the cima-reversa, figure a, the point a is given as the point of greatest projecture, and the sloping direction fb, in the middle of the moulding, is given in position; acdb and dfgh are parallelograms, in which cd and dh are equal; also db and df are equal to each other. Produce dh to m, and make hm equal to hd. Produce dc to e, and make ce equal to cd. Divide hg’ gf> a ^ so a ac ’ eac h into the same number of parts; then proceed to find the points of intersection, and draw the curve as before. Problem XXXIII. To describe a Semiovolar Curve, compounded of Circular Arcs, so as to represent the Section of a Semi-Elliptic Arch to any Length and Height. METHOD FIRST FIGURE 2. Let a b be the length or greater axis. Bisect a b in f, by the perpendicular c r, and make F c and f r each equal to the height of the arch. Draw a n FI 3 Geometry AND COMPLETE DECORATOR. 31 parallel to c r, and cn parallel to ab. Bisect the line an in the point 1, and draw the lines lc and rn, intersecting each other in the point l. Bisect cl by the perpendicular d d, meeting cr in d. Draw de parallel to ab. From the point d, as a centre with the radius dc, describe the arc kcpe. Join e b, and produce e b to meet the circular arc cpe in p. Join p d, intersecting fb in i. Make fh equal to fi, and join dh, which produce to k. From the point h, with the radius h k, describe the arc k a, and from the point i, with the radius i p, describe the arc p b. Then the compound curve a kc pb will resemble the section of an elliptic arch as required. METHOD SECOND, STILL NEARER — FIGURE 3. Let a b be the length or greater axis. Bisect a b in d, by the perpendicular ce. Make dc and de, each equal to the height as before. Draw a 3 parallel to dc, and c3 parallel to ba. Divide ad and a 3, each into three equal parts. From e, through the points 1, 2, in ad, draw the lines ef,eg, and from c through the points 1,2, in a 3, draw the lines cg, cf. Produce c e to h. Bisect g c by the perpendicular b h, and draw the straight line g h, intersecting ab in w. In db make dn equal to b m, and from h, through n, draw hp. Bisect fg by the perpendicular d i, meeting gh in i. Draw i k parallel to a b. From i, with the radius i f, describe the arc fk. Produce ka joined to f; join fi, intersecting da in p. In db make d^ equal to Dp. Produce l# joined to n. From h, with the radius h c, describe the arc gcp. From i, with the radius ig, describe the arc gf. From l, w'ith the radius lp, describe the arc pn. From p, with the radius p¥, describe the arc fa ; and lastly, from q, with the radius q n, describe the arc nb. Problem XXXIV. Given three straight Lines , to find a fourth Proportional. Figure 4. Draw any angle abd. In ba make ba equal to the first of the given lines, and be equal to the second. In bd make bf equal to the third line. Join cf, and draw ad parallel to cf then bd is the fourth proportional. .32 CABINET-MAKER, UPHOLSTERER, Problem XXXV. Given two straight Lines, and one oj them divided into any number oj' Parts, to divide the other into the same number of Parts, and in the same ratio as those of the divided Line. Figure 5. Let a b be the divided line, and c d the undivided line, and let e be a point of division in ab ; also, let hgn be an equilateral triangle. From one of the vertices g-, and upon the adjacent sides, make ga and gb equal to the divided line ab, and draw ab, then ab will be equal to the divided line a b. In ab make ae equal to ae, and join eg. Again, from the vertex g, and upon the adjacent sides, apply the undivided line cd, and draw cd, intersect- ing eg in f, then cd, equal to cd, will be divided in J in the same ratio which a b is divided in e. scholium. It very frequently happens that segments, which have chords of very great extent, but which have a very small height, are required by the Cabinet- maker. It would be very inconvenient in such cases to find a rod of sufficient length to describe the arc, and in others altogether impossible, since the length of the radius would exceed any limited space. It will, therefore, be useful to shew how flat arcs may be described by means of a sufficient number of points being found in the curve, so that it may be drawn by the vertical face of a pliable slip of wood bent round pins placed in the points. We may observe, that, in such cases it is of very little consequence whether the arc be that of a real circle, or that of any other curve, since all curves approach to the arc of a circle near the vertex. Therefore since an error cannot be made visible to the eye by using any curve indifferently, the easiest method must be preferred. The following Problems may be considered as various modes of effecting the object thus circumstanced. AND COMPLETE DECORATOR. 33 Problem XXXVI. To describe the Segment of a Circle by means of Points, having the Chord and the height of the Arc given. Figure 6. Let ab be the chord. Bisect ab by a perpendicular meeting ab in d. Make dc equal to the height of the segment. Draw fe parallel to ab. Join ca and cb. Draw af perpendicular to ca, and be to cb. Also, perpendicular to ab, draw ag and bh, meeting fe in the points g and h. Divide fc, ce, da, db, ag, bh, each into the same number of equal parts, for example, each into four. Join the corresponding points of division in the lines ab and fe. Draw lines from the points 1 , 2, 3, in g a to c, intersecting the corresponding lines drawn from the points in f e to those in a b, in the points a, b, c, d, proceed with the other side in the same maimer ; then fixing pins or nails in the points, draw the curve acb by means of a slip bent round the points, and the curve thus drawn will be the true arc of a circle. Problem XXXVII. To describe the Curve of a Parabola , having a double Ordinate and the Abscissa given. Figure 7. METHOD FIRST — BY POINTS. Let a b be the length or double ordinate. Bisect ab by a perpendicular cd, meeting ab in d. Divide da, db, each into the same number of equal parts, viz. four. Draw e e parallel to ab; also draw a e and b f perpendicular to ab. Through the points 1,2,3, in da and db, draw as many lines perpendicular to a b. Divide ae and bf into the same number of equal parts, viz. four. Through the points 1,2,3, in ae and in bf, draw lines to c, intersecting the perpendiculars, then draw the curve as before. METHOD SECOND — BY TANGENTS. Let a b be the chord, and de the height in the middle of ab. Produce de to c, and make ec equal to ed. Join ca, cb. Divide ac and cb, each into the same number of equal parts, and in the same order. Lines being drawn through the corresponding points of division will form the curve required. i 34 CABINET-MAKER, UPHOLSTERER, ORTHOGRAPHICAL PROJECTION. The most useful methods of representing objects, depend upon the principles of Orthographical Representation, which, as before observed, enables the designer of Cabinet Furniture to exhibit a representation of the object which he conceives ; to shew how the different parts will be connected together; and to foresee their just effect on the eye. By its means the workman comprehends the design intended; as it furnishes him with the angles of position and proportion of the parts, and thus enables him to bring it into actual existence, by forming, joining, and fixing the parts immoveably together. D EFINITIONS. 1. Orthographical projection, is a method of representing objects on a plane, by lines corresponding to those of the object itself, in such a manner, that a straight line drawn from any point of a line in the object to meet the plane perpendicularly, will fall in the corresponding line of representation ; and reciprocally, a straight line drawn perpendicular to the plane from any point of a line, will fall upon the line it represents in the original object. Corol. Hence a perpendicular drawn from the extremity of a line of the object to the plane of projection, will fall in the corresponding extremity of the projection of that line. 2. The plane, on which the representation is made, is called the Plane of Projection, and the representation is called the Projection, as well as the Representation. The straight lines, drawn from corresponding lines of the object and of the plane of projection, are called the Projecting Rays. 3. When the projection is made on a horizontal plane, it is called a Plan ; when on a vertical plane, not cutting the object, it is called an Elevation ; and when it cuts the object, it is called a Section. AND COMPLETE DECORATOR. 35 4. A primitive or original plane, is a plane belonging to the object itself; any line or point in such a plane, is called a primitive line or point, in contra- distinction to its representation, which is also called the projection of that line or point. Though it would not be consistent with a practical treatise to enter into any detail of the theory, yet for the use of the designer and workman, it will be proper to enumerate such principles as will be easily understood, which being fixed in the mind, will greatly facilitate the practice of delineation. Propositions. 1 . Every primitive straight line is projected into a straight line. 2. Every primitive straight line, parallel to the plane of projection, is projected into an equal straight line. 3. Any primitive straight line, not parallel to the plane of projection, is to its projection as radius is to the cosine of inclination. 4. The parts of a divided primitive straight line, have the same ratio among themselves, as the parts of the projected line have among themselves. 5. Any curve line in a plane, parallel to the plane ot projection, is projected into an equal and similar line. 6. Any figure in a plane, parallel to the plane of projection, is projected into an equal and similar figure. 7. A straight line, perpendicular to the plane of projection, is projected into a point. 8. An angle in a plane, parallel to the plane of projection, is projected into an equal angle. 9. The area of any plane figure is to the area of its projection, as radius is to the cosine of inclination of the plane. 10. The projection of a circle is an ellipse, of which axis major is to the axis minor, as radius to the cosine of inclination of the plane of the circle to the plane of projection. Hence the axis major is equal to the diameter of the original circle, and it is parallel to the intersecting lines of the two planes. 36 CABINET-MAKER, UPHOLSTERER, A primitive object is a point, line, or plane figure, of which the projection is required. In order to have a comprehensive idea of orthographical projection, we must first shew the projections of a point, and of lines and figures situated in a plane, and as the intersecting line is the only line that fixes the position of the object to the projection, and its projection must always be given* when the primitive object is given to find its projection. In Plate iv. the intersecting line is understood to be given, as well as the angle of inclination of the primitive plane, and the plane of projection; therefore as these are constant in the data, it will not be necessary to enumerate them, but merely to suppose, that their being given is understood. In the six diagrams of this plate, the intersecting line is denoted by 1 1. Hence, when it is said, “ Given the position of a point, or of a line,” it must be understood, that the position of such a point or line is as it regards the intersecting line ; and when the position of a plane figure is said to be “ given,” the meaning is, that the angle which one of the sides, or of some principal line, makes with the intersecting line, is given. It is evident, that the projection of a point is in a straight line drawn through the point perpendicular to the intersecting line ; for suppose that the primitive plane revolves round the intersecting line as an axis, the point will describe the circumference of a circle in a plane, perpendicular to the intersecting line; hence, the intersection of the plane of the circle with the plane of projection will be perpendicular to the intersecting line. The seat of a point is the foot of the projecting ray of that point, viz. the point where the projecting ray meets the plane of projection. * The Author of this treatise was the first person in this country who introduced the science of orthographical projection in general, and that by means of an intersecting line. He first discovered the principle in 1796, and prosecuted this method with unremitted vigour, as was well known to that able and ingenious engraver, Mr. Wilson Lowry, who recommended him shortly after to Longman and Co. to write the article “ Projection” for Rees’ Cyclopaedia, which was published in the year 1813, see plates 1 and 2. Tig . 3. Fig . 6 E Published by H Fisher Son & C° Cseton London June 24,1826 C 1 rtiuHjraplvicdi Projection . B Fuf . 2 . M~d.u>7ic?wLscn del. \liwcnizd by 2 Ihcholsor^ . AND COMPLETE DECORATOR. 37 Angle of projection, of a plane figure, is the angle of inclination of the primitive plane and the plane of projection. The straight line, which is drawn through a primitive point, perpendicular to the intersecting line, is called the perpendicular locus of that point. A straight line in the plane of projection, parallel to the intersecting line, which contains the seat of a point, is called the parallel locus of that point. In order to preserve perspicuity in referring to the following diagrams, when the primitive object is given in position and magnitude, to find the projection; for the sake of conveniency, the primitive plan is supposed to be one side of the intersecting line, and in the same plane with the plane of projection, which is situate on the other side. Hence, the angle of inclination of the primitive plane, and the plane of projection, must be supposed to be acute. By this means the confusion of lines is avoided, which must necessarily happen when the plane of projection is covered by the piimitive plane, and the object and its representation are completely separated. When the separation of delineation is completed, the primitive object is obliterated, being supposed to be drawn with pencil. The shortest distances of a primitive point, and its projection, are to each other, respectively, as radius is to the cosine of the angle of projection. PLATE IV. Problem I. To find the Projection of a Point b. Draw b b, Figure 1, perpendicular to the intersecting line n, crossing 11 at e. At any point e, in u, draw e n perpendicular to n. Make the angle n e h equal to the angle of the inclination of the planes. Make e b equal to es, Draw bb parallel to ii, and the point b is the projection of the point b. 38 CABINET-MAKER, UPHOLSTERER, Problem II. Two primitive Points , a and b, being given, and the Projection a of one of the Points, to find the Projection of the other. Draw a straight line Ac, to meet the intersecting line n in c, at oblique angles. Join a c. Draw b d parallel to n, meeting ac in Draw de perpendicular to 1 1, meeting ac in e. Lastly, draw eb parallel, and b b perpendicular to n, and the point b is the projection of the primitive point b. N. B. This Problem is given as an exercise to construct the diagram, by assuming an intersecting line, and two primitive points a and b ; hence the figure is not exhibited in the Plate. By this Problem we may find the projection of as many points as we please, having the projection of one of them given, without liav'ng the angle of the inclination oa the planes. And thus the projection of any curve line may be found. Problem III. To find the Projection of a Rectilineal Angle. Let abc be a rectilineal angle. Produce the sides ba, bc, to meet the intersecting line n in the points i\ i 2 . Find the projection b, of the point b, by Problem 1 . Draw the straight lines b» M , b i 2 , and i 1 bP will be the projection of the angle required. Problem IV. Given the Projection f one Extremity of a Line, to find the unlimited Projection of the Line. Case 1 . When the primitive line is perpendicular to the intersecting line. Draw a line through the given point, perpendicular to the intersecting line, and the line thus drawn is the unlimited projection required. AND COMPLETE DECORATOR. 39 Case 2. When the primitive is parallel to the intersecting line. Draw a straight line through the projection of the given extremity, parallel to the intersecting line, and the line thus drawn is the unlimited projection required. Case 3. When the primitive line is inclined to the intersecting line in a given angle. Produce the primitive line at the other extremity, of which the projection is not found, to meet the intersecting line. Join the point thus found to the projection of the extremity given, and the line thus joined will be the unlimited projection required. Problem V. Given the Projection of one Extremity of a Line, and the unlimited Projection of the Line, to find the Determinate Length of the Projection of that Line. Through the extremity of the primitive, of which its projection is not found, draw a line perpendicular to the intersecting line to meet the unlimited projection of the line, and the line comprehended between the two points, of which the one is now found, and the other given, is the projection of the line required. But if the unlimited projection of the line be perpendicular to the intersecting line, and if the projection of one extremity be given, the projection of the other extremity will be found thus. Draw two lines parallel to each other, through each extremity of the primitive line, to meet the intersecting line at oblique angles. Join the intersecting point of the line that passes through the extremity of which the projection is given. Through the other intersecting point draw a line parallel to the line joining the first intersecting point, and the given point of projection, to meet the perpendicular, and the part of the perpendicular comprised between this point and the given point of projection, will be the projection of the line required. / 40 CABINET-MAKER, UPHOLSTERER, Problem VI. To find the Projection of a Parallelogram. Find the projection of one of its angles. Produce each of the other two opposite sides of the figure to be projected to meet the intersecting line. Draw lines from each of these two points in the intersecting line, parallel to the lines which contain the projected angle, to meet each of these lines, and the parallelogram, formed in the plane of projection, will be the projection of the parallelogram required. Example . — Let it be required to find the projection of the parallelogram ABC D. Find b the projection of b, by Problem 1. Produce ba and bc to meet ii in i l i 2 , and join b* 1 , hi 2 . Produce ad and cd to meet 1 1 in i 3 , t 4 . D raw i 3 a parallel to hi 2 , and « 4 c parallel to b«’, and the parallelogram ahcd will be the projection of the parallelogram abcd. This example is an illustration of Problems 1, 2, and 5. Hence, if the projection of an angle be given, the projection of any point in either of the sides, containing that angle, may be found. Thus, let 1 b i 2 be the projection of the angle a bc, the projection of the point A maybe found; for, draw a* 3 , parallel to bc, meeting 1 1 in i 3 . Draw i 3 a parallel to hi 2 , meeting bs 1 in a, and a is the projection of a. Problem VII. To find the Representation of any Rectilineal Figure whatever. Find the projection of the vertex of one of the angles by Problem 1. Draw the diagonals of the primitive figure, from the vertex of which the projection is found to meet the intersecting line. Draw lines from each point so found in the intersecting line, to the point found, which is the projection of the vertex, and the lines thus drawn are the corresponding diagonals of the projection. Draw lines through each of the vertices of the primitive figure, except that of which the projection is found, perpendicular to the intersecting AND COMPLETE DECORATOR. 41 line, to meet the corresponding lines. Join the unconnected points thus found in the same order as in the sides of the primitive figure, and the resulting figure will be the projection of the rectilineal figure or polygon required. Example 1. Figure 2. Let the primitive figure abcd be a pentagon. Find the projection i l a i 2 of the angle eab, by Problem 3. Draw the diagonals a i 3 , aj 4 , to meet the intersecting line in i 3 , t 4 . Draw ai 3 , ai 4 , and these lines are the corresponding diagonals of the figure to be projected to the diagonals a i 3 , a* 4 of the original figure. Draw b&, c c, orf, Ee perpendicular to ii, meeting ai 2 , ai 3 , ai 4 , ai 1 in the points b, c, d, e, and lastly, join be, cd, de, and the pentagon a b c d e is the projection of the pentagon abcde. Example 2. Let the primitive figure be that of a hexagon abcdef, fig. 3. Find a the projection of a. Produce a b, a c, a d, a e, a f to meet 1 1 in i 2 , i 5 , i\ i 3 , i 1 . Draw the lines ai 2 , ai 5 , ai 4 , ai 3 , ai find the points b, c, d,e,f as in Example 1. Join be, cd, de, ef, and a be def will be the projection of the primitive figure abcdef. remark. In the examples here given, if the primitive plane be revolved upon the intersecting line, until it makes an angle equal to the given angle contained by the two planes ; then lines drawn through the vertex of every angle of the primitive figure, perpendicular to the plane of projection, will fall upon the corresponding vertices of the projected figure. Thus suppose, in figure 1, that the angle b e n is made to revolve on the side n e, until its plane become perpendicular to the plane Pbi 2 ; and suppose then, that the primitive plane i l Bi 2 , revolve on the intersecting line, the lines joining the corresponding points a, a; b ,b ; c, c ; d ,d will be perpendicular to the plane of projection. Problem VII. To find the Projection of a Circle. Find the projection of the two diameters, of which one is parallel, and the other perpendicular, to the intersecting line, by Problem V. Upon the two L 42 BINET-MAKER, UPHOLSTERER, given lines thus found as axes, describe an ellipse, and it will be the representation of the circle required. EXAMPLE. Through the centre e, figure 4, draw Bb perpendicular to the intersecting line, crossing it in f. Make the angle nfb , as in Problem 1, equal to the angle of inclination of the two planes. On the side fb , of the angle, make fe equal to f e, and fb equal to f b. Draw ec and 6 b parallel to the intersecting line, and let ec intersect Bb in e, and 6b in b. IneF, make ed equal to eb. Draw a a parallel, b b meeting ec in a. Make ec equal to ea; then ac is the projection of the diameter, which is parallel, and bd the projection of the diameter, which is perpendicular to the intersecting line. Upon ac and bd, as axes, describe an ellipse. Problem VIII. Knowing only the Angle of Projection, to find the Ratio between a primitive straight Line and its Projection , when the primitive Line is perpendicular to the primitive Plane. Let nfb, Figure 4, be the angle of projection. In fb, one of the sides of the angle, take any point h, and draw hi perpendicular to the other side, meeting it in i; then any primitive line in the primitive plane is to its projection, when the said primitive line is perpendicular to the intersecting line, as fh to hi, that is, as radius is to the cosine of the angle of the inclination of the planes. But if fh be the length of any primitive line, perpendicular to the primitive plane, hi will be the length of its projection. Hence, the ratio of the projections of the two diameters of a circle, one of which is parallel to the intersecting line, and the other perpendicular to the primitive plane, are to one another as radius to the sine of the angle of projection. AND COMPLETE DECORATOR. 43 PROJECTION OF SOLIDS. In case of rectangular prisms, and even in parallelepipeds, one intersecting line will be sufficient to find the projection of the entire solid; but in projecting solids, of which its solid angles have more than three faces terminating in one vertex, it will be necessary to find an intersecting line for each face ; this, however, we shall not attempt in this place, as such objects are seldom to be met with in the construction of Cabinet Furniture.* Problem IX. To find the Representation of a Cube, one of its Faces being given in Position and JSIagnitude. Let the square abcd, figure 5, be the given face, which we shall suppose to be the top of the solid in the primitive plane, the body being underneath. Find a bed, the projection of the face abcd. Draw the straight lines dg, ae, bf perpendicular to the intersecting line. Make ae equal to the sine of the angle of projection, to a radius equal to the length of one of the edges of the cube. Draw eg- parallel to a d, and ef parallel to a b, and bedgef is the projection required. OR THUS, Having found a bed the projection of the face abcd, which is given in the primitive plane, let eva be the angle of inclination of the two planes ; and let Fa be equal to fa. Draw «e perpendicular to f a, and make a e equal to the length of one of the edges. Complete the parallelograms a dge, a bfe, and we shall have the solid as before. In the same manner the projection of the prism, figure 6, of which one of the ends is abcd, will be found. * Those who are desirous of obtaining a knowledge of the projection of the regular solids, will rind ample instruction in Rees’ Cyclopaedia, under the article “Projection,” see Plate I. by the author of this work. 44 CABINET-MAKER, UPHOLSTERER, PLATE V. Problem X. Given the Projections da, db, dc, Figure 1. of the three Edges of the solid Angle of a rectangular Prism, and the intersecting Point a, of one of the Edges represented by d a, to find the intersecting Lines of the three Faces. Draw a b and a c respectively perpendicular to dc and d b, meeting d b and dc in b and c. Join cb, and ab, bc, ca are the three intersecting lines of the faces of the solid angle. REMARK. If the point a be not an intersecting point, the plane of the triangle abc will be parallel to the plane of projection, and the three lines ab, bc, ca will be each parallel to the plane of projection. Problem XI. Given the three intersecting Lines ab, bc, ca, Figure 1, of the Faces of a solid Angle of a rectangular Prism , to find the Projections of the three Edges. From the vertices a, b, c, of the triangle abc, formed by the three intersecting lines, draw ad, bd, cd respectively perpendicular to the sides bc, ca, ab, and ad, bd, cd are the projections of the three edges, as required. Problem XII. Given the three intersecting Lines ab, bc, ca, Figure 2, of the Faces of a solid Angle of a rectangular Prism , to find the Distance of the Vertex of the solid Angle from the Plane of Projection. Find ad, bd, cd, the projections of the three edges. Produce any one of them, as a d, to meet the opposite side in h. On a h, as a diameter, describe the semicircle a gh. Draw vg perpendicular to Ah, and ng is the distance of the angle required. AND COMPLETE DECORATOR. 45 Problem XIII. Given the three Projections of the Edges of a solid Angle of a rectangular Prism, and the intersecting Point a, Figure 2, of one of them, to find the Distance of the Vertex from the Plane of Projection. Find the three intersecting lines ab,bc,ca, by Problem I. Produce ad to meet the opposite side bc in h. On a h, as a diameter, describe the semicircle a gh. Draw Dg perpendicular to a h, and Dg will be the distance required. To explain this principle to workmen, to an artisan, or to an amateur : let ad, bd, cd be the projections of three of the edges of a solid angle of a rectangular prism, and let ab, bc, ca be the three intersecting lines of the faces. On each of the three sides ab, bc, ca, as diameters, describe respectively the three semicircles a/b, Aec, eg a. From the point d draw v>f De, Dg respectively perpendicular to ab, bc, ca. Draw AffB ; Be, ec; eg, g a. Then the triangle a/b, being revolved on the line ab, the triangle Bee revolved on the line bc, and the triangle eg - a revolved on the line ca, as axes, until the three vertices f, e,g coincide, it is evident that the solid angle of a rectangular prism will be formed by the three right angles, and that the point d will be the projection of its vertex. This may be done with a stiff piece of paper or pasteboard, by drawing a point, not quite sharp, along the lines ab, bc, cd, with a moderate degree of pressure, so as not to cut the paper or pasteboard, in order to make the three triangles turn more freely upon the said three lines. By uniting the three primitive planes in this manner, it is obvious that any one of them, and its projection, are both in a plane perpendicular to the plane of projection; and it is also obvious, that if the three intersecting lines be equal in length, the three projections of the edges must be also equal in length, and will divide the circumference of a circle, described from the projection d of the vertex, into three equal parts, see figure 4, so that each of the angles must be 120°, therefore, when this happens to be the case, the projections of the three 46 CABINET-MAKER, UPHOLSTERER, edges of every solid angle of a rectangular prism must either be 120° or 60°; that is, they will either be, as in figure 5, where each is 120°, or, in figure 6 , where the two lines a b and a c make 60° each, with the middle line a d. This case has been most absurdly called isometrical perspective. It has nothing to do with perspective; since no point, however distant, can ever project the object on a plane, by lines radiating from that point, and passing through the lines of the object, to meet corresponding lines in the plane of projection; yet the eye is not only talked of, but a line of sight also. The question anay be fairly asked, In what point of the line of sight must the eye be placed in order to project an object isometrically? If the eye be placed in any point of the diagonal of a cube, and if the plane of projection be perpendicular to this diagonal, the edges of the solid angle will certainly be projected, so as to make each of the angles they contain 120°; but this equa- lity will not obtain in more than one of the solid angles of a parallelopiped, this being the form in which framed work and machinery are usually arranged. Projection is a general name, that not only applies to the representation of objects formed by perpendiculars from the object to the plane of projection, but also to radiating lines passing through the object to the plane of projection, or radiating lines intercepted by the plane of projection. When a new science is invented, it must have a new name. New names to inventions, previously known by other names, convey an erroneous idea of the thing intended. And as this case of orthographical projection is founded upon the common principles of the science, and is the same in practice as w hen the three lines w hich form the projections of the angles of a cube are unequal, and since it offers nothing in point of facility to the delineator, except that of taking the measures from one scale, it is not a separate species of projection, but a particular case of orthographical representation, and therefore it is not entitled to any name distinct from that to which it belongs. Ihere wall, however, be no impropriety in applying a single word of qualification, in order to save the explanation of a circumstance which would otherwise require several words ; we shall, therefore, make use of the word AND COMPLETE DECORATOR. 