1889.] of the various Species of Heavenly Bodies. 



181 



Fig. 8 shows the probable origins of some of the lines in the 

 spectrum of the Great Comet of 1882. The horizontal line which 

 runs through the spectrum represents continuous spectrum due to the 

 bright nucleus. 



The Perihelion Conditions of Comet Wells. 



Again, in Comet Wells almost the same phenomena were exhibited 

 as in the Great Comet of 1882. In this case the perihelion passage 

 occurred under such conditions that the spectrum of the comet could 

 not be satisfactorily observed on account of the interference of day- 

 light. Detailed observations, however, were made when the comet 

 was near perihelion and its temperature sufficiently high to give 

 bright lines. The following table gives the bright lines and bands 

 with their probable origins, observed in the comet on May 31st, 1882, 

 by Copeland* (perihelion passage June 10th). 



No origin can at present be suggested for the brightness at 573'8. 

 Copeland only observed it on May 31st, and then noted it as being- 

 but " slightly brighter than neighbourhood." 



Fig. 9 shows how the spectrum of Comet Wells, on May 28th, can 

 be very closely imitated by integrating the lines and flutings in the 

 above table. 



Fig. 10 shows a similar comparison for May 31st, when the comet 

 was a little hotter. In both cases the low temperature fluting of 

 magnesium was recorded; it probably had its origin in some cool 

 part of the comet which was projected on the slit at the same time as 

 the nucleus. 



* ' Copernicus,' vol. 2, p. 229. 



