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 

 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, 

 But 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 

 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 being 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 fondee 

 1'assertion de M. Attfield. . . . 



" Je me suis done mis au travail avec la pensee precon- 

 cue de combattre 1'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- 

 que plus haut. . . . 



" 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 

 realiser sur la combustion des gaz. II se produit, au milieu 

 de la flamme rose'-violdtre du cyanogene, une boule d'un 

 blanc vert eboulissant qui rappelle la lumiere electrique 

 produite par le courant de la pile entre deux charbons de 

 cornue. Si le spectroscope est dirige sur cette brillante 

 lumiere, on apercoit, avec une splendeur merveilleuse, le 

 meme spectre de la partie bleue des flammes hydrocar- 

 bur^es. Ainsi done e'est du charbon seul, mais a I'etat de 

 vapeur, qui forme cette boule brillante qui plus loin, par son 

 union avec l'oxygene, va passer a I'etat d'acid carbonique. 

 Du reste ce spectre n'est pas seul ; avec lui on voit, mais 

 tres-efface, le spectre special du cyanogene, et celui-ci tend 

 de plus en plus a disparaitre a mesure que l'oxygene arrive 

 avec plus d'abondance et brule de mieux en mieux le 



1 Annates de Chimie et de Physique, 4 scrie, tome iv. p, 301;, 312. 



cyanogene. Quant au spectre de l'azote, on ne l'apercoit 

 pas dans cette vive lumiere. Le magnifique eclat 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 brillantes, 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 6 and e are easily seen, 

 y and / 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: defiant 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 9th 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 : — 

 Refractive indices Visibility of silex 



(taken approximately). (Refr. index = 1.43). 



Water . . . . . . = 1.33 • • 10 



Canada balsam . . . . = 1.54 . . n 



Bisulphide of carbon . . = t.68 . . 25 



Sol. of sulphur in bisulph. . . = 1.75 . . 32 

 ,, phosphorus ,, . . =2.10 . . 67 



These data relating to visibility must, doubtless, be re- 

 girded 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 Pleurosigma 

 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 are 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 Phil. Mag., October, 1869. 





