Albert R.. Mann Libkary Cornell University CORNELL UNIVERSITY LIBRARY 3 1924 094 812 173 Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924094812173 0'^ \ /% Printed by RediflpVl & F.l-ot. EXPLANATION OF THE PLATE. 1. Pith of Stem of Hydrangea, transverse section ... -^rds objc 2. Sarcoptes scabiei, female -^tli 3. Human Blood Corpuscles, rapidly dned -j\th ^. Parasite from Field Mouse i-^.^tli 5. Bone-, Mammalian, transverse section iVith 6. Parasite, Louse of Martin ^rds 7. Diatom., Lieraophora fiabeUata -^th S. ,, Disc, from Fossd Earth, Earbadoes ... ^^th !>. ,, Pieurosigma decorum j\ith ID. ,, ,, angulatum ^\-t,h 11. Male Flea of Pigeon 1h nich 12. Diatom, part of the Valve of Pleurosigru-aformosurn -,V,Lh lo. Pemale Mea of the Mole 1 inch HOW TO WOEK THE MICROSCOPE LIONEL S. BEALE, M.B., F.E.S., FBIiLOW OF TITE ROTAI' COLLBGS OF PHT5ICIANS, FHTfllCIAN TO SING'S COLIiEBB HOSPITAL, AND PROFESSOR OF 'fHTSIOI.OG^ IN KING's COLLEGE, LONDON; UOMOBARI FELLOW OF sing's COLLEGE. THIRD EDITION. Illustrated with Pifty-six Plates, containing upwards of 250 Figures, and 3. PtiotograpMc Plate, lONDON : HARRISON, 59, FAhL MALL, publisfetr to itr ilajcstg snij W3S- tfe* |ritWE of ©ialts. 18 6 5. The Author reservea the right of translating this Worlr, PREFACE It is now seven years since the first edition of this work was published, and during this short period very great advance has been made in many branches of microscopical inquiry, both in this country and on the Continent. Since the publication of the original work, Messrs. Powell and Lealand have succeeded in making, at the request of the author, an object-glass magnifying 1,800 diameters. He hopes shortly to receive from them a power as much superior to this as the jjth is to the old Yetli- Microscopical science is greatly indebted to these makers for the advances made by them upon several occasions in the manufacture of object-glasses, and in the con- struction of microscopes. * The author has considered it better to divide the work into chapters instead of lectures, but the original style has been retained, because it was thought to be well adapted for the descripition of practical details, in which clearness is of far greater importance than eWgance of expression. The book now contains more than twice the amount of work in the last edition. Many of the paragraphs have been re-written , and three new chapters, containing nearly one hundred pages, have been introduced. The number of plates has been increased from 32 to 56. The author has still further improved upon the mode of injection and preparation of tissues advocated by him and now adopted by many observers. In this edition the details of the particular mfethod of preparation carried out by the author in his investigations with the aid of the highest magnifying powers yet made, are for the first time published. For the beautiful photograph which formS the frontispiece the author is indebted to. his friend Dr. Maddox, who has also afforded him very great assistance in writing the chapter on VI PEEFACE. photography. This is one of the most valuable chapters in the book. It contains the results of many years' most earnest work, by one of the most successful workers in this department of photography. The detail of some of the photographic illus- trations is so very minute, that many points cannot be seen by the unaided eye. A lens of low magnifying power has therefore been appended to the volume, to enable the reader to see the beautiful microscopical details which have been obtained by this mode of illustration, in which Dr. Maddox is striving to achieve still greater success. Many of the best wood engravings in the volume have been engraved by Miss Powell, to whom, as well as to Messrs. Harrison for the great care bestowed in printing, the author's thanks are due. The author regrets that the book should have been so long out of print, and the publication of the new edition so long delayed. He was anxious to improve it to the utmost of his power and increase its usefulness as a practical work ; and he has, therefore, spared neither time nor trouble, and has refrained -from hurrying it through the ^ress, feeling satisfied that time spent in perfecting practical details connected with demonstration, is well employed. For, however some "may be inclined to disparage hand work as distinguished fro.'n head work, it is certain that no one can become a good microscopical observer, unless he is possessed of considerable manual dexterity, to be acquired only by long practice ; and no work can l:)e higher or more useful than that of assisting to make men original workers in any department of science, and of encouraging original work. Working books by working men will do far more towards these ends than the most brilliant discoveries, and the author believes that earnest men cannot labour more usefully than by endeavouring to make others work. 61, GEOSVENoa Street, W., Avgust, 1864. PEEFACE TO THE SECOND EDITION. With the view of increasing tlie usefulness of this work, numerous explanatory illustrations have been added in the present edition. The author, both in the text and in the explanations to the engravings, has endeavoured to restrict himself, as far as possible, to giving hints and directions which may be practically useful to the student while he is at work. AU matter that would be merely interesting to the general reader has therefore been altogether omitted. Directions for working cannot well be too explicit and precise, and the more simply they are given, the more useful they are likely to be. 61, Grosvenor Street, Jarmary, 1861. PEEFACE TO THE FIEST EDITION. An earnest desire to assist in diffusing a love for microscopical inquiry, not less for the pleasure it affords to the student, than from a conviction of its real utility and increasing practical value in promoting advancement in various branches of art, science, and manufacture, — a wish to simplify, as far as possible, the processes for preparing microscopical specimens, and the methods for demonstrating the anatomy of different textures, — and the belief that many who possess microscopes are deterred from attempting any branch of original investigation solely by the great difficulty they experience in surmounting elementary detail and mere mechanical operations, — are my chief reasons for publishing this elementary course of lectures, which was delivered during the past winjter. It has been thought desirable to append the tables which I have been accustomed to use in my course of practical demon- strations, for the purpose of enabling everyone to practise for himself the most useful branches of manipulation. Each table will occupy the student about two hours. Subjoined is a list of the apparatus required for microscopical research, much of which is simple and inexpensive. A nurajjier has been added to each instrument, by transmitting which to any instrument maker, the observer wUl be furnished with the apparatus required. L. S. B. Pathological LABoaATORY, 27, Carmj Street, Lincoln' s-irm, JuTie^ 1857. TO THE EEADEE. Some persons may prefer to study the contents of tliis iook by referring, in the first instance, to the plates. The boolc may, in fact, be " read " in this way. The figures are explained at the lower part of 'the plate, but under each will be found a reference to the section in which the matter it illustrates is discussed, st^that, with a very little trouble, the observer may render himself familiar with most of the instruments and different pieces of apparatus required in micro- scopical observation. But the author recommends the beginner to " read " the book by practising the tables, commencing at page 249, or if he has not patience for this, he should at least go through the processes in §136, page 73. CONTENTS. CHAPTEB I. Inteodfctiok. — The Microscope — -Simple and Compound Micro- scopes. Optical Pobtion of the Miceoscope. — The Negative Eye-piece — Positive Eye-piece — The Object-giasses — Spherical and Chromatic Aberration — Angle of aperture — The Mirror. Mechanicai/ Pobtion de the Mioboscope. — Adjustments for altering the focus.