1889.] of the various Species of Heavenly Bodies. 187 



case of Winnecke's and Brorsen's Comet, to which reference has 

 already been made, we have evidence to show that this spectrum 

 appeared as the cool carbon spectrum disappeared. 



In Winnecke's Comet (perihelion passage June 25th) Wolf's 

 observations on the 17th of June showed the cool carbon spectrum, as 

 I have already stated. 



On the 22nd of June Huggins* recorded three bands at wave- 

 lengths 469, 517, and 559. Nothing was recorded near 483, the 

 position of the characteristic cool carbon band, so that we are justified 

 in assuming that the low-temperature condition had changed. The 

 517 fluting agrees almost perfectly with the principal hot carbon 

 fluting at 51G'4. We have seen that the variability of the citron band 

 is one of the principal features of cometary spectra, so that the apparent 

 discrepancy in its position is of no importance here. 



The band at 469 was in all probability the hot carbon band which 

 begins at wave-length 474, but has its maximum of brightness at 

 about 468. It is very probable, therefore, that during the time which 

 elapsed between the observations of Wolf and Huggins the spectrum 

 of the comet had changed from that of cool carbon to that of hot 

 carbon. This change is precisely what we should expect, Huggins's 

 observation being the one nearest to perihelion, when the comet was 

 hottest. 



Again, we have evidence of the change from the spectrum of cool 

 carbon to that of hot carbon in Brorsen's Comet (1879), the perihelion 

 passage of which occurred on the 30th of March. Konkoly's observa- 

 tion on the 25th of March showed the characteristic cool carbon 

 fluting afc 483. Later observations were made by Bredichinf on the 

 28th, 29th, and 31st March and April 2nd. Eight observations of the 

 citron band gave the wave-length as 551 '3. Three measurements of 

 the principal green band gave 510'2 as the mean wave-length, and three 

 of the blue band gave 465'5 as its wave-length. Obviously, there was 

 no cool carbon in the comet spectrum on any of these dates, which are 

 all nearer the date of perihelion passage than the date of Konkoly's 

 observations. It may be remarked that if the blue band is corrected 

 as we have to correct the first green one to obtain the true wave- 

 length (516'4), we obtain a wave-length not far removed from that of 

 the hot carbon band, 474. The apparent displacement of the citron 

 carbon band has before been referred to. As in the case of 

 Winnecke's Comet then, as Brorsen's Comet (1879) approached 

 perihelion, its spectrum changed from that of cool carbon to that of 

 hot carbon. 



In Wclls's Comet, as already stated, there was, in all probability, the 

 line spectrum of carbon. All the detailed spectroscopic observations 



* ' Phil. Trans.,' vol. 158, p. 556. 

 f ' Astr. Nachr.,' No. 2257. 



