PROBABLE ORIGIN OF NEBULJC. 311 



quently, when their store of energy is exhausted, they 

 will be non-luminous again. Light and heat are not 

 the permanent possession of a body. A body may 

 retain its energy in the form of motion undiminished 

 and untransformed through all eternity, but not so in 

 the form of heat and light. These are forms of 

 energy which are being constantly dissipated into 

 space and lost in so far as the body is concerned. 



The conclusion to which we are therefore led is that 

 there are in all probability bodies in stellar space 

 which have not yet received their store of light and 

 heat, while there are others which have entirely lost 

 it. The stars are probably only those stellar masses 

 which, having recently had an encounter, have become 

 possessed of light and heat. They have gained in 

 light and heat what they have lost in motion, but they 

 have gained a possession which they cannot retain, 

 and when it is lost they become again what they 

 originally were — dark bodies. 



2nd. " We have no instances of stellar motions com- 

 parable with those demanded by the theory." A little 

 consideration will show that this is an objection which, 

 like the former, can hardly be admitted. No body, of 

 course, moving at the rate of 400 miles per second, 

 could remain a member of our solar system ; and 

 beyond our system the only bodies visible are the 

 nebulae and fixed stars ; and they are according to the 

 theory visible, because, like the sun, they have lost 

 their motion — the lost motion being the origin of their 

 light and heat. Their comparatively small velocities 

 are in reality evidence in favour of the theory than 

 otherwise ; for had the stars been moving with exces- 

 sive velocities, this would have been adduced as proof 

 that their light and heat could not have been derived 

 from motion lost, as the theory assumes. 