==^The Body of the Micro- scope — The Stage-;— Diaphragm — Microscope Makers — Students' Microscopes — Necessary Apparatus — Large Microscopes — Binocular Microscopes — Travelling and Dissecting Microscopes — Clinical, Pocket, Travelling, a.nd Class Microscope — Dissecting Microscope CHAPTER II. Examination by Eeflected Light. Transmitted Light, and Polarized' Light.- Keeiected LraHT. — Different Methods employed — Bull's-eye Condenser — Metallic Side Reflector — Lieberkuhn's — Dark-ground Illumination — Parabolic Illuminator — Annular Condenser. Teansmitted Light. — Diaphragm — Achromatic Condenser — Gillett's Condenser. Polaeized Lioht. — Polarizer — ^Analyzer — Iceland Spar — Tourmaline — lodo-quinine or Herapathite. Illumination bt Aetieicial Light. — . Lamps — Camphine Lamp — Oil Lamps — Argand Lamp — French Moderator Lamps — Gas Lamps — Of the Importance of Pro- tecting the Eyes from the Diffused Light of Lamps. On Deawing Mioeoscopioal Specimens. — Camera Lucida — Steel Disc — ^Neutral Tint Glass Reflector — Arranging the Light — • Of making Drawings which it is intended should be Engraved — Tracing Paper — Retransfer Paper — Wood Blocks^Of obtaining Lithographs of Microscopical Drawings — Drawing on Transfer CONTElfTS. PAGE Paper — Drawing on the Stone — Of Engraving on Stone — Transfer Paper — Lithograpliio Ink — Lithographic Stones — On the Importance of Observers Delineating their own Work. On Meastteing- OsJEfaTS. — Cobweb Micrometer — Test Objects — Nobert's Lines — Jackson's Eye piece Micrometer— Stage Micro- meter — Simple Directions for Measuring Objects — On ascertain- ing the Magnifying Power of Object-glasses — To ascertain the Diameter of an Object — Standards of Measurement — Conversion of Foreign Standards of Measurement — On Finders — On Measuring the Angles of Crystals : Goniometers .... 19 CHAPTER III. Instkuments Requieed in MiceoscoeicaI/ Keseaeoh. — Spirit Lamp — Wire Retort Stands — Tripods — Brass Plate — Water Bath. Insteuments eob CuTTiNa Thin Sections oe Tissues. — Scalpels — Doubled-edge Scalpel — Double-bladed or Valentin's Knife — Scissors — Needles — Forceps — Wooden Forceps. Appaeatus Used eoe Examining Objects in the MiCBOSCOPEii — Plate Glass Slides — Thin Glass — Glass Cells — Watch Glasses. Cements. — Gold Size — Sealing-wax Varnish — Solution of Shell-lac — Bell's Cement — Brunswick Black — Marine Glue — Cement for Attaching India-ruhber or Gutta Percha to Glass Slides — Canada Balsam ^ — Of Vessels for Keeping Canada Balsam in — Solution of Canada Balsam — Gum — French Cement Composed of Lime and India-rubber. Peesektatite Solutions. — Spirit and Water — Glycerine — Thwaites' Fluids Solution of Naphtha and Creosote — Solution of Naphtha and Water — Solution of Carbolic Acid — Solution of Chromic Acid — Preservative Gelatine — Gelatine and Glycerine — Gum and Glycerine — Goadby's Solution — Burnett's Solution — Solution of Chloride of Calcium — ^Alum — Arseuious Acid — Arseninretted Hydrogen — ^Nitrogen .... .... 47 CHAPTER IV. On the Methods oe Making Cells poe Miceoscopicai Peepaeations. — Cells for Preserving Microscopical Specimens — Cells for Dry Objects — Paper Cell — Holder for Pressing Objects, &c. — Brunswick Black Cell — Cells made of Tinfoil and Marine Glue — Of Cutting and Grinding Glass — Of Cutting the Thin Glass — Slone or Pewter Slab for Grinding Glass — Cementing Glass together with Marine Glue — Cleaning off Superfluous Glue — Cells made of Thin Glass — Simple Methods of Perforating the Thin Glass — Deeper Glass Cells — Small deep Glass Cells for Injections — Built Glass Cells — Deep Glass Cells made by Bending a Strip of Glass in the Blowpipe Flame' — Moulded Glass Cells — Gutta Percha — Troughs for Examining Zoophytes — . Animalcule Cages — Bound Cells proposed by Dr. Guy .„. 65 COTfTEHTS. XI PAGE CHAPTITR V. On ExAMiNiira Objects in the Miokoscope — For Beginners only — How to Examine an Object in the Microscope. Genebai CONSIDEEATIONS TIPON THE StEUOTUBE OP TiSSTTES — Plesh or Muscular Tissue — On Demonstrating the Anatomical Peculiarities of Tissues — The Anatomy of Organs more easily Demonstrated in the Lower Animal,s than in Man and the Higher Animals — Of the Time after Death when Tissues should he Examined — Ciliary Motion. Ov PBEPABiNa Tissues eob MiOBOSOOPiOAii Examination. — Of making Minute Dissec- tions — Dissecting under the Surface of Fluid — Loaded Corks — Tahlets upon which Dissections may he pinned out — Of obtaining Thin Sections of Different Textures for Microscopical Examination — Drying the Tissue before Cutting the Sections — Hardening the Tissue — Horn — Hair — Making Thin Sections of Bone — Teeth — Sections of Wood — Of Dissecting Tissues under the Microscope with the Aid of the Compressorium — The Cell or Animalcule Cage. Op the Impoetance op Examin- ing Objects in Vabious Wats. — Appearance of the same Object in AiE, Watee, and Canada Balsam, by Teans- MITIED Light, and under the influence of Replected Light and Polaeizbd Light. .... .... .... .... 73 CHAPTER n. On the Examination op Tissues and thbie Peeseetation AS Peemanent Objects. — General Considerations with reference to the Nature of the Medium in which Tissues should be placed for Examination. Examination and Peeseetation op Stettctitbes in Aie. Examination and Peeseetation op Substances in Aqueous Fluids. Examination and Peeseetation op Sopt Tissues. — Muscle — Villi — Adipose Tissue — Nerve Fibres — Arrangement for pressing down the Thin Glass Cover upon the Preparation while the Brunswick Black is drying — Examination of Vegetable Tissues — Of the Circulation in 'the Cells of Vallisneria — ^Anacharis, Anchusa, &c. Examination and Peeseetation op Objects in Canada Balsam. — Examination of Hard Tissues : Bone. AiB-BUBBLES. OiL-GLOBULES. — Blood-globules — Fungi. Op the Sepabation op Deposits peom Fluids. — Conical Glasses — Pipettes — Removing the Deposit with the Pipettes — • Separation of Deposit when very Small in Quantity — Exami- nation of Infusoria — Vorticellse — Zoophytes — On separating the Coarse from the Finer Particles of a Deposit— Method of obtaining the SiKcious Skeletons of Lower Organisms — Wash- bottle — Of keeping Preparations in the Cabinet .... 89 CHAPTER VIL Op Injecting. — Natural and Artificial Injections— Transparent and Opaque Injections — Instruments required for making Xll CONTENTS. PAGE Injections — Syringe, Pipes, Stop-oocts, BuU's-nose Forceps, Needle for passing the Thread round the Yessel. Of Opaqitb Injections. — Injecting Cans — Size — Colouring Matters — Vermilion — Chromate of Lead — White Lead — Size of the Particles of the Colouring Matter used. Op Teanspabent Injections. — Injecting with Plain Size— Colouring Matters — Gerlach's Carmine Injecting Fluid. — Advantages of einploying Prussian Ulue — Composition of the Prussian Blue Fluid for making Transparent Injections — On injecting different Systems of Vessels with Opaque and Transparent Injections — Acid Carmine Fluid — Mercurial Injections. iNJEOTlNa the Lowee Animais. — Mollusca — Insects. Op the Pbaotical Opera- tion OP Injection.