504 MR BALFOUR STEWART ON SUN-SPOTS. 



The hypothesis herein advocated appears, therefore, to be capable of explain- 

 ing, we may say, all the phenomena both of sun-spots and double stars, so far as 

 these are at present known. 



In conjunction with Professor Tait, the author would beg to make the follow- 

 ing suggestion before concluding this paper: — These phenomena,* appear to lead 

 to the conclusion, that when celestial bodies approach each other, there is an 

 evolution of light. Let us compare this with the analogous fact, that when atoms 

 approach each other we have the same result ; and we are conducted to the belief, 

 that one great law acts in all these cases, although its modus operandi is no doubt 

 circumstantially different in each. (Added 9th April.) We may also be permitted 

 to state our impression, that in the case of atoms, as in that of systems, it is 

 perhaps the largest body which radiates most, for when metals of which the 

 combining equivalent is generally large, unite with oxygen for instance, which 

 has a small equivalent, it is the vibration of the metallic particle, and not of 

 the oxygen, which give a character to the light emitted. Possibly the following 

 may be the explanation of this fact : — 



The idea of the constitution of ether, which involves the fewest assumptions, 

 is that which makes it a medium by means of which a body in motion parts with 

 its motion to neighbouring bodies, and the phenomena of percussion perhaps 

 entitle us to assume, that this property which a body has of stopping the motion 

 of a neighbouring body depends on the size of the former, and its distance from 

 the latter. 



When, therefore, a small body is in violent motion near a large one, the pre- 

 ferential radiation of the motion of the former towards the large body above its 

 radiation to the surrounding bodies will be very great. But when this motion 

 has once been absorbed by the larger body, and taken to a great extent, the shape 

 of heat since energy as well as momentum must be preserved, the preferential 

 radiation of this towards the small body, as compared with its radiation to neigh- 

 bouring bodies, will not be great, but it will radiate nearly equally on all sides. 



The large body will thus, as it were form a reservoir into which the motion 

 of the smaller body is emptied, and from which it is distributed nearly equally 

 in all directions. 



* And the behaviour of comets ? 



