- 2 - 
 
 PHOTOGEAPHED SPECTEA 
 
LONDON : PRINTED BY 
 
 SPOTTI8WOODE 
 
 AND 
 
 AND CO., NEW-STREET SQUARE 
 PARLIAMENT STREET 
 
PHOTOGRAPHED SPECTRA 
 
 ONE HUNDRED AND THIRTY-SIX PHOTOGRAPHS OF 
 METALLIC, GASEOUS, AND OTHER SPECTRA 
 PRINTED BY THE PERMANENT 
 AUTOTYPE PROCESS 
 
 WITH 
 
 INTRODUCTION, DESCRIPTION OF PLATES , AND INDEX 
 
 AND WITH 
 
 AN EXTRA PLATE OP THE SOLAR SPECTRUM 
 (SHOWING- BRIGHT LINES) COMPARED WITH THE AIR SPECTRUM 
 
 BY 
 
 J. RAND CAPRON, F.R.A.S. 
 
 LONDON 
 
 E. & F. N. SPON, 46 CHAFING CROSS 
 
 NEW YORK: 416 BROOME STREET 
 
 1877 
 
Digitized by the Internet Archive 
 in 2017 with funding from 
 Getty Research Institute 
 
 https://archive.org/details/photographedspecOOcapr 
 
PHOTOGRAPHED SPECTBA. 
 
 INTRODUCTION. 
 
 During the course of the last and the preceding 
 winters, I was led, in connection with an investigation 
 bearing on the Spectrum of the Aurora, to take photo- 
 graphs of certain of the metallic and gaseous Spectra 
 with a spectroscope of moderate dispersion. After a 
 time this work gradually extended itself, and ultimately 
 a very considerable collection of such photographic 
 plates was obtained. In these labours I was very 
 efficiently assisted by Mr. G. H. Murray of the Surrey 
 Photographic Company (who superintended the photo- 
 graphic department), and by Mr. E. Dowlen of Guild- 
 ford, to whom I am much indebted for notes and general 
 assistance. The photographic impressions comprised 
 all that could be obtained of the spectrum in each case, 
 ranging from about b to beyond H 1 H 2 in the violet. 
 It was soon apparent from an examination of the plates 
 obtained, — 
 
 1. That considerably more of the spectrum was 
 obtained in the direction of the violet end than 
 is ordinarily delineated in the published works 
 on Spectra. 
 
2 
 
 PHOTOGRAPHED SPECTRA. 
 
 2. That, notwithstanding the moderate dispersion 
 and the limited extent of the spectrum obtained 
 (for want of the red end), each individual 
 photograph had, without actual measurement 
 of its principal lines, a separate and distinct 
 character, easily recognised when once seen, 
 and distinguishing it from all others. This 
 peculiarity we think will be borne out by an 
 examination of the Plates produced, and we 
 ourselves had several practical instances of its 
 application in our process of taking the photo- 
 graphs. 
 
 Under these circumstances we considered we might, 
 with probable advantage to others engaged in spectro- 
 scopic research, reproduce a series of our results as 
 forming at once a handy book of reference to spectra 
 in general, and as also illustrating in each particular 
 case the peculiar features of the spectrum photo- 
 graphed. 
 
 The spectroscope employed (for the metals) was 
 constructed by Mr. John Browning some years ago 
 specially for Auroral observations, and is of the direct 
 vision form. 
 
 The prism is an inch aperture compound (5) one, 
 dividing very easily the D lines with a low eyepiece, 
 a similar second prism can be slipped in for use if 
 desired. The collimator carries an \\ achromatic lens of 
 6 inches focus. The ordinary observing telescope and 
 eyepiece were removed, and an 1^ achromatic projecting 
 lens of 9 inches focus was substituted for them. The 
 
INTRODUCTION. 
 
 s 
 
 short tube carrying the last-mentioned lens was con- 
 nected by a black velvet bag, with an ordinary square 
 camera for plates 4^ + 3^, and the images were taken 
 upon collodion wet plates. (See Frontispiece for 
 arrangement of apparatus). 
 
 The metallic spectra were obtained of two sorts : 
 
 L By the spark. 
 
 2. By the electric arc. 
 
 The metals employed mostly formed part of a 
 German cabinet which came into our hands with a 
 good character. 
 
 For obtaining the spark spectra, the apparatus con- 
 sisted of a large RhumkorfF coil, giving, with four double 
 plate half-gallon bichromates, a thick strong spark 
 about 2 inches long. In the circuit was introduced a 
 condenser, composed of 4 glass plates, each containing 
 50 square inches of coating. By this condenser the 
 spark was reduced to one from ^ to ^ an inch long, 
 and of considerable brilliancy. The time of exposure 
 in the case of the spark spectra varied very con- 
 siderably, averaging perhaps 15 minutes. 
 
 For the arc spectra 40 pint Grove cells (except in 
 one or two instances when 30 only were used) were 
 employed, and with these the arc was steady and of 
 sufficient length. In all cases the slit was placed 
 vertically ; and in our printed Plates we have followed 
 the usual practice of spectroscopists, in keeping the red 
 end of the spectrum to the left hand. Care was taken 
 to have the carbon points and cups well cleansed, and 
 by trial plates, taken from time to time, it was seen 
 
4 
 
 PHOTOGRAPHED SPECTRA. 
 
 that they contained no impurities affecting the spec- 
 trum. 
 
 For the spark, wires or points of metal, held by 
 miniature steel pincers, were used. 
 
 In the case of the arc, sometimes fragments of the 
 metals, sometimes the metal in powder, and in a few 
 instances solid metal electrodes were employed. The 
 time of exposure in the case of the arc ranged from 
 three to five minutes, according to the intensity of the 
 stream of light. The length and brilliancy of the arc 
 were found to alter much according to the nature of 
 the metal placed, in the cup. The spark also varied 
 considerably in length and intensity according to the 
 electrodes. In the spark spectra, the air spectrum is, 
 with a few exceptions, seen in company with the metal 
 lines, the latter being, however, easily distinguished 
 from the former by their passing only partly across the 
 spectrum, while the air lines cross it entirely. 
 
 In the arc spectra some carbon lines of constant place 
 seem the only foreign introductions into the system of 
 metallic lines. These carbon or, as we called them, 
 ‘ point ’ lines, are found useful in placing and compar- 
 ing the several spectra when obtained. The images as 
 thrown on the camera plate were rather more than 
 two inches long ; and these were subsequently enlarged 
 exactly once. The lines required very careful focussing, 
 the slit being in most cases fine, so that where lines 
 are found thickened it is in general due to their 
 character. To supply the want of an approximate 
 scale, and also to indicate the part of the spectrum 
 
INTRODUCTION. 
 
 5 
 
 photographed, I prepared a diagram in which two 
 spectra of the metal manganese were respectively com- 
 pared, and a scale obtained by direct interpolation. 
 The upper horizontal spectrum was a photograph ob- 
 tained from manganese in a rather weak arc (30 cells). 
 The vertical spectrum was an enlarged (by photo- 
 graphy) copy of Monsieur Lecoq de Boisbaudran’s 
 normal spectrum of chloride of manganese ( 4 Spectres 
 Lumineux, Atlas,’ Plate xvii). The curve obtained was 
 regular, and a subsequent comparison of the result with 
 the solar spectrum of the same instrument (Plate xxi) 
 is satisfactory. The scale in most cases fairly coincides 
 for the principal lines with Monsieur de Boisbaudran’s 
 spectra, but instances will be found where the photo- 
 graphed spectral images are not in themselves ab- 
 solutely uniform in exact length and position of 
 fiduciary lines. The causes of this are not yet fully 
 worked out, but we believe the result to be due to a 
 difference in certain cases in distance of the discharge 
 from the slit. To the Description of the Plates are 
 added some notes by way of information as to the 
 behaviour of the metals and on other points. 
 
 The wave lengths of lines (where given) are 
 taken partly from M. Lecoq de Boisbaudran’s work, 
 
 4 Spectres Lumineux,’ and partly from Dr. Watts’ 
 
 4 Index of Spectra.’ The photographs were all taken 
 on separate plates, and have been very well re- 
 produced and printed in permanent pigments by the 
 Autotype Company, in compared sets of four. They 
 are for convenience arranged in alphabetic order, 
 
6 PHOTOGRAPHED SPECTRA. 
 
 the upper metals in the plates being selected for 
 arrangement where electrodes of different metals were 
 employed. Spark and arc spectra of the same metal 
 are in many cases compared. A few of the metals 
 and metalloids are wanting, mainly from the difficulty 
 of obtaining with our apparatus, spectra bright and 
 permanent enough to impress images on the photo- 
 graphic plates. The arc photographs might with 
 advantage bear considerably greater enlargement, but it 
 was thought convenient to keep them, for the purpose 
 of comparison, of the same size as the spark spectra. 
 Some of the metals do not show their full set of lines, 
 probably for want of more coil power ; but there 
 were considerations why a moderate spark was 
 originally selected, and the spectra were subsequently 
 kept uniform in this respect. 
 
 When rough lumps of metal were used for points 
 the spark was generally winged (especially when the 
 batteries were fresh), and played about over the surface 
 of the metal. The wings of the spark were tinged 
 with green in the case of silver and copper, with red in 
 that of iron, white or bluish white with magnesium. 
 Titanium ore gave occasional flashes of red (probably 
 from the iron clips), sodium gave a bright yellow flame. 
 Idle cups used with the spark apparatus were of 
 aluminium, except where glass is mentioned. 
 
 Width of slit averaged *003 inch, except in one or 
 two instances which are especially mentioned. 
 
 When different metals were used as terminals, the 
 current was generally reversed in the middle of the 
 exposure. 
 
INTRODUCTION. 
 
 7 
 
 The carbon terminals used in the arc were cut 
 from ordinary gas carbons, 3 centimetres long and 6 
 millimetres square. Those for the negative pole had 
 one end filed to a point. Those for the positive pole 
 were hollowed out at the end with a drill so as to form 
 a cup. To get rid of impurities (of which iron formed 
 the principal part), the carbons were soaked alternately 
 in acids and water : First, they were soaked in 
 diluted sulphuric acid, 2 parts water, 1 acid, then 
 soaked in water. Secondly, in dilute nitric acid, equal 
 volumes of acid and water. Thirdly, in hydrochloric 
 acid, half volume of water. The acids and water were 
 changed several times during the soaking. Last of all, 
 the carbons were soaked in water alone, which was 
 repeatedly changed until all the acid was washed out. 
 They were then slowly dried in an evaporating dish over 
 the flame of a Bunsen burner. The acids were all pure, £ 
 and the water distilled. The whole process occupied 
 from one to two weeks, according to the density of 
 the carbons, some being more porous than others. 
 
 When metals in powder were used in the arc, 
 small beads of the metal were usually scattered over 
 the inner surface of the cup, the main portion of the 
 metal remaining at the bottom. 
 
 All the metals of the iron group gave out sparks, 
 viz., manganese, iron, cobalt, nickel, chromium, and 
 uranium. Silver gave a melted bead, which revolved 
 in the carbon cup without actual contact with it. The 
 width of the slit was generally *001 inch, distance of arc 
 from slit 1^ inch, but from the flame playing round 
 
 
8 
 
 PHOTOGRAPHED SPECTRA. 
 
 the point and cup, this distance was subject to varia- 
 tion. The adjustment for distance of arc discharge 
 was by rack work worked by hand. The upper 
 carbon was fixed in a balh and- socket joint so as to 
 adjust easily over any part of the cup. 
 
 A fresh pair of carbons was used for each metal. 
 Much trouble was found in keeping the slit, and the slit 
 plate clear from metallic beads and other impurities. 
 It would be a great advantage for future similar work 
 to have the whole slit plate gilded and the slit jaws 
 formed of obsidian, platinum, or gold. 
 
 The gas spectra are represented in the last fifteen 
 Plates ; and for the purpose of obtaining these it was 
 found necessary to resort to a different form of instru- 
 ment to that employed for the spark and arc spectra. 
 
 An attempt was at first made to take all the spectra 
 with the same instrument, but it was soon found that less 
 dispersion and a brighter image would be required to 
 give any useful results with the gases, and one only of the 
 series (viz., spark in coal gas), was taken with the same 
 instrument as the metals. 
 
 Three forms of instrument were then arranged and 
 used for gaseous spectra : — 
 
 A — A compound (5) direct vision prism on stand 
 similar to that used for the spark and arc spectra, but the 
 collimating and projecting lenses of the spectroscope 
 were replaced by two camera lenses of somewhat larger 
 diameter, and each of 4^ inches focus. The image was 
 fairly bright, but not very sharp, as the slit could not be 
 made very fine without loss of light. 
 
INTRODUCTION. 
 
 9 
 
 B — A table spectroscope constructed for me by Mr. 
 Browning with two quartz (inch) prisms of 60° angle, 
 the collimating and projecting lenses being also of 
 quartz 1^ inch in diameter, and of 6 inches focus. 
 The images with this instrument were brighter than 
 those with the last instrument (A), were of fair defini- 
 tion, and penetrated more into the violet. 
 
 C — This last instrument was also a table spectro- 
 scope, made for me by Mr. Browning, with a view to 
 the photographing faint spectra. 
 
 The prism is a large compound (3) one, 1^ inch 
 high, 2 inches across and inches in its longest base. 
 The collimating and projecting lenses are from a fine 
 field glass 2 inches in diameter and of 7 inches focus. 
 Our experience led us to conclude that considerable 
 aperture of prism and of lens was absolutely essential 
 for the production of bright and sharp images. This 
 Mr. Butherford had previously demonstrated in 
 America. The images from our instruments of small 
 aperture bore no comparison whatever with those 
 afforded by the larger instrument now describing. 
 With the latter the images were very bright, and the 
 lines wonderfully well defined and separated for so 
 small an amount of dispersion. The impressions are 
 quite small on the photographic plate (less than half an 
 inch in length), but so sharp that they would bear 
 enlarging nine or ten times without material loss of 
 definition. 
 
 In the Plates of the gases the images obtained from 
 spectroscope A are enlarged twice, those from spectro- 
 
10 
 
 PHOTOGRAPHED SPECTRA. 
 
 scope B, (quartz), are also enlarged twice. Those from 
 spectroscope C are enlarged rather more than five times. 
 
 The spectra from A and C spectroscopes are en- 
 larged so as nearly to correspond in dispersion and in 
 actual dimension. Those from the spectroscope B 
 (quartz) are on a smaller scale altogether, and are 
 mainly used where comparison of spectra is desired. 
 
 The spectra of the gases (except in one or two cases) 
 ■were obtained from the exhausted tubes of the Geissler 
 form commonly used in spectroscopy, some of foreign, 
 some of home preparation. The latter were found best 
 adapted for our work, being larger in the bore and bulbs, 
 and bearing stronger currents without injury. Bor 
 working the tubes, two different coils were used. The 
 smaller one was a half-inch coil such as is generally 
 sold for the purpose of lighting up tubes in spectral 
 work, and was excited by a quart bichromate. The 
 larger coil was that employed for the spark spectra 
 before described ; it was worked by two half-gallon 
 bichromates only. This instrument has a large heavy 
 break of the common form, but with screw adjustments 
 enabling the rate of vibration to be easily controlled 
 during work ; a very steady current was obtained by 
 this means. The smaller coil was used for single tubes ; 
 and such as would light up easily. The larger coil 
 was used in cases where two tubes were employed, for 
 line spectra and for tubes which required much lighting 
 up. When line spectra were wanted, the condenser 
 before mentioned with two plates taken out, or a 
 small Leyden jar was introduced into the circuit, the 
 
INTRODUCTION. 
 
 11 
 
 rate of discharge being regulated by the distance be- 
 tween two platinum points on a stand, which formed part 
 of the connections. When the large coil was employed 
 for a single tube, a second larger tube was usually 
 introduced into the circuit to diminish the heating 
 effect of the current. The time of exposure for the 
 tubes was about twenty minutes with spectroscopes A 
 and B, and from twelve to fifteen minutes with spectro- 
 scope C. The tubes which lighted up most easily and 
 were not damaged by the continuous current, were 
 nitrogen, carbonic acid, coal gas, cyanogen, hydrogen, 
 oxygen, silicic fluoride, and olefiant gas. All these 
 photographed more or less easily. The tubes which 
 gave us more trouble were bromine, iodine, chlorine, 
 ether vapour, turpentine vapour, sulphur, and tin 
 chloride : bromine and chlorine we failed to get 
 photographs of. These tubes broke down before they 
 had been lighted a sufficient length of time to 
 impress an image. Iodine vapour tube failed also in 
 this respect ; but we succeeded in photographing 
 (though not well) the spectrum of the spark in a bulb 
 filled with iodine vapourised. The tin chloride tube 
 also soon broke down, and we obtained only one plate 
 from it. Further particulars of the behaviour of the 
 tubes will be found in the Description of the Plates. In 
 all cases a photograph was first tried of the single tube 
 as filling the whole length of the slit, this last being 
 intentionally as long as the instrument would bear. 
 When the slit was reduced in length, whether by the 
 comparison prism being used or in any other manner, a 
 
12 
 
 PHOTOGRAPHED SPECTRA. 
 
 manifest falling off of the photographic effect in point of 
 brightness of image was apparent. It was only with 
 the instrument C that we could use quite a fine slit. 
 In the course of our experiments we tried the effect of 
 an electro-magnet upon some of the tubes. Our 
 magnet was one of Ladd’s, of the size used for dia- 
 magnetic experiments, with arms 10 i inches long and 
 poles 2 inches across and with large movable coils of 
 insulated copper wire. It was excited by the four 
 half-gallon bichromates before referred to. Probably 
 with more battery power we should have obtained 
 changes in the spectra themselves in accordance with 
 the experiments of Monsieur J. Chautard. It was, also, 
 unfortunate that chlorine, bromine, iodine, sulphur, 
 and tin chloride, from which he obtained his best 
 results, were just the tubes which gave us the most 
 trouble in a photographic way. The magnet was fitted 
 with conically pointed armatures ; between the points 
 of which we placed the capillary part of our tubes. 
 In this way danger arose to the tubes, as the armatures 
 when the current was passing would draw together 
 with sufficient force to crush the glass. We secured 
 the armatures in their places by turning out circular 
 edges on their bases, and so arranged that the blunted 
 points would just take the thickness of the tube between 
 them. Our experiments were mainly without much in 
 the way of positive Results. The stream of light was 
 in most cases narrowed, and appeared to experience a 
 certain amount of resistance in its passage (in the case 
 of silicic fluoride a sort of sharp whistling sound was 
 
INTRODUCTION. 
 