— ^-Of Injecting the Ducts and Secreting Follicles of Glands — Of preparing Portions of Injected Prepa- rations for Microscopical Examination .... .... 107 CHAPTER VIII. Op Chemicai; Analysis in Michoscopioai Intesti&ation — Instances of the use of Eeagents — Preliminary Operations — Eeaction — On Filtering — Evaporation and Drying — Incinera- tion — Apparatus — Chemical Microscope — Examining Substances at A High Temperature. Reagents anu theik Actions.-^ Alcohol — Ether — Effects of Alcohol and Ether — Nitric Acid — Sulphuric Acid — Hydrochloric Acid — Acetic Acid — Chromic Acid — Effects of Acids upon Organic Structures — Solution of Potash — Solution of Soda — Effects of Alkalies upon Organic Structures — Potash and Soda — ^Ammopia — Nitrate of Barytes — Nitrate of Silver — Oxalate of Ammonia — Iodine Solutions. Op AppiiYiBG Tests to Minute Quantities oe Mattee. — Bottles with Capillary Orifices for Tests — Capillary Tubes, with India-rubber tied over the Top — Testing for Carbonates, Phosphates, Sulphates, and Chlorides. Op OBTAiNiNa Cetstalline Substance peom the Fluid and Textuue OP Oeuanisms. — Formation of Crystals — Influence of various Constituents upon the Crystallization — Separation of Crystals from Non-Crystalline Organic Substances — Examination of Crystals under the Microscope. Op Obtainin9 Ceystals POE ESAMINATION. — Preservation of Crystals as Permanent Objects. Op the Haedening- Peopeeties op Dippeeent Chemical Solutions. — Mr. Lockhart Clarke's plan of Pre- paring Thin Sections of tlie Cord — Method of rendering Soft Tissues Hard and Transparent .... .... .... 123 CHAPTER IX. On taking Photogbaphs op Micboscopic Objects. History. Appaeatus.— Camera, with Object-glasses and Stage adapted to it — Mr. Wenham's arrangement without a Camera — Camera applied to the ordinary Microscope — Dr. Maddpx's Camera — Arrangement of Drs. Abercrombie and Wilson. CONTENTS. xiii * PAGE IiiTTMlNATiON. — Sunlight — Artificial Light — Of Focussing Of the Object-glasses — Stereoscopic Photographs — Ohemioai, Solutions. —Collodion— Nitrate Bath — Of the Developing Solutions— The Fixing Solutions. Pbactical Manipulation. — Cleaning the Glass Plates — Arrahging the Camera — Inserting the Plate — Developing the Image— Varnishing the Plate — Of cleaning Old Plates— Of increasing the Intensity of the Negative. Op Printing. — Preparing the Paper and Printing — Toning Solution — Another Toning Solution— Fixing Solution — Of Mounting the Prints — Photographs of Microscopic Objects for 'the Magic Lantern .... .... .... 149 CHAPTER X. New Methods op Peepaeation. — Of Staining Tissues — Process followed by the Eev. Lord S. G. Osborne — Gerlach's Method of Staining — Thiersch's Metliod— Thiersch's Lilac Colouring Fluid — Anilin Colours — :Blue Colours for Staining — Tannic Acid — Solutions of Nitrate of Silver— Other Metallic Salts — Modification of the foregoing plans. The Author's NEW Method op Prepaeation fob ExAMiNiN(f Tissues WITH THE Hiohest Powees. — Conditions to be fulfilled — Action of Glycerine and Syrup — The Injecting Fluid — The Carmine Fluid — Other Colouring Solutions — Glycerine and Acetic Acid — Chemical Reagents in Glycerine — Acetic Acid Syrup — Potash and Soda in Glycerine — Chromic Acid and Bichromate of Potash — Of the advantages of viscid media for the Dissection of Tissues — The practical method of preparing Tissues for examination with the Highest Powers — Of the preparation of Hard Tissues — New Theories relating to Structure and Growth arrived at by this mode of investigation. 189 CHAPTER XI. Of the Use op vert High Maonietinq- Powers. — Objections raised — Of the Highest Magnifying Powers yet made — Of the Covering Glass — Illumination of Objects Magnified by very High Powers — Method of Increasing the Size of the Image without altering the Object-glass — Of Drawing Objects Magnified with very High Powers — The Anatomical Element , or Cell and of .its Life .... .... 215 CHAPTER XIL Of Making and Rbcoeding Mioeosoopioai, Obseevations. — Of drawing Inferences from Observations. Fallacies to be GUAEDBD AGAINST IN MiCEOSCOPlCAL INVESTIGATION. — Errors of Observation — Of the Coimraenceraent and Termi- nation of Tubes — On the Difficulty of seeing Structures from their extreme Transparency — Fibres and Membranes produced Artificially by the Action of Reagents — A Fibrous Appearance xiv ILLTrSTEA.TIONS. PAGE produced in Structureless Membranes — Collections of Oil- globules appearing as if within a Cell — On the accidental Presence of extraneous Substances. Op Eeoobdino Miobo- scopiCAi Obseetations. — Exactness of Description — Of the Importance of making Sketches ' .... Tables eqe PBACTisiif& the Use op the Mioeosoopb .... 240 Beitish AST) FoBEiaN MicEosooPE Makees .... .... 249 rEEPAEEES OP MiCEOSOOPIC OBJECTS .... .... .•■. 263 MatEEIAIS "AND APPAEATITS POB MOTTNTINd OBJECTS .... 263 Aetists, Deauqhtsmen, Wood Eif&EATEES .... .... 263 PEHtTEES, LiTHOaEAPHIO, AND PhOTO-LITHOGEAPHIC PeINTBES 263 LlTHOGEAPHIO SlOlfEa, DlAMOHDS POB EiraBAVINa, AHD APPA- EATU3 Used is LiTHoaBAPHY .... .... — ■ 263 Appaeattts poe DEAWiua ENaEATiiras, &c. .... .... 263 BbITISH and FoEEIGN WoeKS ON THE MiCBOSCOPE, INCLTCTDINa JOUBNAIS .... .... .." •••• ■••• 264 Index .... .... .... ' ••. •■■■ ••■• 2617 ILLUSTEATIONS. Fbontispiece. — Photographs of pith, itch insects, blood corpuscles, bone, &c. By Dr. Maddox. Plate I. — Structure of eye-piece and object-glasses of simple and compound microscopes. plate II.— rObjectives of different angles of aperture. ' Aberration,' spherical, and chromatic. Stage and mirror. . Plate 111. — Microscope. By Messrs. Powell and Lealand. Plate IV. — Student's microscope. Made by Mr. Salmon. • Plate V. — Student's microscope. Designed by Mr. HigUey. Plate VI. — Binocular microscopes. Nachet's microscope for two observers. Plate VII. — Binocular microscopes. Showing the arrangement of the prisms. Plate VIII. — Highley's cheap portable and student's microscopes. Plate IX. — Wenham's original arrangement of the binocular micro- scope. Travelling microscope. Plate X. — Microscope as arranged for examining objects in vivaria, and for making dissections. Plate XI. — View of all the parts of Dr. Beale's pocket microscope. Plate XII. — Dr. Beale's microscope, as arranged for class demonstra- tion. Plate XIII. — Clinical or pocket microscope. Student's microscope . Quekett's dissecting microscope. IIiLTTSTEATIONS. XV Plate XIV. — Prof. Queketfs dissecting microscope. The instrument arranged for observation. The same packed up for travelling. Plate XV. — Illumination by reflected and transmitted light. Plate XVI. — Lieberkuhn — Condensers, Neutral tint glass reflector. Steel disk, Polariscopes, Camphine lamp. Plate XVII. — Reflected light with the Lieberkuhn. Achromatig con- denser. , Parabolip illuminator. Microscope as arranged for drawing objects. ' Plate XVIII. — ^Modes of measuring microscopic oljeots. Finders. Plate XIX. — Bailey's universal indicator. Plate XX. — Goniometer. Microscope for measuring angles of crystals. Plate XXI. — Retort stand. Spirit lamp. Heating plate. Simple hot water batb. Tripods. Plate XXII. — Scissors. Scalpels. Valentin's knives. Needles. Plate XXIII. — Forceps. Section knives. Saws. Glass shades for protecting microscopic objects from dust. Plate XXIV. — ^Apparatus for making round cells. Brass ring for cutting glass circles. Shadholt's apparatus. Diamonds for cutting glass. Plate XXV. — Strong glass cells of various sizes and shapes. Plate XXVI. — Thick built glass cells. Deeps cells. Cells