1869.] On some Recent Spectroscopic Researches. 221 



A fourth line has been detected in spectrum of the nebula 

 of Orion, by Lieut, Herschel, in India, which appears to agree in 

 position with a fourth hne seen by the writer in the nebula 18 H. 

 IV., and which is probably coincident with a line of hydrogen. 

 The fourth line in the nebula of Orion has been also seen by Lord 

 Eosse and by Professor Wmlock, of the Harvard Observatory. 

 These observers also suspect the existence of some other extremely 

 faint lines. 



The writer expects after a short time to continue his researches 

 on the motions of the stars, and on the spectra of the nebulae, with 

 more powerful instruments than those he has hitherto employed. 



In the years 18G6 and 1867 the writer observed the spectra 

 of two small comets. The spectra of both these objects were 

 compound, showing that part of the hght was reflected and part 

 probably emitted by the cometary matter. Last year two comets 

 of superior brightness appeared, which permitted a more complete 

 analysis of their light to be made. 



The first of these was the return of the well-known comet of 

 Brorsen, which was examined from May 2 to May 13. The second 

 comet, a still brighter one, was discovered independently by Win- 

 necke and by one of the assistants at the observatory of Marseilles. 

 This comet was observed in June. 



The spectra of these comets, which consist mainly of three 

 bands of light, are represented in Fig. 2 of the Plate. These sets 

 of bands, though they occur in similar parts of the spectrum, are 

 far from being identical. It may be that from the faintness of 

 Brorsen's comet the bands could not be traced so far; but even 

 if it were so, this circumstance would not explain the considerable 

 difference of position which exists between the bright well-marked 

 beginnmg of the middle band. The positions of the bands in the 

 spectrum are shown by the solar spectrum which is placed at the 

 head of the diagram. 



The morning after the observations of comet II., the writer was 

 surprised to find that its spectrum appeared to agree exactly with 

 one of a series of the spectra of carbon, as obtained from the 

 decomposition of various carbon compounds which the writer had 

 prepared a few years before. Two of these spectra are given in 

 Fig. 2. It will be seen that though the light emitted by the 

 carbon in both cases consists of the same refrangibilities, in the 

 upper spectrum of the diagram the bands in the sjjectrum are 

 resolved into narrow bright lines, while in the second spectrum, 

 under similar conditions of the slit and of temperature, the bands 

 remain undivided. These spectra are given not as exclusively pecu- 

 liar to the particular combinations of carbon from which they were 

 obtained, but as types of the spectra of a wide range of carbon 

 compounds. The upper spectrum of bright fines was obtained 