47 Isometrical adjectively, in order to accompany the substantive Line, when this line is one of the three edges of a solid angle of a cube, or of a rectangular prism, which are equally inclined to the plane of projection. Problem XIV. To find the Inclination of any One of the three Edges to the Plane of Projection. Draw any straight line ab, figure 8, and in ab set off three equal parts of any length from a to b, marking the divisions c and /. From the middle point e , of a b, with the radius a, or eB , describe the semicircle adb. Draw' cd perpendicular to ab, and join bd; then abd will be the angle of inclination required.* OR THUS. In any straight line bc, figure 8, set four equal parts of any length each, and let ce be a fourth of cb. Draw cd perpendicular to c b from e , with the distance es, describe an arc at d ; join bd, and cbd is the angle required. * In order to shew that ac, figure 7, is one-third of the perpendicular ab, we see that the two right-angled triangles eac and f ac arc equal to each other, for ef is bisected in a, and the angles aec and afc opposite the common perpendicular ac, are each 30°, and each of the angles eca,fca are therefore 60°; therefore the two triangles ace and acf might be formed into one equilateral triangle, by uniting the legs ae and af, so that the point e might coincide withy, and a with a, and placing the right angles adjacent in the same plane, then a c would be half one of the sides, viz. equal to the half of ce or cf; that because ce, cf, and cb are equal, ac would be the half of cb, and therefore one-third of a b. Hence ac, cb, and a b are respectively as 1, 2, 3. This is the foundation of the above construction. The method of finding the angle, which each of the edges makes with the plane of projection, is preferable to any other method hitherto given. This angle is the principal thing required by the draughtsman, he has no need of number; however, as the numerical ratios are very easily derived from the construction, we shall shew how this may be done ; for this purpose, cd is a mean proportional between ca and cb; therefore, cd rr V2, ac being 1, and c62; then, with reference to figure 8, we have bc=2 and CDn^/2; hence BDr^B^* x c d 5 ) = V(4 + 2)=6 ; therefore CD, cb, bd are as V 2, 2, >/6, and multiplying these by the >/2, they become 1, 2, \/3. As to the angle of inclination of the primitive line, and the plane of projection, it is nearly equal to 35° 16°, for considering radius equal 1, we shall have b d to D c, as radius to the sine of the angle of projection ; that is, since bd = \/6, and DC— <\/2, \/6 : \/2 ; : 1 : sine of the angle of projection — V-j = •5773+ or more nearly ’5774 — which answers to 35° 10'. 48 C A BI NET-MAKER, UPHOLSTERER, A REASON FOR THE TWO PRECEDING METHODS. These methods are evident by considering figure 7, of which the equilateral triangle bef may be supposed to be formed, by the intersections of the three planes which constitute the solid angle. Since any edge of a solid angle of a rectangular prism, is always perpendicular to the plane passing through the other two; therefore, the primitive line, represented by be, is perpendicular to the primitive plane represented by ecf; and consequently every section of the solid passing through the edge, of which be is the projection, will form a right-angled triangle, of which the primitive vertex of the right angle is represented by c ; and in the present case of equal inclinations of the edges to the plane of projection, if the plane of section be considered as perpen- dicular to the said plane of projection, the perpendicular ba, from any angle b to the opposite side ef must be the base of the triangle. Problem XV. Given any Isometrical Length, to find the Primitive Length. Find abd, Figure 9, the Angle of Inclination. In one of the sides ba, containing the angle abd, make Be equal to the length of the projection of the line. Draw ef perpendicular to ba, meeting b d, or bd produced iny.* then By is the length of the primitive line. Problem XVL Given the Isometrical Length oj the side oj a Rhombus, representing a Square, to describe the Rhombus. From any point b, in the straight line bd, figure 10, with a radius equal to the length of the line given, describe the arc adc. From the point d, with the same radius, describe an arc on each side of the line b d, each intersecting the former arc in the points a and c. Join da and dc; then abcd is the rhombus required. .9 AND COMPLETE DECORATOR. 49 Problem XVII. The Rhombus which represents a Square being given , to find the Axis of the Ellipse which represents the Circle inscribed in that Square. Find the angle cbd, figure 11, No. 1, of inclination of the plane of projection, and the original plane. Let fghi, No. 2, be the given rhombus which represents the circumscribing square. In bc, No. 1. make b k equal to the half of any one of the four sides; that is, because the rhombus consists of two equilateral triangles, equal to the half of the shorter diagonal, viz. equal to ei or eG, No. 2. Draw hi, No. 1, perpendicular to bc, meeting bd in /. Then bI is the semi-axis major, and Ik the semi-axis minor of the ellipse which represents the primitive circle inscribed in the square, represented by the rhombus fghi. Having thus shewn the modes of constructing the projections of points, lines, surfaces, and solids, from their primitives, and the primitive figures from their projections ; we shall now proceed with practical examples, which will at once shew the utility, the superiority, and the generality of our principles above those limited descriptions which may be elsewhere found. PLATE VI. Figure 1, exhibits the projection and development of a cube by the three right-angled triangles. The squares of the cube, which constitute the solid angle at the summit, are so placed that one of the right angles of each square may coincide with the right angle of each of the triangles ; if these right- angled triangles be revolved on their hypothenuses ab , bc, ca, until the vertices d, e,g coincide, three sides to be projected of the solid, would then be brought into their real situation. Then the triangle a bc, of which the sides are the three intersecting lines, being equilateral, the figure airlpn, of the contour of the projection, would be a regular hexagon, divided internally by the projections of the three edges of the solid angle into three equal rhombuses. In this case, all the edges are projected into equal straight N 50 CABINET-MAKER, UPHOLSTERER, lines, which are equal to one another, and any primitive line is to its projection as V3 is to V2. Figure 2, exhibits the development of the sides of a rectangular prism upon the three intersecting lines of their planes, supposed to be extended to meet the plane of projection in the straight lines a b, bh , ha , in the same manner as has been shewn for the cube, figure 1, except that the lengths are not projected into equal measures. In this example the ends are squares, hence the sides are equal rectangles. Because the plane angles, which form the faces of the solid angle, are right angles, they are all contained in a semicircle. Therefore having the three intersecting lines given, in order to prepare this development, we must first find the projection f of the vertex of the solid angle, by drawing lines from each of the three angles perpendicularly to their opposite sides. On each of the said three sides, as a diameter, describe a semicircle. Draw a straight line from f perpendicular to each diameter, to meet the semicircular arc ; from this point of meeting, which is the vertex, draw a line to the extremity of each diameter. Place the end of the solid, which is a square in the right angle acb, and the side adjacent to this angle in the next vertex, so that the two edges of equal length may coincide, then the three sides being turned up as before, will exhibit the three sides of the primitive solid which are to be projected. EXAMPLE i. Find the representation of a prism, with a mortise cut from the upper end, according to given dimensions, by means of isometrical lines. Make a scale p q, of feet and inches, to any convenient size, as exhibited on the right-hand side of Plate VI, between figures 5 and 8, and let this scale be that from which the measures of the parts of the several diagrams of this Plate are taken. Draw a straight line a b, figure 3, to represent one of the arrises of the prism, in the direction of its height. From a , as a centre, with any radius, AND COMPLETE DECORATOR. 51 describe an ar c pq, intersecting ab in r. From r , as a centre, with the same radius ra, describe an arc cutting the former at p on one side of ab, and at q on the other ; and draw ap and aq , which produce if necessary. Suppose the length of the solid to be five feet nine inches, in the breadth three feet one inch, and the thickness one foot seven inches. From the scale p q, take five feet nine inches, and apply the extent from a to b; take three feet one inch from the scale, and apply this extent in the line ap, or ap produced from a to e, and take one foot seven inches from the scale, and apply this distance from a to f. Having now the two sides ab, ae, complete the parallelogram abce; having the two sides ab, af, complete the parallelogam abdf; and having the two sides be, bd, complete the parallelogram cbdg , which will complete the representation of the prism. To exhibit the Mortise. — Suppose the mortise to be nine inches wide in the middle of the thickness ; then as the thickness is one foot seven inches, by deducting nine inches, there will remain ten inches for the thickness of the two substances on each side of the mortise ; hence the thickness of each is five inches. In the line bd make bl and dm each equal to the extent of five inches from the scale; draw the lines Ir and ms parallel to the side be. Suppose now the length of the mortise to be in the middle of the breadth of the prism, and to be one foot five inches, now the breadth of the prism being three feet one inch, deducting one foot five inches, there will remain one foot eight inches, which allows ten inches of substance at each end of the mortise ; therefore, in the edge be make bh and ci , each ten inches. Draw lit and is parallel to bd or eg, and the parallelogram rstu will be the upper end of the- mortise. Draw sv parallel to ba, meeting ru, and the cavity will be exhibited by the two sides which join in sv. Having gone through all the particulars in the construction of figure 3, a complete idea of that of every other prismatic solid, or any solid composed of prisms, may be easily conceived : we shall therefore only give the dimensions, and leave the construction as an exercise to the learner. 52 CABINET-MAKER, UPHOLSTERER, EXAMPLE II. Construct a cross, having the transverse parts of a prismatic form, the one passing through a mortise in the other at right angles. The piece which contains the mortise to stand upon a square base, each side of the base to be seventeen inches ; the length six feet seven inches ; the distance of the arms from the base to be three feet three inches ; the two arms of the cross to project equally on each side, and to be of the following dimensions, viz. the length of both four feet six inches ; the breadth one foot two inches ; and the thickness in the breadth of the solid, which contains the mortise, to be eight inches, and the arm to be fixed in the middle of the breadth which contains the mortise. Also, to represent a mortise in the other side of the same piece which contains the mortise already spoken of, at the same height as the former, and in the middle of the breadth, so that the breadth of this mortise may be equal to the breadth of the other, through which the transverse piece which forms the two arms passes, proceed as in Example I. EXAMPLE III. Represents a cylinder, five feet three inches in length, and three feet in diameter. Let cad, figure 8, be the angle of projection. In ac , make ad equal to three feet of the scale pq. Draw be perpendicular to ac, meeting ad in e; then ae is the primitive measure of ab. In figure 8, draw ac, bd, at right angles, intersecting each other in k. Make kA, kc each equal to the half of ae, figure 8, and make k b, k d, figure 5, each equal to the half of be, figure 8. Upon the lines a c and b d, as axes, describe the ellipse abcd. Draw k l perpendicular to a c. Make k l equal to five feet three inches. Through l draw the lines eg, fh parallel to ac and b d. Make Ze, Z g each equal to k\ or kc, and i h, i f each equal to k b or k d, and describe the ellipse efgh. Draw the tangents ae and cg, which will complete the representation of the solid. AND COMPLETE DECORATOR. 53 EXAMPLE IV. Represent a right cone, so that the diameter of the base may be three feet, and the altitude six feet. — Find the base and height as in the cylinder. Draw lines from the vertex to touch the ellipse representing the base. example v. Represent a table, with a rectangular top and rectangular legs, framed to bearing rails ; the top of the table being six feet in length, two feet ten inches in breadth, and two inches in thickness ; the legs being three inches square, two feet ten inches in height under the table, making the entire height three feet ; the bearing rails being six inches high, framed flush, with the legs on the outside ; the outer surface of each side of the frame being four inches within each side of the table. — We may commence the representation, figure 7, by making the angles ball , cali } as in Example I ; or since the angles hah, hac are constantly the same, we may draw two contiguous angles of 60° each, any where on the paper out of the way, then draw the lines a b, ah, ac parallel to the sides of these angles : then, as we would wish the length to be represented on the left or on the right hand, we must place the length on ab or ac accordingly; the one being fixed, will determine the other. Let us suppose the length to be on the right, therefore make ac equal to six feet, and ab equal to two feet ten inches, and ah three feet. With the two sides ah and ac, complete the parallelogram hacl ; with the two sides ah, ab, complete the parallelogram habi ; and with the two sides hi, hi, complete the parallelogram ihlk , which will form the upper surface of the table. In the line ac make af, cp, each equal to four inches, and fs, pq, each equal to three inches. In the line ab make ad, br, each equal to four inches, and de, rs, each equal to three inches. Through the points d,e,r,s, draw lines parallel to ac, and through the points fg,p, q, draw lines parallel to the side ab. The four parallelo- grams formed by the intersections of the lines parallel to ac, ab, are the o 54 CABINET-MAKER, UPHOLSTERER, lower ends of the feet which stand on the floor. From the three angular points of these parallelograms nearest the bottom, draw lines parallel to ah, which will form the vertical faces of the legs. Make mn equal to two feet ten inches, and draw two lines parallel to a b and ac, to meet the two most remote lines of the legs, and these two lines thus drawn will represent the under lines of the bearing rails, and thus the representation of the table will be complete. On the top of the table we have represented a cup or bason, as also a box at the farther end ; the principles of our projection, by means of intersecting lines, will shew how this box may be drawn, according to given dimensions and in a given position. Let the side of the box be placed accidentally upon the lineMC, the corner being upon u. We shall suppose its form that of a rectangular prism as usual. Draw mu perpendicular to the horizontal planes, viz. parallel to the arrises of the legs of the table, and draw i l perpendicular to mu, intersecting each other in x. Draw mi parallel to the edge hi of the top of the table, and make xv equal to xi. Produce uv to l, and join lu. Draw u z perpendicular to lu, meeting il in z, and join uz. Suppose now that the length of this box is seventeen inches, the breadth nine inches, and the height four inches. Take seventeen inches, nine inches, and four inches from the scale pq, and in figure 8, set off seventeen inches in the line ac, from a to f, draw fg perpendicular to ac, meeting ad in g ; also, in ac set off nine inches from a to h, and draw h i perpendicular to ac, meeting a d in i. Transfer the distances ai, ag to the lines vz, ul, from u to t and from u to v. Draw Tt and \ v perpendicular to il, meeting the lines u z and ml in the points i and v. In mu make uw equal the height hm, from the scale pq. Having thus obtained the lengths of the three ridge lines, the outline of the solid will be completed by drawing parallel lines. REMARK. This Example will shew the great extent and facility of our principles, that they are capable of representing lines and planes at any given angles with each other, and solids of all dimensions and proportions. The limited and AND COMPLETE DECORATOR 55 common place observations which were published for the use of practical men in 1825, and which are pretended to be new, apply only to lines in the direction of the three edges of the solid angles. They will not enable the student to find the proportions of the primitive lines, from their projections in any other direction. Our principles, on the contrary, not only shew how this is to be done, but direct us how to find the angle which is made, when one line is drawn to another lin5 given in position, in order to represent a perpendicular, or to represent any given angle whatever ; as also, how to draw a line parallel to a given line in projection, so that the distance of the two lines may represent a given distance. These positions are not only effected in the three planes which represent the solid angle of a rectangular prism, but in every other plane of which the position is given to any one of these three faces. Thus, if we know the inclinations of all the planes of a solid, however complex, and the figures of the several faces, we shall be enabled to represent that solid ; and, on the contrary, if we have an orthographical representation, we may construct a solid similar to the original or primitive solid. We shall not proceed any farther in the projection of objects by equal measures, since, though useful in the construction of mathematical diagrams, they form the angles which represent those of the solid much too acute in order to exhibit an agreeable representation, and since in point of facility nothing is gained by this case of orthographical projection. We shall, there- fore, proceed with a general method, which does not require to be confined to any particular angles, as they may be assumed at pleasure. A scale may be readily found to each of the three directions, keeping still in view the projection of a solid angle, of which any one of the faces is perpendicular to the line of concourse of the other two. Though the principles of these general methods have been long given by the author, he has never, till now, had an opportunity of exemplifying them in practice, except those two examples published in 1823, mentioned in the second note of the Introduction; he therefore trusts, that the superiority of his original methods to those more recently published, will be evident by a careful perusal. 56 CABINET-MAKER, UPHOLSTERER, If two angles of a projection of a right-angled solid angle be equal, and if any distance be taken upon the line between these equal angles, from the point where the three lines meet, and if upon this distance, as a diagonal, a rhombus be described, then the following proposition will obtain. Either semi-axis of the ellipse, inscribed in the rhombus, is the hypothenuse of a right-angled triangle, of which each of the two legs is one-fourth of the diagonal, of which this semi-axis is a part. * This proposition is of the greatest use under the circumstance now men- tioned ; for the rhombus being given, the two axes will be found instantly, without knowing the angle of inclination of the line which passes through the centre perpendicular to the plane of the circle, by drawing a right angle, and setting a fourth (say of the shorter diagonal) from the vertex upon each side of the angle, and transferring the distance between the two points of extension from the centre, upon the line intended for the minor axis, and the distance of the two remotest points will be the minor axis. The following is another proposition, which will be found to be extremely useful. The sine and cosine of the angle of inclination of any face of a right- angled solid angle to the plane of projection, are respectively equal to the cosine and sine of the line of concourse of the other two faces, to the said plane, and to the same radius, in both cases. The number of propositions or theorems might have been extended, but as our work is designed for the use of practical men, and not for the speculative geometer, what are given will be sufficient to answer the purpose intended. Before we commence our examples of representing solids in the form of rectangular prisms, by lines in given positions, the following observation will be found to be of great use to the student, viz. if the projection of one of the plane angles of a solid angle of a rectangular prism, and the intersecting line of that plane, be given, the intersecting lines of the other two planes may be readily found. Thus in figure 2, suppose we have the angle afb , which represents the projection of the right angle acb, and the intersecting line ab AND COMPLETE DECORATOR. 57 given ; the intersecting lines of the other two faces will be found thus : draw bh perpendicular to af and ah perpendicular to bf then the intersecting lines of the other two planes are ah and bh. Or, if we have the intersecting line of one of the faces of a solid angle of a rectangular prism, and the pro- tection of that face, we may find the projection of the other two faces as before ; for since four of the edges of the solid are always perpendicular to two opposite planes, the projections of these edges must also be perpen- dicular to the intersecting line of either of these planes ; but the length of a straight line, perpendicular to a plane, is to the length of its projection as radius is to the sine of the angle of projection ; therefore having the repre- sentation of one face of a rectangular prism, and the intersecting line, we have only to draw lines through the upper three points of each angle perpen- dicular to the intersecting line, then set off on the perpendicular which passes through the vertex of the angle at the summit, a length equal to the sine of the angle of projection, the primitive length being taken as radius. Or, suppose we assume the intersecting line ah , and the angle afb as the projection of one of the right angles at the summit, we may find the represen- tation of the whole solid without using the angle of projection. Thus on ab, figure 2, as a diameter, describe the semicircle acb. Draw fe perpendicular to ab, and join ac and be. In ca and cb make co and cm equal to the sides of the first face. Draw og and mn, meeting/a and fb in g and n. Find the intersecting ah as before. On ah describe the semicircle avh. Draw' fv perpendicular to ah. Join vh. In vh make vtv equal to the height of the solid. Join fh. Draw wl perpendicular to ah, meeting fh in l: by com- pleting the parallelograms we have the representation required. 58 CABINET-MAKER, UPHOLSTERER, Examples in which a different Scale is used for each of the three Edges . PLATE VII. Example 1 , figure 1 . Represent a writing desk, with drawers, &c. Draw ax as a director for the representation of the perpendicular lines, and draw a b, ac, making any angles with ad that may be agreeable to the eye, for the directors of the lines which represent the horizontal lines of the object. To find the scales agreeable to these three assumed lines, on any convenient part of the paper, as at figure 2 : draw qa, qb, qc respectively parallel to a b, ac, ax, figure 1. Then proceed in figure 2, as follows. From any point a, in qa, draw ab perpendicular to qc, and ac perpendicular to qb, and join be. Then if the three lines qa, qb, qc represent the vertical solid angle of a rectangular prism, ab, be, ca will be the intersecting lines of the three faces. Produce aq to meet the opposite b c in p. On ap, as a diameter, describe the semicircle adp. Draw qd perpendicular to aq; then qd is the height which the apex of the cube is raised above its projection or seat q; therefore draw qh perpendicular to qb, and qf perpendicular to qc. Make qh and qf each equal to qd. Join ad, bh, and cf. Then will the three lines ad, bh, cf be the primitive lines, of which their projections are aq, bq, cq. Therefore we may assume in any one of the three lines aq, bq, cq, a scale of such a length as may be convenient for the size of the drawing. Let, there- fore, in the line qc, the distance qo be taken to represent twelve inches, or one foot. Draw og perpendicular toe q, meeting cf in g ; then fg is the length of a foot of the real object itself. In da make de equal to fg, and in hb make hi also equal to fg. Draw eo perpendicular to aq, meeting it in o; then qo is the length of a foot in the line qa; moreover, draw io perpendi- cular to qb, meeting qb in o ; then qo is the length of the scale in the line qb. In each of the three lines aq, bq, cq, divide the distance oq into twelve equal parts as shewn, and repeat the distance of a foot as often as may be found AND COMPLETE DECORATOR. 09 necessary, and thus we have the three scales required in the three different directions. The method of applying these scales will be evident to most of our readers; but as there are some who do not comprehend so readily as others, we shall accompany our reader a little farther, and transfer these scales to a, b, c, parallel to the lines of which their lengths are to be taken. Suppose the length of the flap or lid to be three feet three inches, the breadth two feet eight inches, and the height of the legs two feet, and the face of the rails to be one inch within the edges of the flap ; the legs to be two inches square. As it will not be necessary to state the dimensions of all the parts, we shall now shew how the lines are to be represented as far as the dimensions are given. Take three feet three inches from the scale b, and apply it on the line ab, figure 1, from a to b. Take two feet eight inches from the scale c, and apply it on the line ac, from a to c. In the lines ab, ac, make ad, a f, b/i, each equal to one inch. Also, make de,fg , hi, c/i, each equal to two inches. Draw the lines fr, gt parallel to ab, and the lines div, eu parallel to ac ; proceed thus, and form the foot of the legs rst,plq, uvw. Draw Id parallel to ax, and make the height of Id equal to two feet from the scale a. Draw Dm parallel to ab, and an parallel to ac. Having conducted the reader thus far in the delineation of this object, we shall now leave him, as it is presumed that he is sufficiently familiar with the method of proceeding to enable him to finish the drawing. Example 2. Represent three circles perpendicular to three straight lines as axes, of which every two form a right angle; the "representation of the three lines being de, df, dg, figure 3, parallel to qa, qb, qc, figure 2. Supposing the plane of the circle upon the axis represented by de to be one foot one inch and a half from d, and the radius ten inches ; also the plane of the circle upon the axis represented by df to be two feet two inches from d, and the radius of this circle six inches, and the plane of the circle upon the line represented, dg, to be one foot two and a half inches from d, and the radius of this circle eight inches. 