 13 
 
 heard when the magnet was excited), but we did not 
 detect any palpable change in or addition to the 
 spectral lines. Only in the case of nitrogen did we get 
 any very marked effects, and this was somewhat 
 peculiar as M. Chautard classes this gas amongst those 
 upon which 4 the influence of the magnet is hardly per- 
 ceptible,’ (‘Phil. Mag.’ S. 4, vol. 50, p. 79). A Geissler 
 nitrogen tube having been placed between the poles of 
 the magnet, it was lighted up by the small coil. The 
 stream of light was steady and brilliant, and (except at 
 the violet pole) of the rosy colour peculiar to a nitrogen 
 vacuum tube. On the excitation of the electro-magnet 
 the discharge at once appeared diminished in volume, 
 with an apparent increase in impetuosity ; and not only 
 the capillary part but in a less degree the bulbs also of 
 the tube changed from a rosy to a well-marked violet 
 tint. We several times connected and disconnected the 
 magnet with its batteries, but always with the same 
 result. 
 
 This effect of shifting tint was very striking, and 
 assuming the Aurora to be wholly or in part of electric 
 origin, is strongly suggestive of a reason for the varying 
 tints of the streamers which are frequently observed. 
 Of the spectrum of the capillary part of this tube we 
 took two plates, taking care that all things should be 
 as equal as possible, the apparatus undisturbed, and the 
 time of exposure exactly the same. One plate was 
 taken while the tube was in its normal condition, the 
 other while the tube was influenced by the magnet. 
 The plate + magnet will be seen to penetrate more into 
 
14 
 
 PHOTOGRAPHED SPECTRA. 
 
 the violet, though the character of the spectrum itself 
 does not appear altered. An eye- view of the tube 
 with the spectroscope also showed us no definite 
 variation in the spectrum, nor could we trace 
 that the violet pole spectrum extended itself under 
 the altered condition of the tube as to tint. We 
 tried also a large bulb Plucker tube in which the aura 
 from the violet pole was condensed into a bright arc 
 under the influence of the magnet. No change of the 
 violet tint was here remarked, but only a brightening of 
 the light consequent upon its condensation. Plates in 
 this case also gave slightly more of result in the violet, 
 In the case of silicic fluoride the stream of light was 
 diminished in volume, and the plate from the tube 
 without the magnet is decidedly the brightest. In 
 other respects the plates are alike. 
 
 Our experiments of course do not conflict as com- 
 pared with M. Chautard’s, as the battery employed on 
 our magnet was far inferior in power to his (he used 
 from twelve to fifteen large Bunsen elements), but our 
 experience with regard to the nitrogen tube seemed 
 worth recording. 
 
 In taking our spectra, and specially the gases with 
 spectroscope C, we had to exercise great care in the 
 focussing on the plate. For this purpose the finest 
 ground glass for the plate and a strong magnifier to 
 view the image w T ere employed. The rough adjust- 
 ment was first of all obtained by moving the camera 
 on its heavy base, and the fine adjustment was then 
 completed by means of a screw motion in the same 
 
INTRODUCTION. 
 
 15 
 
 base. It must not be supposed that the Plates printed 
 were all we obtained, probably not more than one in 
 three which were taken were selected for enlargement. 
 
 In nearly all cases we took two plates of the same 
 spectrum, although the first might be good ; and fre- 
 quently from the heat of the room and other causes 
 plates good as to spectral image were imperfect as 
 photographs. In fact anyone wishing to try the same 
 work on the same or a larger scale must expect partial 
 failure and disappointment, until experience has been 
 gained in it. Kennett’s dry plates would have some 
 advantages over the wet plates we employed, but they 
 would also be subject to the drawback of taking longer 
 to develop, so that except with the loss of much time, 
 one could not, as we did, develop and examine the 
 plates obtained at once and before the points and other 
 apparatus were displaced for a next experiment. Our 
 results of course are not intended to be placed by the 
 side of photographs of spectra of larger dispersion taken 
 for comparison of the metals, study of the solar spectrum, 
 etc., but they may perhaps prove useful to amateurs 
 and others, working with spectroscopes of small dis- 
 persion, for comparison of spectra in their general aspect, 
 and for study of the points and peculiarities attaching 
 to most spectra, which are generally brought out 
 in our prints. To those who have the time and 
 opportunity there seems much to invite a taking up of 
 the whole subject on a more extended scale and with 
 more complete apparatus. 
 
 Absolute truth is everything in spectroscopic work. 
 
1 6 PHOTOGRAPHED SPECTRA . 
 
 and the very best draftsman working with the most 
 perfect micrometer cannot, even at the expense of a 
 vast amount of labour, equal in accuracy a good photo- 
 graph of a set of spectral lines. Photographs, too, have 
 the great advantage that they may be enlarged and 
 tested at leisure ; and if several plates of the same 
 spectrum are taken and subsequently compared, the 
 investigation for certainty of result is only a matter of 
 time and trouble. 
 
 I ought to mention that we tried in the case of the 
 spark spectra (but without advantage) tinted collodion, 
 with a view to work more towards the red end. The 
 tinting substances used were Magenta, Judson’s Violet, 
 Annatto, Saffron, Turmeric, and Chlorophyll. Dr. 
 Huggins’ success in stellar photography with Iceland 
 spar prisms promises a considerable extension of the 
 spectrum in the ultra violet direction, and some recent 
 investigations of Captain Abney and others work in the 
 direction of the yellow and red regions, so that there 
 is good hope of obtaining at no distant date a wide 
 range of photographs including all of the visible 
 spectrum, and more. Of what assistance such faithful 
 light pictures would prove to science, I need not here 
 point out, except as an apology for our present attempt 
 to popularise a subject hitherto somewhat of a sealed 
 book confined to the laboratories of workers in special 
 research. 
 
IT 
 
 DESCRIPTION OF THE PLATES. 
 
 PLATE L 
 
 First Print. The Scale . — The scale has been already 
 referred to in the Introduction. The photographs of 
 the metals are so masked that in general when the 
 scale is applied to them, it falls in its right place or 
 very nearly so. To enable, however, the scale to be 
 applied with greater exactness two fiduciary marks or 
 points are indicated upon it, the one a bright line 
 marked 4 spark ’ situated between h and F, the other a 
 set of seven carbon or point lines between G and h 
 marked 4 arc.’ For the spark spectra the scale is ad- 
 justed by applying the bright line marked 4 spark,’ to 
 the bright line which appears prominently at the left 
 hand of each spark spectrum. To adjust the scale for 
 the arc spectra the set of lines marked 4 arc,’ are to be 
 applied to the corresponding set of lines which are to 
 be distinguished in most of the arc spectra towards the 
 violet end, and which are the principal ones derived 
 from the points and are considered as carbon or carbon 
 compounds. Two prints are given of the scale, one on 
 Plate I., and the other on Plate XXI., so that if direct 
 
 c 
 
18 
 
 PHOTOGRAPHED SPECTRA. 
 
 application and comparison are desired one of them may 
 be cut out and used for the purpose. 
 
 Second Spectrum. Air with wide slit. 
 
 Third Spectrum. Air with fine slit. 
 
 These two spectra may be described at the same 
 time. They differ only in length of the spark (which 
 was taken between platinum points) and width of the 
 slit. 
 
 The lines comprised in them may be traced more or 
 less throughout all the spark spectra, and form useful 
 indices for position of metal lines. 
 
 Lecoq de Boisbaudran gives [Spectres Lumineux, 
 Plate II., Etincelle longue], a spectrum comprising 
 lines (with others) 5003, 4805, 4706, 4648, 4633, 
 4449, 4434, 4347, and a band at 4240. This spectrum 
 resembles generally our present spectrum, though it 
 fails to agree in some respects, probably from the in- 
 troduction of the condenser in our case. Our spectrum 
 is for the stronger lines, identical with that of the line 
 spectrum of the capillary part of a nitrogen tube. (See 
 Plate XXV. Fourth Spectrum). 
 
 Fourth Spectrum. Arsenic Spark . — Small rough 
 lumps of the metal placed in the clips. Spark white, 
 and striking with ease across a considerable distance. 
 Slight fumes of oxide at first, exposed twenty minutes. 
 Two plates taken which were strictly identical, each 
 showing the fuzzy bands on the margin of spectrum 
 midway between F and G from about 4575 to 4475, 
 and the lines in the bright part of the spectrum about 
 4400, 4355, and 4310. Dr. Watts, in his ‘ Index of 
 
DESCRIPTION OF PLATES. 
 
 19 
 
 Spectra,’ does not continue the spectrum of Arsenic 
 beyond 5324 towards the violet ; but faint lines are, 
 given on Huggins’ authority, at 4551, 4537, 4497, a 
 stronger one at 4464 and faint ones at 4369 and 4335. 
 
 PLATE II. 
 
 First Spectrum. Aluminium Spark . — Pieces of the 
 metal in clips. Spark moderate in length, ten minutes 
 exposure ; also tried with condensing lens in front of 
 slit. Slit rather wide. 
 
 Second Spectrum. Aluminium Arc . — Piece of 
 metal cut from small bar, in carbon cup. Arc short, 
 slit fine. 
 
 Principal line in the spark spectrum at about 4500. 
 This is represented in the arc by the edge of one of 
 three sets of shaded bands. 
 
 The two very conspicuous lines in the arc, between 
 H 1 and H 2 , are only represented by one near H 1 in the 
 spark. The edges towards the violet of the shaded 
 bands in the arc are given by Lecoq de Boisbaudran 
 [Plate XV., Aluminium metallique], at 4845, 4652, and 
 4478. And the intense lines between IP and H 2 at 
 3962 and 3943, (H 1 is given in Watts’ ‘Index’ at 3968 
 and H 2 at 3933). 
 
 Third Spectrum. Antimony Spark . — Rough himps 
 of metal in clips. Spark bright and broad. 
 
 Fourth Spectrum. Antimony Arc . — Small pieces 
 of metal in carbon cup, arc of moderate length, much 
 oxide formed. 
 
20 
 
 PHOTOGRAPHED SPECTRA. 
 
 The spark spectrum is peculiar owing to the stream 
 of light running along each margin of the spectrum, 
 apparently thickening at each extremity, not only the 
 metal, but also the air lines. Some of the air lines 
 however escape ; proving that the appearance has not 
 to do with the slit, but must be caused by metallic 
 vapour hanging about each pole. (See also Lead and 
 Antimony, Plate X., Fourth Spectrum.) 
 
 The arc spectrum gives little beyond the point 
 lines. We took several plates, but always with the 
 same result in this respect. The lines given by Lecoq 
 de Boisbaudran, [Plate XXIII., Proto-chlorure d’An- 
 timoine], are 5037, 4947, 4877, 4787, 4711, and 
 Dr. Watts continues with 4693, 4588, 4349, and 4264. 
 (See Lead and Antimony before referred to, where the 
 lines are somewhat more distinct.) 
 
 PLATE III. 
 
 First Spectrum. Bismuth Spark . — Pieces of the 
 metal in each clip, exposed ten minutes, spark bright. 
 
 Second Spectrum. Bismuth and Nickel Spark . — 
 Pieces of metal in clips, exposed ten minutes, current 
 reversed at half. Note extension of metal lines in the 
 middle of the spectrum, in consequence of breaking 
 away of the point. 
 
 Third Spectrum. Bismuth and Tellurium Spark — 
 Pieces of metal in clips, exposure ten minutes, current 
 reversed at half. Tellurium partly fused, spark struck 
 over Tellurium to the clip, (notice some iron lines from 
 
DESCRIPTION OF PLATES. 
 
 21 
 
 the clip projecting beyond centre of the spectrum at 
 Tellurium pole). 
 
 Fourth Spectrum. Bismuth Arc . — Piece of metal 
 in carbon cup, arc moderate. 
 
 The spectrum of bismuth with spark obtains easily, 
 and the lines are well marked, those in the centre of 
 the spectrum widening out considerably and showing 
 in strong contrast to the air lines. 
 
 Lecoq de Boisbaudran gives (Plate XXII., Chlorure 
 de Bismuth), 5209, 5144, 5123, 5049, (4965, 4882), 
 4724 (characteristic), 4303, 4259, 4118 (characteristic). 
 
 Most of these lines appear in our spark spectrum, 
 with others in addition. 
 
 The principal lines in our arc spectrum are about 
 4750 (very bright), and 4120 (probably Boisdaudran’s 
 4118). The vivid lines in the bright part of the spark 
 spectrum do not appear in the arc. 
 
 As to the second spectrum (Bismuth and Xickel), 
 Lecoq de Boisbaudran gives [Plate XIX., Chlorure de 
 Nickel], lines at 4873, 4867, 4856, 4832, 4808, 4788, 
 4762, 4755, 4732, with principal ones at 4715 and 
 4401. Our spectrum extends more into the violet, and 
 shows a very bright line near H 1 . 
 
 The Tellurium spectrum will be referred to in its 
 order further on. 
 
 PLATE IV. 
 
 First Spectrum. Barium Spark . — Small pieces of 
 metal in the clips which fused away rapidly, spai k 
 
22 
 
 PHOTOGRAPHED SPECTRA. 
 
 bright. Spectrum peculiar as containing so little trace 
 of the air lines, and for the fuzzy expansion of the 
 principal lines. The lines generally are not confined to 
 the margin, but cross the spectrum. Lecoq de Bois- 
 baudran (Plate VII., Chlorure de Barium dans le gaz) 
 gives bands at 4974, 4873, 4794, and a barely visible 
 line or band somewhat beyond. Dr. Watts gives bright 
 lines or bands 4934, 4898, 4553, 4524, and 4130. 
 Prom an examination of these last, I think that our 
 spectrum (for want of the air lines) has been some- 
 what wrongly positioned. 
 
 If the Scale be advanced a little to the right, so' 
 that the second bright line in the spectrum coincides 
 with 4898 (4900) on the Scale, the other lines will be 
 found to fall fairly into their places, in accordance with 
 Dr. Watts’ figures. 
 
 Second Spectrum. Beryllium (Glucinum) Arc . — 
 Metal in powder in carbon cup. Arc short. Dr. Watts 
 gives two bright lines for Glucinum, 4572 and 4488. 
 
 These are not prominent in our spectrum, which is 
 chiefly characterised by the bright lines between 4 spark ’ 
 and F, and by other fine lines scattered through the 
 spectrum. The spectrum, however, bears so great a re- 
 semblance to meteoric iron and meteorite (Plate X.), 
 that there was found reason to suspect iron as form- 
 ing the principal part of it. Upon testing the metal 
 powder, it was found to contain iron as an impurity 
 in considerable quantity. 
 
 Third Spectrum. Boron Arc . — Graphitoid in car- 
 bon cup. A dense glass-like crust of oxide formed 
 
DESCRIPTION OF PLATES. 
 
 23 
 
 on the upper carbon, which interfered with the current, 
 and had to be frequently cleared off. Arc short and 
 uncertain. The evidence of the spectrum is mainly 
 towards the red end, where absorption bands seem 
 traceable. 
 
 Fourth Spectrum. Calcium Spark . — Pieces of 
 metal in the clips inclined to fuse quickly. Spark 
 fairly bright. This failed as a Calcium spectrum. The 
 principal lines, a double one at about 4935, and others 
 at about 4830, 4750, 4710, and 4060, are those of zinc. 
 Upon testing the specimen of the metal, zinc was found 
 present in considerable quantity. 
 
 PLATE V. 
 
 First Spectrum. Cadmium Spark . — Small pieces 
 of the metal in clips, exposure moderate, plate rather 
 weak, but clear of air lines. 
 
 Second Spectrum. Cadmium Arc . — Pieces cut 
 from small bars in carbon cup. Clouds of yellow oxide 
 formed. Arc moderate. Metal burnt away quickly, 
 Lecoq de Boisbaudran [Plate XX., Chlorure de Cad- 
 mium], gives principal lines at 5085, 4791, 4677, and 
 a moderate one at 4414. 
 
 These three principal lines appear in our arc 
 spectrum, with an additional conspicuous line about 
 4060. A line inflated at each end also appears at about 
 4425 in the spark spectrum, which may be Lecoq de 
 Boisbaudran’s 4414. 
 
 Third Spectrum. Arc between Carbon points. 
 
24 
 
 PHOTOGRAPHED SPECTRA. 
 
 Fourth Spectrum. — A paper print from the plate 
 of Spectrum 3, with all the lines which could be in 
 any way seen on the glass negative ruled out. 
 
 A description of the preparation of the carbon 
 points has been already given in the Introduction. 
 The Third Spectrum is an example of the plates ob- 
 tained from the points alone. This plate contains, 
 besides those that show in the print, a number of very 
 faint lines seen only when it is held up to the light. 
 
