SCIENCE. 
29 
may be termed, was compared with the corresponding 
chemical flames, that is, with the oxhydrocarbon and oxy- 
nitrocarbon jets of gas burning in air. The characteristic 
lines were present in every case. Lastly, by similar inter- 
observation a few other lines in the electric spectrum of 
the hydrocarbon were proved to be due to the presence of 
hydrogen, and several others in the electric spectrum of the 
nitrocarbon to be caused by the presence of nitrogen. 
“ The spectrum under investigation having then been 
obtained in one case when only carbon and hydrogen were 
present, and in another when all elements but carbon and 
nitrogen were absent, furnishes to mv mind, sufficient evi- 
dence that the spectrum is that of carbon.” 
“ But an interesting confirmation of the conclusion just j 
stated is found in the fact that the same spectrum is ob- 
tained when no other elements but carbon and oxygen are 
present, and also when carbon and sulphur are the only 
elements under examination. And first with regard to 
carbon and oxygen. Carbonic oxide burned in air gives a 
flame possessing a continuous spectrum. A mixture of 
carbonic oxide and oxygen burned from a platinum-tipped 
safety-jet also gives a more or less continuous spectrum, 
Out the light of the spectrum has a tendency to group itself 
in ill-defined ridges. Carbonic oxide, however, ignited by 
the electric discharge in a semi-vacuous tube, gives a 
bright sharp spectrum. This spectrum was proved, by the 
simultaneous method of observation, to be that of carbon 
plus the spectrum of oxygen. With regard to carbon and 
sulphur almost the same remarks may be made. Bisul- 
phide of carbon vapor burns in air with a bluish flame. Its 
spectrum is continuous. Mixed with oxygen and burned 
at the safety-jet, its flame still gives a continuous spectrum, 
though more distinctly furrowed than in the case of car- 
bonic oxide ; but when ignited by the electric current its 
spectrum is well defined, and is that of carbon plus the 
sulphur. That is to say, it is the spectrum of carbon plus I 
the spectrum that is obtained from vapor of sulphur when 
ignited by the electric discharge in an otherwise vacuous 
tube.” 
“ Having thus demonstrated that dissimilar compounds 
containing carbon emit, when sufficiently ignited, similar 
rays of light, I come to the conclusion that those rays are 
characteristic of ignited carbon vapor, and that the pheno- 
mena they give rise to on betng refracted by a prism is the 
spectrum of carbon.” 
This question was next taken up by Morren. He wrote 1 
(in 1865) fifteen years ago : 
“A la reception de cet interessant et substantiel Memoire, 
j’avoue que je ne regardai pas d’abord comme fondde 
{’assertion de M. Attfield. . . . 
“ Je me suis done mis au travail avec la pensee precon- 
gue de combattre l’assertion emise par le savant anglais ; 
mais pas du tout, il resulte au contraire des experiences 
auxquelles je me suis livre que M. Attfield a raison, et que 
e’est bien la vapeur du carbone qui donne le spectre indi- 
qu6 plus haul. . . . 
“ Si on fait bruler le cyanogene au moyen du chalumeau 
a deux courants, en faisant arriver au centre de la flamme 
du cyanogene un courant d’oxygene tres-pur (cette condi- 
tion est indispensable), on voit se produire un des plus 
beaux effets de combustion possible, et cette experience 
est certainement une des plus magnifiques qu’ on puisse 
r6aliser sur la combustion des gaz. II se produit, au milieu 
de la flamme rosd-viol&tre du cyanogfene, une boule d’un 
blanc vert 6boulissant qui rappelle la lumifere electrique 
produite par le courant de la pile entre deux charbons de 
cornue. Si le spectroscope est dirig6 sur cette brillante 
lumi&re, on apergoit, avec une splendeur merveilleuse, le 
meme spectre de la partie bleue des flammes hydrocar- 
burdes. Ainsi done e’est du charbon seul, mais k l’etat de 
vapeur, qui forme cette boule brillante qui plus loin, par son 
union avec l’oxygene, va passer k l’dtat d’acid carbonique. 