60 CABINET-MAKER, UPHOLSTERER, In the line de make d a equal to one foot one inch and a half from the scale b, or from that of qa, figure 2, which is parallel to B. Through a draw be perpendicular to de. Make a b, a c, each equal to ten inches, taken from the oblique scale o-12, No. 1, figure 2, parallel to ad. Place the foot of the compass in the same scale at 10, and fix the other foot at such a distance, as, by making it describe an arc of a circle, the arc will just touch the line qa; this may be done instantly by trial, without drawing a perpendicular to aq, or taking the length of the sine : this may also be otherwise expressed, by taking the shortest distance between the point 10 and the line qa. Transfer the distance thus obtained to figure 3, in the line de, from a to e, and from a to d. Then the ellipse described upon the two axes be and de will represent the circle required. In the same manner the ellipses at Nos. 2 and 3 may be drawn. The reader is requested to find the dimensions of a portable desk repre- sented by figure 4. The method of finding the measure of a foot is shew n in figure 2, on e&cli of the three directors, in order that the original measures may be brought into their real situation by turning up the three triangles of which the bases are the lines qa, qb, qc. This is certainly the most evident method of finding the proportions of the scales; but the following method is the most convenient. Having drawn the three lines qa, qb, qc, figure 2, parallel to the three lines ab, ad, ac, figure 1, and the sides ab, be, ca, figure 2, respectively per- pendicular to the three lines qc, qa, qb, and having found the height qd from the vertex of the solid angle to its reach ; proceed as follows : — In figure 5, draw any straight line be, and draw ba perpendicular to be. Make ba equal to qd, figure 2. In figure 5, on the straight line be, make be, b d, b c respectively equal to qc, qa, qb, figure 2. In figure 5, join ae, a d, ac. Draw a/ parallel to be. Set off a f equal to twelve inches, or one foot, of the scale qc. Draw fi perpendicular to a f, meeting ae in the point*. From a, with the radius a*, cut the lines Ad, ac in the points k and l. Cut the line A^in the points g and h, by the lines kg, O t‘ t/wfl /‘dp /i ic&L /'ro/ c<‘( ion FI cS. r M V-o M ■ ■ . I*. ■ ■ ,-J *- 1 30 I'Yq.4-. Fiy. <( D/ A /•»/. t> . J. 'I >OiT & C° LOJTDOJI. TISHEP.. AND COMPLETE DECORATOR. 61 lh perpendicular to a /,* then a / being the scale in the direction qc , figure 2, ao' and a h will be the respective scales in the directions qa, qb, figure 2. We have here in figure 5, preferred the line a / to be , in order that the points h, g, f might not interfere with the points c and d, as otherwise they might have had some chance, or fall very near them. This method is not only convenient in finding the lengths of the scales, but also in finding the two axes of the ellipse upon any one of the three directions. Thus, suppose it were required to find the ellipse described round the, point k, figure 3, as a centre, to represent a circle, so that the primitive line of dg may pass through the centre of the circle as an axis. To do this in the easiest manner, it would be better to have a scale of the original measures as well as of the three directors, and this we have in any one of the three sloping scales, figure 2. Or the same may be obtained by dividing any one of the three radii a i, a k, a l, figure 5, into twelve equal parts. We may now recollect in example 2, that the radius of the original circle upon the line represented by dg , figure 3, was eight inches. Having drawn fg, figure 3 , through k, perpendicular to dg, take eight inches from the scale aI, figure 5, and in figure 3 make kf and kg equal to it; set the distance kf or kg, figure 3, or eight inches in the line ea , figure 5, from e to m. Draw the sine mn, and transfer mn to figure 3, from k to h, and from k to i; then h i is the semi-axis minor PLATE VIII. example . Represent a semicircular arch in a straight wall, of which the thickness is four feet, the distance of the arch from the corner of the wall three feet and a half, the breadth of the arch fourteen feet, the height from the bottom of the w r all to the springing fifteen feet. Q CABINET-MAKER, UPHOLSTERER, f>2 In figure 3, draw the lines ca , cb, cd in any directions that may he agree- able to the eye, or which the subject to be delineated may require, the directors of the horizontal lines being ca, cb , and that of the vertical lines being cd. In this example the right angles of the solid angle are respectively 143°, 108°, and 30°, the horizontal right angle in front being represented by an angle of 143°, and each of the right angles in the two vertical planes by 71°, 30', which is the half of 143°. In figure 3, the angle acb is therefore 143°, and each of the angles acf, bcf, is 71°, 30'. To find the scale upon each of the lines ca, cb, cd, we may assume ten feet upon any one of these th ree lines, of such length as may be judged proper for the size of the drawing to be made. Suppose, then, in the line cd, which is the director of the ver- tical lines, that co is taken to represent ten feet ; we have now to find ten feet in the lines ca and cb, or only in one of them, as they are equal. If the reader recollects the operation of finding the scales of the writing desk, figure 1, Plate vn. he will be at no loss to find the scales in this example ; but if he does not, he must return to page 58, where the explanation of figure 1, Plate vn. is given. Let, therefore, co, in the line ca, be ten feet according to co, the assumed ten feet in the line cd; the sloping lines 0-10 and 0-10 being their originals. Having fixed the position of the directors of the lines that are to represent the solid angles of the primitive object, and the scales in these three directions, we may now proceed to the delineation of the object. In figure 1, draw j or parallel to its director ca, figure 3, and make pq, qr respectively three feet and a half, and fourteen feet from the scale ca. Draw r s, figure 1, parallel to the director cb, figure 3, and make rs equal to four feet from the same scale. In figure 1, draw qg, rf si parallel to the vertical director cd, or rf, figure 3. In figure 1, make rf equal to fifteen feet from the scale cd, figure 3. In figure 1, draw/* parallel to rs, and fg parallel to rp. Bisect fg in the point e. We must now recollect that each of the three faces of a solid angle of a rectangular prism is perpendicular to the line of con- course of the other tw o ; and that when an ellipse is represented in that face, AND COMPLETE DECORATOR. 03 the axis minor is parallel to the line of concourse, and the axis major perpen- dicular to it. Therefore, through e draw ab parallel, and cd perpendicular to rs ; then the axis major will be in the line cd , and the axis minor in the line ab. We have also to recollect that the axis major is to the axis minor, or the semi-axis major to the semiaxis minor, as radius is to the sine of the angle of the line of concourse of the two planes just mentioned to the plane of projection. Now cb, figure 3, is the representation of this line of concourse; but as ca is equal to cb , we must take our measures from ca instead of cb. Take, therefore, seven feet of the original scale of ca , figure 3, and transfer it to figure 1, in the line cd, from e to c, and from e to d. Now take the sine of the angle of projection to radius seven feet; that is, vw, figure 3, and transfer it in the line ab, from e to a and from e to b. Having now the two axes ab and cd, in position and magnitude, we may describe the ellipse or the part f dbg, which will represent the face of the arch. To represent the arch in the opposite face of the wall, draw kl, mn, & c. parallel to fi; make kl, mn, &c. each equal to fi; through the points i,l, n, &c. draw the cmwe iln, &c. to intersect the curve fc tbg in the points. A building, with arched apertures, requires more attention than one which has only rectangular apertures ; for in the former case we are under the necessity of finding the original measures ; but in the latter we only require the measure from the three scales of the edges of a solid angle. As every good draughtsman has such a command of hand as to describe a curve, through a few points, with sufficient exactness, and perhaps would not be at the trouble to describe portions of the ellipse required to represent the semicir- cular arch from the axis; and as he has now the four points f c , b,g given, he may readily find the fifth point thus, which will enable him to trace it with great exactness. Draw ct parallel to rf, and make et equal to seven feet, from the scale c d, fig. 3, and the point t will be the fifth point required. 64 CABINET-MAKER, UPHOLSTERER, EXAMPLES FOR PRACTICE. Figure 5, exhibits the projection of a flight of steps, and figure 6, repre- sents a series of return steps. These two examples are drawn on the same principles as the others, and therefore need not be explained. Figure 7, exhibits the projection of a line, in a plane perpendicular to the primitive plane, and the projection of the intersection of that perpendicular plane, cut by another plane, of which its intersection and angle of inclination to the primitive plane are given. Let i l be the intersecting line of the primitive plane, and the plane of projection; also, let ac be the intersection of the primitive plane, and the vertical plane. At any point b, in a b, draw bc perpendicular to a b, and draw cd' perpendicular to bc. Make the angle cbd' equal to the inclination of the inclined plane to the primitive plane. Draw c d perpendicular to a c, and produce cd to e. Make the angle cae equal to the inclination of the line in the perpendicular plane, insisting upon ac. Find abc the projection of abc. Draw ce perpendicular to i l. Make cd, ce equal to the sines of the angle of projection respectively to radius cd, c.e ; Join ad and ae: then ae is the projection of the line, and ad that of the intersection required. This Problem is the same as finding the projection ae of a ray of light, and to find the intersection ad of a vertical plane, passing along that ray {ae) with a plane at the given angle cbd. Hence, if ab represents one side of a building, and bc the other side, ab and bc will represent a right angle : and because cd represents a line perpen- dicular to the plane represented by abc, the line cd represents a line perpendicular to the line represented by cb and by ca. Hence, the angle bad represents the plane angle which forms the hypothenuse, and bac, cad represent the legs of a right-angled trehedral. de represents the elevation of the straight line c e above the inclined plane. Thus the use of this problem in the projection of shadows is manifest. We shall therefore leave its appli- cation, in the formation of certain shadows, to the reader. AND COMPLETE DECORATOR. 65 With regard to the scales or lines of measure in the three directors, the measure, representing any length in the line opposite the greatest angle, is greater than the length taken upon either of the other two lines representing the same measure. On the contrary, the measure representing any length upon the line opposite the least angle, is less than the length taken upon either of the other two lines representing the same measure. Hence, the three scales will be easily distinguished from each other wherever they are placed; or, in other words, it will be easy to see to which of the three directors any one of the three measures applies. The three scales will be sufficient for any representation, of which all the parts of the edges of the original are straight lines, parallel and perpendicular to each other ; but where circles are to be represented upon any of these lines as an axis, it will be necessary to find the inclination of each of the three edges of the solid angle, in order to find the two axes of the ellipse which is to represent the circle. Ihe most convenient method of finding the three inclinations is, perhaps, the following : draw a straight line, as a base and a perpendicular, from any point to that straight line ; set the height of the vertex of the solid angle upon the perpendicular, from the point of concourse of the two lines forming the right angle, also from the point of concourse set the lengths of the three lines which represent the three lines of concourse of the solid angle, upon the line representing the base ; then join each of the three points to the top of the perpendicular, and the acute angle, which either of these lines makes with the base, is the angle of inclination. N. B. The least inclination belongs to the director which is opposite to the greatest angle, and the greatest inclination belongs to the director opposite the least angle, representing a right angle of the solid angle. R & 66 CABINET-MAKER, UPHOLSTERER, Part II.— ORTHOGRAPHICAL PROJECTION. On Shadows. We must here have the seat of the sun’s rays and their angle of inclination to the horizon, to find the shadow of any vertical line, and the shadows of any line perpendicular to a vertical plane. In order to find the shadow on the vertical plane, the seat of the sun’s rays must be found on this plane. The plane of the horizon is here represented by the primitive plane. Let abcdefghi, Plate vm. figure 2, represent a penthouse or lean-to, with the ends of several timbers projecting from the front wall, also, with two stalks of chimneys, of which their planes are perpendicular to the horizon, and parallel and perpendicular to the plane of the front. All the walls, except the front, are higher than the sloping plane of the roof. The tops of the chimneys and the back wall terminate in horizontal planes. Moreover, the two gable walls terminate in planes parallel to the sloping side of the roof. It is required to find the shadow of the timbers projecting perpendicularly from the plane of the front, the shadow of the stack of chimneys, and the shadow of the gable wall on the inclined plane of the roof. Let the line a l, figure 4, represent the seat of the sun on the horizon- Draw a a parallel to ef, the lower edge of the plane of the front, figure 2, and in al, figure 4, take any point l, and draw La parallel to ed, the lower edge of the gable, figure 2. Draw the line lc, figure 4, parallel to dc, ea, or fg, figure 2. Draw the angle lac, figure 4, to represent the angle which a ray of the sun makes with its seat ; then a c will represent a ray of the sun. Complete the parallelogram a bcl, and join ab, and ba will be the seat of the sun on the vertical plane. To find the shadows of the timbers projecting from the front of the pent- house, figure 2. Let gf be the arris or edge of one of the timbers, perpen- dicular to the plane aefg of the face of the front wall, g being the point AND COMPLETE DECORATOR. 67 where the line gf meets the plane of the front. Drawee and fe respectively parallel to ba and c a, figure 4, then the straight line ge is the shadow of gf In the same manner the projection of the shadows of the other three perpen- dicular lines may be found. Now v being the shadow of the point v, and w the shadow of the point w, ]omge, ev, vie, and tvx, then gevwx is the shadow of the end of the timber as required. N. B. The edge ev of the shadow is parallel to fv the vertical edge, and vw to vw the horizontal edge of the timber; therefore if we find the seat of a ray of the sun to each of the three lines of the projecting end of the timber that throws the shadow, and having found the point e, in order to complete the shadow, we have only to draw ev parallel to fv, and vw parallel to vw. In the intersection of the sloping plane of the roof and the face of the wall, take any length db. Draw da parallel to ed, and ba parallel to al, figure 4; then the triangle ab d represents a plane parallel to the horizon. Draw ac parallel to dc, ea, or fg. and draw dc parallel to ab or gh, and join be; then be is a section of a vertical plane, passing through the sun in the sloping plane of the roof. To find the shadow'upon the roof by the ledge GZe h, first find the shadow of the vertical line yz thus, draw yfl parallel to be, and xfl parallel to ca, figure 4; then fl will be the shadow of the point z. Draw fly parallel to z«, and fly is the shadow of the sloping line ze . To find the shadow of either of the stalk of chimneys. To do this, it is only necessary to shew how one of the quoin lines of two adjacent vertical surfaces may be found ; therefore let this vertical line be m t. Draw m n parallel to be, and tn parallel to a c, figure 4; then mn is the shadow of the vertical edge mt of the stalk of chimneys. In the same manner the shadow of each of the other vertical lines may be found ; then by joining all the parts, we shall have the shadow complete. Or if we had found the lines h i, mn, and os, and only the extremity of the shadow of the point k, produce hm and kt to meet each other in l ; draw il, intersecting mn in n; draw ns parallel to tu, meet- ing os in s; then liinso is the shadow of the chimney shaft as required. 63 CABINET-MAKER, UPHOLSTERER, It is now expected that the reader is in full possession of the principle, and therefore he cannot be at a loss to form the shadows of all objects, how- ever varied in form from one another; we shall, therefore, close this subject by shewing how the ray and seat of the sun may be found, so as to cause all parallel planes, which are perpendicular to the surface of the wall, in vertical as well as in horizontal positions, to throw shadows equal to their breadth. In order to accomplish this, in figure 8, draw the cube abcdef. Draw the diagonal fc of the base cdeA; also, draw the diagonal fc of the vertical plane bcef ; then ec will be the seat, and fc a ray of the sun on the hori- zontal plane. Likewise, draw the diagonal a c, and ac is the seat of the sun on a vertical plane parallel to the plane abch. This position of the cube is adapted to the example, figure 2. Having thus discussed the shadows of objects, projected orthographically, we shall now 7 give a few of the principles for the shadows of bodies geome- trically represented in planes, elevations, and sections, which in certain cases are indispensable to the draughtsman, and to fix those principles they will be illustrated by a select number of useful examples. Problem XVIII. The Seal and Angle of the Sans Hays being given on any Plane , and the Line of Intersection of a Plane, perpendicular to the first mentioned Plane, to find the Seat of the Suns Rays on the perpendicular Plane. Let ac, figure 1 , Plate VIII. be the intersection of the perpendicular plane, and be the seat of the sun’s rays. Make the angle bed equal to the angle of inclination of the sun’s rays. Draw bd perpendicular to be, and be perpen- dicular, intersecting ac in the point a. Make ae equal to bd, and join ec . D raw ef perpendicular to ec, make ef equal to bd, and join fc. In order that the reader may have some idea of the Problem, draw bg and ah perpendicular to ba, and make bg and all each equal to bd, and join g li. Conceive now the rectangle abgh to be turned upon ab, the triangle cbd to be turned upon cb, and the triangle cae to be turned upon ca, so that the AND COMPLETE DECORATOR. 69 planes of these three figures may be each perpendicular to the plane cab, then will bg coincide with bcl , and ae with ah. These three planes being perpendicular to the plane cab, turn the plane cef round the line ce till it becomes perpendicular to the plane cae ; then will the line ef coincide with hg, and the line cf will coincide with the line cd; and because the plane cbd is perpendicular to the plane cab, and cb is the foot of the plane c b d; there- fore cb is the projection or seat of the line cd on the plane cab. In the same manner it may be shewn that ce is the seat of the line cf, that is, of cd in the plane cbe. Problem XIX. Given the Intersection cb, Figure 2, of the Plane of Projection, and the Seat ca of a Line, the Angle which the Plane of Projection mahes with the given Plane , and the Angle which the Line mahes ivith its Seat, to find the Seat and Angle of Inclination of the Line on the Plane not given. Draw ae perpendicular to be, intersecting be in b, ad perpendicular to ac, and ah perpendicular to ab. Make the angle adg equal to the angle of inclination of the two planes, and the angle acd equal to the inclination of the line to its seat. Also, make ah equal to ad. Draw hg perpendicular to bg, and make be equal to bg, and join ec. Draw ef perpendicular to ce; make ef equal to gh, and join cf; then ce is the seat of the line, and ecf is the angle of inclination. Problem XX. Given be, Figure 3, the Seat of a Ray of Light, and the Angle of Inclination of the Ray to its Seat, also a Line ac parallel to a Line in Space, to find the Angle of Inclination of a Plane of Shade. Draw be perpendicular to ac, intersecting ac \n a. Make the angle bed equal to the inclination of the ray with its seat. Draw bcl perpendicular to be, and bf perpendicular to ba. Make bf equal to bd, and join af, then baf is the angle required. 70 CABINET-MAKER, UPHOLSTERER, Problem XXI. To find the Shadow of a Solid upon a Wall, of which Solid its Planes are all parallel and perpendicular to the Plane of the Wall, given the Plan and Elevation of the Solid. Let bchg, figure 4, represent the elevation of the solid, the lines bc, ad, ef, gh, ch, and bg, represent the planes perpendicular to the wall, and the rectangles a d f e, abcd, efhg represent the planes parallel to the wall. Also, let abcdef gh represent the plan on a plane perpendicular to the plane of the elevation. In this plan, ah represents the w r all line bc, de , fg; the planes abcd, adfe, efhg. Draw b p, a r, e s, g t, h u, parallel to the seat of the sun’s rays on the elevation, and draw am, dn, eo and gi parallel to the seat of the sun’s rays on the plan intersecting ah in m, n, and fg in o. Draw mp, nr perpen- dicular to ah, and bg rs parallel to it ; sw parallel to mp or nr, wt parallel to bg, and tu parallel to gh ; then Bp qrswtua is the shadow of the solid required. From the description here given of figure 4, it will hardly be necessary to enter into any particular explanation of figures 5, 6, and 7. In figure 5, .hough only two of the planes are perpendicular, and the other are inclined to the plane on which the shadow is thrown, yet the lines of intersection of all the planes are either parallel or perpendicular to the plane on which the shadow is thrown; the principle then depends upon this Problem, “ the plan and elevation of a point being given, and the line of elevation, to find the shadow of the point in the elevation .” Figure 6, exhibits the shadow of a cross ; here all the lines are parallel and perpendicular to the plane of eleva- tion. Figure 7, exhibits the shadow of any thing with a circular bow in front, s f and o p are the straight parts of the shadow, and are parallel to the lines bc and de, which projects them; fghilno is the shadow of the circular edge, and as the shadow of a circle is either a circle or ellipse, so the shadow AND COMPLETE DECORATOR. 71 of the segment of this circle is ail ellipse, when the tw r o planes are oblique to each other. With regard to figure 5. continue the directions ed , df of the lines that run through the shadow to meet the wall line ih, and find the elevations of the same points, and these points will give the directions of the shadows mn, po on the elevation. 72 CABINET-MAKER, UPHOLSTERER, PERSPECTIVE. Definitions, &c. Def. 1 . Perspective is the art of representing a rectilineal object upon a plane surface by lines, so that when the representation is placed in a certain position between the eye and the object, every line in the representation will intercept the view of the corresponding line of the object. To render the principles of Perspective easy of comprehension, it is ne- cessary to consider the faces of an object, as composed or formed of different planes, and one of those faces coincident with a plane indefinitely extended on all sides : this plane is called the original plane, ox geometrical plane, and the face of the object which is coincident with the original plane, is called the original figure. The point for viewing the object is given in position to the original plane; that is, some point is fixed upon in the original plane, and the eye at a given distance from that point in a perpendicular drawn from the said point. Def. 2. The point where the eye is placed, is called the point of sight. Def 3. The foot of the perpendicular, is called the station point. As the faces of an object may have all manner of positions, an original plane may in consequence have any inclination to the horizon ; therefore an original figure may be in a horizontal plane, below or above the eye ; a vertical plane on the right or on the left of the spectator; or on an inclined plane in any position to the horizon ; but in whatever plane an original figure is situated, the method of representing the object is the same. Def. 4. T he surface on which the object is represented, is called the plane of the picture, or simply, the picture. In order to have a comprehensive notion of the principles of perspective, the student must consider, that a picture drawn in the utmost degree of per- fection, and placed in its real position, ought to appear to the spectator, the same as the real object itself, when seen from the point of sight. In order AND COMPLETE DECORATOR. 73 to produce this effect, it is necessary that two visual rays, from any two points of the picture, should form the same angle, at the eye, as the visual rays from the two corresponding points of the original object; and that every ray, from the picture to the eye, ought to proceed with the same degrees of light, shade, and colour, as from the corresponding points of the original object. And there can be no doubt, that if these circumstances were attended to in the execution, the deception would be complete; so that if we were looking at the picture from its point of sight, our senses would be so far deceived, as to suppose that we saw the object itself, instead of its repre- sentation on a plane surface. This observation is completely verified by the Diorama now exhibiting in the Regent’s Park. Def. 5. That point in the picture, cut by a line drawn from the point of sight perpendicular to the picture, is called the centre of the picture. Def 6 . The distance between the spectator’s eye and the centre of the picture, is called the distance of the picture , or principal distance. Def. 7. The point where any original line cuts the picture, is called the intersecting point of that line. Def. 8. The line where any original plane cuts the picture, is called the intersecting line of that plane. Def. 9. The point where a line, drawn from the eye of the spectator parallel to an original line, cuts the picture, is called the vanishing point of that original line. Corol. 1 . Hence it is evident, that original lines, which are parallel to each other, have the same vanishing point; for only one line can be drawn through the eye of the spectator that will be parallel to them all. Corol. 2. Those lines which are parallel to the picture have no vanishing points ; because no line can be drawn through the eye parallel to any one of them, that will ever meet the plane of the picture. Corol. 3. The lines that generate the vanishing points of two original lines meeting together, form the same angle at the eye of the spectator, as the two original lines themselves. T 74 CABINET-MAKER, UPHOLSTERER, Def. 10. The line formed in the picture, by a plane passing through the point of sight parallel to an original plane, is called the vanishing line of that original plane. Corol. 1 . Hence original planes, that are parallel, have the same vanishing line, for only one plane can pass through the eye of the spectator, that will be parallel to them all. Corol. 2. All the vanishing points of lines, in parallel planes, are in the vanishing line of these planes ; for the lines which produce those vanishing points are all in the plane that produces the vanishing line, by this definition. Corol. 3. The planes which produce the vanishing lines of two original planes, have their common section in a line passing through the eye of the spectator parallel to the line of common section of the two original planes, and are inclined to each other in the same angle as the two original planes. Corol. 4. Hence the vanishing point of the line of common section of two planes, is the intersection of the vanishing line of those planes. Corol. 5. The vanishing and intersecting lines of the same original plane are parallel to each other, since they are generated by parallel lines. Def. 11 . The point in a vanishing line, cut by a perpendicular drawn from the eye of the spectator to that vanishing line, is called the centre of the vanishing line. Corol. A line drawn from the centre of the picture to the centre of a vanishing line, is perpendicular to that vanishing line. Def. 12 . The distance between the eye of a spectator and the centre of a vanishing line, is called the distance of that vanishing line. Corol. The distance of a vanishing line is the hypothenuse of a right- angled triangle, of which one leg is the principal distance, and the other is the distance between the centre of the picture and the centre of the vanishing line. Def 13. A plane passing through the eye of the spectator, parallel to the picture, is called the directing plane. Def. 14. The representation of any figure, is called its projection . AND COMPLETE DECORATOR. 