 A good paper print was obtained from this plate, and 
 on this was ruled out all the lines that could be traced 
 on the negative. A reversed copy of this is shown 
 in the Fourth Spectrum. The lines are presumably 
 those arising from the points, and a peculiarity of our 
 arc spectra in general seems to be that while these 
 lines are all more or less present in each arc spectrum, 
 the number and intensity differ much. They appear 
 also to depend for number and intensity, to a con 
 siderable degree, upon the metal or other substance 
 burning in the arc, so that spectra of the same metal 
 almost invariably contain, in addition to the metal lines, 
 point lines of the same extent and character. It is this 
 fact that seems to give to each spectrum its individuality 
 referred to in the Introduction. 
 
 PLATE VI. 
 
 First Spectrum. Spark in Coal Gas .— For this 
 spectrum the same spectroscope was employed as in 
 the case of the metals. A glass tube with a bulb 
 
DESCRIPTION OF PLATES. 
 
 25 
 
 blown in the centre, of the form here shown size), 
 with platinum wires fused into the bulb was selected 
 
 to pass the spark through. One end of the glass tube 
 was connected, by means of elastic tubing, with the gas 
 jet in the room. The other end of the tube was also 
 joined to tubing which conveyed the gas out of the 
 room into the air, after passing through the bulb. 
 The two platinum wires were connected with the large 
 coil and condenser, and while the spark was striking 
 across the bulb (vertical with the slit) a current of 
 coal gas at ordinary pressure was kept flowing through 
 the tube. The spark was bright and slightly blue in 
 tint. Carbon was soon deposited on the bulb. The 
 spectrum shows a set of carbon lines, the two brightest 
 at about 4580 and 4220, and also the hydrogen line 
 li considerably expanded. This last line also has the 
 appearance of being either double, or reversed, in the 
 centre. The line 4220, and its accompanying group of 
 fine lines on the right, occupy about the same place as 
 a set of bright lines in the arc spectrum. They are 
 however not identical, the lines in the coal gas diminish- 
 ing in distance from each other towards the bright line, 
 while in the arc the lines diminish towards the violet, 
 (see a better enlargement of this negative on Plate 
 
26 
 
 PHOTOGRAPHED SPECTRA. 
 
 XXVI., Second Spectrum). It is curious that we ob- 
 tained this sharp line spectrum on only one occasion, 
 though we subsequently took several other plates under 
 similar conditions of apparatus and spectroscope. 
 
 In the subsequent plates the line 4580 was replaced 
 by a misty band, with a double or reversed appearance 
 similar to the hydrogen line in our plate. Of its 
 accompanying set of lines towards the violet, one 
 only, the detached one nearest to the violet, remained. 
 Line 4220 nearly disappeared, and remained only 
 misty and indistinct ; while the group lines accompany- 
 ing it were quite gone, and a bright broad band reach- 
 ing to the hydrogen line took their place. 
 
 The hydrogen line h was not so much expanded as 
 in our spectrum, and a continuous spectrum crossed by 
 two narrow bands or broad lines, and two other faint 
 lines (Hydrogen P) appeared beyond it towards the 
 violet. See also a plate of the same spectrum taken 
 with the gas spectroscope C, Plate XXVII. Second 
 Spectrum, and a print from the original plate, from 
 which the present enlargement was made, Plate 
 XXXIII. Fourth Spectrum. 
 
 The plates of the subsequent spectra before de- 
 scribed were altogether more misty and less defined 
 than our first spectrum. 
 
 Second Spectrum. Chromium Arc . — Metal powder 
 in carbon cup, some scintillation during combustion. 
 
 Lecoq de Boisbaudran gives [Plate XVI., Sesqui- 
 chlorure de Chrome], a very bright line at 5205, a 
 double one at 4649, a band of indistinct rays at 4343, 
 
DESCRIPTION OF PLATES. 
 
 27 
 
 and three well-marked lines at 4290, 4275, and 4255. 
 The line 5205 does not appear in our spectrum, (the 
 outside line towards the red is a carbon one). The 
 other lines are easily distinguished. 
 
 A set or band of close lines is also to be noticed at 
 about 4540. 
 
 Third Spectrum. Cobalt Arc . — Small piece of 
 metal in carbon cup, arc moderate. Lecoq de Bois- 
 baudran [Plate XIX., Chlorure de Cobalt] gives a list of 
 twenty-one lines in the part of the spectrum comprised 
 in our photograph, distinguishing for brightness 4868, 
 4840, 4815, and 4533. In our spectrum the lines show 
 pretty much of equal intensity, and it is somewhat diffi- 
 cult to separate them from the carbon lines. 
 
 Fourth Spectrum. Copper Spark . — Small pieces 
 of wire, spark tinged green, spectrum poor, principal 
 line crosses a part of the air spectrum deficient of bright 
 lines, at about 4280. 
 
 PLATE VII. 
 
 First Spectrum. Copper Arc . — Stout pieces 
 of copper wire used as terminals, arc narrow, brilliant 
 green in tint and of moderate length. 
 
 Second Spectrum. Copper Arc . — Small bead of 
 prepared wire, an alloy of gold, silver, and copper in 
 the carbon cup. The wire w r as prepared by a jeweller 
 as an equal part alloy of pure gold and silver, but it 
 subsequently proved that the gold was adulterated with 
 copper. 
 
28 
 
 PHOTOGRAPHED SPECTRA. 
 
 {Note . — The images of these two spectra are not 
 of the same actual size, the carbon arc being some- 
 what the larger, and allowance must be made for this 
 in comparing them with each other and with the 
 Scale). 
 
 In the case of the alloy, the copper, though so inferior 
 in quantity, seems to have mainly appropriated to itself 
 the spectrum. The gold and silver lines are very faint, 
 but they may be traced by comparison with the spectra 
 of these metals. (See also Plate XV., Spectrum Silver 
 and Copper Arc, where copper again monopolises the 
 spectrum). 
 
 Most (but not all) of the lines in the First Spectrum 
 appear in the Second Spectrum, mixed with a few of 
 the principal carbon or point lines. The bright single 
 line about 4400 in the first spectrum appears double 
 in the second spectrum. 
 
 The very conspicuous double line in the first 
 spectrum at about 4075 is replaced by a single bright 
 one, with faint companion in the second. 
 
 Lecoq de Boisbaudran gives [Plate XXIV., 
 Chlorure de Cuivre en solution], a long list of copper 
 lines, including the three characteristic ones (5218, 
 5153, and 5106), seen on the extreme left of our 
 spectrum. 
 
 He also gives on the same plate the spectrum of 
 Chlorure de Cuivre dans le gaz, with brighter groups 
 towards the violet. These spectra do not in general 
 character accord with ours. 
 
 Third Spectrum. Didymium Arc . — Powder in 
 carbon cup, arc short, spectrum full of many coarse 
 
DESCRIPTION OF PLATES. 
 
 29 
 
 lines of the same character ; with traces, especially 
 towards the red and the centre, of absorption bands. 
 The carbon lines are either absent or so obscured by 
 the metal spectrum as almost to cease to serve as 
 guides in masking. Lecoq de Boisbaudran gives [Plate 
 XIII.] two absorption spectra of Didymium, neither of 
 which readily compares with ours in lines or character. 
 
 Fourth Spectrum. Erbium Arc . — Powder in 
 carbon cup, a bead of the fused metal insisted on 
 adhering to the negative pole, the arc being then longer 
 than when the metal remained in the cup. When the 
 metal was burnt in the cup the arc was brightest. 
 The spectrum is characterised by a considerable number 
 of bright lines, with many very fine ones between ; the 
 carbon lines are also in this case either absent or very 
 much obscured, so that position on mask is doubtful. 
 Lecoq de Boisbaudran gives [Plate XIV.] a spectrum of 
 ‘Erbium emission,’ which does not assist in examining 
 ours. Dr. Watts gives a joint spectrum of Erbium and 
 Yttrium, with some lines common to both metals. Our 
 spectrum of Erbium does not accord with that of 
 Yttrium, Plate XIX., in lines or general character. 
 We found in our cabinet, a specimen labelled Terbium, 
 of which we also photographed the spectrum. On 
 comparing it with our present spectrum of Erbium, 
 (except thart the one spectrum has a little less glare 
 than the other) the two spectra were found absolutely 
 and line for line coincident. 
 
 Every line is exactly repeated in each plate, and the 
 relative intensities of the lines are preserved in each 
 spectrum in the most accurate manner. 
 
30 
 
 PHOTOGRAPHED SPECTRA. 
 
 PLATE VIII. 
 
 Pirst Spectrum. Gold Arc . — Small lumps of metal 
 in the carbon cup. Arc short. Spectrum fairly clear of 
 point lines. Lecoq de Boisbaudran gives [Plate XXVI. 
 Chlorure d’Or en solution] lines at 5063, 4812, 4793, 
 4608, 4490, 4437, 4338, 4314, 4064. The lines 4812 
 and 4064 are recognised in our spectrum, as also a 
 strongish line about 4570. 
 
 Second Spectrum. Indium Arc . — Small piece of 
 the metal cut from bar in carbon cup, arc moderate, 
 spectrum with a good deal of glare, point, lines indis- 
 tinct. Two principal broad and expanded metal lines 
 read off at about 4515 and 4100, (Lecoq de Boisban- 
 dran gives Plate XXI., Sels dTndium, 4511 and 4101). 
 For spark spectrum of Indium, see Plate XVI., Third 
 Spectrum. 
 
 Thtrd Spectrum. Iridium Arc . — Piece of metal in 
 carbon cup. Arc short. Spectrum bright. Point lines 
 long in centre. Note group of very fine lines at ex- 
 treme left towards the red, (centre about 4990) with 
 two dark spaces to right of them, also two bright lines 
 about 4550. Dr. Watts gives a spectrum of 4 Iridium, 
 and Ruthenium,’ with lines (Kirchhoff) 6347, 5449, 
 and 5299, For our spectrum of Ruthenium, see 
 Plate XIV., Second Spectrum. The two spectra 
 certainly have a very close general resemblance. Note 
 the group of four lines towards the red end and the 
 outlying short line at the extreme violet end, common 
 to both. 
 
DESCRIPTION OF PLATES. 
 
 31 
 
 Fourth Spectum. Iron and Copper Spark . — Wires 
 of the metals in the clips, condensing lens, in front of 
 slit, slit wide. Image rather coarse. Iron lines pro- 
 jecting in several places beyond the upper edge of the 
 spectrum. Copper line at about 4280 seen projecting 
 on lower edge of the spectrum. 
 
 PLATE IX. 
 
 First Spectrum. Copper and Iron Spark . — Same 
 as last (Iron and Copper), but metals reversed in clips, 
 no condensing lens, slit wide and image confused, but 
 lines can be traced through the glare. 
 
 Second Spectrum. Iron Arc . — Keduced powder 
 in carbon cup. Arc moderate, much scintillation. 
 Thirty cells Grove only used, slit rather wide. Spec- 
 trum imperfect, but introduced to show how battery 
 power may vary general aspect of the spectrum. Note 
 broad dark space about centre of spectrum, also glare 
 of light towards the red, with group of lines at ex- 
 tremity of spectrum in that direction. 
 
 (This spectrum is not positioned to the Scale, but 
 can easily be compared by eye with the next). 
 
 Third Spectrum. Iron Arc . — Eeduced powder in 
 cup forty cells Grove. Slit fine. Spectrum much more 
 uniform than last, point lines absent or indistinct. 
 
 Lecoq de Boisbaudran gives [Plate XVIII., Per- 
 chlorure de Fer en solution Etincelle] a spectrum com- 
 prising a set of groups of lines in the violet separated 
 from those at the other end of the spectrum by a 
 
32 
 
 PHOTOGRAPHED SPECTRA. 
 
 blank space. This blank space is also seen in our 
 photograph separating the four characteristic lines to- 
 wards the red end of the spectrum from the main body 
 of lines towards the violet. 
 
 The lines towards the red in our spectrum evidently 
 correspond with Lecoq de Boisbaudran’s 4959, 4923, 
 4891, and 4874. Our spectrum is slightly out of 
 position on the mask ; but if the scale be moved a 
 little towards the left, so that the first of the set of 
 these four lines be made to coincide with 4959 on the 
 scale, most of the other lines in Lecoq de Boisbaudran’s 
 list may be picked out. 
 
 Fourth Spectrum. Iron and Selenium Spark . — 
 This spectrum is introduced to show the iron lines in 
 spark. Two small pieces of Selenium were placed in 
 the steel clips. When the spark passed, in lieu of 
 striking from pole to pole, it flew with a long and 
 bright flash across the surface of the selenium melting 
 it in its way. 
 
 On examining the spectrum, it was found a com- 
 bined one of air, selenium, and iron, some of the lines 
 of the latter projecting in a most marked manner be- 
 yond the edges of the spectrum. These lines were 
 evidently due to the clips. We tried Selenium two or 
 three times, and always with the same result as to 
 behaviour of the spark. 
 
 Now and then it seemed to cross between the poles, 
 but ordinarily it preferred the longer route across the 
 surface. 
 
 The Spectrum of Selenium will be found referred 
 to in its order further on. 
 
DESCRIPTION OF PLATES. 
 
 33 
 
 PLATE X. 
 
 First Spectrum. Meteoric Iron Arc. 
 
 Second Spectrum. Meteorite Arc. 
 
 Three specimens purchased of Mr. James E. Gregory 
 were used in the arc: — 
 
 No. 1. Meteoric Iron. Atacanna 1827. 
 
 No. 2. Meteoric Iron. Tolucca 1784. 
 
 No. 3. Piece of Meteorite. Ausson 1858. 
 
 They all burnt with much scintillation in the car- 
 bon cup. The spectrum of No. 1 when examined was 
 found identical m all respects with the spectrum of Iron 
 in arc (third spectrum, last plate) and might have been 
 taken for the same photograph. 
 
 No. 2 and No. 3 (the plates which are printed) also 
 gave spectra evidently of iron, but differing from the 
 spectra of No. 1 and of Iron in arc in last plate and 
 from each other. Each of them is characterised by 
 the large number of sharp and fine lines, which more 
 especially in the case of the meteorite, intermediately 
 fill up and occupy nearly the whole spectrum. Some 
 of these lines it is true may be traced very faintly in 
 our spectrum of Iron on Plate IX., but they appear to 
 come out relatively stronger and brighter in our present 
 plates. Meteorite seems also to differ from meteoric 
 Iron in the greater length of spectrum (note group of 
 fine lines to the extreme left), and in the greater 
 number of its fine lines generally. This will be par- 
 ticularly noticed about the brighter and wider part of 
 
 D 
 
34 
 
 PHOTOGRAPHED SPECTRA. 
 
 the spectrum where the coarse and strong lines 
 mainly prevail. Some of these, which have dark in- 
 tervals in the case of meteoric Iron, are connected by 
 and filled up with fine lines in the case of meteorite. 
 Note also a thick double line about 4048 in meteorite, 
 which is doubtfully represented in the meteoric Iron 
 spectrum. 
 
 Third Spectrum. Lead Arc,— Piece of metal in 
 carbon cup. Arc moderate. 
 
 Fourth Spectrum. Lead and Antimony Spark . — - 
 Small lump of antimony in one clip ; small bar of 
 lead in the other. Current reversed at half exposure. 
 Lecoq de Boisbaudran gives [Plate XXIII., Plomb 
 metallique Etincelle] lines at 5044, 5003, 4386, 4245, 
 4167, 4056, noting 4056 as very characteristic. Lines 
 appear in our arc spectrum corresponding with his 
 5003, 4386 (4245 and 4167 are mixed up with the 
 point lines) and very prominently indeed 4056. We 
 have lines also about 4825, 4750, and 4700, which he 
 does not give. In the spark spectra we get prominently 
 Boisbaudran’s 5044, a bright line about 4780, a tre- 
 mendous one at 4400, another still larger at 4250 
 (Boisbaudran’s 4245 P), and lastly 4056, very sharp 
 and well defined. 
 
 The wonderful inflation and flare of the two lines at 
 4400 and 4250 are to be noted. In the case of the 
 latter line the flare appears unequally towards the 
 violet side. Other smaller lines are in the spectrum 
 (see Magnesium and Lead, second spectrum on next 
 plate). 
 
DESCRIPTION OF PLATES. 
 
 35 
 
 The Antimony Spectrum has been already described, 
 but note the glare of light and thickening of the lines 
 before leferred to in reference to that spectrum. 
 
 PLATE XL 
 
 First Spectrum. Lead and Magnesium Spark. 
 
 Small bar of Lead in clip ; Magnesium ribbon cut to a 
 point in other clip. Current reversed at half time. 
 
 Second Spectrum. Same as above, except that the 
 metals are reversed in position. A condensing lens 
 was used in front of slit. 
 
 Third Spectrum. Magnesium Spark. A piece of 
 
 magnesium ribbon, cut to a point, used in each clip. 
 Slit *001 inch. Exposure fifteen minutes. 
 
 Fourth Spectrum. Magnesium Arc Piece of 
 
 ribbon coiled up in the carbon cup, quickly ignited, 
 and long arc obtained ; much oxide formed. 
 
 Lecoq de Boisbaudran gives [Plate XII. Chlorurede 
 Magnesium] lines as follows : group, 5183, 5172, 5167, 
 very bright (5 in solar spectrum), then a band of rays, 
 commencing with 5006 and ending with 4958, and 
 then single lines, 4705 and 4483. 
 
