MECHANICAL PRESSURE OF LIGHT; ITS CONSEQUENCES. 239 



and the lines of force proceed from pole to pole. Now the 

 corpuscles must arrive most thickly over the equatorial 

 region of the earth where the earth is directly exposed to 

 them. They must be at once caught by the lines of force 

 and must travel along them in winding helices ever coming 

 closer and closer and farther and farther down into the 

 atmosphere as they approach the poles. At a certain dis- 

 tance from the poles they find themselves in an atmosphere 

 comparable with our high vacua and they then begin to 

 give out the shifting and darting lights of the cathode rays, 

 though this can be only at the cost of their existence for 

 their energy is absorbed in causing the luminosity. These 

 " darting and shifting lights of the cathode rays " in ac- 

 cordance with this speculation account for the Aurora 

 Borealis as well as for " the dark circles around the magnetic 

 poles from which, as from behind a curtain, the leaping 

 pillars of the Aurora rise." If the theory is true, there 

 should be some connection between the earth's magnetic 

 field and the Aurora and since they are both due to solar 

 influence they should be related, as well, to the sun's 

 activity as revealed in the number of sun spots. 



In fact, the Aurora Borealis, the earth's magnetism and 

 sun spots should all vary together. It has long been known 

 that they all do vary together in a very remarkable way. 



ATMOSPHERIC ELECTRICITY. 



Another peculiarity possessed by corpuscles travelling 

 with high velocity is their ability to knock to pieces or 

 ionize a gas through which they pass, and that these 

 ions act as nuclei of condensation of clouds. If, there- 

 fore, the earth is bombarded by solar corpuscles they should 

 ionize the air in the upper regions and this should result' 

 in the formation of clouds. We have here a beautiful 