75 Plate I. — Perspective. In order to comprehend the sense of these definitions more readily, let deh, fig. 1 , be the original plane, and let o be the point of sight, Def. 2, p the station point, j Def. 3, and abl the plane of the picture, Def. 4 : then if o c be perpen- dicular to the plane abl, meeting it in c, c is the centre of the picture, Def. 5, and oc its distance, or the principal distance, Def. 6 . If ki be an original line, and produced to meet the picture in b, b is the intersecting point of the line ki , Def. 7. If o v be drawn parallel to f, meeting the picture in v, v is the vanishing point of f g, Def. 9. If v l be drawn through v, parallel to the original plane deh,vl is the vanishing line of that plane, or of de h, Def. 10. If o s be drawn perpendicular to v l, to cut it in s, s is the centre of the vanishing line v l, Def. 11 , and o s its distance, Def. 12, which is, therefore, the liypothenuse of the right-angled triangle ocs. If a plane, ode, be parallel to the plane of the picture, ode is called the directing plane, Def. 13. PROPOSITION I. — THEOREM. The representation of a line, is part of a line passing thruogh the inter- secting and vanishing points of the original line. Figure 1. For the visual rays io, ko, &c. which produce the represen- tations i, k of the points i, k, &c. of the original line i k, by their intersec- tions with the picture, are all in a plane passing through the original line ik, and the spectator’s eye is at o. But the point b, which is the intersection of the original line i k, is in that plane, because it is in the line l k ; and the line o v is in the same plane, because it is parallel to the original line i k, Def. 5 ; wherefore the line vb is the intersection of the plane iok with the picture; and consequently ik, which is the representation of the line ik, is part of the line k b which passes through the vanishing point v, and the intersection b of the original line ik. Corol. 1. Hence the representation of any number of lines that are parallel to each other, but not to the picture, will pass through the same point. For CABINET-MAKER, UPHOLSTERER, 76 they all pass through the same vanishing point by this theorem, and by corollary 1, Def 9. Corol. 2. But if the original lines are parallel to the picture, as well as to each other, their representations will be parallel to each other, and to the originals. For the line passing through the spectator’s eye, which lin*e in other cases produces the vanishing point by its intersection with the picture, is, in this case, parallel to it, and therefore produces no vanishing point, so that the representations can never meet each other, nor that of the line pass- ing through the spectator’s eye, and consequently they are parallel to each other, to that line, and to the originals. Corol. 3. Hence it appears, that the representation of plane figures, parallel to the picture, are similar to their originals. For in figure 2, the picture being ab, the original figure cdef being parallel to it, and the repre- sentation being cdef. If the original figure he resolved into triangles, by diagonals as d f, the representation will he resolved into triangles by corre- sponding diagonals df. Whence all the lines in the representation being parallel to all the lines in the original, every triangle edf will he similar to the corresponding original triangle edf; and consequently, all the lines in the representation cdef will he in the same proportion to one another as the corresponding lines in the original figure cdef. PROPOSITION II. THEOREM. Any line in the representation of a figure parallel to the picture, is to its original line, as the principal distance is to the distance between the specta- tor’s eye and the plane of the original figure. Let og, figure 2, be perpendicular to the original plane and to the picture, cutting them in g and g: the original plane being parallel to the picture, therefore all the visual rays oc, od, oe, &c. are cut in the same proportion, by the points c, d, e, &c. as og is by the point g ; and dc being parallel to dc the triangle, ode is similar to the triangle odc; therefore dc: dc : : od: od; but from what has here been observed, od: od : : og: og whence by AND COMPLETE DECORATOR. 77 equality dc : dc : : og : og, that is, representation cd is to its original line c d, as the principal distance o g is to the distance between the spectator’s eye and the plane of the original figure. PROPOSITION III. THEOREM. The distance between the vanishing point of a line and the representation of any point in it, is to the distance between the vanishing point and the inter- section, as the distance between the directing point and the intersection, is to the distance between the directing point and the original point. Figure 3. Let b be the intersecting point, and g the directing point, of the original line ik, and v is its vanishing point; then k being the represen- tation of k, and v k parallel to og. Now the triangles okv and kog are similar ; wherefore & v:og::ov:kg, but o g is equal to v b, and o v equal to gb; therefore & v:vb::gb:kg. PROPOSITION IV. — THEOREM. The radial or parallel of an original line, producing the vanishing point, makes the same angle with the vanishing line as the original line makes with the intersecting line. For the intersecting line, the vanishing line and the parallel of the eye are parallel to each other, and the radial, producing the vanishing point of an original line, is parallel to the original line ; therefore whatever inclination the original has to the intersecting line, the radial of that line has the same inclination to the parallel of the eye ; and because the vanishing line is paral- lel to the parallel of the eye, and the radial joins the parallel of the eye and the vanishing line ; the acute angle, formed by the radial and the parallel of the eye, is equal to the acute angle formed by the same radial and the vanish- ing line, being alternate angles ; therefore the acute angle, formed by the radial and the vanishing line, is equal to the acute angle formed by the origi- nal line and the intersection. u 78 CABINET-MAKER, UPHOLSTERER, PROPOSITION V. — THEOREM. If from any point b, fig. 4, taken at pleasure in the vanishing line ab, a straight line be drawn to any two points d and e in the intersecting line, so as to cut the indefinite representation a i of any original line in the points d and e, then will the radial o a be to the distance a b, between the vanishing point a and the assumed point b, as the original of d e is to d e. Produce the indefinite representation a i to meet the intersecting line in i : draw i d parallel to o a, and draw d d and e e parallel to o b, and through e draw ef parallel to gi. Now because ob is parallel to dD and eE, and because ob meets the vanishing line in b, b is the vanishing point of the lines dD and eE ; but d b and e b are the indefinite representations of d d and eE ; therefore the repre- sentations of the original points d and e are in the lines ds and eB. Again, because o a is parallel to the original line d e, and because o a meets the vanishing line a b in a, a is the vanishing point of the original line de, and since i is its intersecting point, a i is the whole indefinite representation of d e ; therefore the points d and e are represented in the line a i ; but since they are also represented in d b and e b, the points d and e, the intersections of these three lines, are the representations of d and e. Then because of the similar triangles oab and dep,oa:ab::de:ef; but ef is equal to ed, and de is the original of de, whence o a is to ab, as the original of de is to d e. Corol. Hence if the length of the original of de be known, de will be found, and consequently de, without having d e in its real position. PROPOSITION VI.- — THEOREM. If the angle eof, fig. 5, formed by the radials of any two indefinite represen- tations a e and b f, be bisected, and if from the point g in the vanishing line, cut by the bisecting line, be drawn lines g a, g c, g b, and g d, cutting each indefinite representation in two points, and any line drawn parallel to the AND COMPLETE DECORATOR. 79 vanishing line in four points a, c, b, d, then the originals of the two intercepted distances ac, bd, in the indefinite representations, will be to each other as the corresponding intercepted distances ac, bd, on the line drawn parallel to the vanishing line. Take o q in the one radial at pleasure, and make o s on the other equal to oq, and join qs, which will be bisected in t by on. Now in the two right- angled triangles otq and ots, the base to is equal to the base ts, and the perpendicular t o is common, therefore the hypothenuse o q is equal to the hypothenuse os. Draw qp and sr parallel to o g, and through o draw pr parallel to the vanishing line e f ; then p r will also be bisected in o ; pro- duce or to any point u, and draw uv parallel to og, cutting o f in v. Now by the preceding proposition oe is to eg as the original of ac is to ac, and o f is to f g as the original of bd is to bd ; but by the similar triangles o eg and qop, oe:eg::oq:op; therefore the original of ac is to ac as OQ is to op: again, in the similar triangles ofg and sor, of:fg::os : or; therefore the original of bd is to bd as os is to or : and because u v is parallel to s R, the triangles o u v and o r s are ^similar ; whence o v : o u : : os : o r : but op is equal to or, and oq equal to os ; whence ov : ou : : oq : op, hence, alternately oq:ov::op:ou; therefore the original of ac is to the original of bd , as op to ou, or or to ou; whence if op or or be equal to ac, and ou equal to bd, oq and ov will be the originals of ac and bd. „ PROPOSITION VII. — PROBLEM. Given the centre and distance of the picture, and the seat of a point on the picture, and its distance from it, to find the representation of that point. Let c, figure 6, be the centre of the picture, s the seat of the given point. Through c and s draw at pleasure c o and s p parallel to each other ; make co equal to the distance of the picture, and sp equal to the distance of the original point from its seat s. Draw op and sc, cutting each other in p, which will be the representation of the original point required. 80 CABINET-MAKER, UPHOLSTERER, For imagine the eye of the spectator to be placed at o, and p to be the original point in their proper places ; then will o p be a visual ray, projecting the point p at p ; and because of the similar triangles p s p and p c o, s p : : pc : : s p : co ; therefore sp + pc :pc : : sp + co : co, or cs : cp : : sp + co : co : now cs, sp + co and co are constant quantities; therefore the distance cp is invariable, and consequently the point p must also be invariable. Hence the point p may be found by calculation thus : — s p + c o : c o : : cox c s cs : cp= -- - - - c o which is the distance of the point p from c, the centre of the picture. PROPOSITION VIII. — PROBLEM. Given the centre and distance of the picture, the intersecting point of an original line, and the seat of the line on the picture, and the inclination of the line to its seat, to find the vanishing point of the original line and its inde- finite representation. Let c, figure 7, be the centre of the picture, i the intersecting point of the original line, and i d its seat. Make the angle dia equal to the angle which the original line makes with its seat id; draw cv parallel, and co perpendicular, to id, and make co equal to the distance of the picture. Draw o v parallel to ia, and join i v ; then v will be the vanishing point, and i v the indefinite representation of the original line. Suppose the triangles cvo and dia to be turned round the lines cv and id; c v i being turned towards the front, and d i a on the back, of the picture, so that each two adjoining planes may be perpendicular to each other, then the point o will be in the point of sight, and i a will be the original line ; then o v will be still parallel to a i ; therefore o v will be the radial of a i, v its vanishing point, and i v its indefinite representation. AND COMPLETE DECORATOR. . 81 PROPOSITION IX. — PROBLEM IV. Prom a given point in the indefinite representation of a straight line, to cut off a part of that indefinite representation that shall represent a given portion of the original. METHOD FIRST. Let a v, fig. 8, be the given indefinite representation ; it is required to cut off fi om a v a part which shall represent a line of a given magnitude, vl being the vanishing line, Plate x. ; o the point of sight, and in the intersecting line. Through o draw co parallel to vl ; make od equal to the original line. In vl take any point l, draw ol and dc parallel to ol. Draw La, cutting in in a; make ab equal to oc, and join Lb, cutting av in b, then ah is the part required. This method is excellent when only one or two distances are required to be ascertained; but when many are wanted, the following method will be found to be productive of very great facility. The principle and methods of performing this operation are quite new, and entirely free from the defects of the method first introduced by Dr. Brook Taylor, and in practice in every recent publication founded upon his principles. METHOD SECOND. The same data being referred to by the same letters, will be known by the preceding diagram. Diaw oc, figure 9, parallel to vl; make oc equal to the distance be- tween the vanishing line vl and intersecting line in; then the point l being taken as before, draw o l and c d parallel to o l. Make the dis- tance between the vanishing line vl and the parallel line ab equal to od. Through l draw La, which produce to meet ba in a, and make ab equal to the length of the original line, and join bL, cutting a v in b, then ab is the line required. x 82 CABINET-MAKER, UPHOLSTERER, This depends upon the same principle as the foregoing method. These methods have the peculiar advantage, that the measuring centre may be placed on any point of the vanishing line, and consequently may be brought immediately over the representation of the line to be divided ; by this means the dividing lines cut the representation given more directly or less obliquely than the usual process. In the common method the measuring point cannot have any change, and as it is always situated at a distance from the centre of the vanishing line, the intersections made in this indefinite representation are so very oblique, that the points required must, in fact, be guessed at. Taking given portions of the distance of a vanishing point, as J, J, f, &c, is very troublesome, and does not always obviate the inconvenience. PROPOSITION X. — PROBLEM V. To divide the representation of a line, whose vanishing point is given, into any number of parts, so that their originals shall have a given ratio among themselves. Let ab, figure 10, be the given representation of the line to be divided, and v its vanishing point. Draw vo at pleasure, and draw ab parallel to vo. Through any point o, in the line v o, draw o a and o b, cutting ab in a and b : divide a b in c, d, &c. in the given ratio, and draw oc, od, &c. cutting a, b in c, d, &c. then a, b will be divided as required. For c v being parallel to ab, a b may be considered as the original line, and ov its parallel; and consequently o as the point of sight, and oa, oc, o d, &c. visual rays, projecting the points a, c, d, &c. PROPOSITION XI. — PROBLEM VI. From a given point in a given indefinite representation of a line, to cut off a part, of which the original shall have a given ratio to the original of another given part of that indefinite representation. AND COMPLETE DECORATOR. 83 Let b v, figure 11, be the given indefinite representation of the line, v its vanishing point, be the given part; it is required to cut off from a a part of which the original shall have a given ratio to the original of the part represented by be. Through v draw v l at pleasure, and a b parallel to v l, and at any distance from v l draw l c and l b, which produce to meet a b in c and b ; also draw l a, cutting ab at a : make Ad equal to bc, in the ratio required, and join dL, cutting b v at d, then the original of ad is to the original of bc as Ad is to bc. This is evident by considering it upon the same principle as that in the preceding proposition. The above Problem very frequently occurs in the following case, viz : — supposing ab to be given in perspective, it is required to cut off a part, ad, from a, so that the originals of ad and ab may have a given ratio. The description is shortly thus — PLATE XI. Draw l a, l b, figure 1, cutting ab at A and b; make Ad equal to a b in the ratio required; join dL, cutting the indefinite representation \b as required. Or if a d is given, ab may be found exactly in the same manner. PROPOSITION XII. — PROBLEM VII. At a given point in the indefinite representation of an original Line, to represent a Line equal to, or in a given Ratio to, the original of another given Line, the vanishing Line, and the proposition of the Rye, being given. CASE FIRST. Let a b, figures 2, 3, and 4, be the vanishing line, o the point of sight, ab the given indefinite representation, a its vanishing point ; c b the indefinite representation from which the part is required to be taken, and c the point at one of its extremities, and let b be the vanishing point of cb. 84 CABINET-MAKER, UPHOLSTERER, Parallel to ab draw any straight line ad; oin ao and bo, and draw op, cutting ah in p, so that the angle aob may be bisected. Draw p a, p b, pc, cutting ad in a, b, c. Make cd toab in the ratio required, and join pd, cutting cb in «?, then the original of ab will be to the original of cd as ab is to cd. In figures 3 and 4, as ab is parallel to the vanishing line, the radial oa is also parallel to the vanishing line. In figure 4, the angle aob being a right angle, and being bisected, bp will be equal to bo, the distance of the picture. CASE SECOND. Suppose the points b and c to coincide, then the points b and c will also coincide. In this case let b become c, and b will also become c ; the opera- tion will still continue to be the same, except there is only one line to produce nstead of the two p b and pc; but that the method may be clearly under- stood, we shall shew the construction according to this simplification, parti- cularly as this case more frequently occurs than the other. Parallel to ab, figure 5, draw any straight line ad. Draw p a, p c, meet- ing ad in a and c ; make cd equal to ca, in the ratio of the two original lines, and join pd, cutting cb in d. Then the original of ab will be to the original of cd, as ca is to cd. This method obtains the result, whether the two lines lie on both sides of the line pc, or on the same side of it. Hence it is evident, that if ca and cd be equal to each other, the original lines, represented by ca, cd, ce, and cf, will be all equal to each other. But here it may be observed, supposing d a and f b not to be parallel, that is, to incline to each other, that we should not have had more trouble in representing the triangle abc, figure 6, formed by producing da and fb to meet each other in c ; so that to find the representation of a triangle in the original plane, we have only to produce the three sides, and find the indefinite representations of these three sides, as the triangle abc i« the repre- sentation of the original triangle abc. AMD COMPLETE DECORATOR. 85 This same idea will extend to all kinds of right-lined figures, by merely finding the indefinite representations of the sides of the original figure, without resolving it into triangles ; and their mutual intersections w ith each other, will form the representation of that figure, whatever it may be. This method is so evident, that more examples will not be necessary, and more particularly as the figures, being drawn out in their real places, would be attended with great inconveniences, and would require more surface to draw r upon than can generally be found. The principle will be clearly understood by turning the plane y upon the plane of the picture towards the eye, and the plane x behind the picture, so that the planes x and y may be parallel to each other ; then the picture and the other two planes being supposed to be transparent, and tbe eye placed at o, each indefinite representation will intercept the view of its original, whether point or line. PROPOSITION XIII.- -PROBLEM VIII. Given the vanishing and intersecting Lines of a Plane , the Centre and Dist- ance of the vanishing Line , to find the Projection of any Line , or Side of a Figure , given in the original Plane. Let gh, figure 6, Plate xi. be the vanishing line, s its centre, and let the intersecting line be d e. Draw so perpendicular to g h, and make so eeual to the distance of the picture. Then to find the representation of the straight line a b, in the original plane x, folded on the plane of the picture, as well as the vanishing plane y. Draw og parallel to a b, meeting the vanishing line g h in g, and produce a b to meet the intersecting line in e, then e is the intersecting point of ab; joinGE; and g e is the indefinite representation of ab. Now, to find the representation of any point in the original plane, we must make two lines pass through that point, and find the indefinite representations of these two lines, and their intersection will give the representation of that point. With 86 CABINET-MAKER, UPHOLSTERER, respect to the representations of the points a, b, which mark the extremities of the original line ab; a common indefinite representation g e has been found for each of the points a, b ; then as one indefinite representation has been found for each point, we have only to find another for each of these points; therefore, draw any line ad, and find its indefinite representation dh, also any line be, and find its indefinite representation fi, then the intersec- tions a and b , of these two indefinite representations, mark the extremities of the line ab. which is the representation of a b as required. PROPOSITION XIV. — PROBLEM IX. Given the vanishing and intersecting Lines of a Plane , and the Centre and Distance of the vanishing Line, to find the original of a given Repi esentation. Let it be proposed to find the original of the triangle abc , fig. 6. Produce the sides ba,ac,bc, of the given representation to their vanishing points g, h, i, and to their intersecting points e, d, f, and draw r the radials go, ho, io; draw ea parallel to og, dc parallel to oh, and fc parallel to oi, then the triangle abc, formed by the intersections of these three parallels, will be the original of the triangle abc as required. This is evident from the last proposition being only the reverse of it. PROPOSITION xv.' — PROBLEM X. Given the vanishing and intersecting Lines of a Plane, and the Centre and Distance of the vanishing Line, to find only the Length of the Original of a Projection given. Let g h, fig. 7, and a b, be the intersecting and vanishing lines, s the centre of the vanishing line gh,o the point of sight placed as usual, and ab the given projection or indefinite representation. Produce ba to its vanishing point g ; join g o, and make g h equal to go. Draw h« and ub, cutting the intersecting line ab in a and b ; then ab will represent a distance equal to the original of ab. AND COMPLETE DECORATOR. 87 Demonstration. Let c be the intersection of the given representation a b. Now g h being equal to go, the distance of the vanishing point g, and ac being parallel to g h, the point h may be considered as the point of sight, and a bc as the original line, ha and hb, as visual rays, producing the projection or indefinite representation a b. PROPOSITION XVI. PROBLEM XI. (riven the vanishing Line of aP lane , the Centre and Distance of that vanish- ing Line , and the vanishing Point of a Line in that Plane , to find the vanishing Point of another Line in the said Plane , so that the two original Lines shall form a given Angle. Let g h, figure 8, be the vanishing line, o the point of sight, and g the given vanishing point situated as before. Join g o. Draw o h, making the angle goh equal to the given angle, then h is the vanishing point required. If the sides of the original angle produced are not subtended by the inter- secting line, make the angle goi, not subtended by the vanishing line, equal to the original angle, and produce i o to meet the vanishing line in h, then h is the vanishing point required. This is evident, since the radials make the same angle at the point of sight that the originals make with each other. PROPOSITION XVII. PROBLEM XII. Given the vanishing Points of an Angle , and the Representation of the Angular Point , to represent that Angle. Let g and h, figure 8, be the vanishing points, and b the representation of the angular point ; then if the original angle is subtended by the intersecting line, draw bo, and b h, and g6h will be the representation required. But if the original angle is not subtended by the intersecting line, produce Gb or nb, according to which side it may lie upon; suppose h b produced to c, then the angle g bc, or a bc, will represent the angle required. 88 CABINET-MAKER, UPHOLSTERER, PROPOSITION XVIII. — PROBLEM XIII. Given the vanishing Line of a Plane , the Centre and Distance of the vanishing Line , and the Representation of one Side of a Triangle of a given Species in that Plane , to find the Projection of the whole Triangle. Let vl, figure 9, Plate xi. be the vanishing line, s its centre, and o the point of sight as before, and ah the representation given. Produce ah to its vanishing point v, or let v be the vanishing point of ah; and let ah subtend the angle, which is also subtended by the intersecting line. Make the angle v ok equal to the original of the angle at h, the side ok cut- ting v l in k ; draw k he, and suppose the original of the angle at a , not sub- tended by the intersecting line : make the angle vop equal to the original of the angle a, and produce po to its vanishing point l, and draw l ac, then ahe is the triangle required. OR THUS. Draw a b, fig. 9, parallel to v o. Then on a b describe a triangle similar and similarly situated to the original triangle. Draw o l parallel to a c, and o k parallel to bc; then the intersections of these lines give the vanishing points l and k ; then the angles, subtended by the intersecting line, will be the opposite angles to those subtended by the vanishing line ; therefore the same angles of the triangle abc, that are subtended by the vanishing v l, will have their representations also subtended by the vanishing line v l ; and the same angles in the triangle abc, of which the contained sides would meet the vanishing line when produced to form an opposite angle, will have their representation also subtended by the vanishing line; thus the angle ach represents an angle equal to acb, and the angle c ha represents an angle equal to cba ; because ab and cb would meet the vanishing line the same as a h and ch. AND COMPLETE DECORATOR. 89 PROPOSITION XIX. — PROBLEM XIV. Given the Vanishing Line of a Plane , and the Centre and Distance of the Vanishing Line , and the Representation of any Side of a Figure in that Plane, to find the Representation of the whole Figure. Resolve the original figure into triangles, by means of diagonals, and find the representations of these triangles one after the other, by Proposition xvm. beginning with the triangle which has the line given, then every triangle, as it is represented, will give a new line for the next to be represented. EXAMPLE. Given the Vanishing Line of a Plane, the Centre and Distance of the Vanishing Line, and the Representation of one Side of a Square , to find the Representation of the entire Figure. Let vl, figure 10, be the vanishing line, s its centre, o the point of sight as usual, and let ah be the representation of the given side. Produce ah to its vanishing point v, if not already done ; join vo, and draw o l perpendicular to v o. Draw o m, bisecting the angle vol, and meet- *» . ing the vanishing line v l in m. Also, draw a m and l h, cutting each other in c : again, through a and c draw a l and \c, cutting each other in d ; then ahcd is the representation of the square required. The representation of a square is described with great ease, knowing that the diagonal being drawn, bisects the opposite angles ; and by attending to the foregoing instruction, the representations of figures with more sides may be executed with equal facility. PROPOSITION XX. — PROBLEM XV. Given the Vanishing Line of a Plane, the Centre and Distance of the Vanishing Line, and a Line representing a Perpendicular drawn through the Centre of a Square to one of its Sides, to describe the entire Representation of the Square. ' Let v l, fig. 1 1, be the vanishing line, s the centre of the vanishing line, and o the point of sight as usual. Also, let a be the representation of the centre of the square, and ah the representation of the perpendicular. 