 Our first two spark spectra are mainly conspicuous 
 for the great blaze of light at about 4500. This is 
 very marked and characteristic, and extends in each 
 case considerably beyond the margin of the spectrum. 
 In our third spectrum (Magnesium ribbon in each clip) 
 the print is cut off in vertical by the limited width of 
 mask ; but upon examining the original plate the glare 
 
PHOTOGRAPHED SPECTRA. 
 
 36 
 
 of light on the lower margin of the spectrum at 4500 
 is distinctly traced to extend beyond the margin of the 
 spectrum to a length equal to the glare itself (nearly 
 half the width of the spectrum) as a single hne ter- 
 minating in a minute knob or inflation (limit of prism 
 surface?). Two bright lines at about 4725 (Boisbau- 
 dran’s 4705?) and 4360 are also seen to project 
 beyond the spectrum, though not to so great an extent. 
 Both of these last lines appear to be repeated in the 
 arc spectrum, while the large 4500 is missing there. 
 The group b in solar spectrum is seen in both spark 
 and arc spectra as a double line only (tested by this, 
 our Scale is a little too much extended towards the 
 extreme left). Then in the arc comes the band of 
 lines at 5006, then 4725 and 4360, and lastly two 
 bright lines at about 4245 and 4180. The other and 
 fainter lines in the arc seem due to carbon. 
 
 PLATE XII. 
 
 First Spectrum. Manganese Arc . — Powder metal 
 in the carbon cup ; arc moderate, with some scintil- 
 lation, taken with battery of 30 Grove cells. 
 
 Second Spectrum. Same, but taken with battery 
 of forty Grove cells. Lecoq de Boisbaudran s Plate 
 XVII., Chlorure de Manganese en solution, Etincelle 
 courte, is found closely to compare with our spectrum 
 in principal lines, and the two spectra were selected to 
 form a scale by comparison and interpolation as 
 described in the Introduction. The lines given by 
 
DESCRIPTION OF PLATES. 
 
 37 
 
 Boisbaudran are 4825, 4784, 4766, 4755, 4738, 4727, 
 4710, 4502, 4462, 4437, 4415, 4282, 4266, 4260, 
 4237, 4084, 4063, 4047, 4039. These were also com- 
 pared with Dr. Watts’ list of (Huggins’) lines of Man- 
 ganese ; and then those most easily recognised with 
 corresponding ones in our spectrum were used as 
 materials for the Scale. The principal lines are easily 
 sorted out by the aid of the upper spectrum. 
 
 Third Spectrum. Mercury Spark . — Globule of 
 the metal in a small glass cup with Platinum commu- 
 nication passing through the bottom of the cup. 
 Platinum wire electrode above. Exposure twenty 
 minutes. Spark brilliant and rapid. 
 
 The spectrum is characterised by the misty and 
 indistinct appearance of the air lines. They are, how- 
 ever, sufficiently defined to indicate position of the 
 metal lines, these last being coarse and thickened. 
 Lecoq de Boisbaudran gives [Plate XXV., Bichlorure 
 de Mercure] a strong line at 4357, and two other lines 
 at 4078 (faint), and 4047 : 4357 is well marked in our 
 spectrum, also 4047, and there is an additional strong 
 line at the end of the spectrum about 3985. 
 
 Fourth Spectrum. Molybdenum Arc . — Powder , 
 metal in carbon cup. Soon formed a bead, which re - 
 mained quiet at bottom of the cup. Arc long, and 
 gave a bright lambent glow rather than a brilliant 
 stream. 
 
 Dr. Watts gives lines (Thalen), 4979, 4867, 4829, 
 4818, 4757, 4730, 4706, 4536, 4475, 4433, 4411, 
 4380, 4326, 4277. 
 
38 
 
 PHOTOGRAPHED SPECTRA. 
 
 The group 4737, 4730 and 4706, is easily dis- 
 tinguished, and other of the foregoing lines may be 
 picked out in the clearer parts of the spectrum. 
 
 PLATE XIII. 
 
 First Spectrum. Nickel Arc . — Small pieces of metal 
 in the carbon cup, arc short, spectrum tolerably clear 
 of point lines. Lecoq de Boisbaudran gives [Plate 
 XIX., Chlorure de Xickel] a long list of lines com- 
 mencing with a strong one 4984, and ending at 4288, 
 and with characteristic ones at 4715 and 4401. 
 
 4715, 4647, 4606, 4550, 4461, and 4401 (strong), 
 may be picked out in the clearer part of our spectrum 
 towards the red end. Notice also a sharp bright line 
 in a clear space about 4000. 
 
 A small bottle without a label containing a powder 
 was found in our cabinet. The spectrum when photo- 
 graphed was at once easily identified with our present 
 plate. 
 
 Second Spectrum. Niobium Arc . — Powder metal 
 in carbon cup, arc moderate. Dr. Watts quotes 
 Thalen as stating that the lines of Niobium are too 
 faint to be measured satisfactorily. 
 
 Our spectrum, however, after excluding the carbon 
 lines has a considerable set of bright ones which must 
 belong to the metal. These may be seen at about 
 4861 (F), 4615, 4590 (strong double), two bright lines 
 with a fine one between them about 4435 and 4405, a 
 set of three lines, (a single and then a double) about 
 
DESCRIPTION OF PIATES. 
 
 39 
 
 4260, a bright one with shading towards the violet, at 
 4100 (A), (it is curious that F and A places of 
 hydrogen lines should each have prominent lines 
 falling in the same or very closely approximate 
 positions in this spectrum), a thickened or double line 
 about 4050 (position also of a carbon line), and a 
 double one near to the last about 4040. 
 
 Third Spectrum. Palladium Arc . — Piece of metal 
 in the carbon cup, arc moderate, spectrum showing 
 carbon lines indistinctly. 
 
 Lecoq de Boisbaudran gives [Plate XXVII., 
 Chlorure de Palladium,] a set of lines at 5118, 5114, 
 and 5111, then single lines at 5063, 4969, and 
 4917, then three well-marked lines at 4874, 4818, 
 and 4788, then one at 4475, then a strong one at 4214, 
 concluding with two at 4170 and 4088. The lines at 
 5111 and 5063, and the stronger ones at 4874, 4818, 
 4788, 4475, and 4088, may be all picked out from our 
 spectrum. A carbon line between H 1 and H 2 , seems 
 also to have another by its side not belonging to it. 
 Xote also extension of spectrum towards the violet, as 
 in the cases of Iridium and Euthenium. 
 
 Fourth Spectrum. Platinum Arc . — Small roll of 
 foil in the carbon cup, arc short, spectrum poor, 
 mainly carbon lines. Lecoq de Boisbaudran gives 
 [Plate XXVII., Chlorure de Platine] a set of lines com- 
 prising (with others) 4554, 4524, 4501, 4415, 4390, 
 4118. These seem distinguishable in our spectrum, 
 and there are also two bright lines about 4250, not 
 given by Boisbaudran. 
 
40 
 
 PHOTOGRAPHED SPECTRA. 
 
 PLATE XIV. 
 
 First Spectrum. Rhodium Arc.— Piece of metal in 
 the carbon cup. Spectrum of even character, with 
 many sharp metal lines. Point lines not prominent, 
 except in the centre of the spectrum, 
 
 Here again Dr. Watts quotes Thalen, that the lines 
 are too faint to measure, but many may be picked out 
 from our print. Note especially two sharp lines 
 between 5000 and 4950, a double line near F, a line 
 about 4590 near two point lines, another about 4420, 
 with two fine ones towards the red, and a strong one 
 near a carbon line about 4400. Other lines will also 
 be found, intermediate of the point lines, in the region 
 extending from 4400 towards the red end of the 
 spectrum. Note also a set of three lines (strongest 
 towards the red), about 4265, and a strong set of three 
 lines of equal intensity, the centre one about 4125. 
 N.B. In this and other cases in which no authentic list 
 of lines is referred to, it is useful to test the spectrum 
 by the carbon points ruled out, Plate V., so as to 
 eliminate the point lines from the spectrum. 
 
 Second Spectrum. Ruthenium Arc . — Piece of 
 metal in the carbon cup, arc short. This spectrum has 
 already been referred to under the head of 4 Iridium.’ 
 
 Third Spectrum. Selenium and Tellurium . — 
 Small piece of these in each clip, current reversed 
 at half. 
 
 Fourth Spectrum. Selenium and Aluminium . — 
 Small piece of Selenium in one clip, Aluminium 
 
DESCRIPTION OF PLATES. 
 
 41 
 
 wire in the other, current not reversed. The Aluminium 
 spectrum, Plate II., has been described ante , p. 19. It 
 is, however, from the absence of air lines, well shown 
 in the present print. See also Plate XYII , Second 
 Spectrum, Titanium and Aluminium. The spark passed 
 more freely than when both electrodes were of Selenium, 
 but still played over the surface of the Selenium partly 
 fusing it. (Compare Iron and Selenium Spark, Plate 
 IX., and note the Iron lines in each of the present 
 spectra as affecting the Selenium pole of the spec- 
 trum). 
 
 In the third spectrum the Selenium has partly 
 melted away, and the spectrum is doubled. 
 
 The spectrum of Selenium is distinguished by its 
 quantity of very fine sharp lines towards the red 
 running into bands towards the violet. Many of these 
 lines in our plates are too fine to print satisfactorily. 
 The lines are best seen in the spectrum Iron and Sele- 
 nium, Plate IX., the bands in our two present plates. 
 
 In each case the metal lines and bands follow 
 the ordinary rule of being found at the edges of the 
 spectrum. There is an inclination to mistiness or glare 
 at the poles, as in the case of Antimony. Dr. Watts 
 gives from Pliicker a long list of close lines towards the 
 red end, and of bands towards the violet end of the 
 spectrum. 
 
 We pick out conspicuously in our spectrum bright 
 lines at about 5000 (Pliicker ’s 4994 P), 4850 (Pliicker’s 
 4845 and 4840 P), 4880 (Pliicker’s 4776 ?), 4600 
 (Pliicker’s 4606 ?), and 4425. The bands towards the 
 
42 
 
 PHOTOGRAPHED SPECTRA. 
 
 violet are also well seen about 4225, 4190, and 4140. 
 The two sharp lines about 4015 and 3998 are Iron 
 lines. 
 
 PLATE XV. 
 
 First Spectrum. Silver Spark . — Small bars of the 
 metal in clips. Spark short and white, edged with 
 greenish glare. Exposure twenty minutes. 
 
 Second Spectrum. Silver Arc . — Piece cut from 
 bar of the metal in the carbon cup. Soon became red 
 hot, and melted into a bead, which rotated in the cup, 
 and from which the arc sprang. Arc moderate, and 
 tinged with green. 
 
 Lecoqde Boisbaudran gives [Plate XXV., Azotate 
 d’ Argent en solution] a set of lines commencing with 
 two very strong ones at 5464 and 5208, a band or set 
 of lines at 5022, 4997, 4968, and following on with 
 4669, 4622, 4570, 4518, 4475, 4434, 4396, 4208. 
 
 In our spark spectrum we have in our plate a line 
 about 5150, which has not printed. 4997 seems indi- 
 cated by the breadth and strength of the ‘ spark ’ line. 
 Four air lines, 4960 to 4900, are unusually strong. 
 4669 is marked by projecting slightly beyond the 
 spectrum. The other lines do not show. The battery 
 and coil power does not seem to have been sufficient 
 to bring out the metal lines satisfactorily. In our arc 
 spectrum we find brilliant lines corresponding with 
 5208 (our Scale, as we have noticed before, is a little 
 too much extended towards the red in this part of it), 
 
DESCRIPTION OF PLATES. 
 
 43 
 
 4690 (Boisbaudran’s 4669?), 4480 (his 4475?), and 
 two very strong lines, about 4215 (place of a point 
 line), and 4050. 
 
 Third Spectrum. Silver and Copper Arc . — A 
 small piece of metal wire in the carbon cup. This was 
 procured from a jeweller, and warranted pure as 
 being the silver wire employed by the natives of India 
 in making filagree and other ornamental work. It had, 
 however, I thought, a slightly reddish tint, and upon 
 combustion (behaving much the same as the last spe- 
 cimen) the spectrum proved a mixed one of copper and 
 silver. 
 
 For some reason which we do not trace, the 
 spectral image is smaller in size than that of Silver arc. 
 The enlargements are both once, and the difference is 
 in the original plates. It is however almost exactly 
 the same size as Copper arc, first spectrum, Plate VII. ; 
 and this last can be used to distinguish the copper lines 
 in our present spectrum. They mainly usurp the spec- 
 trum, but the Silver line at 5208 (apparently doubling 
 the copper line 5218), and those at 4215 and 4050, 
 are easily recognised. 
 
 Fourth Spectrum. Solar Spectrum. — This spec- 
 trum was photographed mainly for the purpose of 
 comparison with the metal spectra in regard to the 
 dispersion of the spectroscope, but also as a sort of 
 check upon our Scale, see Plate XXI., Scale and Solar 
 Spectrum. The solar lines are fairly seen, but they are 
 too fine and close together, and on too small a scale to 
 make them available for comparison with the coarser 
 
44 
 
 PHOTOGRAPHED SPECTRA. 
 
 metal lines. Indeed, this comparison did not form 
 part of our intended work. The photograph was 
 taken on a fine, but not absolutely clear, day in winter 
 with the sun near the meridian. A table was arranged 
 in the open air, facing the south, with the spectroscope 
 and camera as used for the metals upon it, the photo- 
 grapher’s back being to the sun. The slit was made 
 as fine as possible, and a plane mirror and condensing 
 ]ens were used to throw the sun’s image in a parallel 
 direction upon it. The slit was covered with a cap, 
 which was removed when it was desired to take the 
 photograph. Of the two successful plates, one was 
 exposed three seconds, the other two seconds. The 
 last has the lines sharpest and most distinct. This 
 plate indeed is very sharp, and the lines are well de- 
 fined ; but it is difficult to get as good an effect in the 
 prints. 
 
 The lines in the plate are seen nearly as far towards 
 the red as b. In the print they stop short midway 
 between b and 4 Spark.’ F, G, and h are well marked. 
 The print stops short at H 1 ; but in the plate a 
 brght space with four dark lines succeeding H 1 is seen, 
 and then the spectrum terminates abruptly with the 
 dark interval representing H 2 . 
 
 PLATE XVI. 
 
 First Spectrum. Strontium Spark . — Pieces of metal 
 in the clips. Spark bright, metal melted rapidly. 
 Spectrum (like Barium) characterised by the absence of 
 
DESCRIPTION OF PLATES. 
 
 45 
 
 air lines, and by the broad fuzzy character of the 
 metal lines. Lecoq de Boisbaudran gives [Plate IX., 
 Chlorure de Strontium en solution] four lines (second 
 and fourth the strongest) with places as follows : — 
 4307, 4215, 4163, 4079. 
 
 Assuming the first expanded line to be 4307, and 
 placing the Scale accordingly, the other three lines 
 4215, 4163, 4079, towards the violet, fall into their 
 proper places. The bright unexpanded line towards 
 the left of 4307 seems to be an air line. 
 
 Second Spectrum. Tellurium Spark , (see also 
 Plate XIV., Selenium and Tellurium Spark). — Rough 
 pieces in each of the clips, which wore away 
 quickly, the spark occasionally running to the clips. 
 Spectrum characterised by comparative absence of air 
 fines and a general likeness to Selenium without its 
 very sharp fines. Dr. Watts gives lines (Thalen) 
 4895, from his own observation 4866, 4832, 4785, then 
 three (Huggins’) 4709, 4664, 4652, then one of his 
 own 4602, and then (Huggins’) 4599, 4544, 4479, 
 4352, 4302, 4259, 4063. In our Spectrum, fines or 
 bands are well traced between 4900 and 4650 in 
 places nearly corresponding with some of the above, as 
 also a band at about 4485 (4479 P) and some bright 
 bands in the margins of the lighted-up region 4350 to 
 4225. 
 
 The line or band 4063 seems also recognisable on 
 the lower margin of the spectrum. 
 
 Third Spectrum. Thallium and Indium Spark 
 (for Indium Arc, see Second Spectrum, Plate VIII.) 
 
46 
 
 PHOTOGRAPHED SPECTRA. 
 
 — Small pieces of the metal in the clip, current reversed 
 at half, spark bright. Spectrum characterised by 
 absence of air lines, and distinctness of metal lines. 
 On the print, seven lines belonging to Thallium may 
 be counted. Two if not more, finer ones appear on 
 the plate. Seven lines at least are seen on the 
 Indium margin of the spectrum, including the large 
 ones seen in the Arc Spectrum of Indium which, as 
 in the case of the arc, are very sharp and well defined 
 and run nearly across the spectrum. (This spectrum 
 was originally a short image, and is also very slightly 
 under enlarged so that the whole is slightly shorter 
 than the Indium Arc Spectrum. Allowance must be 
 made for this in placing the Scale.) 
 
 Lecoq de Boisbaudran gives no lines for Thallium 
 in our part of the spectrum, and only the two referred 
 to ante for Indium. Dr. W atts gives for Thallium, on 
 his own, Huggins’, and Thalen’s authority lines at 5153, 
 5085, 5078, 5054, 4980, 4945, 4893, 4767, 4737, 
 4112. Our Scale indicates on our spectrum lines which 
 correspond with 5153 (scale too much extended in that 
 part), 5078, and notably 4767 (very bright and broad). 
 A line is shown about 4300, and one about 4120 (4112 P) 
 is faintly indicated. Two lines appear in the plate 
 about 4945 and 4893 which do not show in the print. 
 Dr. Watts gives for Indium (Thalen) 5532, 4509, 
 4101. Allowing for the difference in size of the 
 image before referred to, 4509 and 4101 are easily 
 distinguished sharp and well defined and projecting 
 beyond the spectrum ; 4532 is not definitely traced, 
 
DESCRIPTION OF PLATES. 
 
