196 Mr. J. N. Lockyer. On the Classification [Jan. 10, 



the spectroscope was not directed on the nucleus itself, but on parts 

 of the comet close to it." He further states that he observed a bright 

 band fading towards the blue, to which reference has been made 

 above, and for which he obtained the wave-length 613. This we have 

 seen was probably a contrast band due to the dark iron fluting at 615. 

 From this date until the comet was lost to view no further change of 

 note took place in the spectrum of this comet. 



On June 2nd Vogel observed dark bands in the spectrum of Comet 

 Wells,* but suggests that they might have been due to atmospheric 

 absorption. He says: "The dark absorption-bands, which are still 

 visible in the comet's spectrum, may probably have their origin in 

 our atmosphere, the absorbent action of which, at the inconsiderable 

 height of the comet above the horizon, is very powerful." 



Again. Vogel states that dark absorption-bands were possibly 

 present on July 1st, the perihelion passage occurring on the 10th of 

 June. Vogel's suggestion is very important, but since no wave- 

 lengths were determined, it is not possible to say how far it is sup- 

 ported by the facts. 



It might, on first consideration, be expected that the changes in 

 the spectrum of a comet as it approaches the sun must be perfectly 

 continuous. The spectrum of Comet Wells, however, was a case in 

 which the changes in the spectrum were apparently discontinuous. 



On May 30th and 31st, as already stated, dark bands were observed 

 by Mr. Maunder,f which were in all probability due to manganese 

 absorption. 



Between these two dates, i.e., on May 28th, Copeland observed a 

 bright part at 558 which was clearly due to manganese radiation. I 

 have already shown that manganese radiation occurs further from 

 perihelion than manganese absorption. The Greenwich observation 

 of absorption on May 20th, whilst radiation occurs on May 28th, 

 nearer to perihelion, is therefore apparently a discontinuity. 



I showed in the Bakerian Lecture that variable stars may be 

 explained by considering the meeting of two meteor-swarms and the 

 consequent increase of temperature due to the impacts. Comets, 

 apparently, go through similar changes and suddenly increase in 

 brightness, as I show in another part of the paper. The explana- 

 tion is probably the same for comets as for stars, and Comet 

 Wells affords a good example of the fact. It is most probable that on 

 May 20th the comet met another meteor-swarm in its orbit, and an 

 increase of temperature took place ; this meant manganese absorption, 

 and this was what was observed. 



All the other changes in the spectrum were perfectly continuous as 



* ' Astr. Nachr./ No. 2437. 



t l Greenwich. Observations,' 1882, p. 34. 