of peculiar shape. Plate XXVII. — Portion of the diaphragm of the white monse. showing elementary muscular fibres. Nerve fibres, and Capillary vessels. Plate XXVIII. — Yellow fibrous tissue. White fibrous tissue. Muscular fibre. Nerve fibre. Tracheae. Adipose tissue. Plate XXIX. — Pat. Small vessel dividing into capillaries. Dissecting under water. Newt dissected. Plate XXX. — Loaded Cork. Instrament for cutting thin - sections of wood. Compressoria. Plate XXXI. — Carbonate of lime. Difierent appearances of the same olgeet in different media, by transmitted, refiected, and polarized light. Crystals. Plate XXXII. — Villi. Epithelium. Altered nerve fibres. Entozoa. Plate XXXIII. — Vivaria. Fern cases. Branch of anacharis aJsi- nastrum. Cells of anacharis. Plate XXXIX. — .Hau: of anchusa. Shells of rare diatoms. Egg of common bug, Plate XXXV. — Animalcule cage. Heating apparatus. Pressing apparatus. Air Fump. Plate XXXVI. — ^Air bubbles. Oil globules. Blood corpuscles. Liver cells. Yeast fungus. Crystals of fatty acids. Plate XXXVII. — Using the pipette. Wash bottle. Placing on the thin glass cover. Apparatus tor exerting a continued pressure upon the thin glass cover. Plate XXXVIII. — Corks for the injecting pipe. Bull's nose forceps. Injecting can.- Syringe. Plate XXXIX. — Comparative sizes of the particles of some of the different colouring matters used as injections. Plate XL. — Portion of gall bladder injected. Capillaries of liver. Portion of intestine arranged for injection. XVI ILLTJSTBATIONS. Plate XLT. — Funnel arranged for filtering. Folding of the filtering paper. Test tubes. Rack and drainer. Box with reagents, &c. Plate XLII. — Dr. J. Lawrence Smith's inverted microscope. Plate XLIII. — Capillary tubes. Box of capillary-necked bottles. Crystals of creatine. Plate XLIV. — Crystals of snow. Plate XLV.— Spinal Cord. Transverse and longitudjnal section. Plate XLVI. — Photographic microscope camera. Plate XLVII. — Photographic camera, as arranged by Dr. Maddox. Plate XL VIII. — Photographic plate holder. Sectional views. Lamp with condensing lenses. Pressure frame. Camera adapted to the microscope. Plate XLIX. — Oxy-hydrogen lantern with gas bag, arranged for throwing mici'oscopic objects upon a screen. Plate L. — Cells, Animal and vegetable. Formation of starch, fkt, &e. Blood corpuscles, their development, growth, crystallization, &c. Plate LI. — Blood crystals. Blood corpuscles. Mucus corpuscle. Bacteria; Plate LII. — Mildew. Cells of sea weed. Plate LIU. — Portion of mylohyoid muscle of the Hyla arborea X 1700. Plate LIV. — Ganglion cell with straight and spiral fibres. Plate LV. — Ganglion cells, showing mode of development. Plate LVI. — Extraneous matters : Potate starch. Fibres of deal. Fragments of hair. Portions of feather. Spiral vessels of tea leaf, &c. Instrument for containing glycerine and other preservative fluids, p. 214. The same object magnified by difierent magnifying powers, p. 218. THE MICROSCOPE AND CROSCOPICAL MAnPULATION. CHAPTEE I. BUOTioH'. — The Microscope — Simple and Oompov/nd '•oscopes. Optical Pobtioit of the Microscope. — Negative M/e-piece — Positive M/e-piece — The Ohject- es — Spherical and Chromatic Aberration — Angle of "ture — The Mirror. MeohaistoaIi PoeTion op the soscoPB. — Adjicstmenfs for altering the Focus — The I of the Microscope^— The Stage — Diaphragm — Micros- Makers — Students' Microscopes — Necessary Appa- i— Large Microscopes — Binocular Microscopes — Tra- rtg and Dissecting Microscopes — GUnical, Pocket, elling, and Glass Microscope — Dissecting Microscope: troduotion. — The course of instruction which I am about nance will embrace the consideration of many subjects ?iotly practical character, and although it may be found )f that interest which necessarily attends the description tructure of living beings, or the theoretical speculations e causes of vital phenomena, I trust it will prove prac- useful to those who desire to prosecute microscopical I. m will be to describe the mode of examining diflferent in the microscope, the best methods of displaying their e, and the manner in which they may be preserved sntly. How best to demonstrate the peculiarities of a e is a question often asked by the microscopist, and it is )rtant one, for upon the method employed very much 2 HOW TO WOEK • depends. The success which attends our efforts in this field of research is, I believe, in great measure dependent upon our knowledge of the various methods which experience has shown to be advantageous for rendering the anatomical peculiarities of a texture clear and distinct, and it will be found that the most important new facts which have lately been added to science have been discovered by men who have paid the greatest atten- tion to the action of various re-agents, and have devised new and ingenious modes of investigation. From my position as a teacher of physiology and morbid anatomy and of clinical medicine in a large medical school, I have been naturally led to direct my attention chiefly to those branches of microscopical investigation which belong more par- ticularly to my own department, or which bear directly upon the investigation and treatment of disease ; but in this work I shall exclude everything of a strictly professional character. I shall allude only to those processes applicable to general microscopical research, and to the investigation of animal and vegetable tissues. Many little points to which I shall have to refer may perhaps be stigmatized as merely mechanical ; others may be regarded as belonging rather to the province of the chemist than to the microscopical observer; and not a few will perhaps seem to some readers unimportant and hardly worthy of attention. Some may consider such matters of manipulative detail to be out of the province, or even beneath the notice, of a scientific observer or a medical practitioner ; but those who feel the reality and the usefulness of thorough work will not think this. No man ever did perform real work until he had himself mastered minute practical details. Every one who has experienced the happiness of devoting himself to original research naturally desires to encourage others in the same course ; and how can this be done better than by showing as clearly as is possible how good work may be carried out ? There are few matters upon which more misapprehension exists among young men than this : how to master elementary prac- tical details, by which alone real success in the higher branches of work can be attained. Not a few express contempt for elementary work and mechanical skiU, by the aid of which ' alone can any one hope to add to existing knowledge. This false notion has not been discountenanced by teachers in the firm WITH THE MICEOSCOPE. 