 47 
 
 but on each side of 4700 broad and bright lines or 
 bands are seen. Note also a bright line about 4090, 
 with a faint one beyond. A slight flare seems to run 
 along the Indium margin of the spectrum. 
 
 Fourth Spectrum. Thallium Arc. — Piece of the 
 metal in the carbon cup. Arc moderate, metal very 
 soon volatilised, and we doubted whether any trace of it 
 was impressed upon the spectrum. A fine line at the 
 extreme red end of the spectrum about 5250, and 
 others about 4610, 4405, 4260, and 4100, are however 
 intermediate of the point lines ruled out. They may 
 be metal lines, but their character is not what one 
 would expect in that case. 
 
 PLATE XVII. 
 
 First Spectrum. Titanium. , Spark. — Two pieces of 
 ore in the clips. Spark occasionally gave a reddish 
 flare. 
 
 Second Spectrum. Titanium , Aluminium , and 
 Palladium. — Palladium in clip, for upper pole. Lower 
 pole a small Aluminium cup, (with Platinum wire let 
 through the bottom) filled with Titanium in powder. 
 Current reversed half time. Spark long and bright, 
 and occasionally played round edge of the cup, from 
 which some of the powder was from time to time 
 ejected. Aluminium spectrum due to the cup very 
 apparent on upper edge of spectrum in print. Air lines 
 in first spectrum weak towards the red end. 
 
 Third Spectrum. Titanium Arc. — Metal powder 
 
48 
 
 PHOTOGRAPHED SPECTRA. 
 
 in the carbon cup. Soon formed a bead, which remained 
 quiet in the cup. Arc long and lambent. 
 
 Dr. Watts gives (with wave lengths by Thalen) a 
 long list of Titanium lines, most of them of considerable 
 intensity, and in some parts of the spectrum very 
 closely packed together. Between 5300 and 4163 we 
 count no fewer than 149, the greater number being of 
 the higher range in intensity. 
 
 Our spectrum contains several groups of fine lines 
 close together. One to the extreme left at about 
 5025 to 4975. A wider set, about 4925 to 4850 ; 
 another wide set, 4700 to 4625. A set of fine bright 
 lines 4560 to 4525, and another set about 4390 to 
 4340. Single bright lines are distinguished about 
 4775, 4550, 4460. A set of five of about equal 
 distance apart between 4450 and 4400, and a single 
 one about 4300. The single ones may be Thalen’s 
 4779, 4549, 4468, and 4299, the first being of Watts’ 
 intensity 6 and the three last his intensity 10. Going 
 back to the spark spectra, we fail to trace much evidence 
 of the metal lines. In the first spectrum the principal 
 evidence of the metal is confined to a few sharp faint 
 lines partly crossing the spectrum. 4549 is thus seen, 
 and two others about 4420. 
 
 The strong well-defined lines in the bright part of 
 the Spectrum are Iron (hence the red flare in the 
 spark). In the second Spark Spectrum no more is 
 seen, the strong lines on the upper margin being those 
 of Aluminium. 
 
 Dr. Watts gives lines for Palladium (Huggins and 
 
DESCRIPTION OF PLATES. 
 
 49 
 
 Thalen) 5062,4876, 4818, 4787, 4474, 4278, 4212. 
 In our spectrum 4876 is indistinctly traced, then a 
 line thickened at margin about 4710, 4474 seems 
 well marked. About 4300 is a conspicuous bright line 
 projecting beyond the spectrum (4278?) with" others 
 near it. A bright line is well seen at 4225 (4212?) 
 and another not so bright at about 4165. A faint line is 
 also seen beyond H 1 , which may belong to the metal. 
 
 Fourth Spectrum. Tin Arc— Some granular 
 metal in the carbon cup. Arc short, spectrum con- 
 spicuous for a few metal lines and the brightness of the 
 lines in the region of H 1 and H 2 . All the other point 
 lines (except 4225) indistinct. Lecoq de Boisbaudran 
 gives only one- line in our part of the spectrum which 
 is easily recognised, 4526 ; but note also a line about 
 4100, which does not seem to be a point line, and which 
 has the peculiarity of only partly crossing the spec- 
 trum, 
 
 PLATE XVIII. 
 
 First Spectrum. Tin and Zinc Spark — Small Zinc 
 bar in one clip. Granular tin same as used in arc 
 in small glass cup, with platinum wire connection for 
 other electrode, current reversed at half, slit rather 
 wide. 
 
 Second Spectrum. Tin and Zinc Spark Second 
 
 plate of same. 
 
 Dr. Watts gives for Tin (Thalen) 5100, 5021, 
 4923, 4858, 4585, 4524, (Boisbaudran’s 4526). The 
 First Spectrum shows towards the red end 5100 and 
 
50 
 
 PHOTOGRAPHED SPECTRA. 
 
 4923. Then referring to the second spectrum, we get 
 4858, 4605 (4585 P), 4550, 4540, and about 4515 
 (4524 ?). The one bright line in the arc (4524) is 
 but faintly represented in the spark spectrum.' 
 
 Third Spectrum. Uranium Arc . — Powder metal 
 in the carbon cup. Arc moderate, some scintillation. 
 Spectrum much glared, with many indistinct rather 
 coarse lines, from among which the point lines about 
 H 1 and H 2 and 4225 shine out conspicuously. Dr. 
 Watts gives a set of lines (Thalen), among which 447 2, 
 4393, 4374, 4362, and 4340, may perhaps be selected 
 in our spectrum. 
 
 Fourth • Spectrum. Vanadium Arc . — Powder 
 metal in carbon cup. Arc moderate. A splendid spec- 
 trum, characterised by a family likeness to Titanium, 
 but with a yet greater quantity of bands of close sharp 
 lines. Dr. Watts gives a list (Thalen) of thirty- 
 two lines between 4881 and 4085 (about where our 
 spectrum begins and ends). Groups of lines are found 
 with centres about 4843, 4585, 4389, and faint lines 
 extending from 4130 to 4085. This will be seen to 
 very closely agree with our spectrum, in which the 
 groups quoted (with others) stand out very beautifully. 
 
 PLATE XIX. 
 
 First Spectrum. Wolfram Arc.— Powder metal 
 in carbon cup. Arc moderate. Spectrum somewhat 
 like Uranium in character, but with brighter lines and 
 
 longer. 
 
DESCRIPTION OF PLATES. 
 
 51 
 
 Dr. Watts gives lines (Thalen) for Tungsten 5014, 
 5007, 4981, 4887, 4842, 4680, 4660, 4659, 4302, 
 4295, 4269. Most of these may be recognised in our 
 spectrum. 
 
 Second Spectrum. Yttrium Arc Powder metal in 
 
 carbon cup. Spectrum well defined, point lines absent, 
 notably those about H 1 and H 2 and others generally 
 seen towards the violet. Yttrium and Erbium are 
 given as a combined spectrum by Dr. Watts, but our 
 photographed spectra have little in common. 
 
 Dr. Watts gives in our part of the spectrum, 4822 ; 
 then two we do not find ; and then 4674, 4643, 4505, 
 4422, 4397, 4374, 4357, 4309, 4236, 4227,’ 4176,’ 
 4167, 4142, 4127, 4102. 4102 is very well marked, 
 and if the Scale be adjusted to this line, many of the 
 others may be picked out. 
 
 Third Spectrum. Brass Arc Two pieces of 
 
 stout brass wire. Arc did not form well. A mixed 
 spectrum of Zinc and Copper, the principal lines of each 
 metal being easily .distinguished, the zinc lines towards 
 the red end of the spectrum, the copper towards the 
 violet end. 
 
 Fourth Spectrum. Brass Spark.— Two points of 
 brass wire as electrodes. Spark passed freely, spectrum 
 deficient towards the violet, introduced to show the 
 double zinc line about 4925. 
 
52 
 
 PHOTOGRAPHED SPECTRA. 
 
 PLATE XX. 
 
 First Spectrum. Zinc Arc . — Small piece of the 
 metal in carbon cup. Arc brilliant. Much oxide 
 formed. Lecoq de Boisbaudran gives [Plate XX., 
 Chlorure de Zinc en solution] three brilliant lines 4812, 
 4721, 4681, and another not so strong at 4630. Dr. 
 Watts gives (Huggins’) faint lines at 5049 and 4970, 
 two strong ones at 4924 and 4911, a faint one at 4867, 
 and then three strong ones at 4809, 4722, 4679, 
 (Boisbaudran ’s 4812, 4721, and 4681). Compare the 
 arc spectrum, the two tin and zinc spark spectra 
 on Plate XVIII. and the brass spark spectrum on 
 Plate XIX. 
 
 Boisbaudran’s 4812, 4721, 4681, and 4630, are all 
 very prominent in the arc spectrum, together with a 
 double one at the other end of the spectrum, about 
 4060, (sed qurnre a point line. It or a line very 
 approximate occurs in other arc spectra). In the tin 
 and zinc spark spectrum No. 1, 5049, 4924, and 4911, 
 and 4809, 4722, and 4681 are seen without 4630. 
 
 In tin and zinc spark No. 2 the three stronger lines 
 alone are seen, while in brass spark 4924 and 4911 
 alone appear. 
 
 Such effects are probably due in the case of a single 
 metal to difference in strength, and temperature of 
 spark or arc ; but in the case of mixed metals the effects 
 produced, and the causes leading to them, seem to have 
 a complication of their own. 
 
DESCRIPTION OF PLATES. 
 
 53 
 
 Second Spectrum. Zirconium Arc . — Thin flakes 
 of the metal in carbon cup. Arc short and brilliant, 
 thick coat of oxide formed, occasionally stopping the 
 current and requiring pole to be cleaned ; slit fine. 
 Spectrum characterised by three prominent shaded 
 sets of bands or lines towards the red end. Dr. Watts 
 gives (Thalen) five strong lines (intensity 10) at 4815, 
 4771, 4738, 4709, 4686, then follow (intensity 4) 
 4497, 4494, 4443, 4380, 4370, 4360, 4242, 4241, 
 4228, 4210, 4209, and lastly (intensity 8) 4155, 4149. 
 
 The five strong lines 4815 to 4686 are easily dis- 
 tinguished in our spectrum ; and 4155, 4149, may be 
 picked out in the brighter part of the spectrum. There 
 also appear metal lines beyond ; until, at the extreme 
 violet end of the spectrum; we find two intense lines, 
 one midway between H l and H 2 , and the other a little 
 beyond H 2 . 
 
 Third Spectrum. Zirconium and Palladium 
 Spark . — Small pieces of the metal in clips. Many in- 
 dications of sharp metal lines on the upper (Zirconium) 
 margin of spectrum about 4686, 4575, 4550, 4540, 
 4530, 4380, 4370, 4228, and 4155, (the last two 
 rather strong), and in other places. A line (two are 
 seen in the original plate), appears also in this and the 
 next spectrum at the extremity of the violet end, which 
 probably corresponds with the intense one in the arc. 
 Palladium margin weak, and lines not easily distin- 
 guished. 
 
 Pourth Spectrum. Zirconium Spark . — Small 
 flakes of the metal in the clips. Spectrum confined to 
 
54 
 
 PHOTOGRAPHED SPECTRA. 
 
 centre, dark strong lines corresponding to 4228, and 
 4155 in last spectrum well seen. Three lines (Iron P) 
 project from the upper margin of last spectrum in the 
 region about G, which may be also identified in this 
 spectrum. Note also line at extreme violet end. 
 
 PLATE XXL 
 
 Scale and Solar Spectrum . — Both have been 
 previously referred to and described. 
 
 N.B. Potassium and Sodium were tried in arc and 
 spark, but caught fire and would not last long enough 
 to give an image. Caesium alum was tried (moistened 
 in glass cup) with spark, but gave no result. Silicon 
 in arc, the upper pole was quickly covered with a white 
 crust of oxide which stopped the arc current. Tan- 
 talum in arc gave only point lines. 
 
 THE GASES. 
 
 Some of the gases have been added by way of 
 supplement to the arc and spark spectra. The set 
 of the gas photographs is by no means complete ; and 
 they are rather experimental than otherwise, as three 
 different instruments have been used for their pro- 
 duction, and the one which gave the best results came 
 last in the field. The spectroscopes employed have been 
 already described in the Introduction ; and are there 
 and in the following notes distinguished respectively as 
 A, B and C. As the dispersion (to preserve light) was 
 
DESCRIPTION OF PLATES. 
 
 55 
 
 necessarily small, and as the gases give each a whole 
 and complete spectrum due to itself, it has not been 
 considered necessary to adapt a scale to the photographs. 
 Some of the gases are compared, the one with the 
 other ; and others are compared with hydrogen, or 
 show one or more of the hydrogen lines : and in this 
 way a general idea is in most cases obtained of the 
 position of the principal lines or bands in the spectrum 
 without reference to scale. Of course individual aspect 
 is still more marked in the case of the gas spectra than 
 in the more complicated spark and arc spectra of the 
 metals. The remarks appended to the gas spectra will 
 mainly consist of notes as to the behaviour of the tubes 
 and brief indications of any special features in the 
 spectrum. 
 
 PLATE XXII. 
 
 NITROGEN . 
 
 First Print. Line Spectrum of Nitrogen. 
 
 Third Print. Band Spectrum of Nitrogen. 
 
 Centre Print. Line and Band Spectra of 
 Nitrogen compared. 
 
 The first photograph (line only) was taken with 
 spectroscope A. The centre and third with spectroscope 
 C. Two nitrogen tubes were employed, the one with 
 coarse capillary part for the line spectra, the other with 
 fine capillary for the band spectrst. 
 
 The spectra were easily taken with twelve to fifteen 
 minutes exposure, and the small coil was generally 
 enough to work a single tube. To procure the line 
 
56 
 
 PHOTOGRAPHED SPECTRA. 
 
 spectra, the condenser (with two plates only) was in- 
 troduced into the circuit. The nitrogen line first spec- 
 trum is remarkable for its brightness towards the red 
 end, but with a falling off in light towards the violet. 
 This feature seems characteristic of the line spectra in 
 general. The line spectrum in the centre print is weak 
 and poor in lines as compared with the first line 
 spectrum, partly perhaps for want of illumination in the 
 tube, but mainly that being the side tube, (the band tube 
 was in front of the slit) the image was weakened by 
 reflection from the comparison prism used to obtain the 
 second spectrum. 
 
 A fine line is noticed on the extreme left of the 
 band spectrum (centre print), which is attributed to 
 F hydrogen, and serves to mark the position of the 
 nitrogen bands. Twenty of these are counted in the 
 lower band spectrum. 
 
 PLATE XXIII. 
 
 NITROGEN (continued). 
 
 First Print. Nitrogen Line and Band Spectra 
 compared . 
 
 Second Print. Nitrogen Band. 
 
 Third Print. Nitrogen Band and Hydrogen com- 
 pared. 
 
 Fourth Print. Nitrogen Capillary part of Tube 
 and Nitrogen Bulb part of Tube , (near red pole, as dis- 
 tinguished from violet pole on next plate), compared. 
 
 All these were taken with the spectroscope B 
 (quartz), and are on the smaller scale. In the nitrogen 
 
DESCRIPTION OF PLATES. 
 
 57 
 
 line and band compared spectrum, the band tube was 
 in front of the slit and the line tube at the side. In the 
 hydrogen and nitrogen compared spectra the hydrogen 
 tube was in front, and the nitrogen at the side ; and 
 unless the contrary is stated, it holds good throughout 
 as to all the compared spectra, that the tube at the side 
 is the upper spectrum and the tube in front of the slit 
 is the lower spectrum in the resulting plate. 
 
 As might be expected, the spectral images in the case 
 of the quartz spectroscope lose somewhat towards the 
 red end of the spectrum, but gain much in the direction 
 of the violet. About as many of the nitrogen bands 
 are counted as in the last plate, but they are not the 
 same. They commence at the bright edge of the band 
 spectrum in centre print of last plate, and extend con- 
 siderably further into the violet. An examination of 
 hydrogen and nitrogen compared spectra (third print) 
 will illustrate this. The faint line to the extreme left is 
 F hydrogen. The bright line meeting the edge of the 
 upper spectrum is near-G, the next is A, and then two 
 other fainter lines of hydrogen. 
 
 PLATE XXIY. 
 
 NITROGEN (continued). 
 
 First Print. Nitrogen Band (Capillary) compared 
 with Nitrogen Violet Pole. Spectroscope C. 
 
 Second Print. Same, but reversed in position. 
 Spectroscope B. 
 
 Third Print. Violet Pole . — Spectroscope B. 
 
 In the first (large) print the nitrogen capillary 
 
58 
 
 PHOTOGRAPHED SPECTRA. 
 
 bands, probably from the tube not being well adjusted 
 in front of the comparison prism, appear like lines. 
 This is, however, not without advantage, as they thus 
 indicate more clearly their position in regard to the 
 violet pole lines and bands. F hydrogen may be seen 
 as a faint line to the left of the violet pole spectrum in 
 this print. The following wave lengths, as given by 
 Dr. Vogel, may be interesting for comparison : — ■ 
 
 Capillary part of Tube . 
 
 Violet Pole. 
 
 5066 bright. 
 
 5147 faint. 
 
 4975 „ 
 
 5002 bright. 
 
 4913 „ 
 
 4912 „ 
 
 4862 very faint. 
 
 — 
 
 4811 bright. 
 
 4808 very faint. 
 
 4721 „ 
 
 4704 very intense. 
 
 4666 faint. 
 
 — 
 
 4644 bright. 
 
 4646 very faint. 
 
 4570 very bright. 
 
