The Evolution of the Sciences 



This is a question which confronts all who 

 study problems of solar physics. As early as 

 1871 Young had shown that the spectrum 

 and the shape of the coronal rays are quite 

 comparable to those presented by the tail of 

 comets. This analogy has since been confirmed 

 by numerous observations. Now it has long 

 been known that the tails of comets are invariably 

 averted from the sun, which proves that the 

 luminary exercises a repulsion on the cosmic 

 matter composing the tail. It seems reasonable 

 to admit that the same repulsive force acts on 

 the solid dusts of the corona, balancing their 

 weight, and thus enabling them to shoot to a 

 great distance from their centre of attraction. 

 If this hypothesis were founded on fact 

 we should have to explain the origin of this 

 repulsive force. Electrical actions have natur- 

 ally been suggested, but a force of an entirely 

 different origin has also been put forward. 

 About twenty years ago Maxwell and then 

 Bartoli showed that light or heat radiations 

 falling on a body which absorbs them must 

 necessarily repel it. This action, originally 



predicted from theoretical considerations, is 



216 