3 manner in which it should have been met. In this particular branch of inquiry, for example, the importance of injection and of preparing specimens and other practical work has been very much underrated, and in some cases even contemned as useless waste of time. It is the very grammar of the subject, which must be mastered and mastered thoroughly. The number of original observers emanating from our schools will vary in pro- portion to the encouragement afforded to this kind of work. I feel so very strongly that success in microscopical as well a,s chemical inquiries is connected with a readiness in sur- mounting comparatively small difficulties and with the possession of mechanical dexterity, that I feel it a duty to dwell somewhat on the subject ; and I should be doing a great injustice to my pupils if I did not instruct them in microscopical manipulation, and endeavour to facilitate, as far as possible, the performance of those operations which are essential to the successful demon- stration of the structure of textures under the microscope. These are questions not beneath the consideration of any one who takes a real interest in studying the structure of the differ- ent organisms by which he is surrounded, — and it is the same in this as in other branches of inquiry, that he who is most fully conversant with elementary detaU will be the most successful in the consideration of the higher and more abstruse problems, while he will feel a real love for his work, which is denied to the mere superficial inquirer. To endeavour to discover new methods of investigation appears to me to be one of the most important duties of every observer. To communicate these to his pupils must be the desire of every teacher of any branch of natural science. I am strongly of opinion that it is more necessary than ever that we should teach as much as possible by the eye. In teaching any branch of natural science the demonstration should be com- bined with oral teaching. The student should see what is described ; and where it is not possible for the teacher to exhibit illustrative specimens, good models, drawings, and explanatory diagrams should be supplied. It is the duty of gvery teacher to study how to communicate knowledge most easily and most charly and to save the student as much time as possible, for it is not likely that the amount of work which is required by the various examining boards will be reduced, nor indeed is it desirable that it should be. It is therefore incumbent upon teachers to facili- js 2 4 HOW TO WOEK tate the communication of knowledge in every possible way. A lecturer on every branch of microscopic inquiry can now show his pupils the structures he describes. For the last three years I have carried out this plan myself, and have found that it works admirably. I am able to demonstrate from eight to twelve microscopical specimens to a large class in the course of an hour, and, it need scarcely be added, such a system adds greatly to the interest of lectures, and enables the student to acquire a correct idea of structure, which it is impossible for him to obtain by reading or from mere description with the aid of diagrams. By describing the results of the investigations of others, we are enabled to diffuse knowledge. By detailing the conclusions we have arrived at from our own investigations, each may contribute his mite to the gradually increasing stock of information ; but in impressing strongly on his pupils the nature of the successive steps by which conclusions in scientific inquiries have been at length arrived at, and by describing to them minutely the methods employed in investigations, the teacher not only encou- rages his pupils to become original observers, and to investigate for themselves, but he places them in a position to commence new researches at a point where they have been abandoned by pre- ceding observers. Microscopical inquiry may be undertaken by persons in almost any position. The numerous cheap and excellent microscopes which have lately been made by many English makers have largely contributed to diffuse a knowledge of minute structure. The annually increasing sale of instruments of all classes shows how popular this branch of inquiry is becoming ; yet, I fear, it must be confessed that the additions to scientific knowledge are by no means so great, as a consideration of these circumstances would have led one to anticipate, and although there are many instruments, I fear it must be confessed that the observers are comparatively few. The opinion, that it is only necessary to place an object in the field of the microscope in order to make out its structure, seems far too prevalent. To this erroneous idea much of the disap- pointment suffered by many who are provided with microscopes may be traced. 2. The Microscope. — I shaU first of aU draw attention to the reouisite qualities of a good practical instrument, and the WITH THE MICEOSCOPE. 5 necessary accessory apparatus. The many excellent books in our own language render it unnecessary for me to occupy time in a minute description of the parts of which the instrument is composed, and to these works I must refer for information on this head.* At the same time it will be well for me to allude in general terms, and very cursorily, to certain points which every good microscope should possess, and to refer very briefly to the general form of instrument required by the student. The GompouThd Microscope is the only one now used for micro- scopical research. Until those great improvements in the mode of making the glasses, now universally employed, had been introduced by the successful labours of Mr. Lister, Mr. Boss, and others, the compound microscope was a very imperfect instru- ment, and even up to the present century the simple microscope, as employed by Leeuwenhoek, and improved by WoUaston and others, possessed many advantages over its more complex but imperfect rival. I shall not attempt to explain those beautiful optical principles upon which the value of the microscope, as an instrument for minute research, depends. There are, however, several terms in constant use to which I shall have occasion to aUude which it seems to me desirable to explain briefly. 3. Simple and Compoimd Microscopes. — In the simple micro- scope (Fig. 1, Plate I) the magnified image of the object passes at once to the eye of the observer. In the compound microscope (Pig. 2) the object is magnified in the first instance by the object-glass, o, and brought to a focus .within the tube, as represented at a, in the diagram. This magnified image is again magnified by the eye-piece, b. The image is of course inverted, but this inconvenience may be obviated by causing it to pass through another set of lenses inserted in the tube of the microscope, and termed the errector. The magnifying power, then, of the compound microscope may be increased either by increasing the power of the object-glass or that of the eye-piece, or by increasing the distance between the object-glass and the eye-piece. It must be borne in mind, however, that in increasing the power of the eye-piece we do not magnify the direct itself in a greater degree, but simply increase the size of the image of the object formed by the object-glass. Any imperfections which may * Tor list of works soe end of the volume. 6 HOW TO WOEK exist in the object-glass are thus greatly increased. Hence we should never work with deep eye-pieces, but when we wish to magnify an object to a greater degree, we should adapt a higher power to the instrument. Information upon obtaining very high powers will be given in the last chapter. In glancing cursorily at the structure of the microscope, it will be convenient for me to allude in the first place to the optical portion of the instrument, and secondly to the mechanical appliances for moving the object, altering the focus, c ^ —'/, V- - ^'"^"11 \ X \ » \,'' ;§ 41, 44, 45, 63. rig. 56. To illustrate tlie mode of examining an object by reflected liglit with tlie Lieberluhn. The light rf iiected from tiie mirror, tt, passes througli the glass slide, 6, around the object, and impinges on the concave annular mirror, d, by which the rays are brought to a focus and condensed upon the object placed at c. Fig. 57. Achromatic condenser mounted with a lever handle, iig. 68. Parabolic illuminator, showina course of a ray of light, m. m, /, when an uncovered object, p, is placed in focus. Fig. 59. Position of microscope for drawing [To face page 24.] WITH THE MICEOSCOPE. 