 4569 bright. 
 
 4487 bright. 
 
 4486 „ 
 
 4417 „ 
 
 4417 very faint. 
 
 4363 „ 
 
 — 
 
 4357 „ 
 
 — 
 
 4345 „ 
 
 4346 bright. 
 
 4273 „ 
 
 4273 very bright. 
 
 Our lines extend considerably more into the violet. 
 The violet pole has attracted considerable attention in 
 connection w T ith the Spectrum of the Aurora, mainly o 
 
 o 
 
 account of the late Prof. Angstrom’s opinion, that 4 the 
 4 feeble bands of the Aurora spectrum belong to the spec- 
 4 trum of the negative pole, possibly changed more or 
 4 less by additions from the banded or the line air 
 4 spectrum.’ 
 
DESCRIPTION OF PLATES. 
 
 59 
 
 I have discussed this question at length in a paper, 
 on the Aurora Spectrum, published in the 4 Philoso- 
 phical Magazine’ for April 1875 ; and I only refer to 
 it now to point out that the difficulty of actual line 
 comparison which then existed might perhaps now 
 be conquered. 
 
 With one or other of the instruments we have used, 
 there really seems no reason why a photographic 
 image of the more refrangible rays of the Aurora Spec- 
 trum should not be obtained without difficulty. I saw 
 at Kyle Akin in Skye in September 1874, aline double 
 arc Aurora of great brilliancy which lighted up the 
 whole landscape, and strongly impressed me with the 
 idea that if proper apparatus had been at hand some- 
 thing in that direction might have been accomplished. 
 Aurorae have unfortunately been quite quiescent lately. 
 Should this state of things alter, the experiment would 
 be well worth trying. As much as possible, say two 
 thirds, of a long slit should be given to the Aurora, and 
 the remaining one third kept in reserve for a com- 
 parison spectrum. Dry plates might be used and a 
 considerable amount of exposure given. The Camera 
 should be directly pointed to the brightest part of the 
 Aurora. After exposure and before disturbing the 
 apparatus, the two thirds of the slit used for the Aurora 
 should be covered, and the remaining third which was 
 covered during exposure should be employed for the 
 projection of a tube or solar spectrum on the same 
 plate. 
 
 If a tube spectrum only were desired for comparison, 
 
GO 
 
 PHOTOGRAPHED SPECTRA. 
 
 a prism might be used on the slit in the usual way, but 
 I prefer a direct image when practicable. 
 
 To obtain absolute measurements of the lines a 
 double slit (the upper half moveable by a micrometer 
 screw) like one I have deposited at South Kensington, 
 might be employed. Two photographic images being- 
 taken, one under the other, the lines are measured by the 
 relative position of the same lines in the two images 
 being compared with the ascertained value of the micro- 
 meter movement. 
 
 PLATE XXV. 
 
 NITROGEN (continued). 
 
 First Print. Band Spectrum of Nitrogen [Capillary) 
 with Magnet. 
 
 Second Print. Band Spectrum of Nitrogen 
 (i Capillary ) without Magnet. 
 
 The Electro-magnetic experiments leading to these 
 plates have been fully detailed in the Introduction : 
 Spectroscope B (quartz) was used for them. The 
 plate with magnet is brighter, especially towards the 
 violet. 
 
 Centre Print. Ammonia (NR S ) Tube , capillary 
 part fine, tube lighted up easily. A nitrogen spectrum 
 is alone prominent. 
 
 Fourth Print. Line Spectrum of Nitrogen Tube , and 
 Spark in Air compared. — This print is from the original 
 without enlargement, and does not show so much as 
 the plate. The line tube spectrum was obtained by 
 use of the Condenser in the usual manner. The spark 
 
DESCRIPTION OF PLATES. 
 
 61 
 
 passed between two platinum points introduced into 
 the circuit. The stronger lines correspond in posi- 
 tion. 
 
 Fifth Print, is introduced into the plate in con- 
 nection with the second spectrum (Spark in Coal Gas) on 
 Plate XXVII. 
 
 The upper spectrum is that of spark in air as taken 
 between Platinum points. The lower is spark in coal 
 gas (after referred to) and the combined spectra are 
 printed to illustrate the approximate position of the 
 lines in the spectrum of spark in coal gas at ordinary 
 pressure as compared with spark in air. Spectroscope 
 C was used. linage not very good, but better on plate 
 than in the print. It would not bear enlargement with 
 any advantage. 
 
 PLATE XXVI. 
 
 HYDROGEN. 
 
 First Print. Hydrogen Tube . — Small in capillary 
 part, lighted up well with small coil. A portion of 
 the capillary bore, comprising the whole circumference 
 of the tube is decomposed, and has the appearance of 
 being obscured by a yellow white coating. The 
 bright red tint of the discharge was lost here, and 
 the lines of the spectrum were partly extinguished 
 in a white misty haze. This effect is seen in the 
 print. 
 
 The spectrum, as to principal lines, will be seen to 
 consist of — 
 
62 
 
 PHOTOGRAPHED SPECTRA. 
 
 No. 1. F. 4861. 
 
 2. Near-G, 4340 (G 4307). 
 
 3. h 4101. 
 
 4. A sharp bright line, not quite as distant 
 
 from /i as li is from G. 
 
 5. A line faintly seen in the print beyond 
 
 No. 4, not quite as distant from No. 4, as 
 
 No. 4 is from h. 
 
 No. 5, in the original plate, is fairly strong, and 
 close to, and on each side of it, are also seen two single 
 fine lines, the one on the violet side being rather the 
 more distant (see also Centre Print, Plate XXVIII.). 
 
 Lines of some breadth and intensity are to be 
 remarked between the more prominent lines before 
 described. Two short ones between No. 1 and No. 2 
 (five are counted on the plate), three or more between 
 No. 2 and No. 3, and three between No. 4 and No. 5. 
 The spectrum is also filled with a number of very 
 fine and sharp lines, traces of which are indicated in 
 the print. Whether these intermediate lines are due 
 to hydrogen or to tube impurity is not clear ; but as 
 some of the coarser ones are traced in the second 
 spectrum on next plate, (Spark in Coal Gas), it is 
 probable that these at least are due to the gas. 
 
 Second Print. Spark in Coal Gas .-. — This spectrum 
 and the way it was obtained have been already 
 described in connection with the Carbon Spectra. 
 Another but less bright print is found on Plate VI. 
 
 This spectrum is on the same scale as the arc 
 and spark spectra, and therefore larger than our Gas 
 
DESCRIPTION OF PLATES. 63 
 
 spectra in general. The original, before enlargement 
 is found on Plate XXXIII. The print is here intro- 
 duced to illustrate the expansion of a hydrogen line. 
 Note traces of a ijarrow dark space dividing the centre 
 of the expanded line. The sharp lines are attributed 
 to Carbon. 
 
 Third Print. Hydrogen Tube , taken with spectro- 
 scope B, wide slit. Lines 1, 2, 3, 4, and 5, in last 
 spectrum are brightly seen, (No. 5 very bright), a sixth 
 is easily traced some distance beyond, and a seventh 
 faintly indicated where the continuous spectrum ends. 
 
 PLATE XXVII. 
 
 HYDROGEN (continued). 
 
 First Print, Compared spectrum. Spark in Air 
 between Platinum Points, and Hydrogen Tube. Spectro- 
 
 scope C. Large coil and condenser used for spark. 
 Small coil for the tube. Exposure for tube 15 minutes 
 for spark 5. 
 
 The spark spectrum is seen to extend far into the 
 violet ; considerably beyond the spark in air, as taken 
 in combination with the metals. The four principal 
 hydrogen lines, commencing with F, are well seen, 
 some intermediate ones faintly. 
 
 Near-G is the only hydrogen line that can be 
 absolutely traced into and through the air spectrum. 
 
 Second Print. Spark in Coal Gas at ordinary 
 pressure. — The manner in which this spectrum was 
 obtained has been described under the head of Carbon 
 
64 
 
 PHOTOGRAPHED SPECTRA. 
 
 among the Arc and Spark Spectra, and the peculiar 
 difference between this and the print, on Plate XXVI. 
 (also spark in Coal Gas) has been noticed. 
 
 This spectrum should be compared with the first 
 print in this plate, (Spark and Hydrogen) and 
 with hydrogen on the last plate. The image is en- 
 larged very slightly more than the other two spectra, 
 but not enough to prevent easy comparison. Taking 
 the principal lines of Hydrogen in their order, — 
 
 F is seen as a bold very bright expanded line. 
 
 Near-G is seen to the left of a well defined line 
 not found in the ordinary hydrogen spectrum, as a 
 still more expanded bright band or stripe with conical 
 ends. A bright sharp line between F and near-G, 
 surrounded by a nebulous halo coincides with one of 
 two short lines in the hydrogen tube. 
 
 Beyond near-G, we have a blaze of continuous 
 spectrum, crossed by four prominent lines. 
 
 The first of these lines has been already noticed, 
 and does not appear in the hydrogen spectrum. 
 
 The second falls very close upon the place of h 
 in the hydrogen tube. 
 
 The third does not appear in the hydrogen tube. 
 
 The fourth, and last, and the most expanded, falls 
 close upon the place of Ho. 5 in the hydrogen spectrum. 
 
 Intermediate of Nos. 1 and 2, and of Nos. 2 and 3, 
 are faintly but distinctly traced some of the less strong 
 lines of the hydrogen tube. The general position of 
 this spectrum as compared with air is indicated by the 
 small print on Plate XXV. before described. 
 
DESCRIPTION OF PLATES. 
 
 65 
 
 PLATE XXVIII. 
 
 OXYGEN . 
 
 First Print. Band Spectrum of Oxygen , tube 
 No. 1, spectroscope C. 
 
 Second Print. Band Spectrum of Oxygen , tube 
 No. 2, same spectroscope. 
 
 These two tubes were worked by the larger coil, 
 with batteries purposely weak ; exposure fifteen 
 minutes. In the case of No. 1 tube the colour of the 
 capillary stream was a pale pink. There was consi- 
 derable stratification in the bulbs of both tubes. 
 
 The spectrum of No, 1 is a short bright one, com- 
 posed of a mixture of oxygen and hydrogen lines, the 
 latter probably due to moisture in the tube. F hydro- 
 gen is seen as a single line to the extreme left; 
 near-G is seen very bright at the edge of the illuminated 
 part of the spectrum, h is seen in the centre of the 
 spectrum, apparently doubled by a strong oxygen line. 
 The other less distinct lines or bands are those of 
 oxygen. In the plate some finer lines are seen inter- 
 mediate of the coarser ones. Professor Draper is said 
 to have recently found some of the oxygen lines as 
 bright ones in the solar spectrum. 
 
 The capillary stream of tube No. 2 was somewhat 
 redder in tint. The spectrum was taken and enlarged 
 as one of oxygen, to accompany that of No. 1 ; but a 
 comparison with the upper print on Plate XXVI. will 
 show that while the continuous spectrum and some 
 
 F 
 
66 
 
 PHOTOGRAPHED SPECTRA. 
 
 indistinct lines or bands are probably due to oxygen, 
 the principal bright lines are those of hydrogen. It 
 will be noticed, too, that the triple line mentioned as 
 No. 5 and faintly seen in the hydrogen spectrum, shows 
 in the spectrum now examining (to the extreme right) 
 as a strong double line, with shading off towards the 
 violet. 
 
 Third Spectrum. Line Spectrum of Oxygen . — - 
 This was obtained in the usual way, by introduction of 
 the Condenser (with two plates) into the circuit. The 
 spectroscope used was A. 
 
 Four line spectra are printed which have been 
 taken with this instrument : Nitrogen, Plate XXII. ; 
 the present (Oxygen) ; Carbonic Acid, Plate XXX. ; 
 and Coal Gas, Plate XXXIII. Each of the three last 
 spectra, though differing in other respects, has a marked 
 character in common, viz. a bright line to the left, 
 as Aimed to be F hydrogen, and a bright broad band of 
 light more towards the centre with a sharp line close 
 adjoining on the violet side. The other lines by their 
 variation show that the spectra, as a whole, are not 
 by any means identical ; but these particulars seem 
 constant. It might be expected that the bright line 
 adjoining the band would be 4 near-G ’ hydrogen, but 
 this is not the case. An examination of the original 
 plates shows that the enlargements are strictly correct, 
 and that the broad band itself exactly occupies the 
 place of 4 near-G 5 in the hydrogen spectrum. It would 
 seem that the images of spectroscope A give the line 
 spectrum towards the red end, while those of spectro 
 
DESCRIPTION OF PLATES. 
 
 67 
 
 scope B (quartz) give the line "spectrum towards the 
 violet (see Plate XXIX. line oxygen). 
 
 PLATE XXIX. 
 
 OXYGEN (continued). 
 
 All the photographs on this plate were taken with 
 spectroscope B (quartz). 
 
 First Print. Band Spectrum of Oxygen , tube No. 1. 
 — This spectrum extends, in an even series of bands, 
 considerably into the violet. In the spectrum of 
 oxygen on last plate, we count only six principal coarse 
 lines or bands. In this print we count no less than 
 fifteen. Probably from some difference in lighting up 
 of the tube, one hydrogen line only shows in this 
 spectrum, and the bright oxygen line doubling the 
 hydrogen line in the spectrum on last plate though 
 present is not nearly so conspicuous. 
 
 Print No. 2. Water Gas. -Tube marked H 2 0, 
 worked as above, colour of capillary red, but not so 
 red as hydrogen. The principal lines of the latter are 
 well distinguished. The oxygen spectrum is not so 
 bright, especially towards the violet as in the last print. 
 
 Third Print. Band Spectra of Oxygen and Ni- 
 trogen compared.— Nitrogen tube and spectrum much 
 the brightest. Oxygen spectrum towards red a com- 
 paratively even set of bands. Nitrogen, in sets of 
 bands. 
 
 Fourth Print. Line and Band Spectra of Oxygen 
 
68 
 
 PHOTOGRAPHED SPECTRA. 
 
 compared .— Line tube the brightest. Line spectrum 
 very bright towards the red, but obscured towards the 
 violet. 
 
 PLATE XXX. 
 
 CARBONIC ACID . 
 
 First Spectrum. Band Spectrum of Carbonic Acid. 
 —Spectroscope C. Tube marked C A of rather large 
 bore, worked by large coil, much stratification extending 
 even through the capillary, stream of capillary light, 
 bright and of silvery grey green tint. Spectrum much 
 filled up by obscure sets of bands or lines, except in the 
 positions occupied by a bright line in the centre and a 
 dark space more towards the violet. F hydrogen shows 
 to the extreme left. The other hydrogen lines are not 
 seen. Note sharp bright line separated from main 
 body of the spectrum towards the red. 
 
 Second Print. Spectroscope C. — This was a tube 
 marked S0 3 . The light was pearly white. The 
 spectrum turned out to be carbonic acid, probably 
 from some impurity in the tube. See also second and 
 third prints on Plate XXXV. The tube was worked 
 by the large coil and two weak bichromates. 
 
 Third Print. Line Spectrum of Carbonic Acid. 
 —Spectroscope A. Condenser in circuit. Tube filled 
 with stream of white light. Compare line specti a of 
 oxygen and of coal gas taken with same instrument. 
 
DESCRIPTION OF PLATES. 
 
 69 
 
 PLATE XXXI. 
 
 CARBONIC ACID (continued). 
 
 First Print. Spectral image, taken with spectro- 
 scope A, of capillary part of carbonic acid tube (C A) 
 wide slit. Stratification well seen. Print from original 
 negative not enlarged. 
 
 The three remaining spectra on this plate w T ere 
 taken with spectroscope B. 
 
 Second Print. Carbonic Acid Tube , Band Spectrum. 
 — This spectrum as taken with the quartz instrument, 
 though the same, differs somewhat in actual appearance 
 from our print on last page. The two left-hand single 
 lines are absent. The left-hand edge of the centre 
 part of the spectrum is comparatively brighter. The 
 bright band and dark interval before referred to are 
 still more strongly defined. 
 
 Beyond the bright band and next to the dark inter- 
 val which nearly ends the spectrum on the last plate, 
 we get in our present spectrum a set of six lines or 
 bands, the first only of which is faintly indicated in the 
 spectrum taken with instrument C. 
 
 Third Print. Line Spectrum of Carbonic Acid 
 compared with Line Spectrum of Oocygen. 
 
 Fourth Print. Band Spectrum of Carbonic Acid 
 compared with Band Spectrum of Oxygen. 
 
 Some years ago Mr. Henry E. Procter and myself 
 were much struck with the closeness in position of the 
 three prominent bright lines or bands in the yellow, 
 
70 
 
 PHOTOGRAPHED SPECTRA. 
 
 green, green and blue, in hydrocarbon tubes as compared 
 with like lines in an oxygen tube. The three lines 
 were so nearly identical in position in the compared 
 tubes that a fine pointer and high power eyepiece 
 failed to distinguish apart their sharper margins. But 
 for a certain want of accord in tint and intensity of the 
 two spectra, we began to suspect the identity of the 
 oxygen spectrum, and Mr. Procter even conjectured 
 that oxygen might have only a continuous spectrum, 
 and that the bright lines might arise from carbon 
 impurity in the 0 tubes. 
 
 Our compared photographic spectra lie much more 
 towards the violet end of the spectrum (beginning with 
 the more refrangible of the three lines or bands above 
 referred to), but it is pretty clear from an examination 
 of them that, in this part of the spectrum at least, the 
 spectra differ considerably. The line spectra approach 
 the nearest in position, but there is a marked and 
 distinct character to each of these. The band spectra 
 are widely different. The smooth and even character 
 of the band spectrum of oxygen contrasts strongly 
 with the sharper and more defined lines and bands of 
 the carbon spectrum. Some few lines only towards 
 the violet of carbonic acid appear to correspond with 
 bands in the oxygen spectrum. The one extremely 
 bright line or band in carbonic acid is conspicuous 
 for its absence as such in oxygen. 
 