90 CABINET-MAKER, UPHOLSTERER, Produce ba to its vanishing point v ; then having drawn vo and ol per- pendicular to vo : draw o m, bisecting the angle vol, and cutting the vanish- ing line v l in m ; then m is the vanishing point of the diagonal of the square. Draw m a and l 6, cutting each other in d; also draw mb and a l, cutting each other in c. Through c draw vc, cutting d l at e, and du at f ; lastly, draw l / and dv, cutting each other at^; then defg is the representation of the square required. This method is evident, since a line drawn perpendicular from the centre to one of the sides of a square makes half a right angle with either of the diagonals; therefore 6 m must cut ac, to represent a line equal to the line represented by ab. This operation is also evident from the next Proposition. PROPOSITION XXI. — PROBLEM XVI. Given the Vanishing Line of a Plane , the Centre and Distance of the Vanishing Line , and a Line representing a Perpendicular drawn through the Centre of an Octagon to one of its Sides, to describe the entire Representation of the Octagon. Complete the square defg , fig. 12, as in the last Proposition. Draw n h parallel to v l. Produce m b and m d to meet n h at b and d. Draw b q per- pendicular to n h, and make bq equal to bd, and join dq. Make dH and d n each equal to dq ; bp equal to bH, and do equal to dp. Draw m n, cutting the sides gf and gd of the square at m and n; and draw m h, cutting ed and e/at h and i; draw om, cutting gf and gdoXl and o ; and, lastly, draw pM, cutting ef and e d at k and p. Draw Ik and op , then hiklmnop is the representation of the octagon required. This method is evident from the construction of the real octagon, (see the adjacent figure,) for it is well known that each side of a regular octagon is equal to the difference between the side and diagonal of a square having the diameter of its inscribed circle equal to that of the octagon. Now dr is half AND COMPLETE DECORATOR. 91 the side of the square, and since r s is equal to dr or r e, d s is therefore equal to half the diagonal; and Rh, which is half the side of the octagon, is equal to the difference between the half diagonal and half side of the octagon. PROPOSITION XXII. — PROBLEM XVII. Given the Vanishing Line of a Plane , the Centre and Distance of the Vanishing Line , and the Representation of the Centre and Radius of a Circle , to complete the whole Representation of that Circle. It is known that a circle in perspective is an ellipsis, for it is demonstrated by writers on conics, that the section of a cone is an ellipsis. m Now the repre- sentation of a circle is the section made by the plane of the picture intercept- ing the rays which proceed from the original circle to the eye, and which form a conic surface, consequently the representation is an ellipse. Therefore in order to form the curve correctly, we must find its axis, or such diameters that it may be described by continued motion. But though the difficulty of doing this is not very great, yet to understand the principle thoroughly requires more geometrical knowledge than most people are possessed of. We shall, therefore, shew how to find a convenient number of points, or of points and lines representing as many points of the original circle ; which, when ascertained, the curve must be drawn through them by hand, observing the elliptic figure, which will greatly contribute to the accu- racy of the representation. method first. Let a £, figure 13, represent the given radius, the vanishing line and its centre and distances being as before. Find the representation hiklmno of the octagon, as in the preceding Problem. Produce ah to cut the opposite side ml in v, and produce ca to cut the side no at w: let the diagonal fd cut the two sides Ik, op in r and s; draw the diagonal ge, cutting mn and hi in t and u , then through the eight points h, u , c , r, v, t, w, s, draw the curve of an ellipse ; which may be very 92 CABINET-MAKER, UPHOLSTERER, correctly done, since the circle is supposed to be inscribed in the octagon, its representation will touch the representation of the octagon; therefore the eight points of representation are as many points of contact, which are equi- valent to sixteen points, without tangents. When the representation is very small, we need not be at the trouble to represent the octagon, the four points b, c, v, w, in the representation of the sides of the square, will be sufficient; for these being points of contact, the curve may be drawn with considerable accuracy. However, in most cases it would be eligible to find the sides mn and hi of the representation of the octagon, as also the points of contact t and u, which would limit the length of the curve witfi much greater accuracy than would otherwise be obtained, and this may be done without increasing any confusion of lines, even though the curve should be ever so narrow, or ever so near the vanishing line. This is one of the best practical methods that has ever been invented. In short, the operation is not only performed with fewer constructive lines, but with much more facility, and the curve described with greater accuracy than has been done by any other method hitherto published. PLATE XII. METHOD SECOND. The data, fig. 1, being as before, produce the representation ab of the given radius to its vanishing point v. In the vanishing line v l, take any number of vanishing points k, 1,l, &c.: and draw the radials vo, ko, lo, lo, &c. : through the representation of the centre a draw the indefinite radii \b, k», 1A, L g, &c. Make af to represent a part equal to the part represented by a A by Proposition xi. Bisect the angles v o k, ko 1, lo l, &c. and let the bisecting lines meet the vanishing line in m, n, p, &c. Through one extremity f, of the first perspective diameter fb, draw mf cutting the second in i ; through the other extremity b draw m b , cutting the second diameter in e. AND COMPLETE DECORATOR. 93 Having now obtained the second diameter ei , we may find the third from the second, the same as the second was found from the first; and so on, from one to another, till the whole are found. For if the indefinite representations of any two lines intersect each other, and if the two radials be bisected, a line drawn from the vanishing point of the bisecting line, cutting the two indefinite representations, will intercept two parts between the points of section and the point where these indefinite representations cut each other, of which the originals will be equal. PROPOSITION XXIII. PROBLEM XVIII. Given the Centre and Distance of the Picture , the Intersection and Inclina- tion of an original Plane to the Plane of the Picture , to find the Vanish- ing Line of that Plane , and the Centre and Distance of the Vanishing Line. Let a b, figure 2, be the given intersecting line of the original plane, and c the centre of the picture. Draw co parallel, and cs perpendicular, to ab; make co equal to the distance of the picture. Draw o s, so that the angle o s c may be equal to the inclination of the original plane to the picture. Draw sd parallel to ab ; then will sd be the vanishing line, s its centre, and o s its distance. For, imagine the triangle o cs to be raised on the picture, so that oc may be perpendicular to it ; then the point o will be the point of sight, and s d being parallel to a b, a plane passing through the line s d and the point o, will be the parallel of the original plane, passing through a b, and inclined to the picture in the angle o s c ; therefore sd is the vanishing line, o s the distance of the vanishing line from the point of sight o, and s the centre of the said vanishing line. 94 CABINET-MAKER, UPHOLSTERER, PROPOSITION XXIV. — PROBLEM XIX. Given the Centre and Distance of the Picture , and the Vanishing Line of a Plane , to find the Vanishing Point of Lines perpendicular to that Plane. Let a b, figure 3, be the vanishing line given, and c the centre of the picture. Through c draw ad perpendicular, and co parallel, to ab. Make co equal to the distance of the picture; join oa, and draw od perpendicular to oa ; then d will be the vanishing point required. When the vanishing line a b passes through the centre of the picture, then co will coincide with ab, and as od is drawn perpendicular to ca, both a d and od will be perpendicular to ab; or, ad and od being parallel, the vanishing point d will be at an infinite distance. See figure 4. In this case the representations of lines, perpendicular to the plane pro- posed, will all be perpendicular to their vanishing line a b. This is actually the case when we would represent perpendiculars to a plane perpendicular to the picture, or in a vertical picture, upon a plane perpendicular to the horizon. Demoyistration. — Figure 3. Imagine the triangle ao d to be turned round a d until it is perpendicular to the picture ; then o will be brought into the point of sight ; therefore the plane passing through o and a b, will be parallel to the original plane, and the line o d, passing through the point of sight o, will be perpendicular to it, and as od meets the picture in o, o will be the vanishing point of all original lines parallel to o d, or perpendicular to the original plane. AND COMPLETE DECORATOR. 95 PROPOSITION XXY. — PROBLEM XX. Given the Centre and Distance of the Picture , and the Vanishing Point of a Line , to find the Vanishing Line of a Plane, perpendicular to the origi- nal of the Line whose Vanishing Point is given, and the Centre and Distance of the Vanishing Line. Let c, fig. 3, be the centre of the picture, and d the vanishing point given. Through c draw da and co perpendicular to da, and make co equal to the distance of the picture: draw do and oa perpendicular to do; and, lastly, draw ab parallel to co; then ab is the vanishing line required, and a its centre. This construction here is the reverse of that in the preceding Problem, therefore the same observations apply here, and the same demonstration as in the Problem alluded to. PROPOSITJON XXVI. — PROBLEM XXI. Given the Centre and Distance of the Picture, and the Vanishing Line of a Plane, through a given Point, to draw the Vanishing Line of another Plane, perpendicular to the Plane whose Vanishing Line is given, and to find the Centre and Distance of that Vanishing Line. Let c, figure 4, be the centre of the picture, and a b the given vanish- ing line. Find the vanishing point d of a line perpendicular to a plane whose vanishing line is ab, by Problem xix ; join d e, and draw c i perpendicular to d e, cutting d e in f ; then d e is the vanishing line, and f its centre. Its distance may be thus found ; let c o, parallel to a b, be the distance of the picture ; from d, as a centre with the radius d o, describe an arc, cutting c i at i ; then f i is the distance of the vanishing line d e. Demonstration. — Because the plane, whose vanishing line was required, is perpendicular to the other plane, its vanishing line must pass through the point d of lines perpendicular to that other plane ; but as this vanishing line 96 CABINET-MAKER, UPHOLSTERER, must also passf through the point e, de will be the vanishing line required : and, because a line drawn through the centre of the picture, perpendicular to a vanishing line, gives by its intersection the centre of that vanishing line ; the point f is the centre of the vanishing line de. The rest will be evident by turning up the triangle dao perpendicular to the plane of the picture, then turning the triangle d i f round d e, until g falls upon o, then d g will coincide with d o. Corollary 1. -If fc be produced till it meet the vanishing line given in the point b, b will be the vanishing point of lines perpendicular to the original plane of the vanishing line de: for that vanishing point is in the line fc, by the construction of Proposition x. and it is in the vanishing line given by the demonstration of the present Proposition. Corol. 2.— If the vanishing lines ab and de meet in g, the points b, d, and g, will be the vanishing points of the three plane angles forming the solid angle of a cube ; these planes being perpendicular to each other, and if d b be joined, bg.gd, and d b will be the vanishing lines of the three planes that contain that solid angle. Corol. 3. — The distance of the vanishing line dg is also equal to the line f i ; the point i being in the semi-circumference described upon dg as a diameter. Corol. 4.— In the construction of the vanishing lines forming the solid angle, when the point of sight is found for each vanishing line, and the radials of the common intersections of the planes drawn, every two radials at the point of sight will be at right angles to each other, and every two of these radials, which terminate in the intersection of two vanishing lines, will be equal to each other. Hence in every two vanishing lines, if the centre and direct radial be drawn in the one, the direct radial can be found in the other, for the point of sight in this other will be in the circumference of a circle described from the intersection of the two vanishing lines, with a radius equal to the radial joining that intersection and the point of sight given. AND COMPLETE DECORATOR. 97 Thus let G b and gd be the vanishing lines of two planes, and let A and f be their centres, and let h be the point of sight for the vanishing line g b. Draw fi perpendicular to gd; from the centre g, with the radius gh, de- scribe an arc, cutting f i in I ; then f i will be the direct radial. Corol. 5. — If the point of position of the eye for each of two of the vanish- ing lines be found, the third will also be found ; for it must be in the inter- section of two circles described from the two vanishing points of the third vanishing line, with radii which are respectively equal to the two adjacent radials. Corol. 6 . — The length of any direct radial is a mean proportion between the segments of the vanishing line, on each side of the centre ; because the plane angle, formed at the eye, is a right angle; and hence, as before observed, if we draw the perpendicular from the centre of the vanishing line, and de- scribe a semicirtcle on the said line, the point where it intersects the perpen- dicular will be the point of sight. PROPOSITION XXVII. — PROBLEM XXII. Given the Centre and Distance of the Picture , and the Vanishing Point of the common Intersection of two Planes , inclined to each other in a given Angle , and the Vanishing Line of one of them , to find the Vanishing Line of the other. Let c, figure 5, be the centre of the picture, b g the given vanishing line of one of the planes, and b the vanishing point of their common section, and h the angle of their inclination to one another. Find the vanishing line gd of planes perpendicular to the lines whose vanishing point is b, (by Proposition xxv.) and let that vanishing line cut the vanishing line given in g. In gd find the vanishing point e of lpies, making the given angle H with the lines, whose vanishing point is g ; that is, in bcf, perpendicular to g fd, take f p equal to the distance of the vanishing line g d. If c o be parallel to g d, and equal to the distance of the picture, make fp equal to fo; join pg, and draw pe, meeting gd in e, so that the 2 B 93 CABINET-MAKER, UPHOLSTERER, angle gpe may be equal to h, and draw b e, then b e will be the vanish- ing line required. Demonstration. — For imagine the triangle gpe to be turned on the line gd, so that the point p may fall in the perpendicular drawn from c to the plane of the paper or picture ; then p will be the point of sight, and the apex of three imaginary planes, bpg, g p d, d p b, supposed to be raised on the vanish- ing lines bg, gd, db. Then also the three planes, thus supposed to be raised, will be parallel to the three original planes which have bg, g d, d b, for their vanishing lines. Now the plane, whose vanishing line is dg, being perpendicular to the other two by construction, because it is perpendicular to their common section, whose vanishing point is b, will measure the inclination of these two other planes ; therefore, by joining be, be will be the vanishing line required. PROPOSITION XXVIII. — PROBLEM XXIII. Having the Centre of the Picture , the Vanishing Lines of two original contiguous Planes , and the Centre and direct Radial of one of the Vanishing Lines , to find the Centre and direct Radial of the other Vanishing Line. — The reader to supply the figure himself Let c be the centre of the picture, a b and b d the two vanishing lines, h the centre of the vanishing line, ab and ho its direct radial. Draw c m perpendicular to b d, cutting bd at l ; make b m equal to bo; that is, with the radius b o describe an arc, cutting c m at m : then l is the centre and lm the distance of the vanishing line lm. PROPOSITION XXIX. — PROBLEM XXIV. Given the Centre and Distance of the Picture, the Vanishing Line of a Plane, the Inclination of a Line to that Plane , and the Angle which the Seat of the Line upon that Plane males with the Intersecting Line , to find the Vanishing Point of that Line. Let c, figure 5, be the centre of the picture, b g the given vanishing lines AND COMPLETE DECOKATOK. 99 Find d, the vanishing point of lines perpendicular to planes whose vanishing line is eg, and let dc cut bg in s, which is the centre of the vanishing line bg : make s i equal to the distance of the vanishing line bg ; that is, if co, parallel to bg, be equal to the distance of the picture, make si equal to so. Draw ik parallel to bg; and make the angle kig equal to the angle which the seat of the line makes with the intersection. Join dg. Find the centre f and distance fp of the vanishing line d g ; that is, draw p f perpendicular to d g, cutting dg in f ; make g p equal to gi; and draw pe, meeting dg in e, so that the angle gpe may be equal to the inclination of the line to the plane, then e will be the vanishing point of the line required. This construction is evident from the foregoing demonstration, and more particularly from the las t. When the vanishing line b g passes through the centre of the picture, the original plane and that of the picture will be perpendicular to each other. In this case the vanishing point d will be infinitely distant from the centre of the picture, and consequently the vanishing line d g will be perpendicular to the vanishing line b g ; and because s and c are supposed to coincide, the points f and g will also coincide : the construction will, therefore, be simplified as follows : — ■* ' Draw c i, fig. 7, perpendicular to b g ; make c i equal to the distance of the picture. Draw i k parallel to bg, and make the angle kig equal to the angle which the seat of the line makes with the intersecting line. Draw d g perpendicular to bg; make g p equal to g i, and draw p e, meeting dg in e, so that the angle gpe may be equal to the inclination of the line to the plane; then e will be the vanishing point of the line required. 100 CABINET-MAKER, UPHOLSTERER, PROPOSITION XXX. — PROBLEM XXV. Given the Vanishing Line of a Plane , the Centre and Distance of the Picture , the finite and indefinite Representations of two Lines in that Plane ; from a given Point in the indefinite Representation , to cut off a Part , which shall represent a Line equal to the Line represented by the finite Representation. Let vl, figure 8, be the vanishing line, c the centre of the picture, ab the finite representation of a line, and c l the indefinite representation of another; it is required to cut off from c a portion of the line c l, of which the original shall be equal to the original of the line represented by a b. Draw c o perpendicular to v l, intersecting vl in the point s, the centre of the vanishing line. Draw c e parallel to v l, and make c e equal to the distance of the picture. Join se, and make s o equal to se. Join o v and ol. Draw the radial om, bisecting the angle vol. Draw the straight line bd parallel to vl. From the vanishing point m, ana through the points a and b , draw the straight lines ma, mb, meeting the line bd in the points a and b ; also, from the same vanishing point m, and through the point c, draw the straight line me, meeting b d in c. In bd, make the line cd to ab, as the original of cd is to the original of ab. Draw the straight line dm, intersecting cl in d, and cd is the line required. SCHOLIUM. This Problem is useful in the representation of solids ; for it sometimes happens, after we have finished the representation of one plane, that we have another to represent, and having already determined the vanishing line from the circumstances of the Problem, and having the centre and distance of the picture, which were necessary in the representation of that plane, we have the same data still, and consequently we may, by these means, represent lines, of which the originals may have any ratio to each other, and thus find the representation of any figure : in short, perform any of the foregoing Problems. AND COMPLETE DECORATOR. 101 Part II.— PERSPECTIVE. Of the Representation of Solids. All objects whatever, that are formed by art, come under the denomination of some geometrical solid, as a prism, a pyramid, a cylinder, a cone, a sphere, &c. Thus the body of a house is generally a rectangular prism, and the roof may either be a right triangular prism, as in pediment roofs, or the frustum of a pyramid, as in hip-roofs. Or, if the body of a building be a cylinder, the roof may either be a cone or a segment or zone of a sphere, as in domes. The surfaces of these solids are, therefore, triangles, rectangles, circles, & c. Therefore to represent any object of Cabinet Furniture, or building, it will be necessary to represent the several kinds of geometrical solids ; but more particularly the rectangular parallelopiped. And as most objects stand per- pendicular to the horizon, they will be represented as if they stood upon a plane perpendicular to the picture. A cube, or rectangular prism, is perpendicular to the horizon when one of its faces coincides with a horizontal plane; a right cylinder, or cone, is said to stand perpendi- cular to the horizon when the axis is perpendicular to the horizon ; there- fore in representing such objects, the axis will be parallel to the picture, and will therefore be represented by straight lines perpendicular to the vanishing line. Having treated of the representations of various kinds of plane figures, nothing now remains to be done in order to represent a solid bounded by a plane figure, but to combine the faces according to their angles of inclination. To enable the student to execute this part in the most general manner, he has only to know from having given the centre and distance of the picture , the angle of inclination of two planes , the vanishing point of their common 2 c 102 CABINET-MAKER, UPHOLSTERER, section , and the vanishing line of one of the planes , in order to he able to find the vanishing line of the other , as also its centre and distance * If he has studied the preceding propositions with care, he is already in possession of the principle for accomplishing this object: but as this gene- rality in the method of representing solids is seldom required in perspective, and less perhaps by the designer of cabinet work than by the architect or builder, we shall here trace the principle as applied to a parallelopiped to that of a rectangular prism, according to the various positions of the faces of the solid. We must consider, that as a rectangular object is bounded by six faces, which are plane surfaces, and since every plane has its parallel, every two planes may have a vanishing line, since the six faces may be inclined to the picture. The number of vanishing lines, and the number of vanishing points, can never exceed three of each kind. Moreover, since the solid cannot have more than two of its faces parallel to the picture, it cannot have fewer vanishing lines than two, nor fewer van- ishing points than one, and in this case, where two of the planes are parallel to the picture, the other four planes are perpendicular to the same ; therefore, the vanishing line of each pair of these four planes, must pass through the centre of the picture. When two of the faces of the solid are parallel to the picture, the other four faces being perpendicular, have their four edges also perpendicular to the picture ; therefore, these four edges, being parallel to the intersection of the two planes, which passes through the eye parallel to the four planes perpendicular to the picture, have only one vanishing point in the centre of the picture. * It may be proper to mention in this note, a simplification of a proposition which leads to the solution of the above Problem, perhaps, in a more simple manner. The proposition which we allude to is this : — “ Given the Centre and Distance of the Picture , and the Vanishing Point of a Line, in a Plane perpendicular to the Picture, to find the Vanishing Point of another Line in that Plane , perpendicular to the Line whose Vanishing Point is given.' 9 AND COMPLETE DECORATOR. 103 The remaining two faces, being parallel to the picture, are represented by equal and similar rectangles. In this case, since a line which is parallel to the picture, has its representation parallel to the vanishing line of the plane, passing through the original line ; the eight edges of the solid, which are parallel to the picture, are in the four perpendicular planes to the picture therefore, the representations of these eight lines are parallel to the vanishing lines of these four planes. When four of the edges of the solid are parallel to the picture, and per- pendicular to the horizon, and the planes between these edges inclined to the picture, the remaining two planes are perpendicular to the plane of the picture, and parallel to the horizon, but the edges of these two planes are inclined to the picture; therefore, these eight edges being thus inclined, and in planes perpendicular to the picture, have two vanishing points in the vanishing line of the two planes which are perpendicular to the picture, and therefore in the horizontal line ; and as straight lines, perpendicular to a plane which is perpendicular to the picture, are represented by straight lines perpendicular to the vanishing line of that plane, the represen- tations of these four edges are perpendicular to the vanishing line of the horizon. Having thus traced the different positions of the representations of lines, frpm the different positions of the faces of the rectangular prism to the plane of the picture; it will be of the greatest use to trace the same positions of representation from the angles of inclination of the planes of the solid, which are all right angles, and from the properties of their vanishing lines, in order to trace the principle through the various stages of position. When the centre of the picture falls in the centre of the given vanishing line, we shall find the vanishing point of the four lines perpendicular to the planes, of which the vanishing line is given at an infinite distance, and in a line passing through the centre of the picture perpendicularly to the vanish- ishing line given of the two planes, which are perpendicular to the plane of the picture. 104 CABINET-MAKER, UPHOLSTERER, This indicates that the representations of the four lines are perpendicular to the vanishing line. , In this case the edges of the two planes, of which the vanishing line is given, may either have one or two vanishing points; if they have two vanish- ing points, four of the edges of the solid will be parallel to the picture, and the faces terminated by these edges inclined to the picture. In the case where there are three vanishing lines, which will form a triangle, and the three vanishing points will be in the vertices of the tri- angles, and consequently there will be two vanishing points in each vanish- ing line. Since the vanishing point of lines perpendicular to a plane, of which the vanishing line is given, always passes through the centre of the picture ; there- fore, when one of the vanishing lines is given, and the centre of the picture is in the centre of the vanishing line, the vanishing point of these lines will be in the perpendicular to the vanishing line, at an infinite distance from the centre of the picture ; the other two vanishing lines, which join the vanishing point, and the two vanishing points in the vanishing line given, must be also perpendicular to the same vanishing line given. For in performing this operation, we at first draw a straight line from the centre of the picture, perpendicular to the vanishing line given, and set the distance of the picture from its centre, upon the perpendicular ; then the other extremity of this distance is the point of sight. When this is done, we draw the radial which joins the vanishing point of the common section of the two original planes and the point of sight, and from the point of sight we draw another radial perpendicular to the first, and consequently perpendicular to the vanishing line given, and then a line through the vanishing point found by the second radial perpendicular to the vanishing lines ; and this last perpendicular will be the vanishing line of a plane perpendicular to the line of which the vanishing point is given, and the point of intersection of the two vanishing lines, will be the centre of this last vanishing line, and the length of the last radial is its distance; so that the AND COMPLETE DECORATOR. 