IO 



PRESSURE OF LIGHT 



pressure which may hereafter be verified by 

 astronomical observation. 



A hundred years ago it would have been much 

 easier to explain how light exercises pressure than 

 it is to-day. Then almost every one believed that 



o 



FIG. i. 



light consisted of corpuscles, inconceivably small 

 bodies, darting out at enormous speed from every 

 glowing surface. Each molecule or atom of the 

 surface was supposed to be a little battery of guns, 

 keeping up a continuous fire of shot, each shot 

 immensely smaller than the atom which fired it ofif. 

 Every surface exposed to the light was regarded as 