DESCRIPTION OF PLATES. 
 
 71 
 
 PLATE XXXII. 
 
 COAL GAS . 
 
 First Print. Band Spectrum of Coal Gas. — Spec- 
 troscope C. Stream in tube whiter and brighter 
 than carbonic acid, much stratification, exposure 15 
 minutes. Spectrum as reading from the red composed 
 of four faint single lines followed by an evenly lighted 
 broad continuous portion, crossed by many well-defined 
 bright lines or narrow bands. 
 
 This continuous portion terminates with a most bril- 
 liant band or set of lines shading off towards the violet, 
 which is immediately succeeded by a fairly strong and 
 then a faint line as the last indication of the spectrum. 
 
 Compared with the Hydrogen spectrum, F is 
 seen faintly to the extreme left, followed by the two 
 short lines seen in the Hydrogen spectrum between F 
 and near-G. Next comes an outstanding sharp line, 
 also seen in the Carbonic Acid spectrum. 
 
 Near-G Hydrogen is next seen as a well-defined 
 line on the edge of the continuous portion. The 
 very bright line exactly in the centre of the print does not 
 fall in the place of h but of a line a little beyond A, also 
 seen in the Hydrogen spectrum. The spectrum forms 
 a fine photograph, and nearly all that is seen in the 
 plate is got out in the print. 
 
 Second Print. Cyanogen . — Tube lent to me by 
 Mr. W. G. Lettsom, lighted up easily with a white 
 glow, lines and bands sharper and more separated by 
 
72 
 
 PHOTOGRAPHED SPECTRA. 
 
 dark intervals than in the Coal Gas spectrum. As- 
 suming the first (single) line on the left to be near-G 
 Hydrogen, a few lines in the spectra of coal gas and 
 cyanogen fairly correspond, and the general character 
 of the two spectra is somewhat alike. They, however, 
 differ in detail. 
 
 Third Print. Coal Gas Tube. — Spectroscope B. 
 The general aspect of the spectrum is that of the first 
 print, except that the lines are not so well defined, but 
 blend into bands. 
 
 The especially bright band towards the violet is 
 easily recognised, and beyond it extend three bright 
 bands not seen in the large spectrum. 
 
 PLATE XXXIII. 
 
 COAL GAS (continued). 
 
 First Print. Line Spectrum of Coal Gas. — Con- 
 denser in circuit, exposure 20 minutes. Note former 
 remarks on line spectra of oxygen and carbonic 
 acid. 
 
 Second Print. Line and Band Spectra of Coal Gas 
 compared. — -The line spectrum commences with the 
 band and bright line so conspicuous in the first print, 
 and then succeed two other bright lines or bands, with 
 fine lines between. The last band towards the violet 
 in the line spectrum corresponds with the very bright 
 band in the band spectrum. 
 
 Third Print. Coal Gas Band Spectrum compared 
 
DESCRIPTION OF PLATES. 
 
 73 
 
 with Hydrogen Lines. — Spectroscope A. Print from the 
 original negative, not enlarged ; near-G is seen on the 
 edge of the first bright band or set of lines in coal 
 gas. 
 
 Fourth Print. Spark in Coal Gas at ordinary 
 pressure. — Same spectroscope as used for Arc and Spark 
 Spectra. Print from original negative, which was after- 
 wards enlarged to form prints on Plates VI. and 
 XXVI. 
 
 PLATE XXXIV. 
 
 OTHER HYDROCARBONS. 
 
 First Print. Olefiant Gas. — Tube fairly bright. 
 Spectroscope A. A broad bright band, (probably a set 
 of lines or bands), and a nebulous bright line beyond, 
 towards the violet, are very marked in this spectrum. 
 As these are only feebly indicated in the other two 
 spectra of this gas, they may probably have depended 
 upon the lighting up of the tube. 
 
 Second Print. Olefiant Gas. — Spectroscope C. 
 Spectrum with well-defined fines. The faint one 
 towards the extreme left seems to be one of the lines in 
 Hydrogen intermediate of F and near-G. As in the 
 case of coal gas, near-G is on the margin of the con- 
 tinuous part of the spectrum, while the fifth bright line 
 in the spectrum falls upon the place of the line in 
 Hydrogen just beyond h. 
 
 The bright broad band in the first print is indicated 
 by a few faint lines. 
 
74 
 
 PHOTOGRAPHED SPECTRA. 
 
 Third Print. Olefiant GW— Spectroscope B. 
 The set of two double and two single bright lines in the 
 last spectrum is easily recognised on a smaller scale. 
 Three other bright bands are seen towards the violet. 
 
 Fourth Print. Turpentine Vapour . — Tube not 
 bright, large coil used. Exposure fifteen minutes. 
 As might be expected, the print bears a likeness to the 
 Olefiant spectrum, 
 
 Fifth Spectrum. Ether Vapour . — Spectroscope C, 
 tube difficult to light up. What is seen of spectrum 
 resembles Olefiant and Turpentine spectra. 
 
 PLATE XXXV. 
 
 SULPHUR . 
 
 First Print. Sulphur .— A short German tube, 
 with small bulbs and a bent capillary part. The bulbs 
 contained a small quantity of solid sulphur. The tube 
 was suspended, and the lower bulb heated by a spirit- 
 lamp. When the sulphur was partly melted, one half 
 of the capillary was white in colour and the other half 
 red. As the heat was gradually applied the spectrum 
 of sulphur of first order was seen to spread up the tube 
 as a set of bright bands, which by management of the 
 lamp could be kept at a definite height. The spectrum 
 independent of the sulphur vapour was found to be 
 hydrogen, with the principal lines very bright. Photo- 
 graphs were first tried with A and B spectroscopes, but 
 were not satisfactory. Several plates were subsequently 
 
DESCRIPTION OF PLATES. 
 
 75 
 
 taken with spectroscope C. We tried to take the spec- 
 trum lower half sulphur and upper half hydrogen, but 
 failed, probably for want of proper adjustment of the 
 lamp. In each case we found only the sulphur spec- 
 trum on the plate. The plates were all much alike, and 
 only differed in distinctness of the bands. 
 
 Second Print. Another print of SO 3 Tube Spec- 
 trum . — Spectroscope C, see Plate XXX., where by con- 
 parison the spectrum is seen to be a carbonic acid one, 
 arising we presume from impurity in the tube. 
 
 Third Print. S0 s Tube . — Spectroscope B, same 
 result as above. Compare with carbonic acid spectra, 
 Plate XXXI. The slit must have been a little wider, 
 or the tube less bright in this instance, as the spectrum 
 is more continuous and the lines not so sharp. 
 
 PLATE XXXVI. 
 
 First Print. Silicic Fluoride Spectrum . — Tube 
 easily worked, capillary a beautiful violet, bulbs golden 
 brown. Under influence of large electro-magnet, stream 
 of light became less violet and more red in tint, con- 
 tracted itself, and ran through the bulbs from pole to 
 pole. At the same time a slight noise, between a 
 whistling and a metallic ring of high pitch, was heard. 
 
 The stream was curved in the bulbs towards one 
 side or the other as the current was reversed. Good 
 photograph, lines some twenty-four in number, sharp, 
 and well separated. A fine shaded group commences 
 the spectrum towards the red end. This group in 
 
76 
 
 PHOTOGRAPHED SPECTRA. 
 
 the spectroscope is of a brilliant violet tint, and at once 
 identifies the spectrum. 
 
 Second Print. Silicic Fluoride Spectrum. — Spec- 
 troscope B. The spectrum does not seem more ex- 
 tended into the violet in this instance, but a band or 
 set of fines towards the centre is brightened up. A 
 second photograph was taken with the tube under the 
 influence of the electro-magnet, same time of exposure. 
 The image was identical, but very decidedly fainter. 
 
 Third Print. Tin Chloride . — Spectroscope B. This 
 tube was very difficult to photograph. The small coil 
 only did not sufficiently light the tube, the large coil 
 was too much for it. The discharge was in the form 
 of a slender bright green thread running through the 
 tube. For a short time all went well, after that the stream 
 intermitted and almost broke up, and flashes of fight 
 only took its place. At the same time the metal fines 
 grew fainter in the spectrum, and the bulbs of the tube 
 were filled with a yellowish flare. These, on subsequent 
 examination, were found covered with a whitish crust. 
 Only one fair plate was obtained, of which a print is 
 given. Some fine metallic looking fines seen in the 
 spectrum do not come out in the photograph. 
 
 Fourth Print. Iodine Tube . — This was lighted by 
 the small coil only. The photograph shows two sets of 
 bands, each gradually degrading towards the violet, with 
 a dark interval between them. 
 
 Many fine fines seen in the tube spectrum do not 
 appear in the photograph. 
 
 Fifth Print. Spark in Iodine Vapour . — A bulb 
 
DESCRIPTION OF PLATES. 
 
 77 
 
 similar to that employed for spark in coal gas was used. 
 The ends were lightly plugged with cork and the iodine 
 vapourised by a spirit-lamp. 
 
 When the vapour filled the bulb, the spark spectrum 
 as seen through it with a small direct vision spectro- 
 scope showed marked absorption bands. 
 
 Traces of these (better on the plate than in the 
 print) may be found on the photograph. 
 
 A Chlorine Tube , it has been mentioned, baffled us. 
 We tried it with the small coil, and exposure gave no 
 image apparently for want of brightness. We then 
 tried it with the larger coil. At first the tube shone 
 with a yellowish green stream running from pole to 
 pole, the bulbs being filled with a somewhat dull purple 
 glow. Almost suddenly one pole and then the other 
 changed to a brighter and whiter purple. One pole 
 then changed to a rich salmon colour, the opposite 
 pole remaining white surrounded by a purple glow. 
 Current reversed, and both bulbs then became salmon 
 colour, with considerable stratification. Ultimately the 
 capillary became a pinkish white, one pole a red buff 
 and the other a bright lilac. The yellow green line 
 was then altogether lost. 
 
 On reversing current, the poles changed. The 
 spectrum when the plate was examined was found to 
 be nitrogen. 
 
NOTE TO OXYGEN SPECTRUM. 
 
 Since the foregoing has been penned, Professor Draper’s in- 
 teresting paper and photograph have been made public. 
 The solar spectrum from about 4350 to 3900 is photo- 
 graphically compared with the lines of oxygen, as seen in 
 spark in air, and coincidences are shown, principally at the 
 double lines 4319 4317, 4190 4184, and the triple line 
 4076 4072 4069. The air spark spectrum in Professor 
 Draper’s photograph, making allowance that it is on a scale 
 of three times the size, and that it has less of continuous 
 spectrum filling up between the lines, very closely resembles 
 our air spectrum fine slit Plate I. Most of the lines 
 in each are easily compared and identified. The three 
 principal nitrogen lines are recognised, the one near 4000 
 by its strength and brightness, and the other two by 
 their fuzzy expanded character : the oxygen lines by their 
 comparative sharpness. In our solar spectrum, we find 
 faint traces of the bright lines which are alluded to by 
 Professor Draper, and their character suggested. It is 
 curious that these bright lines in the solar spectrum should 
 have been so long overlooked, or not more closely examined ; 
 for in the spectrum taken from an illuminated cloud 
 with a large direct Vision spectroscope their existence is 
 readily detected. Doubtless they have been generally re- 
 garded as spaces or effect of contrast between the dark lines, 
 and it is indeed only after a certain amount of study whether 
 of the spectrum or of a photograph, that they appear to 
 stand forward from among the dark lines in an independent 
 character. Judging from his paper, Professor Draper seems 
 to have found with his incomparably larger and more perfect 
 
80 
 
 PHOTOGRAPHED SPECTRA. 
 
 apparatus, the same sort of difficulty in the tube work that 
 we experienced in ours on a smaller scale. Professor Draper 
 makes the remark, 6 1 do not think that in comparisons of 
 the spectra of the elements and sun, enough stress has been 
 laid on the general appearance of lines apart from their mere 
 position ; in photographic representations this point is very 
 prominent.’ 
 
 Our set of Plates amply illustrates the justice of this 
 remark of the Professor’s. 
 
 Aurora, double Arc and Streamers, Kyle Akin, Isle of Skye, Sept. 11, 1874, 
 11 p.m. From a sketch by J. Rand Capron. 
 
INDEX 
 
 TO AEC AND SPAKK SPECTRA. 
 
 Air wide Slit ..... 
 Air fine Slit ..... 
 Arsenic Spark .... 
 Aluminium Spark .... 
 Aluminium Arc .... 
 Antimony Spark .... 
 Antimony Arc .... 
 Bismuth Spark .... 
 Bismuth and Nickel Spark 
 Bismuth and Tellurium Spark' 
 Bismuth Arc ..... 
 Barium Spark .... 
 Beryllium (Iron) Arc 
 Boron Arc 
 
 Calcium (Zinc) Spark 
 Cadmium Spark .... 
 Cadmium Arc .... 
 Carbon Points . 
 
 Carbon Points ruled out . 
 
 Coal Gas Spark in . . . . 
 Chromium Arc .... 
 Cobalt Arc ..... 
 
 Copper Spark 
 
 Copper Arc . . . . 
 
 Copper and Silver Arc . . 
 
 Copper, Gold, and Silver (Alloy) Arc 
 Copper and Iron Spark . 
 
 Didymium Arc .... 
 Erbium Arc ..... 
 
 Gold Arc 
 
 Indium Arc 
 
 Indium Spark .... 
 
 PLATE PAGE 
 
 I. 18 
 
 I. 18 
 
 I. 18 
 . II. XIV. XVII. 19, 40, 47 
 
 II. 19 
 . II. X. 19, 34 
 
 II. 19 
 
 III. 20 
 
 III. 20 
 
 III. 20 
 
 III. 21 
 
 IV. 21 
 
 IV. 22 
 
 IV. 22 
 
 IV. 23 
 
 V. 23 
 
 V. 23 
 
 V. 23 
 
 V. 24 
 
 VI. 24 
 
 VI. 26 
 
 VI. 27 
 
 VI. 27 
 
 VII. 27 
 
 XV. 43 
 
 VII. 27 
 
 . VIII. IX. 31 
 
 . . . VII. 28 
 
 VII. 29 
 
 VIII. 30 
 
 VIII. 30 
 
 XVI. 45 
 
 G 
 
82 
 
 INDEX. 
 
 Iridium Arc .... 
 
 
 
 PLATE 
 
 VIII. 
 
 PAGE 
 
 30 
 
 Iron and Copper Spark . 
 
 
 
 VIII. 
 
 31 
 
 Iron and Copper Spark . 
 
 
 
 IX. 
 
 31 
 
 Iron Arc .... 
 
 
 
 IX. 
 
 31 
 
 Iron Arc .... 
 
 
 
 IX. 
 
 31 
 
 Iron and Selenium Spark 
 
 
 
 IX. 
 
 32 
 
 Iron Meteoric Arc . 
 
 
 
 X. 
 
 33 
 
 Iron Meteorite Arc 
 
 
 
 X. 
 
 33 
 
 Lead Arc .... 
 
 
 
 X. 
 
 34 
 
 Lead and Antimony Spark 
 
 
 
 X. 
 
 34 
 
 Lead and Magnesium Spark . 
 
 
 
 XI. 
 
 35 
 
 Magnesium and Lead Spark . 
 
 
 
 XI. 
 
 35 
 
 Magnesium Spark . 
 
 
 
 XI. 
 
 35 
 
 Magnesium Arc 
 
 
 
 XI. 
 
 35 
 
 Manganese Arc 
 
 
 
 XII. 
 
 36 
 
 Manganese Arc 
 
 
 
 XII. 
 
 36 
 
 Mercury Spark 
 
 
 
 XII. 
 
 37 
 
 Molybdenum Arc . 
 
 
 
 XII. 
 
 37 
 
 Nickel Arc .... 
 
 
 
 XIII. 
 
 38 
 
 Nickel Spark .... 
 
 
 
 III. 
 
 20 
 
 Niobium Arc .... 
 
 
 
 XIII. 
 
 38 
 
 Palladium Arc 
 
 
 
 XIII. 
 
 39 
 
 Palladium Spark 
 
 
 . XVII. XX. 47, 
 
 48, 53 
 
 Platinum Arc 
 
 
 
 XIII. 
 
 39 
 
 Rhodium Arc 
 
 
 
 XIV. 
 
 40 
 
 Ruthenium Arc 
 
 
 
 XIV. 
 
 40 
 
 Scale ..... 
 
 
 
 I. XXI. 
 
 17 
 
 Selenium and Tellurium Spark 
 
 
 
 XIV. 
 
 40 
 
 Selenium and Iron Spark 
 
 
 
 IX. 
 
 32 
 
 Selenium and Aluminium Spark 
 
 
 
 XIV. 
 
 40 
 
 Silver Spark .... 
 
 
 
 XV. 
 
 42 
 
 Silver Arc .... 
 
 
 
 XV. 
 
 42 
 
 Silver and Copper (Alloy) Arc 
 
 
 
 XV. 
 
 43 
 
 Solar Spectrum 
 
 
 
 XV. XXI. 
 
 43 
 
 Strontium Spark 
 
 
 
 XVI. 
 
 44 
 
 Tellurium Spark . . 
 
 
 . III. XIV. 
 
 XVI. 20, 
 
 40,45 
 
 Thallium and Indium Spark . 
 
 
 , v , 
 
 XVI. 
 