105 point of sight for this new vanishing line will be in the first vanishing line, as the two vanishing lines intersect each other at right angles. We now proceed to set off the angle of inclination of the two planes, at this new point of sight, for the second vanishing line, so that the first vanish- ing line may be one side of the angle ; and by producing the line forming the other side of the angle to meet the second vanishing line, we shall have the vanishing point of all those lines which are perpendicular to the common section of the two original planes, and which form their angle of inclination. This circumstance will enable the artist to represent the lid of a box at any angle of inclination with the top ; to represent a ladder in any position to the horizon, or to represent the rafters of a building perpendicularly to the wall-plates, and making a given angle with the horizon, or top of the building. But if all the faces of a solid are planes, which are at right angles to each other, it will not be necessary to find more vanishing lines than that which is already given ; for in this case, though we may have a second vanishing line, it would not be used in the operation; for the angle of inclination of the planes being a right angle, and when this right angle is set off from the second point of sight, so that the perpendicular radial, which is part of the first vanishing line, may form one side of the angle, the other side of the angle must therefore be parallel to the second vanishing line, and consequently perpendicular to the first. This therefore indicates that the vanishing point is at an infinite distance, and therefore the representation of all lines, perpendicular to the plane of which the vanishing line is given, are also perpendicular to the same vanishing line. So that in representing a rect- angular solid, which can have only three vanishing points at most, and of which one of the vanishing points is not in the centre of the picture, two of them must be in the vanishing line given ; and the third series of lines, which represent the edges, are perpendicular to the said vanishing line, i These preliminary observations will be evident in the examples of repre- senting solids in perspective. 2 D 106 CABINET-MAKER, UPHOLSTERER, Observation, With respect to general methods of practice in the representation of objects comprehended under the forms of rectangular parallelopipeds, or rectangular prisms, deduced from the immediately preceding observations. — The first consideration is, to fix on the point of view ; this will determine the centre and distance of the picture ; therefore, in what follows, we shall always suppose the centre and distance of the picture to be given, the determination of these will therefore form no part of the operation in repre- senting rectangular objects in perspective. There are two positions, in respect to the picture, of representing rectan- gular bodies, commonly called rectangular parallelopipeds, or rectangular prisms ; the one is, by considering two of the faces parallel to the picture ; and consequently, the other four perpendicular to the same. Hence, in this case, the vanishing point of the four parallel lines, in the meeting of the four planes, which planes being perpendicular to the plane of the picture, will be in the centre of the picture ; the outlines of the figures representing the other two planes, which are parallel to the picture, are rectangles, which have their sides parallel and perpendicular to the vanishing line of the four planes which are perpendicular to the picture. The common sections of those two planes, of which the vanishing line is given, and of the two planes which are parallel to the picture, are represented by straight lines parallel to the vanishing line, and consequently, the other two edges of the planes, which are parallel to the picture, are represented by lines which are perpendicular to the vanishing line. The other position of the solid is, by considering two of the planes to be perpendicular to the picture, and each pair of the other four inclined. In representing such a solid, only one vanishing line, as we have already seen, will be necessary, and this vanishing line will be that of the two faces of the solid which are perpendicular to the picture, therefore each vanishing point will be the vanishing point of four lines, viz. those of the opposite parallel AND COMPLETE DECORATOR. 107 planes. Therefore, eight of the edges or arrises of the solid have their vanishing points in the vanishing line; because the vanishing line is the inter- section of a plane with the picture passing through the eye, parallel to the two perpendicular planes. The arrises of the four planes, which are inclined to the picture, being perpendicular to the other two planes, which are perpendicular to the picture, are therefore parallel to the picture, and are consequently represented by lines which are perpendicular to the vanishing line. There are, therefore, three positions of the object in respect of the picture: one is, when all the sides are inclined to the picture ; a second is, when two parallel faces are perpendicular to the picture ; and the third, when two parallel faces are parallel, and consequently the other four perpendicular to the picture. The first of these is called the triple inclined position , or simply the inclined position of the picture ; the picture being inclined to all the three pairs of parallel planes, or parallel faces of the object. The second is called the single perpendicular position of the object , or only the perpendicular position, the picture being perpendicular only to one pair of parallel sides of the object. The third is called the parallel position , or double perpendicular position of the picture , the picture being parallel to one pair only of the faces of the object, or perpendicular. to two pair of faces. The art of representing rectangular bodies having one pair of its faces parallel to the picture, has been denominated parallel perspective . In all positions of the picture, its centre and distance must always be a part of the data; and where the object is inclined, the inclination of one of its sides to the plane of the picture must be given, or some other equivalent. Practice in representing a Rectangular Object according to the Triple Inclined Position. As the position of the object to the picture depends upon choice, to save a great deal of useless trouble, it is customary to assume the vanishing line of 108 CABINET-MAKER, UPHOLSTERER, one pair of its parallel faces, and the centre of the picture, as also to assume the vanishing' point of a pair of sides of the rectangles of these two parallel faces of the object; this assumed point must therefore be in the assumed vanishing line ; for the vanishing points of all lines in the same plane are in the vanishing line of that plane. This vanishing point is, therefore, the vanishing point of the line of concourse of two faces of the object that are reciprocally perpendicular to each other, viz. of one of the faces of which its vanishing line is assumed, and one of the four perpendicular faces to that of which the vanishing line was assumed. We have now given the centre and distance of the picture, and the vanish- ing line of a plane, to find the vanishing point of lines perpendicular to that plane ; and this being found with the vanishing point of the line of concourse of two of the faces, will give two of the vertices of the triangle formed by the three vanishing lines of the three pair of parallel faces of the object. In order to find the third vertex of the vanishing triangle, find the point of position of the eye to the vanishing line ; join this point of position to the assumed vanishing point, and from the point of position draw a radial perpen- dicular to the line thus joined, and the vanishing point made by this radial is the vanishing point of the vertex of the remaining angle of the vanishing triangle. These three vertices are the vanishing points of the twelve arrises or lines of concourse of the faces of the solid, there being four parallel lines for each of the three vanishing points. Therefore, by drawing a straight line from each of the two vanishing points in the vanishing line given, to the third vanishing point found, we shall have the three vanishing lines ; two of these are, however, only necessary. But in order to represent the three faces which constitute the solid angle next to the eye of the observer, it will be necessary to find the centre and distance of one of the last drawn vanishing lines, which being done, find the representation of each rectangle, of which the vanishing line, its centre and distance, as well as the vanishing points of the sides of each, are both now given. The representation of the remaining face or rectangle will be found To Fublisked br H.Fislier. Son k V. Caxtan.Iandon. Ju2y.l835. AND COMPLETE DECORATOR. 109 by only drawing lines from the ends of the lines in the adjacent edges of the trapeziums, which represent the two first rectangles to the vanishing points of this last rectangle. To represent or find the image of a rectangular solid, its position in respect of the eye, and the picture being determined ; by knowing the distance of the eye and the distance of the vertex of the nearest solid angle, each from the picture, and having given in position in the plane of the picture, its centre and the vanishing line of one of the faces. — This single example very nearly embraces the whole of Perspective ; we shall therefore, in order to be distinct, number the propositions. ^ • We hav e given the distance of the picture, c its centre, l the vanishing point of a line ; to find the vanishing line of a plane, perpendicular to the line of which the vanishing point l is given. (See Prop, xxv.) Through the points L and c draw the straight line ls 2 , and cn perpendicular to ls 2 . • Make cn equal to the distance of the picture, and join ln. Draw ns 2 perpendicular to ln, and through s 2 draw vm perpendicular to ls 2 , and vm is the vanishing line here required. In this part of the operation we have also found s 2 the centre, and a line s 2 n equal to the dis- tance of the vanishing line vm, as also v the vanishing point of the line of intersection of the planes, of which vm and vl are the vanishing lines. This vanishing line being now found, will be enumerated among the data in the following Problem, as one of the given parts. No. 2.— Given in the picture in respect of two lines in a plane, making a given angle with each other, vm the vanishing line of their plane, s 2 its centre, and a line s 2 n equal to its distance, to find the vanishing point of the other line. Draw s 2 p 2 perpendicular to vm, (or, since cs 2 is already perpendicular to vm, prolong, if neces- sary, cs 2 to p 2 .) Join vp 2 , and make the angle vp 2 m equal to the angle which the two lines make with each other; and as this angle in the present case is a right angle, draw p 2 m perpendicular to vp 2 , and m is the point here required. This vanishing point being found, it will make a part of the data of the following Problem. No. 3. — Given in the picture of two straight lines in a plane, their vanish- ing points l and m, to find the vanishing line of the plane. 2 E no CABINET-MAKER, UPHOLSTERER, Join the points L and M, and lm will evidently be the vanishing line required; for the vanishing points of all lines in the same plane are in the vanishing line of that plane. By these operations, one grand Problem, which embraces the whole, is solved. The Problem which we now allude to is as follows : — Given with respect to two planes, making a given angle with each other, the centre and distance of the picture, the vanishing line of one of the planes, and the vanishing point of their line of concourse, to find the vanishing line of the other plane. This Problem has been solved in finding the vanishing line lm, therefore vl and vm are the vanishing lines of the two planes of the solid, and v the vanishing point of their line of con- course, or common section. But in the solution of this Problem we found vm the vanishing line of a plane perpendicular to the line of concourse of the two planes, of which the vanishing lines are vl, lm. But since iu each solid angle of a rectangular solid, any one of the three faces is perpendicular to the line of concourse of the other two, therefore vm is the vanishing line of the third plane. The object being rectangular, supersedes the necessity of finding the third vanishing line. In con- sequence of v M being the vanishing line of the third plane, y and M are the vanishing points of the remaining two arrises which are common to the third plane and each of the two first. In these operations we have found the radials P 2 v and p 2 m of the sides of the rectangles in the two planes of the solid, which have v M for their vanishing line ; w r e must now find the radials of the plane which have vl for their vanishing line. We shall, therefore, proceed to enume- rate the Problem. No. 4. — Given in the picture with respect to a rectangle, the vanishing points of the sides, and the lengths vr 2 and ln of the two radials, to find the radials in position to the vanishing line v l. From the point L, as a centre with the distance ln, describe an arc; and from the point v, as a centre, with the distance vp 2 , describe another arc, intersecting the former in p. Join pv and pl, then p v and pl are the two radials which were to be found. It is evident, that in the triangle formed by the three vanishing lines, a line drawn from any one of the vertices, through the centre of the picture, will be perpendicular to the opposite side of the triangle, and this can very easily be proved from the geometry of solids. For if a straight line be drawn from the vertex of any angle of a triangle, perpendicular to the opposite side, dividing this side into two segments ; and if a semicircle be described on the perpen- dicular as a diameter, and if the mean proportional between the segments be applied as a chord in the semicircular arc, so that the point of division may be one extremity of the chord, and if from the other extremity of the chord a perpendicular be let fall upon the diameter, a straight line drawn from any one of the three vertices, through the foot of the perpendicular, will be perpen- dicular to the opposite side of the triangle. Hence, with respect to a plane, and a line perpendicular to that plane, if we have the centre of the picture, the vanishing line of the plane, and the vanishing point of the line, a straight line drawn through the vanishing point of the line, and through the centre of the picture, will meet or intersect the vanishing line in its centre. AND COMPLETE DECORATOR. Ill Having thus obtained the three vanishing lines of the planes of the nearest solid angle, we shall now proceed first to find the image of the vertex. No. 5. -Given the distances from the eye, and from a point each to the plane of the picture, and in this plane, its centre, and the seat of the point, to find the image of the point. Join cv, and the representation of the point will be in the line Cv; and here we might proceed with the operation, but to prevent the confusion of lines which would arise in the course of so many operations, the reader is referred to the separate Diagram, No. 2; where, by first drawing cv, and making cv equal to cv in the figure, he may proceed with No. 2 as follows: draw c n' and vd' parallel to each other, making any convenient angle with vc'. Take cW equal to the distance of the picture or any part of it, and take vd’ equal to the distance of the point from its seat, or the same part of this distance that c'n' is of the distance of the picture. As we have sufficient room on the surface we have to draw upon for this subsidiary operation, we shall employ the whole distance, therefore draw n'cT, intersecting v'c' in a. Transfer the distance va to the figure of the solid, to he represented from v to a in the straight line vC. We have now the image of the vertex of the nearest solid angle, and by joining the point now found with each of the vertices v, l, m of the triangle formed by the vanishing lines, we shall have a L, «v, and am, the indefinite images of the three lines of concourse in the plane of the picture. We have, therefore, all the vanishing lines, the vanishing points, and the radials of these points for two of the vanishing lines ; as also the image of the vertex of the nearest solid angle, and theiefoie we have for each of two adjacent rectangular faces of the solid, the vanishing line of toe indefinite images of the two sides of the rectangle of that face ; but for want of an intersecting line, we cannot cut off from the two indefinite images a portion from each, so that the original of the parts may be the length of the arrises or line of concourse of the adjacent faces of the solid. We must, therefore, proceed to find an intersecting line, or line on which the measures may be applied. There is no occasion, however, to find the real intersecting lines, for if we have the indefinite image of a line perpendicular to the picture, the intersecting point of the line, and the image of a point in this line, we can find such measures as may be applied upon a line drawn through the indefinite image of the point, parallel to the vanishing line ; and as would be found by the real intersecting line in a more convenient manner, from this consideration that the whole distance between a plane passing through the eye parallel to the picture, and a point in space is to the distance between the eye and the picture, as the length of a line parallel to the picture passing through that point is to the length of a line passing through its image parallel to the vanishing line. There- fore if the line which passes through the original point be equal to any one of the three dimensions of the solid, the length of the line found, as the fourth term of the proportion, will be the length of the side to be applied on the parallel passing through the image of the point. To do what has now been explained, is equivalent to finding the image of a similar solid and similaily situated, having the vertex of its nearest solid angle in the point a, from dimensions which would be those found by the proportion just stated. Or by calling the perpendicular distance between the eye and a plane passing through the vertex of the nearest solid angle parallel to the picture, the entire distance, and calling any line from the intersecting point before the picture an 312 CABINET-MAKER, UPHOLSTERER, entire indefinite line ; the distance between the intersecting and vanishing points, the entire inde- finite image ; and moreover calling that part of the entire indefinite image of a straight line between the image of a point and the vanishing point, the indefinite part of the entire image from the image of the point. Then any dimension of the solid proposed to be delineated, and the corresponding dimensions of the similar solid which touches the picture, will be to one another in the ratio of the entire indefinite image of the line passing through the vertex of the nearest solid angle perpendicularly to the picture, and the indefinite part from the image of the vertex ; that is, in the ratio of cv to c a. Let the lengths of the three arrises between every two faces of the solid angle be respectively equal to the three lines r', s', t'; transfer the three lengths r', s', t' to No. 1, upon the line v d! respectively, from v to r , from v to s', and from v to t'. Draw a! w parallel to v d' , and join dr' , ds , dw, intersecting a w in the points u , v , w , then the lengths corresponding to r', s', t are respectively a'u, a'v', and a'w'. These are the dimensions of the body which answer to the intersecting line in the figure, passing through a parallel to the vanishing line. Hence we may suppose, that a'u is the length of the arris to be represented in the line a L, a'v the length of the arris to be represented in the line a v, and a'w the length of the arris to be represented in the line am. No. 6. — Given in the picture of two lines meeting in a point, one finite, and the other indefinite ; the two representations and their radials to cut off a part from the indefinite image, so that the originals of the finite images may be to one another in a given ratio. In the radials pl and p v, from p, the point of position of the eye to the vanishing line vl, make P h and P j respectively equal to the lines r', s', or in any ratio of these lines, as |, J, J, &e. and complete the rectangle p hij. Draw the diagonal pi, and prolong it to meet the vanish- ing line v L in li; find q in the same manner with regard to the vanishing line vm; that is, make p 2 /, P 2 o in the ratio of the lines s' and t' ; complete the rectangle p 2 lmo, and draw thediagonal p ~m, and produce it to q. In the vanishing line lv, make L d' equal to the radial lp; and through a draw au parallel to vl. Make au equal to a'u' in the subsidiary figure; join du, intersecting aL in d; join dv and ak, intersecting each other in c; join lc, and produce lc to meet av in the point b; join 6 m and aq, intersecting each other in g; and lastly, join xg, and prolong xg to meet aM in f; then abcefg is the rectangular prism required. The perspective representation of any parallelopiped would have been found in the same manner, by finding the vanishing lines so as to answer the inclination of the planes, instead of the right angles in the construction. AND COMPLETE DECORATOR. 113 PRACTICAL EXAMPLES OF SOLIDS. The diagram 5, plate xn, exhibits the representation of a cube. Having by the preceding principles found ab, a c, the perspective representations of the two front lines of the base of the cube ; prolong one of them as ab, to meet the intersecting line PQ in the point H. Draw Hi perpendicular to PQ and make hi equal to the height of the solid, that is equal to the side of the cube, and as v is the vanishing point of ab, v will also be the vanishing point of the opposite and parallel side: therefore join hv, and ad and be perpen- dicular to P Q, meeting I v in the points d and e. Again, because L is the vanishing point of the side a c, L will also be the vanishing point of the side opposite and parallel to a c, there- fore join a L and draw eg parallel to H I meeting cZl in g. Draw g v and e L meeting each other in the point/, then baegfe will be the representation of the solid. Figure 6, plate xn, gives the representations of two rectangular parallelo- pipedons attached to each other, the one being higher than the level of the vanishing line, and the other lower. Having put the front lines of the bases into perspective as before, prolong one side of each base to the intersecting line, and draw a perpendicular from each intersecting point to the inter- secting line : call each of these perpendiculars a line of heights. Set the height of each solid upon its respective line of heights, and complete the apparent sides and the top of each solid as in figure 5, and we shall have the representation of both solids thus attached. These solids may represent two parts of a building at different heights, as is frequently the case in complex objects, or it may represent a piece of furniture of the same forms. Fig. 9, represents a kind of forum building of the most simple con- struction; the walls are all rectangular parallelopipedons, and consequently represented as in figures 5 and 6. The main building, as well as the barn and other offices, are roofed in the same manner with gables, and all at the same angle of inclination, therefore all the gables which stand parallel will have the same two vanishing points ; and as the walls are at right angles to one another, and perpendicular to the horizon, the vanishing points of the gables, which are in one set of parallel planes, will have their vanishing points in the line drawn through the vanishing point of the level lines of these walls, perpendicular to the vanishing line, and those in the other series of parallel walls will have their vanishing points in a line drawn through the vanishing point of the level lines of these walls, perpendicular to the vanishing line. Let v L be the vanishing line, and P Q the intersecting line of the horizontal plane, upon which the objects are supposed to be placed, also let c be the centre of the picture, and c o its distance, o being the place of the eye. 2 F 114 CABINET-MAKER, UPHOLSTERER, To find the vanishing points of those gables which are in the planes that have their vanishing lines on the right hand of the centre of the picture. Take the distance between the vanish- ing point L and the eye at o, and transfer this distance upon the vanishing line vl: from the point of distance make an angle with v L equal to the inclination at the plane of the roof to the plain of the horizon, and the point where the other side of this angle meets the vertical vanishing line, passing through L, will be the vanishing point of one side of the roof. By setting the distauce between the vanishing point L, and the vanishing point now found above L, downwards from L upon the vertical vanishing line passing through l, we shall have the vanishing point of the remote lines of all the gables in the planes of which their vanishing line is the perpendicular to v l, passing through the vanishing point l. Again, transfer the distance v o of the vanishing point v, and the eye o upon the vanishing line vl, and from this point of distance make an angle with the vanishing line l v, equal to the angle which the sloping sides of the pediments in the w'alls, at right angles, to the former, makes with the horizon, and let the other side of this angle meet the perpendicular to v l, passing through the point v; and as the angle thus constructed, may be upon either side of the vanishing line tl, the point where the side of this angle meets the perpendicular drawn through v to the line v L, will be above or below the point v accordingly, so that upon which- ever side of v this happens, the other vanishing point must be set upon the contrary side. By means of the two vanishing points found on the right hand, we shall have the vanishing point of all the gables on the right hand, and by means of the two vanishing points found on the left hand, we shall have the vanishing points of all the gables on the left hand, of which the two sloping sides of each, and the sloping sides of every two, make the same angle with the horizon. The roof of the pent-house on the right hand has only one sloping side; this sort of roof is called a shed roof. As the plane of the two ends of this roof of the two sloping walls are parallel to the planes of the gables of the dwelling-house, the vanishing point of the sloping top will be in the vertical vanishing line drawn through l ; the vanishing point of this sloping side is found exactly in the same manner as either of the sloping sides of the roof of the dwelling-house, or of the other gables which have the same inclination. The upper vanishing point in the vertical vanishing line, is the vanishing point of the two sloping sides of the visible plane of the roof of the dwelling- house, and of the small triangular front which terminates the door over the stable ; and the vanishing point at the same distance below l, is the vanish- AND COMPLETE DECORATOR. 115 ing point of the two sloping edges of the side of the roof which is not visible, also the vanishing point of the other sloping line which terminates the door over the stable. The vanishing point of the two equal sloping lines which terminate the gable of the stable, are in the vertical vanishing line passing through v, equally distant from v . As two of the planes of the chimney shaft of the dwelling-house are parallel to the gable of the same house, these planes will be intersected by the inclined plane of the roof; and the line of intersection, and the plane of the horizon, will form the same angle as each of the two sloping sides which ter- minate this inclined side of the roof, therefore the intersection of the visible planes of the chimney shaft, and inclined side of the roof, will have the same vanishing points as the two lines which terminate the visible inclined side of the roof. As the vanishing points of all lines in the same plane are in the vanishing line of that plane, if the vanishing points of any two lines in any plane be given, the vanishing line of their plane will be found by drawing a straight line through the two vanishing points. To apply this observation to the present purpose, the vanishing point v of the line w r hich terminates the top of the wall, is also the vanishing point of a line in the visible inclined plane of the roof, and the vanishing point of the line which terminates this visible inclined side of the loof, and the visible gable, is therefore another vanishing point in the visible inclined plane of the roof; therefore as the inclined planes of the roofs run in two different direc- tions, they will have two different vanishing lines. Let these two vanishing lines be found, and the point where they intersect each other will be the vanishing point of the common intersection of the two inclined planes, to which the two vanishing lines belong. This vanishing point will be the vanishing point of the visible side of the roof of the dormer, in the front over the stable, with the visible side of the root of the stable. 116 CABINET-MAKER, UPHOLSTERER, PLATE XIV. Pig. 1.