36 



the same effect, it is quite unphilosophical to resort to a 

 special hypothesis. Encke's comet ought not to be quoted 

 as evidence of the existence of such a medium until electric 

 disturbance is shown by calculation to be insufficient to 

 account for the observed diminution of period. 



" On Cometary Phenomena/' by Professor Osborne Rey- 

 nolds, M.A. 



In all comets which have been observed through powerful 

 telescopes there is an action going on which appears to be 

 the result of evaporation. Jets of something like vapour 

 are seen to issue from what is supposed to be a solid nucleus 

 on that side which is toAvards the sun. 



No such signs of evaporation are observed on the planets, 

 nor is there any phenomenon, that we are aware of, which 

 can be compared with this taking place on our earth. At 

 first sio'ht it seems strange that the sun should act to more 

 effect on such small bodies as comets than it does on the 

 larger bodies, even when the lattei* are nearer to it than the 

 former. When, hoAvever, we come to look closer, I think 

 good reason may be given for this ; and I think that the 

 difference of evaporation on the earth and on a comet insiy 

 probably be the cause of electrical phenomena existing on 

 the latter which certainly do not exist on the earth, and 

 that the relation between the motion of the comet and the 

 evaporation which might be expected to take place is 

 precisely that which is observed between the motion and 

 those appearances which I would explain on an electrical 

 hypothesis. 



The first thing to be done is to take notice of the following 

 facts : — 



1. Comets move in very eccentric orbits, whereas the 

 planets move in orbits nearly circular. 



2. Comets are supposed to be much smaller than the 

 planets. 