 45 
 
 Thallium Arc .... 
 
 
 
 XVI. 
 
 47 
 
 Titanium Spark 
 
 
 
 XVII. 
 
 47 
 
 Titanium, Aluminium, and Palladium 
 
 Spark . 
 
 XVII. 
 
 47 
 
 Titanium Arc 
 
 
 XVII. 
 
 47 
 
 Tin Arc 
 
 
 
 XVII. 
 
 49 
 
 Tin and Zinc Spark 
 
 
 
 XVIII. 
 
 49 
 
 Tin and Zinc Spark 
 
 
 
 XVIII. 
 
 49 
 
INDEX. 
 
 
 83 
 
 
 PLATE 
 
 PAGE 
 
 Uranium Arc ....... 
 
 . XVIII. 
 
 50 
 
 Vanadium Arc ...... 
 
 . XVIII. 
 
 50 
 
 Wolfram Arc 
 
 XIX. 
 
 50 
 
 Yttrium Arc . . . . . 
 
 XIX. 
 
 51 
 
 Zinc Alloy (Brass) Arc 
 
 XIX. 
 
 51 
 
 Zinc Alloy (Brass) Spark .... 
 
 XIX. 
 
 51 
 
 Zinc and Tin Spark 
 
 . XVIII. 
 
 49 
 
 Zinc Arc ....... 
 
 XX. 
 
 52 
 
 Zirconium Arc ...... 
 
 XX. 
 
 53 
 
 Zirconium and Palladium Spark 
 
 XX. 
 
 53 
 
 Zirconium Spark ...... 
 
 XX. 
 
 53 
 
 INDEX TO 
 
 THE GASES. 
 
 
 Ammonia .... 
 
 
 XXV. 
 
 60 
 
 Carbonic Acid Band 
 
 
 XXX. 
 
 68 
 
 Carbonic Acid Band [SO s ] 
 
 .... 
 
 XXX. 
 
 68 
 
 „ Line 
 
 
 XXX. 
 
 68 
 
 „ Band Quartz . 
 
 .... 
 
 XXXI. 
 
 69 
 
 „ Stratification . 
 
 • • • • 
 
 XXXI. 
 
 69 
 
 „ Band and 0. Band 
 
 . • . • 
 
 XXXI. 
 
 69 
 
 „ Line and 0. Line 
 
 
 XXXI. 
 
 69 
 
 Coal Gas Band 
 
 
 XXXII. 
 
 71 
 
 „ Band Quartz . 
 
 
 XXXII. 
 
 72 
 
 „ Line 
 
 
 XXXIII. 
 
 72 
 
 „ Line and Band 
 
 
 XXXIII. 
 
 • 72 
 
 „ Band and H 
 
 , 
 
 XXXIII. 
 
 72 
 
 „ Spark in . 
 
 XXVI. XXVII. 
 
 XXXIII. 
 
 62, 72 
 
 „ Spark in, and Spark in Air 
 
 XXV. 
 
 61 
 
 Cyanogen .... 
 
 
 XXXII. 
 
 71 
 
 Ether Vapour 
 
 
 XXXIV. 
 
 74 
 
 Hydrogen Tube 
 
 . 
 
 XXVI. 
 
 61 
 
 „ in Coal Gas . 
 
 
 XXVI. 
 
 62 
 
 ,, Quartz . 
 
 
 XXVI. 
 
 63 
 
 ,, and Spark in Air . 
 
 
 XXVII. 
 
 63 
 
 „ Lines in Coal Gas . 
 
 
 XXVII. 
 
 63 
 
 Iodine Vapour 
 
 
 XXXVI. 
 
 76 
 
 „ Spark in 
 
 
 XXXVI. 
 
 76 
 
 Nitrogen Line 
 
 
 XXII. 
 
 55 
 
84 
 
 INDEX. 
 
 Nitrogen Line and Band 
 
 PLATE 
 
 XXII. 
 
 PAGE 
 
 55 
 
 » 
 
 Band .... 
 
 . XXII. 
 
 55 
 
 )) 
 
 Band Quartz . 
 
 . XXIII. 
 
 56 
 
 V 
 
 Line and Band 
 
 . XXIII. 
 
 56 
 
 V 
 
 Capillary and Bulb . 
 
 . XXIII. 
 
 56 
 
 » 
 
 Band and H . 
 
 . XXIII. 
 
 56 
 
 V 
 
 Band (Capillary) and Violet Pole . . XXIV. 
 
 57 
 
 V 
 
 Violet Pole Quartz . 
 
 . XXIV. 
 
 57 
 
 » 
 
 Violet Pole and Capillary 
 
 . XXIV. 
 
 57 
 
 n 
 
 without Magnet 
 
 . XXV. 
 
 60 
 
 V 
 
 with Magnet . 
 
 . XXV. 
 
 60 
 
 V 
 
 Line and Spark in Air 
 
 XXV. 
 
 60 
 
 V 
 
 Spark in Air and Spark in 
 
 Coal Gas . . XXV. 
 
 61 
 
 Olefiant 
 
 . XXXIV. 
 
 73 
 
 
 
 . XXXIV. 
 
 73 
 
 V 
 
 Quartz .... 
 
 . XXXIV. 
 
 74 
 
 Oxygen Band, Tube No. 1 
 
 . XXVIII. 
 
 65 
 
 
 „ Tube No. 2 
 
 . XXVIII. 
 
 65 
 
 }) 
 
 Line ..... 
 
 . XXVIII. 
 
 66 
 
 V 
 
 Band Quartz 
 
 . XXIX. 
 
 67 
 
 V 
 
 (Water Gas) 
 
 . XXIX. 
 
 67 
 
 V 
 
 Line and Band . 
 
 . XXIX. 
 
 67 
 
 U 
 
 Band and Nitrogen Band . 
 
 . XXIX. 
 
 67 
 
 Silicic Fluoride . 
 
 . XXXVI. 
 
 75 
 
 V 
 
 Quartz ..... 
 
 . XXXVI. 
 
 76 
 
 Sulphur 
 
 . XXXV. 
 
 74 
 
 Sulphuric Acid [S0 3 ] 
 
 . XXX. XXXV. 
 
 68, 75 
 
 
 Quartz .... 
 
 . XXXV. 
 
 75 
 
 Tin Chloride 
 
 . XXXVI. 
 
 76 
 
 Turpentine Vapour 
 
 . XXXIV. 
 
 74 
 
 LONDON : PRINTED By 
 
 SPOTTISWOODE AND CO., NEW-STREET SQUARE 
 AND PARLIAMENT STREET 
 
A? PAR AT Vi USED TwR SPARK SPECTRA 
 
 I 
 
 5J 
 
 V 
 
 *!A 
 
 O 
 
 ir 
 
 A* 
 
 V 
 
 .1 
 
 </T 
 
 \f* 
 
 j 
 
 r 
 
 •o* 
 
 jf 
 
 . .i 
 
 
 
 r< 
 
 r n 
 
 r 
 
 1 
 
 o? 
 
 1 
 
 < 
 
 **• 
 
 
 ?*-> 
 
 J 
 
 f 
 
 ft 
 
 V 
 
 -?T 
 
 mJ> 
 
 T3 
 
 d 
 
 O 
 
 l 
 
 U 
 
 r- 
 
 * m# 
 
 < 
 
 s*-- 
 
 
 
 (-* 
 
 u 
 
 
 *f* 
 
 e# 
 
 i 
 
 & 
 
 * 
 
 c 
 
 3 
 
 eq 
 
 W 
 
 <► 
 
 r* 
 
 
 p 
 
 -u H 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ♦ 
 
 
 
 
 
 
 
 
 
 
 
 
J. 
 
 SCALE. 
 
 AIR. FINE SLIT. 
 
 ARSENIC. SPARK 
 
JZ. 
 
 ALUMINIUM. SPARK. 
 
 ALUMINIUM. ARC. 
 
 ANTIMONY. SPARK. 
 
 ANTIMONY. ARC. 
 

 
 
 
 
 
 
 
 
BISMUTH, SPARK. 
 
 BIS M U TH. S PARK. 
 
 TELLURIUM. 
 
 BISMUTH, A RC. 
 
IV 
 
 BARIUM. SPARK. 
 
 BERYLLIUM. (iRON) ARC. 
 
 BORON. ARC. 
 
 CALCIUM.(ZINC) SPARK. 
 
YYaY V 
 
 C ADMIUM. SPARK. 
 
 CADM I U M. ARC. 
 
 CARBON POI NTS. 
 
 CARBON POINTS RULED OUT. 
 
JYaf'e W[ 
 
 SPARK IN COAL GAS. 
 
 CHROMIUM. ARC. 
 
 COBALT. ARC 
 
 COPPELR. SPARK. 
 
CHOPPER POINTS. ARC. 
 
 DIDYMIUM. arc. 
 
mr. 
 
 GOLD. ARC. 
 
 INDIUM. ARC. 
 
 IRIDIUM. ARC. 
 
 IRON. SPARK. 
 
 COPPER. 
 
J>/a£e IT. 
 
 I RON. ARC. 
 
 IRON &. SELENIUM. SPARK. 
 
.jPfate JC. 
 
 IRON, M ETEORI C. ARC. 
 
 IRON, METEORITE. ARC. 
 
 LEAD. ARC. 
 
 LEAD. SPARK. 
 
 ANTIMONY. 
 

 LEAD. SPARK. 
 
 MAGN ESIUM. 
 
 MAGNESIUM, spark. 
 
 LEAD. 
 
 MAGNESIUM. SPARK. 
 
 MAGNESIUM. ARC. 
 
MANGANESE. ARC. 
 
 MANGANESE. ARC. 
 
 MERCURY. SPARK. 
 
 MOLYBDENUM. ARC. 
 
NICKEL. ARC. 
 
 PA L LA D 1 UM. ARC. 
 
 PLATINUM. ARC. 
 
jPIate XIV. 
 
 RUTHENIUM. ARC. 
 
 SELENIUM. SPARK. 
 
 TELLURIUM. 
 
 SELENIUM. SPARK 
 
Pfate XV. 
 
 SILVER SPARK. 
 
 SILVER ARC. 
 
 ALLOY. SILVER 8c COPPER. ARC. 
 
 SOLAR SPECTRUM. 
 
P/ate XVI. 
 
 TELLURIUM. SPARK. 
 
 THALLIUM. SPARK. 
 
 INDIUM, 
 

 TITANIUM. SPARK. 
 
 T I TAN I U M . ARC. 
 
 TIN. ARC . 
 
.P fate XML 
 
 U RAN I U M . ARC. 
 
 VANADI UM. ARC. 
 
J>/ate XIX. 
 
 WOLFRAM. ARC. 
 
 YTTRIUM. ARC. 
 
 SAME. SPARK. 
 
-P/afe JDL. 
 
 ZINC. ARC. 
 
 ZIRCONIUM. SPARK. 
 
J>/bfe -XXT. 
 
 S GALE. 
 
 SOLAR SPECTRUM. 
 

N ITROG EN. 
 
 jP/ate XXH. 
 
 N LINE. 
 
 N LINE. 
 
 N BAND. 
 
 N BAND. 
 
NITROGEN. 
 
 JP/ate XXZR. 
 
 N. LI N E QUARTZ. 
 
 N . BAND. 
 
 N . BAN D QUARTZ. 
 
 N. BAND QUARTZ. 
 
 N. CAPILLARY QUARTZ. 
 
N VIOLET POLE. 
 
 Plate, xm: 
 
 N BAND CAPILLARY 
 
 N VIOLET POLE. 
 
 N V.P. QUARTZ. N V.P. QUARTZ. 
 
 N CA PI LLA RY. 
 
NITROGEN. 
 
 Xfate XW 
 
 N WITH MAGNET. N WITHOUT MAGNET. 
 
 AMMONIA. QUARTZ. 
 
 N LINE. SPARK IN AIR. 
 
 SPARK IN AIR. 
 
 S PARK IN C.G. 
 
HYDROGEN. 
 
 JP/ate XXVT. 
 
 H TUBE. 
 
 H IN COAL GAS. h LINE EXPANDED. 
 

HYD ROGEN. 
 
 jPfate XKVH 
 
 SPARK IN A ! R. 
 
 H TUBE. 
 
 S PA RK IN COAL GAS. 
 
OXYGEN. 
 
 J>/ate-XmiL 
 
 0 BAND. TUBE N? I. 
 
 0 BAND. TUBE N 92. 
 
 0 LINE. 
 
OXYGEN. 
 
 -XXZX 
 
 0 BAND. QUARTZ. 
 
 WATER GAS. QUARTZ. 
 
 N BAND. 
 
 0 BAND. 
 
 0 BAND. QUARTZ. 
 
 0 LI N E QUARTZ. 
 
CARBONIC ACID. 
 
 PfaJe XXK. 
 
 5.03. (FOR COMPARISON.) 
 
 C.02. LINE. 
 

 
 I 
 
 
 
CARBONIC ACID. 
 
 S>/ate XXXI. 
 
 C.O 2 STRATIFICATION. C.02 BAND. QUARTZ. 
 
 C. 0 2 LINE. C. 02 BAND. 
 
 0. LINE. 
 
 0. BAND. 
 
COAL GAS. 
 
 J>£ate XXX7I. 
 
 COAL GAS BAND. 
 
 CYAN OGEN. 
 
 C.G. BAND. QUARTZ. 
 

 
COAL GAS. 
 
 J>/ate XXX 721 
 
 C.G. LINE. QUARTZ. 
 
 C.G. BAND. 
 
 C.G. BAND. 
 
 H 
 
 SPARK IN C.G. 
 
OLEFIANT GAS. 
 
 J J /ate XXXIV 
 
 I 
 
 l 
 
 i 
 
 C2. H4. 
 
 SAM E. 
 
 TURPENTINE VAPOUR. 
 
 ETHER VAPQUR. 
 
SULPHUR. 
 
 jP/trte XXXV. 
 
 SULPHUR. 
 
 S.03. QUARTZ „ 
 
SILICIC FLUORIDE. 
 
 Mate xmr. 
 
 S L.F4. 
 
 SAM E . QUARTZ. 
 
 TIN CHLORIDE . QUARTZ. 
 
 SPARK IN 
 
 IODINE VAPOUR. QUARTZ. I ODI N E VAPOU R . 
 


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
DRAPER 
 
 Extra plate. 
 
 & £ 
 
 a > 
 
 03 
 
 <b -R 
 u o 
 SD © 
 
 o 
 
 CD 
 
 CD 
 
 02 
 
 ■d si 
 
 x-N .t5 CD 
 
 10 £ .g 
 
 £ 
 
 d 
 
 35 
 
 d 
 
 .£p ^ 
 
 d 
 
 d 
 
 d 
 
 o 
 
 CD 
 
 Pd 
 
 pc. 
 
 d 
 
 I 
 
 if 
 
 W 
 
 d 
 
 d 
 
 d 
 
 d 
 
 2 
 
 d 4 
 
 Q 
 
 d 
 
 d 
 
 d 
 
 PP 
 
 d 
 
 -r 
 
 o 
 
 O 
 
 03 
 
 02 
 
 1-^ 
 
 O 
 
 Pi 
 
 a 
 
 a 
 
 d 
 
 33 
 
 
 
 o 
 
 R 
 
 03 
 
 rd 
 
 ’P 
 
 d 
 
 R 
 
 4s 
 
 d 
 
 pc 
 
 CD 
 
 d 
 
 03 
 
 &X) 
 
 03 
 
 a 
 
 CD 
 
 02 
 
 d 
 
 d 
 
 R 
 
 03 
 
 d 
 
 £ 
 
 o 
 
 R 
 
 -R 
 
 CD 
 
 02 
 
 «2 
 
 Id 
 
 © 
 
 bD 
 
 O 
 
 -R 
 
 O 
 
 s 
 
 
 d 
 
 03 
 
 d 
 
 o 
 
 •2 
 
 
 ,d 
 
 CD 
 
 
 33 
 
 o 
 
 fi 
 
 03 
 
 R 
 
 d 
 
 g 
 
 _d 
 
 d 
 
 
 d 
 
 d 
 
 &D 
 
 '-+3 
 
 o 
 
 o 
 
 -r 
 
 rC> 
 
 d 
 
 i 
 
 03 
 
 b/l 
 
 O 
 
 -r 
 
 J§ 
 
 o 
 
 *o* 
 
 R 
 
 d 
 
 d 
 
 *R 
 
 d 
 
 a 
 
 s 
 
 R 
 
 -R 
 
 03 
 
 rN 
 
 o 
 
 J>» 
 
 "33 
 
 > 
 
 CD 
 
 JK 
 
 *R 
 
 03 
 
 CD 
 
 CD 
 
 'o 
 
 .a 
 
 © 
 
 R 
 
 d 
 
 02 
 
 Dd 
 
 CD 
 
 33 
 
 d 
 
 o 
 
 -R 
 
 d © 
 
 CD CD 
 
 « 02 
 
 d 
 
 05 
 
 d 
 
 CD 
 
 a 
 
 o 
 
 o 
 
 r 
 
 d 
 
 d O 
 , Ph 
 
 a Pd 
 
 o 
 
 <33 
 
 CD 
 
 m 
 
 M 
 
 d 
 
 CD 
 
 02 
 
 33 
 
 DC 
 
 <13 O 
 R 03 
 
 a cd 
 
 a 
 
 2 © 
 
 p c ^ 
 
 d 
 
 &o >-3 
 
 <A d 
 
 o .5 d 
 
 DC O 
 O ^ 
 
 a >» 
 
 "T rd 
 
 ° d 
 
 a J3 
 
 m r 
 
 •d o 
 Ph £