— Shews the method of representing a cone, p being the point of sight, s the station point, v 1 v 2 the vanishing line, 1 1 the intersecting line. In this diagram two cones are represented ; that on the right hand is done by means of the plan, and that on the left by means of the measures applied upon the ground line. The first of the representations is to find the perspective projection of the plan, and the perspective of the centre of the circle ; from this point draw a perpendicular to the vanishing fine, then the height of this perpendicular being found, we shall have the perspective repre- sentations of the axis ; then join the upper extremity of this axis to each extremity of the curve <>f the ellipse, which represents the base of the cone, as a tangent, and these two tangents and the convex part of the curve intercepted between them, will be the perspective representation of the cone. big. 2. Exhibits the method of representing a pyramid operating in the same manner as in the cone. In this, as in the former examples of a cone, there are two representations of a pyramid, the one with and the other with- out the plan ; the base is first represented, the centre of the base next, then the summit of the pyramid, then join this summit to the points of concourse of the sides of the trapezium representing the base, and we shall thus have the perspective representation required of the pyramid. The representation of the summit of the pyramid, or that of the cone, may be found thus : Draw a straight line from any convenient point in the intersecting line perpendicular to the vanishing line, then upon this perpendicular set the height of the axis. Join the foot of the perpendicular to the foot of the axis, and prolong the line thus joined to meet the vanishing me. Join the upper extremity of the perpendicular end, and the point found in the vanishing me, and the line thus joined will cut the axis in the summit. Fig. 3. Exhibits the method of putting an isosceles roof in perspective intersected by a cylindrical wall. The vertical planes of the wall are here found by means of the plan: v 1 v 2 is the vanishing line of the horizontal planes , v v the vanishing line of the vertical parallel planes, two of which are the gables ; v 3 is the vanishing point of one of the sloping sides, which terminate the top of each gable. AND COMPLETE DECORATOR. 117 wf perpendicular to the intersecting line is the height of the ridge line of the roof, the point w being found by producing the ridge line on the plan below. The line gf is the inter- section of the plane of the roof with the plane of the picture. The circular base of the wall is here drawn on the plan. The circle on the plan is here supposed to be divided into eight equal parts ; first into four by two diameters, each parallel to one of the sides of the plan of the building, the one being parallel to one side of this plan, and the other parallel to the other side of the same, and consequently these two diameters are at right angles to each other ; then a square is circumscribed about the circle, so that the sides may be parallel to the plans of the sides of the wall, and the diagonals of the square being drawn will divide the circumference of the circle also into four equal parts : so that the whole will be divided into eight equal parts. Through the point where one of the diagonals intersects the circumference, draw a line parallel to the side line, to meet the intersection or ground ; the line thus drawn being in the visible plane of the roof. In the same visible plane of the roof draw a tangent to the circle parallel to the ridge line, to meet the same intersecting or ground line. From these two points in the intersecting line draw perpendiculars to the vanishing line to meet the intersection gf of the visible side of the roof. From the points b, d, where these perpendiculars meet the intersection gf of the sloping visible side of the roof, draw lines to the vanishing point v 1 . Also from each of the visible extremities of the side of the square next to the front in the visible side of the roof, draw a line to the station point to meet the intersecting line; then draw two lines perpendicular to the intersecting line, to intersect the line du in the points r and u. From the points r and u draw lines to v 3 to meet the line drawn from f towards v 1 repre- senting the ridge, and thus we have a trapezium, in which the portion of the ellipse which represents the intersection of the cylindric surface and the plane of the roof is inscribed. Draw the two diagonals su and sr, and draw a line from v 3 through s to meet the line ur, and this point in Mr is one of the points through w'hich the curve of the ellipse must pass; two other points are in the line representing the ridge, and two other points are in the diagonals su and sr, so that we have five points in the representation of the visible part of this inter- section of the cylindric surface, and the plane of the roof. Draw a curve through these five points, and the representation of this intersection will be complete. Then drawing the representation of the horizontal circle which terminates the top of the cylindric surface, and drawing the two vertical tangents to this circle, we shall have the repre- sentation of the visible part of the cylindric wall above the roof. To give the most clear idea of this subject, the two elevations are given below at E and F, with the intersections of the principal points. To those who have a clear idea of the subject, these elevations may be dispensed with. Fig. 4. — Exhibits the process of finding the perspective representation of the two diagonal ribs of a cylindric ground vault. This is found by applying the measures to the intersecting line. — Fig. 5, exhibits the perspec- tive representation of a cylindric ground vault, the external and internal cylindric surfaces being both concentric cylindrical surfaces. 2 G 118 CABINET-MAKER, UPHOLSTERER, PLATE XV. Fig. 1. — Exhibits the method of finding the perspective representation of a dome supported upon pendentives. Fig. 1, No. 2, is the plan of the dome, and fig. 4, No. 1, the section. From this the several heights to be applied to the perspective drawn, fig. 1, are found, the corresponding points are marked, 1, 2, 3, 4, 5, both in the section and in the representation. In the perspective drawing, the heights are applied upon the intersecting lines, and by this means the representation of the circles which terminate the pendentives are found. As to the base of the dome, it is a horizontal circle, and is therefore put in perspective in the usual manner of representing a circle in such a position. One of the faces of the object being parallel to the picture, the objects in this face, when represented in perspective, are similar to the figures in the original face. * Fig. 2. — Exhibits the representation of a dome divided into coffers or pannels. Fig. 2, No. 3, is the plane of the same. The base of this dome is represented by the dotted circle below. Fig. 3. — Shews the representation of square posts at equal distances from each other. Fig. 1, No. 1, exhibits the heights and distances of the posts, r is the vanishing line of the tops of each row, found as usual by bringing down the distance of the eye on the vanishing line, and making the angle equal to that in No. 1. The measures in the base of No. 1, are applied on the intersecting line. PLATE XVI. In the twelve following diagrams let v v be the vanishing line, 1 1 the inter- secting line, c the centre of the picture, c p its distance, and p the point of sight in relation to the vanishing line v v : here observe, that wherever s is placed in p c the distance p s is equal to the height of the picture ; so that the distance from s to the intersecting line is equal to the distance of the picture. AND COMPLETE DECORATOR. 119 Hence from what has now been observed, c p is perpendicular and 1 1 parallel to v v. In order to make one connected operation, the planes of each of the twelve diagrams are placed contiguous to each other, so that when each operation is performed, the vanishing plane, the plane of the juncture, and the original or ground plane, may be all brought into their real positions, and the eye being placed in the point of sight, the spectator would see the originals as he would in nature, or as they would appear as described in the definition of perspective. The reader is to observe once for ail, in the twelve diagrams above alluded to, that as the lines vl, n, and cp, and the points c and p, are given in position, it will not be necessary to mention them in the enunciations of the problems. PROBLEM. To find the representations of lines perpendicular to the intersecting line. METHOD FIRST. Let ba and rfc be two original lines: cut n in the points e and g, by lines drawn towards s from the points b and a, and again cut n in k by producing ba. Join kc, and cut Ac in a' and b' by the lines e a', gb gb' perpendicular to n, and a' b' will be the representation of a b. In the same manner c' d' , the representation of cd, will be found. » , METHOD SECOND, FIG. 2. Cut the line ii in k by producing ba, and in e and g by making ke equal to ka , and kg equal to kb. Cut the vv mn by drawing p n parallel to ac. Join kc. Find the points a' U in up, by joining en and gn and a'b', will be the representation of ah; c' d’ found in the same manner, will be the representation of cd. PROBLEM. To find the representation of lines that are obliquely situated to the inter- secting line. METHOD FIRST, FIG. 3. In ii find the point e by producing ba, and the points m and n by the lines as, b s. In vv find the point n by drawing pn parallel to ba. Join en; and find a'b' by the lines ma , nb perpendicular to n, and a b' will be the representation of ab. In the same manner, and by means of the same vanishing point, c' d' the representation of erf will be found. METHOD SECOND, FIG. 4. In ii find the points mn, by drawing am and bn perpendicular to ii, and the points e and g by making me equal to ma, and ng equal to nb. In vv find the point r by making E r equal to cp. Find the point a' by joining me and er, and the point b' by joining nc and gr: then a' b' joined is the representation of a b. In the same manner, and by the same vanishing point r, c'rf', the representation of the line erf is found. 120 CABINET-MAKER, UPHOLSTERER, PROBLEM. To find the representation of a triangle abc, fig. 5. Find the points in the intersecting line, where the prolongation of the accessible sides would meet it; find the vanishing points of these sides and their indefinite representations, by joining the intersecting and vanishing points. In each indefinite representation, find the extremity of each end of the remaining side, and join the two points thus found, and the triangle will be the representa- tion of the given triangle. Thus, in n find ef, by producing cb and ab. Find n and r, the vanishing points of ab, be by- drawing p n, p r, parallel to ab, cb. Find the indefinite representations fn and er by joining/n and er, and the points a! and c, by drawing as and cs> gives the triangle a'b'c the representation of a be. The triangle inay also be found as in fig. 6, in the same manner as has been shewn in fig. 4. PROBLEM. To find the representation of a square, fig. 7, having its sides perpendicular and parallel to the intersecting line. In II find the points e,f, by producing ba and cd, and the points g, h i, by drawing s a, s d, sc. Join ec and/c. In ec and /c find the points a' d' c by drawing g a, lid and ic perpendicular to II. Find the point b‘ by drawing c' b’ parallel to 1 1 ; then the trapezoid a'b'c d' will be the representation of the square abed. PROBLEM. To find the representation of a square obliquely situated to the intersecting line, see the same figure, viz. fig. 7. In the intersecting line il, find the points e, r, o,p by drawing ae, br, do, cp each perpen- dicular to 1 1. In II find the points c, A, D, B by making ec, ca, cd, eB respectively equal to the per- pendiculars od, ea, pc, rb. In vv find the point n by making c n equal to CP. Join ec, and in ec find the points f,a,g , h by drawing the lines cn, An, Bn, Bn, the point a is the representation of the point a. Find the points b' c d' by drawing hb' gefd parallel to 1 1 , and by joining r c, p c, and o c, and a V c' d' will be the representation of the square abed. If it be found inconvenient to have the plan on the picture, we may proceed in the following manner, see fig. 8. Let the plan be drawn on one piece of paper, and posited to the intersecting line, as shewn at fig. 7. Find the points e, r, o, p, as in fig. 7, and transfer them to the intersecting line 1 1, fig. 8, from e to the points r, o, p. Draw the lines r c, o c, p c. In 1 1 , fig. 8, make ea, od, pc, rb equal to the perpendiculars ea, od, pc, rb, fig. 7. In fig. 8, draw the lines an, bn, cn, dn, intersecting AND COMPLETE DECORATOR. 121 the line e c, r c, p c, o c, in the points a',b',c',d'. Join ab',b' c', c d',d' a', and the trapezium a' U c d' is the square required ; and similarly that which is parallel to the picture on the left hand may be represented. In the representation of rectangular solids, the plans must be first repre- sented; but before we proceed to any general method of representation, it is advisable to familiarize them by a few examples. In the following solids, the rectangular faces, which join the two ends, are called sides of the solid, and the faces to which the sides are joined are called the ends ; the end which coincides with the original plane is called the base, and the other end is called the top of the solid ; the line in which any two faces meet is called an edge, or the edge of those two faces. Since the sides of the solid stand upon the base, we shall, first of all, shew how the several bases are found in perspective. Fig. 9, the base of the solid to be represented, is a square, aide. In the intersecting line n, find the points g and /by producing ad and db, the two sides which terminate in the nearest angular point to 1 1 . Find the vanishing points n, m of the lines a b and db. Find the representation of the nearest point b of the base, by drawing gn,fm. In x i, find the points e and h, by making g e equal to g a, and fli equal to f d. In v v, find the points A and b, by making ota.mb, respectively equal to the radials m p, n p. Find the points amg n and dmfm by joining e B and h A ; and as the base is a square, this is as much as will be required, the other two edges being covered by the sides of the solid. The same process is employed in fig. 10, in finding the representations a’ d', d' c', of the two edges da, dc of the square abed. In fig. 11, the point c which represents the nearest point of the base, is found as in fig. 5, and the points a and b are found as in fig. 6. As it has already been observed, that it is often very inconvenient to have the plan and the perspective drawing on the same paper, fig. 12 is supposed to be done without the plan attached to it ; a preparation, however, as in fig. 11, must be first made, and the intersecting points of the perpendiculars and their lengths must be transferred to the intersecting line n, fig. 12, as shewn by the dotted circles ; from these the representations of the two edges 2 H 122 CABINET-MAKER, UPHOLSTERER, of the base, which terminate in the nearest point to the intersecting line, will be found. Having found the edges of the visible sides in the plan, we shall now proceed to the elevations of the representations of the solids. Produce to the intersecting line one of the representations of the two edges of the base, which terminate in the point of the base which is nearest the intersecting line ; from the point where the prolongation meets the intersecting line, draw a line perpendicular to the vanishing line ; call this perpendicular the line of heights ; on the line of heights set up the height of the solid. Draw a line from the upper point to the vanishing point of the side produced. Thus, in fig. 9, produce d b' to g, and draw gm perpendicular to v v. Make gm equal to the height of the solid. Join mn. In mn find the points o and r, by drawing b' o, dr. Find the point t by joining o to the vanishing point m, and drawing d t perpendicular to v v. Lastly, find the point s in fogs g and 10, by joining t and r to the vanishing points n, m, and thus we have the complete representations, figs. 9 and 10. Figs. 11 and 12 are completed by joining iu. PLATE XVII. DIAGRAMS ILLUSTRATING THE PRINCIPLES OF PERSPECTIVE. \ In all the diagrams of this Plate, let ps be the point of sight, s p the station point, nw the directing line, or the parallel of the eye, and vl is the vanishing line. Fig. 1 is the representation of straight lines in three different planes, two being horizontal and one parallel to the picture; these planes in all the six diagrams are represented as if they were five of the sides of a room, the sixth side being left open for the purpose of seeing into the interior, and one of the five sides, which is the plane of the picture, is supposed to be transpa- rent ; one of the two horizontal planes, which is the perpendicular to the picture, represents the floor, and the other the ceiling. In fig. 1, the lines He and lo on the floor, are parallel, and therefore have a vanishing point f found by drawing a line psf through the point of sight p-s parallel to these lines ; the same observation applies to the lines vr and sn; all these lines are here represented on the plane of the picture by the same letter. In every one of the planes in each of the six diagrams, the lines and AND COMPLETE DECORATOR. 123 points in the picture have the same letters of reference as the corresponding lines and points of the objects themselves. In fig. 2, a triangle is exhibited as if lying on the floor, and another on the ceiling. In fig. 3, a pentagon abode is placed on the side of the room which is parallel to the picture. The method of representing this object is by drawing lines from all the vertices of the figure perpendicular to the floor, and drawing lines from the points where those lines meet the floor to the station point, and again drawing lines on the plane of the picture from the points where the floor and the picture intersect perpendicularly to the line of inter- section ; then these lines, intersected by visual rays drawn from all the vertices of the polygon upon the opposite wall, will give the vertices of the perspective representation. The trapezium upon the plane of the wall, which is perpen- dicular to the picture, is represented in a similar manner. In fig. 4, a table is here represented as if standing on the floor. This is done by drawing lines from the feet of the table upon the floor to s-p the station point, and drawing lines on the plane of the picture from the points of intersection perpendicular to the intersecting line, and by drawing lines or visual rays from the extremities of all the lines of the object to the point of sight, and the points where these lines intersect the former in the plane of the picture will be the perspective representations of the corresponding points of the object thus drawn from. In this figure a hatchway is represented in the ceiling. In each of these objects the sides are parallel and perpendicular to the plane of the picture, therefore the lines which are perpendicular to the picture vanish in its centre. The method of representing the objects in figs. 5 and 6, is similar to that now explained, and therefore need not be repeated. Fig. 7 is the plan of fig. 5, and fig. 8 the plan of fig. 6 ; these plans exhibit the positions of the objects, the station point, and the manner of drawing the lines towards it from all the points of the object, so as to give their intersecting points on the plane of the picture. 124 CABINET-MAKER, UPHOLSTERER PLATE XVIII. ILLUSTRATION OF VARIOUS PROBLEMS. i , Figs. 1 and 2, exhibit the method of finding the perspective of an octagon, both horizontal, and inclined to the horizon at a given angle. The repre- sentation, fig. 1, is made from the plan, and that in fig. 2, is found from the measures being applied upon the horizontal vanishing line. Figs. 3 and 4, exhibit the method of finding the perspective representation of a semicircle, both in a horizontal and in an inclined plane, as if they were connected together by the same common diameter. Both these representa- tions are found by means of the measures of the object applied to the inter- secting line. In fig. 3, the diameter which connects the two semicircles, is parallel to the picture ; but in fig. 4, it is oblique. In fig. 3, the centre c of the picture is the vanishing point of the lines that are perpendicular ; the other parallel series of lines, being parallel in the object, are represented by lines parallel to the intersecting line. In fig. 4, neither of the two series of parallel lines of the object being parallel to the intersecting line, the vanishing point of one series will be on one side of the centre, and that of the other series on the other side of the centre. The manner of finding the intersecting points, and the angle which the two semicircles make with each other, is exhibited above, fig. 3. Figs. 5, 6, 7, exhibit the perspective representation of a room where the floors are laid with various kinds of pavement. In fig. 2, the lines of the pave- ment being perpendicular to the plane of the picture, the vanishing point of these lines is in the centre ; the breadths are regulated by the point of distance v 2 . In fig. 6, the lines are regulated by two vanishing points, equally distant from the centre of the picture. Fig. 7, is a combination of the two. USHER, SOU, & C° LONDON", 1833 . AND COMPLETE DECORATOR. 125 THE METHOD OF DRAWING LINES TO INACCESSIBLE VANISHING POINTS. The drawing of lines to a point out of reach was long a desideratum, and numerous complex schemes were introduced to accomplish this desirable object: at length, Mr. J. Fary and Mr. P. Nicholson produced instruments nearly at the same time, which would completely effect the purpose. In May, 1814, the Society of Arts voted to Mr. P. Nicholson the sum of twent\r guineas, for the invention of the centrolinead. Mr. Fary produced his instru- ment for drawing lines converging to an inaccessible point, very shortly after, and was also rewarded by the Society of Arts. The principle of these instruments, though they had the same object to accomplish, was very dif- ferent. The one invented by Mr. Nicholson, in performing, moved in the manner of a parallel ruler; but the other, invented by Mr. Fary, consisted of three bars, so that two of them being moved to any given angle, the edge of the third bar always besected those of the other two, and the motion of the instrument was regulated by sliding these two last edges each upon a pin, in the same manner and upon a similar principle to that of describing the seg- ment of a circle by means of an angle. However, as Mr. Nicholson had previously shewn another instrument, upon the same principle as Mr. Fary’s, to several of the members of the Society of Arts, he was encouraged by those gentlemen to bring forward his second invention of the centrolinead, which he produced accordingly, and was rewarded with the silver medal of the Society in the year 1815. This last instrument has been found to be of the greatest use to artists. It is much more simple in its construction than Mr. Fary’s, which required him to perform a geometrical operation, before the pins, upon which the instrument moved, could be fixed. Mr. Nicholson’s last instrument for drawing lines to a vanishing point, as presented to the Society of Arts, was simply constructed upon the principle of a double bevel, in which each angle was independent of the other, and might be set to any two angles less than 180°. 126 CABINET-MAKER, UPHOLSTERER, This instrument was made to shift to the right or left by means of screws and brass plates. Shortly after his reward, Mr. Nicholson published a small tract on the use of the centrolinead. In this little work he exhibited and explained the manner of making an immoveable or solid centrolinead, to answer the drawing of lines which would converge to a point at any given distance. He now makes three solid or fixed centrolineads, at one-fourth of the expense, to answer every degree of convergency, and these he applies with the greatest expedition ; but before the centrolinead can be used, it will be necessary to shew how the first two converging lines on the right or left hand sides of a building, or piece of furniture, of which the plan is a rect- angle, are found. Let a be, fig. 1 , Plate xvill. for instance, be the plan of two sides of the frame of a table, or two sides of a building, and let 1 l be the sectional line of the picture, placed in the position required by the draughtsman. In order to avoid distortion, every picture should be viewed in the middle, and the horizontal visual angle should be given ; that is, the distance of the eye ought to bear some ratio or proportion to the length of the picture. We shall here suppose that the picture is viewed at a distance which will be two and a half times its length ; that is, supposing the picture to be two feet long, as in large drawings, the distance of the eye would be five feet; therefore, from any convenient point k, in the line l L, draw km perpendicular to I L. In I L, take the point i at any convenient distance from k, and in I L make kl equal to hi. In km set off il two and a half times from k to m, and join m i and m l. In I l cut off the length of the picture de, by drawing ad parallel to m l, and ce parallel to mi. The picture must now be viewed at a distance equal to two and a half times de; that is, about ten inches and five sixteens. Now, this distance would exceed the extension of the surface which we have here to work upon ; but if it can be shewn how the drawing may be completed equally well, without extending the lines ad and ce till they meet, we should be most happy, to avail ourselves of the information, in avoiding so great an inconvenience and so much more labour. Bisect, then, de in the pointy, and draw y^r perpendicular to I L. Divide df into five equal parts. Cut the lin efg in g, by drawing lig through the fourth point h of division parallel to ad or m l, then will y <7 be a fifth part of the real distance of the picture; and if the drawing or paper had not admitted of this distance, df must have been divided into a greater number of equal parts; for f g would be shorter in proportion to the greater number of equal parts which are contained in df; so that if df had been divided into six equal parts, fg would have been one-sixth part of the distance of the picture, and so on. In 1 l, cut the points n and c, by drawing gn parallel to b a, one side of the plan, and g c parallel to b c, the other side. Let v L, fig. 2, be the vanishing line, either on the same paper, or on another, as may be con- venient. In v L assume the point p for the centre of the picture. AND COMPLETE DECORATOR. 127 In vl cut off the distances p r and pu respectively, equal to fn and fc in the line i L, fig. 1. In fig. 2, draw the lines r s, p F, and uy perpendicular to v L. Set the points of the dividers at any convenient distance from each other, and set off as many equal parts in p F, and as many equal parts wanting one in r s and uy, as df, fig. 1, was divided into: now, df was divided into five equal parts, therefore p F contains five, rs and uy contain each four of such parts as the dividers were set to. Draw the straight lines fs and F y. Produce FstoE. hipcd represents the instrument, H i, i p are the two straight edges that run upon the pins, and I D is the edge of the instrument by which the lines are drawn. There are here given two straight lines E F and v L, which would tend to the proper vanishing point, if produced. The distance in which they will meet the line v L produced on the left, is five iines the distance nf, fig. 1. Suppose, now, the edge CD of the centrolinead to be placed on the vanishing line v L, put a pin in the paper in any convenient point A of the running edge I H, and draw a line I P on the paper by the other running edge I p. Shift the instrument, so that the edge I D of the blade may coincide with the line ef, and the edge i h still rest against the point A; then draw a new line ip. Put another pin in the intersection B of the two lines I p, I p. Lastly, move the centrolinead until the edge c D fall upon any given point between the lines ef and v L, so that the edge ih may rest against the point A, and the edge ip against the point B, and draw a straight line by the edge i D, and the straight line thus drawn will tend to the same point in which the other two given lines E D and v l would meet each other, if produced. In this manner lines tending to a vanishing point, may be drawn with as much expedition, as perpendicular lines could be drawn by a common T-square, or parallel lines by a parallel ruler; and more lines may be drawn by the instrument in five minutes, than could be drawn in twenty four hours by finding each line separately by a geometrical problem. THE PERSPECTIVE OF SHADOWS. The shadows of objects are the dark parts on the surface of a body or plane, occasioned by the intervention of another body which intercepts the rays of light. In projecting shadows by the sun, there are three different positions of the luminary to be considered; viz. it must either be in the plane of the picture, or on the same side of the picture with the spectator, or behind the picture 12P CABINET-MAKER, UPHOLSTERER, In order to determine the shadows of objects on the plane of the picture, the situation and altitude of the sun must be determined ; then, whether the sun is before or behind the picture, the ■vanishing point of the rays of light must either he found or assumed ; but when the sun is in the plane of the picture, the rays will be parallel to the picture, and therefore the representa- tions will be parallel. When the sun is on the same side of the picture as the spectator, it is obvious that the vanishing point of the rays of light will be below the hori- zontal line ; and if on the other side, above it. When a straight line obstructs the sun’s rays, it is evident that the rays thus intercepted are all in a plane passing through the luminary and through that line. The opaque surface occasioned by the obstruction of the sun’s rays, is called a plane of shade. It is therefore evident, that the plane of shade passes through the luminary and through the straight line. Hence the indefinite shadow of a line upon a plane is the intersection of that plane and the plane of shade. If therefore we have the vanishing point of a line that throws a shadow upon a plane, and the vanishing point of the sun’s rays, we have the vanish- ing points of two lines in the plane of shade, and therefore the vanishing line of the plane of shade ; and if we have the vanishing line of the plane of shade, and the vanishing line of the plane on which the shadow is thrown, we shall have the vanishing point of the shadow. For the shadow itself is the inter- section of the plane of shade, and the plane on which the shadow is thrown; therefore the vanishing point of the shadow is the intersection of the two vanishing lines of these planes. If the vanishing line of the plane of shade be parallel to the vanishing line of the plane on which the shadow is thrown, it is evident the shadow of the line will be parallel to the vanishing line of the plane on which the shadow is thrown, or parallel to the vanishing line of the plane of shade ; for these two vanishing lines can never intersect each other. If the line which throws a shadow be parallel to the plane on which the AND COMPLETE DECORATOR. 