ya pare My ‘ ‘eu ee ee vase a= * 
, : ~e Leen 
546 
The telescope was then set to the angle corresponding to this 
approximate wave-length for the spectrum of the fourth order. 
The lower half of the slit was closed by a shutter, and the 
photographic slide having been adjusted for level, the plate was 
exposed to the light which came through the upper half of the 
slit, and gave an image of the lines in the lower half of the 
field. When this exposure was completed, the photographic 
slide was turned round through 180° about the axis of the tele- 
scope, so as to bring to the top that part of the sensitive plate 
which had been before lowest. It was then exposed a second 
time, and thus two images of the same line were impressed on 
the plate, which were necessarily at equal distances on either 
side of the point where the axis of the telescope met the plate. 
By a subsequent measurement with a micrometer under a micro- 
scope of the distance between the two images, and the conversion 
of this distance into angular measure, a correction was found, 
which was added to, or subtracted from, the reading of the circle 
to get the exact deviation of the ray producing the line under 
observation. Another photograph of the same line was next 
taken in the same way as before, except that the tele cope was 
placed at the corresponding angle on the other side of the colli- 
mator. From the two angles thus found, the wave-length of the 
line was calculated. The process was repeated three or four 
times for each line, and the mean wave-lengths thus found for 
carbon lines were 2296°5, 2478°3, 25090, 2511°9, 283673, and 
2837°2. The wave-lengths of the remaining lines were obtained 
by interpolation from measures of photographs on which the iron 
as well as the carbon lines were shown. ‘The wave-lengths of 
the iron lines used in the interpolations were deduced from 
photographs taken with the grating in the Same way as that 
above described for the carbon lines. The wave-lengths thus 
formed for the remaining carbon lines are given in the table 
below. 
Table of Carbon Lines 
Authors, Colour. Wave-length. Intensity. 
6583°0 
6577'5 
5694'1 
5660°9 
5646°5 
5638°6 
53790 
5150°5 
5144/2 
5133'0 
4266'0 
Red Da 
Orange. 
Angstrom and Thalén ¢ 
Yellow ...| 
Green 
UB ANWAR eH D 
Indigo ... I, diffuse 
= 
3919°3 
3876°5 4; ” 
|| 29950 | 4, very diffuse 
2968 '0 5) ” 
2837°3 2 
2836°3 2 
2746'5 3, very diffuse 
27332 6, ” ” 
26407 | 4 5 » 
2541°5 | 
2528°2 
2523°6 
2518°7 
25158 
2514'0 
25119 
2509°0 
2506°6 
| 2478°3 
Ultra- 
Liveing and Dewar violet, 
WenwhuhuUmu dD 
2206°5 
They have also examined the spectrum of Swan’s incandescent 
lamps. So long as the carbon thread is unbroken, it emits a 
continuons spectrum, on which neither bright nor dark lines are 
visible. By gradually increasing the number of cells in the 
battery, until the thread gave way, they found at the instant of 
fracture, for a small fraction of a second only, that a set of 
fintings in the green appeared. In some of those lamps, when 
NATURE 
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5 ‘ wey ¢ 
m1 ~2 
' 
ke eRe 
[April 6, 1882. 
the current was nearly as much as the carbon thread would bear 
without rupture, a sort of flame appeared in the lamp. On 
examining the spectrum of this flame, it gave the flutings of 
carbonic oxide very distinctly. Closer examination showed that 
this flame was strongest about the junction of the carbon thread — 
with one of the conducting wires, and that, on reversing the 
current, it shifted from one wire to the other, and the wire about 
which it appeared was always the positive electrode. In fact, — 
the flame was the glow of the positive pole attending a discharge 
in rarefied gas ; when the resistance of the carbon thread became 
too great in proportion to the intensity of the current, the dis- 
charge began to occur through the rarefied atmosphere within 
the envelope of the lamp. The spectrum showed that this 
atmosphere contained carbonic oxide. 
By interposing differeut flames between the incandescent lamp 
and the slit of the spectroscope, they have made some compari- — 
sons of the probable temperatures of the flames and filament. 
When the flame was that of a Bunsin burner, in which was a 
platinum wire with sodium carbonate, the yellow sodium lines 
were seen bright above and below the continuous spectrum of — 
the carbon thread, but reversed where they crossed it. When 
lithium was substituted for sodium in the flame, the ret lithium 
line was also seen bright above and below the continuous spec- 
trum, but reversed where they crossed it. When an oxyhydro- — 
gen jet was substituted for the Bunsen burner, and sodium car- 
bonate held in it, the yellow sodium lines were not only bright above 
and below the continuous spectrum of the carbon, but showed as 
bright lines where they crossed it; in fact, they were conspicu- 
ously brighter than the carbon. When coal-gas was substituted 
for hydrogen in the jet, the same appearance presented itvelf, 
only the sodium lines were not so much brighter than the carbon 
as they were before. Fifty Grove’s cells were used with the 
incandescent lamp, which were as many as could be used with- 
out danger of rupturing the threads. When barium chloride 
was held in the hydrogen flame fed with only a little oxygen, the 
bright green line of barium (wave-length 5534) was well seen 
above and below the continuous spectrum, but could not be 
traced either bright or dark across it. When a flame of cyano- 
gen burning in air was interposed, the bright bands of that — 
flame could be seen above and below the continuous spectrum, 
but could not be traced either bright or dark across it, When 
sodium carbonate was held in this flame, the yellow sodium lines 
were seen feebly reversed where they crossed the spectrum of 
the incandescent lamp. They infer from these experiments, that 
the emissive power of the carbon thread for light of the refran- 
gibility of the D lines is nearly balanced by that of sod.um in 
the flame of cyanogen burning in air, but is sensibly less than 
that of sodium, at the temperature of a jet of coal-gas and 
oxygen, much less than that of sodium in the oxyhydrogen jer. 
This seems to render it probable that the temperature of the in- 
candescent thread is not far different from that given to sodium 
by a cyanogen flame burning in air, but is less than that of an 
oxyhydrogen flame, though this does not necessarily fullow fromthe 
experiments, inasmuch as the radiation of the sodium is so much 
more limited as to range than that of the carbon, When a 
Bunsen burner or a gas blowpipe flame was interpoSed between 
the lens and slit, no reversal of the hydrocarbon bands cv.uld be 
seen. When magnesium was burnt between the Jens and slit, 
the magnesium lines (4) were seen bright, eclipsing the carbon. 
Possibly the smoke of magnesia may have considerably helped 
to eclip:e the light of the carbon. 
Chemical Society, March 16.—Prof. Roscoe, president, in 
the chair—The following papers were read :—On valency, by 
Dr. Armstrong, The bulk of this paper is taken up with a con- © 
sideration of the valency of carbon in the hydrocarbons, and 
especially with the formulz proposed by Kekule and others for 
benzene. The author concludes that a simple hexagon in which 
carbon acts practically as a triad, agrees best with the various 
reactions of benzene.—Contributions to the chemical history of 
the aromatic derivatives of methane, by R. Meldola. The author 
investigates the action of benzyl chloride upon diphenylamine, 
and the action of oxidising agents upon the product. The sub- 
stance thus produced is a green dye, ‘‘viridin,”” which by the 
action of strong sulphuric acid forms sulphonic acids, the alkaline 
salts of one of these acids dyes woollen fabrics from an alkaline 
bath. This colour is the chloride of a base which the author bas 
proved to be diphenyl diamidotriphenyl carbinol.—On some 
constituents of resin spirits, by G. H. Morris. —The lower frac- 
tions of resin spirit yield on standing a crystalline substance. 
This body has been examined by the author. — It has the formula 