25 through the object after it has been reflected from the surface of the mirror. And, 4. The object may be placed under tlie influ- ence of polarized light. Now the very different appearances observed should be care- fully noted, and after each examination the student should endeavour to form a notion of the probable nature of the substance, and the precise arrangement of the elementary parts of which it is made up. Lastly, the conclusion arrived at with reference to the nature of the structure after having been submitted to the-se four modes of examination should be con- trasted with the idea which would have been formed of it if an observation had been made by one mode of illumination only. 38. Artificial Illummation. — It may be said with truth that microscopical work should, if possible, be undertaken only by day- light, since the most perfect artificial light which can be obtained is far inferior for delicate observation, while it strains the eyes very much more; StiU many of us are compelled by necessity to work principally by night, and it is therefore a matter of the greatest importance to be provided with the best kind of artificial illumination. , 39. Lamps. — From time to' time various microscope lamps have been proposed. The small 'camphine lamp of Messrs. Smith and Beck represented in Plate XVI, Fig. 55, is one of the most perfect smaU lamps which I have seen. It gives a beautiful white light, and produces very little heat. Of oil lamps there are several which serve for microscopical examination. The German Argand lamp, lately imported into this country %y Mr. Pillisoher, is a good microscope lamp, and so also is the French moderator, especially if provided with a blue or neutral tint glass, and a shade. The common paraflin lamps give a most excellent light for the microscope, but Belmontine afibrds still better and whiter illumination. A cheap and at the same time very efficient microscope lamp is still a desideratum. 40. Gas Lamps.— For those provided with gas I recommend very strongly the gas lamp of Mr. Highley, which is provided with a flat brass plate and a water bath, instruments of great use in microscopical investigation. The light is made to pass through an opening in a diaphragm, so that the eyes are quite protected from 26 HOW TO ■WOEK the diffused light. A very pleasant light is produced by causing the rays to be transmitted through a blue chimney glass and a flat piece of neutral tint glass. The only objection to this lamp is its great heating power. One of these lamps is represented in Plate XVIII, Fig. 66. In all cases the eye should be carefully protected from the dazzling light when not employed in looking through the instru- ment. The eye not observing should always be kept open, but should be protected from the direct glare of the microscope lamp. For this purpose a shade made of black paper may be fitted to the body of the instrument at a convenient distance below the eye- piece. In all cases the light should be perfectly steady, and so situated that it may be conveniently reflected upon the object by the mirror. Of Dbawino, Engbavino, and Measubing Objects. 41. Of Drawing Objects. — It may almost be said that all real advance in our knowledge of the minute structure of both animal and vegetable tissues, depends upon the drawings which are made. It is almost hopeless for an observer to attempt to describe what he sees in words, and such descriptions, however careful they may be, cannot possibly be compared with those of others. On the other hand, a truthful drawing of what a man has seen lately may be compared with others which may be made a hundred years hence, although the means of observation will be far more perfect then than they are at present. Much may be learned by such comparisons. I am sure that an honest inquirer cannot be of • greater use in his time than by making good drawings of what he has seen ; — they will be of far greater help to our successors than any amount of description we can write for them, and we may feel sure they will look at our drawings if they are honest Copies of nature, while we all know that comparatively very little of what we write will be read when the whole aspect of this department of science shall be changed, as it wiU be. In delineating an object magnified by the microscope it is important to copy it correctly, both as regards the relative posi- tion of the several structures to each other, and also with respect to size. To copy the size exactly will be found extremely difficult by the eye alone, but there are several ways of proceeding by WITH THE MICEOSCOPE. 27 wMch accuracy may be ensured. Some of these I shall now briefly describe, ^e simplest method is to place the paper upon the same level as the stage upon which the object is situated. If we now look steadily at the object with one eye, while the other is employed to govern the movements of the pencil, the object will appear to be thrown, as it were, upon the paper, and its outline may be very readily traced. By a little practice the relative size of objects may be insured in this manner, but it is troublesome and difficult to keep both the object and paper per- fectly stiU. 48. Camera Iiucida. — The principle of the camera lucida has been applied to taking microscopical drawings, and has been found to succeed admirably. The object appears to be thrown down upon the paper, and with a little practice the observer may trace the lines with great accuracy. 43. Steel Disk.— If a little steel disk be placed at an angle of 45° with the eye-glass, it will receive the magnified image of the object and reflect it upwards upon the retina of the observer. The disk is smaller than the aperture of the pupil, and the pencil can at the same time be seen very weU as it traces the image apparently thrown down upon the paper beneath. The steel disk is represented in Plate XVI, Pig. 52. 44. Neutral Tint Glass Keflector. — The simplest and cheapest reflector for microscopical drawing, consists of a small piece of plate-glass slightly coloured, in order to improve its refl«cting power, but still not so dark as to prevent an object being seen through it perfectly. This is also arranged at an angle of 45° with the eye-glass, and the draughtsman can very easily follow his pencU upon the paper. This instrument is represented in Plate XVI, Pig. 51. In order to use these instruments, the microscope is arranged horizontally, and the paper placed on the table, as shown in Plate XVII, Pig. 59. 