129 shadow is thrown, the line and its shadow will have the same vanishing point. When the line which throws a shadow on a plane is perpendicular to that plane, and when the plane is parallel to the picture, the vanishing point of the line will be in the centre of the picture ; therefore the vanishing line of the plane of shade will be the line joining the vanishing point of the sun’s rays, and the centre of the picture; and since in this case the shadows of lines thrown upon any plane, by lines perpendicular to that plane, are all parallel among themselves, the shadows of these lines will be all parallel among themselves. The shadows of objects projected upon horizontal planes, bylines inclined at any given angle to these planes, will have their vanishing points in the vanishing line of horizontal planes. MOST USEFUL PRACTICAL OBSERVATIONS. With respect to the shadows of perspective drawings of Cabinet Furniture, and Architectural objects, as the objects are placed upon the horizon, and since generally the surfaces are planes, and rise perpendicular to the base, the edges of every two adjacent surfaces thus rising from the base will be straight lines perpendicular to the horizon: and as the picture is generally perpendicular to the horizon, the perpendicular lines of the object will be parallel straight lines to the plane of the picture, and will therefore have their perspective representations perpendicular to the vanishing line of the hori- zontal planes. Again, as every two planes of the object are generally at right angles to each other, those planes which are perpendicular to the horizon will have their two vanishing lines perpendicular to the vanishing line of the horizontal planes; and because the base on which the object stands, and all the oppo- site planes above the base, are parallel to the horizon, the lines which terminate these planes will have their vanishing points in the vanishing line of the 2 K 130 CABINET-MAKER, UPHOLSTERER, horizontal planes ; and as all the horizontal lines of the object belong also to the vertical planes of the same object, the horizontal lines will also have their vanishing points in the two vanishing lines, which are perpendicular to the horizontal vanishing line. Hence, the points of intersection of the two vanishing lines of the planes which are perpendicular to the horizon, and the vanishing line of the hori- zontal planes, will be the vanishing points of all the horizontal lines of the object. The vanishing point on the one side is the vanishing point of every line which is perpendicular to any one of the parallel vertical planes, of which the perpendicular passing through the other vanishing point is their vanishing line. Or these two vanishing points may be considered the vanishing points of two lines in a horizontal plane at right angles to each other. With regard to the effect which the position of the planes of such objects have upon the shadows, we shall observe, that whatever position the luminous point has in respect of the three vanishing lines now alluded to in these observations, as the vertical lines of the object are represented by lines which are perpendicular to the vanishing line of the horizontal plane, these lines may be considered as having their vanishing point in a line drawn through the centre o the picture perpendicular to the vanishing line of the horizontal planes, and at an infinite distance in the line thus drawn. And since the vanishing line of the plane of shade of a straight line pro- jecting a shadow on a given plane, is a straight line passing through the vanishing point of the sun’s rays, and through the vanishing point of the line which throws the shadow ; therefore, with regard to the perspective repre- sentation of the shadows of the lines which are perpendicular to the horizon upon any horizontal plane, as these lines have their vanishing points at an infi- nite distance from the centre of the picture, and in a perpendicular to the vanish- ing line of the horizontal planes, a line drawn from the vanishing point of the sun’s rays to this infinitely distant vanishing point, must be perpendicular to the vanishing line of the horizontal planes, the conclusion is, that — AND COMPLETE DECORATOR. 131 The vanishing line of a plane of shade of a line perpendicular' to a hori- zontal plane, is a straight line drawn through the vanishing point of the suns rays perpendicular to the vanishing line of the horizontal planes. And because the vanishing point of the shadow of any line meeting a plane upon that plane, is in the vanishing line of that plane — The vanishing point of the shadow of a line perpendicular to a horizontal plane, projected upon any horizontal plane whatever, is that point in the vanishing line of the horizontal planes, where a straight line drarvn from the vanishing point of the suns rays perpendicular to this said vanishing line of the horizontal planes, meets it. With regard to the representation of the shadows of the lines of the object which are perpendicular to the vertical planes upon these vertical planes, as the vanishing point of the lines which throw the shadow are one of the two vanishing points in the vanishing line of the horizontal planes — The vanishing line of the plane of shade of a straight line perpendicular to a vertical plane, projecting a shadow on this vertical plane, is a straight line drawn from the vanishing point of the line to the vanishing point of the sun's rays, the vanishing j ' of the line which throws the shadow being one of the two vanishing points in the horizontal vanishing line. But as the plane on which the shadow is thrown is vertical, the vanishing line is the line drawn through the other vanishing point perpendicular to the vanishing line of the horizontal plane ; hence — The vanishing point of the shadow of a straight line perpendicular to a vertical plane upon this plane, is in the perpendicular drawn through the other vanishing point, which is not the vanishing point of the line to the vanishing line of the horizontal planes. 132 CABINET-MAKER, UPHOLSTERER, PLATE XIX. APPLICATION OF THE THEORY OF SHADOWS TO REAL PRACTICE. b c d e, fig 3, represents a wall in perspective. In this example the sun is supposed to be in the plane of the picture, therefore the perspective repre- sentation of every ray of light makes the same angle with the vanishing line of the horizontal planes, as the altitude of the sun makes with the horizon ; and consequently, the sun's rays have no vanishing point but what is in- finitely distant. Now the vanishing line of the plane bcde is the line v A drawn through the left hand v per- pendicular to vv, the vanishing line of the horizontal planes, and the vanishing point of the lines which throw the shadow is the right hand point v in the vanishing line vv of the horizontal planes. Therefore as v is the vanishing point of the lines which throw the shadow, the vanishing line of the plane of shade must pass through v, making an angle with vv, the vanishing line of the hori- zontal planes, equal to the angle which a ray of the sun makes with the horizon ; therefore draw the sloping line VA through the right-hand vanishing point v, making the angle vva equal to the angle which a ray of light makes with the horizon, and the sloping line v A will be the vanishing line of the plane of shade. But v A perpendicular tow is the vanishing line of the plane on which the shadow is thrown, therefore the point A in which the sloping vanishing line v a of the plane of shade, and the vertical vanishing line v A of the plane on which the shadow is thrown, meet each other, is the vanishing point of the shadow. From what has been said, the perspective representations of the rays are all parallel to the sloping line v A, and the indefinite shadow' of any line perpendicular to the plan represented by bcde w r ill pass through the point A, and through the foot of the lines, and we have the law for drawing the indefinite perspective shadow of the line and the perspective of the ray of light which passes through the unconnected extremity of the line. Therefore to find the shadow of any such line, we have only to draw a line from A the vanish- ing point of the shadow, and through the foot of the line, and to draw another line through the unconnected extremity parallel to the sloping line v A, and the point where this line intersects the indefinite perspective shadow will terminate the shadow required, or the portion of the indefinite shadow between the foot of the line which throws the shadow and the point of intersection of the perspective representation of the indefinite shadow of the line, and the perspective of the ray of light drawn through the unconnected extremity, will be the shadow of the line. Fig. 4, is the plan of a body projecting from the face of the wall, consist- ing of several faces which are plane surfaces, every two adjacent planes being prependicular to each other, and those which are adjacent to the wall AND COMPLETE DECORATOR. 133 perpendicular to the plane of the wall; hence all the straight lines formed by the intersection of the planes perpendicular to the wall, will also be per- pendicular to the wall, and therefore parallel to the horizon; hence their Vanishing point will be on the horizontal vanishing line, and consequently, in the right-hand point v, which is the vanishing point of lines perpendicular to the plane represented by b c d e, of which the vanishing line is v a, perpen- dicular to the horizontal vanishing line v v ; and as these planes are either perpendicular or parallel to the horizon, the intersections of the planes which are parallel to the wall, with the planes which are perpendicular to the wall, but at the same time parallel to the horizon, will be both parallel to the wall and to the horizon; and the intersections of all those planes which are parallel to the wall, with those which are at the same perpendicular to the wall and to the horizon, are all perpendicular to the horizon, and consequently parallel to the picture. Therefore, all the lines which are perpendicular to the horizon and parallel to the picture will be represented by lines perpendicular to the vanishing line of the horizon, and the representation of the shadows of these lines will also be perpendicular to the vanishing line v v of horizontal planes Fig. 1 is an end elevation of the plan fig. 4, and fig. 2 is a front elevation of the same project- ing body. H I projecting from the plane represented by BCD E is one of the upper edges, L being the upper extremity, and H the foot of the line LH. To find the shadow of the line LH. From the vanishing point A of the sun’s rays, and through the foot H of the line, draw ai, and draw Li parallel to Avthe vanishing line of the plane of shade ; then H I is the shadow of the line, h l and i the shadow of the point L. The edge of the vertical line under L will be found by drawing a line through I downwards perpendicular to the vanishing line vv of the horizon. In the same manner the si a ow of the opposite side of the rectangle will be found, as also the shadows of all the lines which are perpendicular to the plane represented by BCD e. We now come to the shadows of those solids which are situate upon the plane of the horizon, and of which their surfaces are planes at right angles to one another, and parallel and perpendicular to the horizon. In this case the perspective representation of the rays of light will still be found by drawing lines parallel to the sloping vanishing line v a of the plane of shade. 2 L 134 CABINET-MAKER, UPHOLSTERER, But now the vanishing point of lines perpendicular to the horizontal plane, being in a perpendicular drawn through the centre of the picture, and being infinitely distant from this centre, therefore the line which is thus parallel to the sloping line av drawn, this infinitely distant point can never reach the vanishing line vv of the plane on which the shadow is thrown; hence the vanishing point of the shadow must be in the line v v, infinitely distant from the centre of the picture ; therefore the perspective representa- tion of all lines perpendicular to the horizon, will be parallel to the vanishing line v v of the horizontal plane. Let hi represent one of the edges of a solid of which each pair of the adjacent sides are per- pendicular to each other, and let this solid be so situate that one of its planes may coincide with the plane of the horizon, then calling this plane the base, the other four planes which join the base will be perpendicular to the horizon ; and consequently, the four edges formed by every two of these planes will be perpendicular to the horizon, and all of an equal height above it. The line h i being one of these four perpendicular edges, the shadow of the line h i will be found thus : Draw h k parallel to v v, and i k parallel to the sloping line A v, then hk will be the perspective shadow of the line represented by hi. In the same manner the shadow of the other edges will be found ; then to complete the shadow, we have only to join the corresponding points. PLATE XX. Fig. 1, exhibits a prismatic solid, with a projecture in front: o is the vanishing point of the sun’s rays. As the shadows are to be thrown upon a horizontal plane by lines perpendicular to the horizon, the vanishing point of the perspective representation of the shadow will be the point in the vanish- ing line of the horizontal plane, cut by a perpendicular to the said horizontal vanishing line, drawn through the vanishing point of the sun’s rays. Hence, by drawing o l perpendicular to v l, we have the vanishing point of the sun’s rays. Thus now, to find the shadow of any line, as a b, draw a L and bo, intersecting each other in the point c, thus ac is the shadow of the line a b. In the same manner the shadow df of ‘he line de will be found, and joining cf, cf will be the shadow of the line be, and acfd will be the shadow of the plane abed. In the same manner we shall find the shadow of the other planes. /Y . ,. 9 . Shadows . Mlisl^a. ty Pisnei . San & C? Caxton. London. 1834 J>icA sc. A % AND COMPLETE DECORAT 135 In fig. 2, after having found c,f, n, r , t , the representations of the shadows of the upper extremities a, b , e, k, Z, m, p, s of the perpendiculars ba, de , gk , &c. in order to complete the shadow, there is nothing more to do than 4 to trace a curve through the points c,f, i, n , r, /. Fig. 3, exhibits an obelisk projecting a shadow' upon a cylinder, and upon the plane of the horizon : the obelisk stands with its base perpendicular tc the horizontal plane, and with its edges equally inclined to the axis which is perpendicular to the horizon. The perspective representation of the square on the top must be also found in the base; by this means the perpendiculars from the upper extremities will be found in the same manner as in the two preceding examples, and by connecting the extremities the whole will be found complete. The shadow of the cylinder upon the horizontal plane is found by making a sufficient number of sections through the cylinder, and in the plane passing through the line that throws the shadow, and the sun. We have now finished our article upon Perspective. Its application to the following elegant subjects will explain more of its use to the designer and cabinet-maker than volumes of words could explain. — The subjects to which it is applied throughout this work are the following : Four-post beds Sofa Occasional table Side-board Library table Bed in the Grecian style Couch in the Grecian style Drawing-room chairs Card-tables Music-stool Circular table Chair in which the Duke of York died Book-case. In the design of the Grecian couch, the vanishing line is out of the picture ; but as it is now supposed that the reader is in possession of the principles, he can very easily supply its place in imagination. The measures are applied along the ground line as exhibited at the bottom, and the per- spective lengths are cut off by means of the points of distance ; these points 136 CABINET-MAKER, UPHOLSTERER, of distance being the distance between each vanishing point and the eye transferred upon the vanishing line. SCHOLIUM. The use of perspective representation is to shew objects in the most natural manner, and to the greatest advantage, so as to give a correct idea of the combinations of their various parts ; and though by having the centre and distance of the picture, and knowing that the angles of the object are right angles, the correct length of every line might be obtained ; or, if the centre and distance of the picture be given, and the two vanishing points, we shall be able to obtain the original lengths and angles of all the parts of the object; but the centre and distance of the picture are seldom given ; and if they were, the reverse process of finding the original lengths and angles of the lines would be so tedious, as to exhaust the patience of the draughtsman, or persons employed to execute the work A perspective drawing may answer to innumerable angles; but one thing we should observe, that when the distance of the picture is a mean propor- tional between the distance on the vanishing line from the centre of the picture, and each vanishing point; and if the object have only two vanishing points, the angles are all right angles. It is necessary to mention these circumstances, that the reader may see the whole extent of the use of perspective, which will save his time by pre- venting him from making useless researches Once for all, in perspective, as far as regards the cabinet-maker: — Though a plan of the object is often drawn for the use of the workman, yet he or the draughtsman generally applies the measures upon the ground line, and they do not draw from a station point, as architectural draughtsmen are accustomed. Orthographical representation gives the same connexion of parts as perspective representations; and though it does not shew the object quite so natural, it has this great advantage, that all the parts can be measured by means of a scale, and therefore the object can be readily put into execution AND COMPLETE DECORATOR. 137 Indeed, the difference between perspective representation taken at a very long distance, and an orthographical representation, is so trifling, as hardly, in many instances, to be perceived, as will be easily seen from the following objects, which are all orthographically represented : Escritoir Sofa Lady’s wardrobe Chiffonier Dressing-table and dressing-glasses. We cannot say more than we have already observed under the article of orthographical projection, and shall only repeat, that the three directions of the solid angle may be assumed by any three lines which may be agreeable to the eye ; the scale may be found for lines in each of the three directions. In order that the reader may know which of the scales belongs to any given direction, the scale is always applied parallel to the lines which are measured by it ; that is, vertical lines by the vertical scale, oblique lines by the oblique scale, parallel to these lines. In point of drawing, orthographical representation admits of much more rapid execution than perspective representation. Throughout the whole of “ The Cabinet-maker,” wherever the sides of furniture are geometrically represented, we have always affixed a scale, in order to obtain the dimensions of the parts, so that any of the designs may be put into execution. The designs thus represented are — W indo w-curtains Candelabra Firescreen Chairs French bed Tea-poy Tripod and Stand Sofa Stools Pier-tables Window-seats Side-board Side-board and Celeret Cabinet and looking-glass Looking-glass Circular-table , * Drapery for three windows Ladies’ work-tables Hall-seat, bason-stands, and pot- de-chambre recess 2 M 138 CABINET-MAKER, UPHOLSTERER, Card-tables Couch Music-stools Circular library-table" Plan of a circular-table Wine-coolers Upright piano-forte in the Grecian , style Upright piano-forte in the Gothic style. PLATE XXL Finding the angle ribs for canopies upon square, rectangular, polygonal, and circular plans ; describing the forms of their veneers, mitering trays in the form of the frustum of a pyramid ; method of enlarging and diminishing moulding, and of tracing the sections and mitres of raking mouldings. PROBLEM. To describe the ribs of a canopy upon a square plan, the section perpen- dicular to the front being given. Let a, b, c, d, fig. 1, be the plans of the posts upon which the canopy is supported, and let the given rib be q 1 2 3 4 5 6, placed with its base perpen- dicular to the side d c. The curve q 1-2-3-4-5# being of any form required. In this example it is the quadrantal arc of a circle ; e h being perpendicular to e q. Draw the mitre lines between the inner points of the plans a, c, and d, b, crossing each other at e. First, to find the angle rib. — In the curve of the given rib, take the inter- mediate points I, 2, 3, 4, 5 at equal distances or at pleasure. Draw the lines 1 #, 2 r, 3 g, 4 e, 6 c, meeting the mitre line in the points t, r, g, e, c , and cross- ing the base p e in the points v, o, n , m, l. Draw the lines tu, r s, g h , ef,cd, e b perpendicular to the mitre line on the plan. Transfer the perpendiculars p 1 , o2, n3, m4, 1 6 between the base and the curve of the given rib to the AND COMPLETE DECORATOR. 139 perpendiculars t a, r s, g h, ej \ c d, & b raised upon the diagonal or mitre line, and through the points d, u, s, h,f d , b draw a curve which will give the outer edge of the angle rib. The inner edge will be found in the same manner. Fig. 1, No. 1, fig. 2, No. 2, and fig. 2, No. 3, exhibits the method of backing the ribs of figs. 1 and 2. The diagonal ribs in fig. 2, are found in the same manner as in fig. 1 ; but in order to find the form of the covering or cloth upon each side, divide the curve line e 1 2 3 4 5 into any number of equal parts, the more, the truer the operation will be ; we shall, however, suppose that five parts are sufficient, then extend these parts upon a straight line b 5 perpendicular from the point b to ac , and through the points 1, 2, 3, 4, 5 in the line b 5, draw the lines 1 a, 2 a, 3 a, 4 a parallel to a c \ Make 1 a, 2 a, 3 a, 4 a, respectively equal to the lines e n, e n, e n, &c. between the lines l b and e b on the plan which are parallel to le ; and through the points a, a, a, a, &c. draw the curve a aaaab, and in the same manner draw the curve c 5 on the other side, then a c 5 will be the entire covering of the canopy. In the same manner the covering a 6 c, fig. 3, will be found, and likewise the spherical canopy exhibited in fig. 4. These bod'ies not only exhibit the coverings of canopies, but the figure of a veneer to any square, rectangular, or circular plan. Fig. 5, shews another method besides that exhibited in fig. 4, for finding the figure of a veneer upon a spherical surface. Let abc be a vertical section of the spherical surface. Divide the curve into the equal parts b h, fig, gffe, &c. Let a bisect the line a b. Draw a c perpendicular to ab . Prolong a c and fig to meet each other in d, and from d with the distances d fi, dg, describe the arcs ho and gn, and these arcs will be the edge of the veneer, in order to cover the spheric surface of which g h is a section. In the same manner will be found f g ml, effci, &c. the figures of the succeeding veneers. 140 CABINET-MAKER, UPHOLSTERER, To find the mitres at the angles of a knife-box. — Let abcd, fig. 6, be the plan at the top or wide part, and abdc the plan of the bottom or narrow part, a a, d c, c d, b b, being the plans of the diagonals, and let ef be the elevation. Through any point a in the plan a a of a diagonal, draw p n perpendicular to a a, meeting the sides a d and a b in p and n. From the point a in the lin e pn make am equal to the height of the elevation, and join a m. Draw ag perpendicular to Am, meeting Am in g, and from a in the line a a make ah equal to ag. Join hn by drawing a straight line from h to n , and nha will be the angle of the mitre required. The same bevel will answer each of the other three mitres, as is evident. To diminish a cornice in any given proportions. — Let ck be the given cornice, consisting of a fillet cima-recta, corona fillet, and cima-reversa. Upon the height line be make b f equal to the height of the required cornice. Join c c, and draw fa parallel to c c, meeting be in a. At the point c draw the straight line c a, making any angle c a with c b. Make c a equal to ba, and join b a. Through the points in the height c b, where the horizontal lines of the given cornice cut the line cb, draw lines parallel to b a, meeting the line c a. Draw a b perpendicular to a c , and make a b equal to ba. Draw r c d perpen- dicular to cb, the height of the" given cornice, and from all the points in the projection of the given cornices draw lines to meet cd perpendicularly. Draw b d perpendicular to ba, and draw cd 1 , making any convenient angle with cd. Join d d, and through the points where the perpendiculars meet c d draw lines parallel to d d to meet c d. Through the points in the height cb cut by the horizontal lines, draw straight lines parallel to bA to meet the line ca. Through the points in ca draw straight lines parallel to ab, and through the points in cd draw lines parallel to ca, and the points where these lines meet will be the points of projecture in the cornice required. To find the angle-bars of return glass frames. — In fig. 8, b is the given bar, a is an angle-bar placed in a right angle, and c is an angle-bar placed in AND COMPLETE DECORATOR. 141 an obtuse angle, all the three bars being made to the same thickness. Draw parallel lines to the sides to meet the mitre lines of each angle-bar w, two from each point. Take the line 1 1 in a, and make 1 1 in f the section b equal to 1 1 in a, and draw the oblique line 1 1 in b ; also in b draw 22, 33, &c. parallel to the oblique line 1 1 ; then in tlhe section a make 22, 33, &c. respec- tively equal to 22, 33 in the given section b, and thus we shall find the curves on both sides of the section a, and in th*e same manner those of the section c will be found. Given a horizontal moulding, in a vertical plane, to find the section of a moulding upon the rake to meet the horizontal moulding, and the section of another horizontal moulding to meet the raking moulding on a line parallel to the direction of the horizontal moulding, so that the three mouldings shall be in three vertical planes at right angles to each other. In fig. 9, let the cavetto 1234 be tha Sc C°Casi on, London. Oct? 16.26. Curtains for two Wi / / d c iv s. Published by Pf.Pisher So- &C°Caxton London ISS'l' . Draper 1/ for three Windows Greek Faleras. Drawn, by M A Itfichj l- on . Fig.X Fy.3. Published hy Fisher. Son & C° Caxton, London.. 1834. •gzgrx 3 ™!! Txo-pio'x T&xprao ;o=?-o°S /a T^STMU-I Elements of T\ uiae/e . — ----- - FISHES-, SON, &. C9 LONDON, 1835. ' ' ^ - ; -- Grecian 0 rnament. LookiiKj Glass. Published by H. Fi'sber.Scm & C?CaxtOE.Io3lon, 1834. mmmt t a oin e ? and 1,0 Published dry Fisher. Son 8c C° Caxton. Loudon 182 T- S’y.J IMl! ( haul Dress inn -Glass . i7 Pubhsned "b^H. Fisher. Son k CPCaxton. London. Sep t 30 1834^. •3zar>2 kc-th h a i wm* Chair legs and Sofa kgs with part of the dads. S idc Board L egs & Rails. Published i>y PL. Fisher. Son Sc CPCazt on. London, Sen*; 9,1826 , TUTU r~ - . i l i mm Mod 6 Min id Me (1 6 Min 'Entablature JJlod. Pedestal 7 Mod. 18 j Modules or . 9 ^ Miametm zMcd 6Min 17 Mod 12 Min Cornice rriejje ~Pfitatdature i Mott ' 1 Pedestal 7 Jhod. 21 Modules or w?$ S ideboard. Published by Fisher, Son Sc C° Caxton . London . Jan. 29 , 1834 . Gothic SidcBoard. Side Board and C el r reft. Published by Fisher. Son Sc C°. Caxton London. 1834. 'xy jD f7 joyr Dcst.jncA fcJlra.U'n bu UfAMchciscn. PaVJislietL Tj j ifislLeT Sarnie C? CaxtoiL. L cmxkm. May 1826 . '?*? '“e'j-'V-'urrn Published by Fisher. Son k C? Caxton. London, 1835. Music Stools. Published by Fisher. Son Sc C e Caxton Londoa Jan. 1834 Circular Table Published by Ti Fisher. So:: & C° Canton. London. June 17. 1826 : — L ibrary Table . Card Tables Published "b j Fisher, Son & C° Caxton. London. Dee. 1834 Z>uJc jculf . ’jpofvwT __ _ ■ w 'uonvimmi Card Tab Us. ' V? uosio-ipwvjZ' O ccasioital Table/. ■