Du reste ce spectre n’est pas seul ; avec lui on voit, mais 
trds-effacd, le spectre special du cyanogdne, et celui-ci tend 
de plus en plus it disparaitre & mesure que f’oxygdne arrive 
avec plus d’abondance et brule de mieux en mieux le 
cyanogdne. Quant au spectre de l’azote, on ne l’apergoit 
pas dans cette vive lumiere. Le magnifique dclat de ce 
beau spectre, le plus beau qu’il m’ait ete donne de voir, 
permet de bien comprendre l’aspect creuse et ombre avec 
une teinte croissante qu’on remarque dans les parties qui 
n’ont pas de raies brill.antes, et meme entre ces raies.” 
Four years later Dr. Watts devoted himself to this sub- 
ject, and in 1869 his work was thus summarized by 
himself 
“ This spectrum [that consisting of the flutings in ques- 
tion] may be obtained from the flame of any hydrocarbon, 
though in many cases, owing to the faintness of the spec- 
trum, only some of the groups can be recognized. In the 
flame of an ordinary Bunsen burner d and e are easily seen, 
y and f are much fainter, and the red group can not be 
detected. 
“ This spectrum is proved to be that of carbon, inasmuch 
as it can be obtained alike from compounds of carbon with 
hydrogen , with nitrogen , with oxygen , with sulphur , and with 
chlorine. I have obtained it, namely, from each of the fol- 
lowing compounds : olefiant gas, cyanogen, carbonic oxide, 
naphthalin, carbonic disulphide, carbonic tetrachloride, 
amylic alcohol, and marsh-gas.” 
That these conclusions, successively arrived at by Att- 
field, Morren, and Watts, are sound, I shall show in my 
next notice. — (“ Nature .”) J. Norman Lockyer. 
( To be continued.) 
VALUE OF BISULPHIDE OF CARBON IN 
MICROSCOPICAL DEFINITION. 
At the last meeting of the R. M. S. (the last of the ses- 
sion), on the gth instant, a paper was read by Mr. J. W. 
Stephenson, treasurer of the society, discussing the relative 
visibility of objects mounted in media of different re- 
fractive indices. Some time ago, Mr. Stevenson called 
attention to the fact that if diatoms were mounted in bisul- 
phide of carbon their fine structure was rendered far more 
visible than when mounted in Canada balsam. Since the 
explanations given by Professor E. Abbe on the intro- 
duction of his new expression for apertures (i.e., “ numeri- 
cal aperture ”), by which the relative resolving power of 
different objectives is seen by the reading of the numerical 
apertures, Mr. Stephenson has come to the conclusion (in 
which he stated Professor Abbe agreed with him) that the 
visibility of objects is dependent on the difference of the re- 
fractive indices of the object observed and the medium in 
which it is placed. This he illustrates as follows : 
Taking the refractive index of air as 1.0, and diatomace- 
ous silex as 1.43, the visibility may be expressed by the 
difference 43. 
Mr. Stephenson gave the following table 
Visibility of silex 
(Refr. index = 1.43). 
= i -33 • ■ 
10 
= i -54 • ■ 
11 
= 1.68 . . 
25 
= i -75 • • 
32 
= 2.10 . . 
67 
Refractive indices 
(taken approximately). 
Water 
Canada balsam . . 
Bisulphide of carbon 
Sol. of sulphur in bisulph. 
,, phosphorus ,, 
These data relating to visibility must, doubtless, be re- 
garded in direct connection with the numerical aperture of 
the objectives of the illumination, as pointed out by Mr. 
Stephenson. He gave practical demonstrations of the views 
explained in his paper by exhibiting several slides mounted 
in the different media. I mention one slide of P leurosigma 
Elongatum, mounted in sol of phosphorus in bisulphide of 
carbon, as presenting to the eye the strongest image that has 
come under my notice. According to Mr. Stephenson’s 
theory, the visibility under these conditions would be about 
six times as great as that of the same object mounted in bal- 
sam. Is it possible to induce our professional object- 
mounters to take up the subject? Surely there arc many 
amateurs of fine definition who would like to see the condi- 
tions of visibility pushed to the highest point, and who 
would amply repay the modicum of exertion needed to 
produce them. 
1 A rtnaies de Chimie et de Physique, 4 serie, tome iv. p. 309, 312, 
1 Phil. Mag., October, 1869. 