45. Arranging Light. — It is important, however, in using these instruments, to arrange the light carefully. The image should not be illuminated too intensely, and the paper upon which the drawing is made should not be too muph in the shade, or the 28 HOW TO WOEK point of the pencil will not be seen distinctly. Experiment can alone decide the relative intensity of the light upon the object and upon the paper, but with a little practice the proper amount of illumination will be discovered. The distance betweeii the reflector and the paper should be precisely the same as from the object to the eye-piece, for otherwise the size of the object delineated will be altered. The object appears to be thrown upon the paper, and its outline is very readily traced. If it is to be drawn smaller, it is only necessary to place the paper upon a stand closer to the reflector. If, on the other hand, a large diagram is required, the distance must be increased. By placing the diagram paper upon the floor, the object can be readily traced with a long pencil. In this manner many of my diagrams have been made. They must of course be accurate copies of the objects themselves, and are therefore far more truthful than diagrams copied from drawings representing microscopical structure, can be. If the distance of the diagram paper be always the same, the drawings so obtained may be compared with each other, and scales of measurement may be appended to them by proceeding in the manner described in 46. Of makingr Brawingrs 'nrhich it is intended should be Engraved. — With a little practice, the observer may acquire the power of drawing on wood, and the engraver will often be able to produce a more faithful representation of the object than he could by copying the drawings of the microscopical observer. It is, however, necessary to practise the plan of producing varieties of tints, by straight lines, whenever this can be 'done, aSfithe labour of engraving is thus much economised. The drawing should first be made roughly on paper, in order to obtain the size and general characters of the object. A piece of retransfer paper is then placed upon the prepared block, and the prominent lines of the drawing retraced with some blunt-pointed instrument (a needle, the point of which has been made blunt by filing it, answers very well). By using a slight pressure, the colour of the retransfer paper is transferred to the wood block in the lines corresponding to those of the drawing. These lines are after- wards reproduced by lead pencil, corrected, if necessary, and the delicate parts of the drawing filled in by carefully copying from the object. ■WITH THE MICEOSOOPE. 29 If the engraving is to be a fao-simUe of the drawing with the different parts on corresponding sides, it is necessary, in the first place, to copy the picture with ordinary tracing paper, and invert the tracing upon the retransfer paper on the wood block, as the impressions are of course always reversed ; or a reverse may be obtained by copying the image of the drawing reflected from a looking-glass. Beautiful specimens of wood engraving are seen in some of the plates in Chapters V, VI and X. 47. Traoingr Paper is a very transparent paper, obtained by soaking tissue paper in some oily material, and allowing it to dry. 48. Retracing' Paper consists of tracing paper, upon one side of which a fine red or black powder has been rubbed, which adheres to the paper pretty firmly, but which, at the same time, may be made to adhere to another surface by firm pressure. 49. "Wood Blocks are prqiared by rubbing a little dry car- bonate of lead and brick dust moistened with water upon the- surface, and allowing a very little to dry on. In this way a smooth white surface is obtained, admirably adapted for receiving the most delicate drawing. It is well to moisten the white lead with a little very weak gum water, which makes it adhere firmly to the surface and gives a very smooth face. Wood blocks may be obtained of Williamson and Son, Picket-place, Strand. Every observer should draw on the wood block himself. 50. Of obtainingr Lithographs of Btiorosoopioal Drawings. — I think it desirable to give a few directions for drawing on stone, as I believe there are many observers who would wUlingly give up the necessary time required to place their work on the stone, who could not afford to employ a lithographic artist. I made many drawings in this manner some years ago, and with the help of a boy, who could at first draw but little, have been able to publish numerous drawings, which are very accurate copies of the objects, although in execution will not bear -comparison with artists' work.* 51. Drawing on Transfer Paper. — If the drawing does not contain much very minute work, it may be drawn on properly * See the earlier numberB of my ' Archives.' 30 HOW TO WOEK prepared transfer paper with lead pencil, direct from the microscope. Afterwards, the lines are to be traced with a pen with lithographic ink ; the shading may be effected by delicate lines made with the pen, or with lithographic chalk. The latter plan, however, is not well adapted for making transfer drawings. The drawing is then to be sent to the lithographic printer, where it is damped, placed downwards on a dry stone, and after being subjected to firm pressure, the' paper may be peeled off, leaving the preparation, with the drawing, on the stone. The latter is removed with water, the drawing properly set, and then the printing ink applied with the roller. 53. Transfer Paper is prepared for the purpose. That which was made of India paper, I found answered exceedingly well.* 53. Drawing on the Stone. — There are two plans for drawing on the stone itself, which produce better results than the pre- ceding method, but they require more practice for their perform- ance, When much shading is required, and extreme delicacy of outline is unnecessary, the outline is first made on paper, and the drawing retraced on the stone Lti the manner designated in § 46 ; the outline may then be traced with ink, a pen, or very fine sable hair brush, being used for the purpose ; the shading is to be given with the lithographic chalk. The chalk is to be very finely pointed by cutting downwards, the point being uppermost (as in pointing an ordinary chalk crayon), and held in a handle made out of & common quiU. The lines are to be made very gently, repeating the strokes frequently with a light hand, when depth of colour is required, rather than by leaning heavily so as to remove a cc Ill O « 1^ III ? usi bove Table. 1 the value in British Inches. e " Encyc. Metro ssian foot =1-020 CD ? " ? s s s ill M W S is wis 10 S S g III in III ^ us 1 si e of the a XAMPLE. es. Bequire Irilish Inches. -00007874158 -000003937079 -000001968539 * ■« o> ill S " ' CO 3 S 5 o» An ^ 3 1 i r Son |fc a n ! 1 1 ! CO ill S S 5 1 ^ _^ ill at 00 «» tish "Inches.. ..J Do. Millimetres Do. Old Paris Lines .. " ^ n .«ioto t^ooci o FflM ■WITH THE MIOEOSCOPB. 41 Most microscopic measurements are under the hundredth of an inch, and a hundred-thousandth of an inch cannot be measured with certainty. The requirements of the case therefore may be stated in decimals of an English inch by 'OOlOl, and if the two ciphers next the decimal point be struck out, and the first number be considered the unit, it may be written 1''01, in which a thousandth of an inch is the unit. This method will embrace nearly every microscopic magnitude in three consecutive figures. The foreign measures are the millimetre and the French and Prussian lines. The two latter are so nearly equal, that in the small fraction required in the present subject they do not differ sensibly, and the same rule will serve for the conversion of both. A millimetre cont3,ins '03937 English inches or 39''37 ; accord- ing to the method proposed, the length to be converted will seldom amount to one-fourth of this. To convert millimetres into thousandths, shift the decimal point one place to the right and multiply by 4 ; if greater accuracy be required, substract 1^ from the second place of decimals for each of the nearest numbers of units of the product. Thus 0"™-250 becomes 250 which X 4 = 10''00, from which subtract ''15; and 9''35 is obtained as the value in thousandths of an English inch, while O^^'SS is equal to 9''84, which differs from the former by a quantity too smaU to measure. To convert thousandths of English inches into millimetres, add 1^ in the second place of decimals for the nearest number of units in the sum, divide by 4, and shift the decimal point one place to the left, thus— to 9'-84 add '-15 and the sum 9-999 -^ 4 = 2'498, and shifting the decimal point ™"'2498 which' does not differ sensibly from ™™-25, the correct quantity. A French line, contains '0888 English inches. To convert lines into thousandths of an inch, shift the decimal point one place to the right, and multiply by 9 ; if greater accuracy be required, subtract I5 from the second place of decimals for each of the nearest number of units in the product. Thus 0"'-l-25 becomes 1-25 which X 9 = 11''25, from which subtract '-14, and the value in thousandths is found to be ll'lO, which is correct. To count thousandths into lines add I4 in the second place of decimals for each of the nearest number of- units in the sum, divide by 9, and shift the decimal point one place to the left, thus, —to ll'-lO add '-14, the sum 11-25 divided by 9, and the decimal point shifted one place to the left gives 0"'-125 as before. 