ASTRO-PHYSICS 287 



on our conceptions of the nature of solar pro- 

 cesses. The leak of electricity from hot bodies, 

 studied in the physical laboratory, shows that 

 corpuscles or electrons must be emitted in 

 enormous quantities by the substance of the 

 sun and hot stars. The likelihood of the 

 presence of radio-active matter, too, and of the 

 ejection of other corpuscles, with the transcendent 

 velocities impressed on them by a radio-active 

 origin, must not be forgotten. Although the 

 corpuscles, before they reached the surface of 

 the earth, would be absorbed by its atmosphere — 

 equivalent as that atmosphere is to a thickness 

 of thirty inches of mercury — they might produce 

 striking phenomena in the regions of the upper 

 air. Perhaps on these lines is to be explained 

 the appearance of the Aurora Borealis and 

 kindred manifestations, while the luminosity of 

 the solar corona may well have an electric 

 origin. 



One important application of photography 

 to astronomy consists in the better estimation 

 of stellar distances. Even the nearest fixed star 

 is so far away from us that accurate measure- 

 ment is difficult, while some stars are so in- 

 conceivably remote that all ordinary methods 

 fail. 



Nearer objects seem to move past more 

 distant ones as we look at them from the window 

 of a train ; and, if some stars are nearer to the 

 earth than others, they also should seem to 

 move in one direction as the earth moves in 

 the other. We should therefore expect to see 

 the nearer stars shift over a background of more 



