342 ANNUAL OF SCIENTIFIC DISCOVERY. 



nebulse, which is coincident with the double line in the spectrum 

 of nitrogen. 



This comet, then, resembles the others above named in this re- 

 spect, that the nucleus and part of the coma shine by their own 

 light, with the difference that nearly the whole of the coma of 

 Brorsen's comet is self-luminous. — Comjotes Rendus. 



The conclusion of Secchi, from spectrum analysis, that most of 

 the cometary light belongs to these bodies, and is not the reflected 

 light of the sun, from the absence in the spectrum of this comet 

 of the lines of Fraunhofer, and the presence of luminous bands, 

 is doubted by M. Prazmowski. He maintains that the results of 

 spectroscopic observations are greatly modified by the width of 

 the slit of the spectroscope ; if the object is feebly illuminated, 

 even a colored band of paper, the slit must be of a certain width 

 to render the spectrum visible. If the angular opening surpasses 

 the angle which the widest Fraunhofer lines subtend, not the least 

 trace of these will be seen, and yet we know in the experiment 

 that the light is the reflected light of the sun ; the lines of Fraun- 

 hofer exist in the spectrum, but we do not see them. He thinks, 

 therefore, that the light of Brorsen's and Donati's comets has a 

 solar origin. — Comptes Eendus, June 1, 1868. 



Spectrum of Comet ii., 1868. — Mr. Huggins, in a paper commu- 

 nicated to the Royal Society in July, 1868, describes the appear- 

 ance of this comet on June 22d, as consisting of a nearly circular 

 coma, becoming suddenly brighter toward the centre, where 

 there was a nearly round spot of light; a tail was traced for 

 nearly a degree. Under the spectroscope, with two prisms of 60°, 

 the light was resolved into three broad, bright bands, — the bright- 

 est commencing at about h and extending nearly to F, — and then 

 beginning at a distance beyond F, rather greater than half the in- 

 terval between h and F, — the third about midway between D and 

 E. In the two more refrangible of these bands the light was bright- 

 est at the less refrangible end, and gradually diminished toward 

 the other limit of the bands ; the least refrangible of the three bands 

 did not exhibit a similar gradation of brightness ; they could not 

 be resolved into lines, nor was any light seen beyond them toward 

 the violet and the red. He found this spectrum to agree exactly 

 with a form of the spectrum of carbon which he had observed 

 in 1864, when an induction spark is taken in a current of olefiant 

 gas. This resemblance of spectra suggests the identity of the 

 substances by which the light was emitted in both cases. Some 

 comets have approached sufficiently near the sun to acquire a tem- 

 perature high enough to vaporize carbon ; as to others, we do not 

 know the conditions under which even a gas permanent at the 

 temperature of the earth could maintain sufficient heat to emit 

 light. He gives reasons why cometary light cannot be considered 

 as of a phosphorescent character. The spectrum shows that the 

 color of this comet was bluish-o-reen. If carbon be the substance 

 of some comets, if incandescent in the solid state, or reflecting in 

 a condition of minute division the light of the sun, this substance 

 would afford a light which, in comparison with that emitted by 

 the luminous vapor of carbon, would appear j'ellowish or ap- 