42 HOW TO WOEK In most cases it will be unnecessary to apply the corrections noticed above, but by remembering the short rules given, any one on reading a foreign work may correct the measurements as he reads, and insert them in the margin without delay or interfering with his progress. 67. On Finders. — Various plans have been proposed from time to time for marking the exact position of a minute object in a specimen, so that it can be placed in the field of the microscope whenever required. A fine line of varnish or Brunswick black may be drawn round it, or a small and very thin metal tube (about the tenth of an inch in diameter) may be moistened with the varnish and pressed upon the glass cover, so as to encircle the particular object required with the line. Mr. Bridgman, of Norwich, has designed an instrument for drawing a circle upon the thin glass with a diamond point {"Microscopical Journal," Vol III, p. 237), This instrument is represented in Plate XVIII, Fig. 65. A, a brass cap fitting upon the end of the object glass, which it entirely covers up and protects from injury ; B, a stem soldered to the side of the cap with the upper end having two projecting sides to steady the ends of C, e, and /, which are firmly secured to it; C, an elastic arm of hammered brass, which carries at its lower end D, a lever of thin brass plsite, having a fragment of diamond inserted in its thinner end, and directly under the centre of the cap A ; c and / are two springs, pressing upon the shorter end of the lever D, the longer one /has a hole to allow the screw h to pass without touching it; g, a screw holding the two springs and the elastic arm to the arm of the cap ; h, a milled screw to adjust the elastic arm C, so as to • bring the diamond point away from the centra, according to the size of the ring required. When the object has been found, the cap carrying the diamond point is placed on the object glass and carefully adjusted, so that the diamond point is brought into contact with the surface of the glass, it is then turned round, and thus a line is drawn round any object which can be readily found at any future time. This same end has been gained in another manner. Graduated scales have been affixed to the stage of the microscope so as to measure the exact amount of movement in the vertical and horizontal direction ; the slide being placed in position against a stop at the side. The number on the two scales is noted when the PLATTil XIX. Bailee's indicator. [To fiicc piige d;i.] WITH THE MICROSCOPE. 43 object is seen in the field, and, by placing the stage opposite the same numbers, at any future time the object must appear in the same position. Various ingenious "finders" have been proposed. A very simple and efficient one is represented in Plate XVIII, Fig. 64, in which the scales are ruled on paper (Mr Wright, "ilfic. Jour." Vol. I, p. 302, 1853), which' is afterwards fixed upon the stags,' but it is better to have the lines ruled on the brass itself. Bailey's Universal Indicator. — Mr. J. W. Bailey; of the United States, has described an instrument for registering the positions of various objects upon a slide, in Vol. IV of the " Quarterly Jonrnal of Microscopical Science." The arrangement is seen in Plate XIX. The centre of the field of view corresponds to the point ■where the horizontal line D intersects the vertical line E, P. The piece 6, 1, H is moveable. The slides upon which the objects are mounted must have guide lines, as shown in Figs. 1 and 2. This indicator is to be firmly fixed to the stage of the microscope, care being taken that the centre of the indicator corresponds to the centre of the object glass. The mode of using the indicator is obvious. All such devices have, however, been superseded in cases where the microscope is provided with a travelling stage, by the very clever arrangement suggested by Mr. Maltwood (" Trans. Mic. &c." Vol. VI, p. 69, 1858). A little stop is placed upon one side of the stage, in contact with which one end of the finder, and afterwards the glass slide can be placed. The finder consists of a plate of glass, upon which numbers are arranged in minute squares. These run in two directions, vertically and horizontally, so that in each square there are two difierent numbers, except in the case of the central square, which of course contains two 25's. Any object having been found, its exact position may be registered by removing the slide and placing on the stage the finder. The numbers seen in the field are then marked on the slide itself, and the same spot can always be found, by looking for' these numbers on the finder, moving the stage so that they come in the centre, and then substituting the slide for the finder. The numbers and lines are photographed on the finder which is made by Messrs. Smith and Beck, and costs 7s. 6d. A few of the squares of a Maltwood's finder are represented in Plate XVIII, Fig. 63. 68. On SCeasuring' the Angles of Crystals— G-omometers. — Measming the Angles of Crystals. I have already adverted to the 44 HOTV TO WOEK principal methods of measuring objects, but have not discussed the mode of ascertaining the value of the angles ot microscopic crystals in the microscope. The simplest instrument for this purpose is the one represented in Fig. 68, Plate XX, which is a slight modification of Schmidt's goniometer. It consists of a cobweb stretched across the field of an eje-pieoe, and capable of being moved by an arm which passes round an accurately graduated arc. The cobweb line is placed parallel to one face of the crystal, the circle being moved round until the bar stands at zero. The latter is then made to rotate until the cobweb is brought parallel with another face. The number of degrees through which the bar has passed marks the angle of the crystal. It is absolutely necessary that in taking this measurement the crystal should be perfectly flat, for otherwise a false angle will be obtained. Dr. Leeson has proposed a beautiful and much more perfect arrangement for measuring the angles of small crystals. The plan has been improved by Mr. Highley, who describes, in the Fourth volume of the " Quarterly Journal of Microscopical Science^' page 281, a mineralogical microscope. This instrument is represented in Plate XX, Fig. 71. It may thus be briefly described with the aid of the figure : — On a central pivot screwed into a solid circular base rotates a plate that carries the body, prism box P, object glass, and fine adjustment A ; to the side of the base is fixed a square bar G, that carries the principal stage with its coarse adjustment, and the secondary stage into which fits the diaphragm polarizer, selenite plates,