BODIES SMALLER THAN ATOMS. 243 



suggested long ago that the variation on the earth's magnetic Held was 

 caused by currents in the upper regions of the atmosphere, and Schus- 

 ter has shown, by the application of Gauss's method, that the seat of 

 these variations is above the surface of the earth. 



The negative charge in the earth's atmosphere will not increase indefi- 

 nitely in consequence of the stream of negatively electrified corpuscles 

 coming into it from the sun, for as soon as it gets negatively electrified 

 it begins to repel negatively electrified corpuscles from the ionized 

 gas in the upper regions of the air, and a state of equilibrium will be 

 reached when the earth has such a negative charge that the corpuscles 

 driven by it from the upper regions of the atmosphere are equal in 

 number to those reaching the earth from the sun. Thus, on this view, 

 interplanetary space is thronged with corpuscular traffic, rapidly mov- 

 ing corpuscles coming out from the sun while more slowl} r moving- 

 ones stream into it. 



In the case of a planet which, like the moon, has no atmosphere, 

 there will be no gas for the corpuscles to ionize, and the negative elec- 

 trification will increase until it is so intense that the repulsion exerted 

 by it on the corpuscles is great enough to prevent them from reaching 

 the surface of the planet. 



Arrhenius has suggested that the luminosity of nebulae may not be 

 due to high temperature, but may be produced by the passage through 

 their outer regions of the corpuscles wandering about in space, the 

 gas in the nebulae being quite cold. This view seems in some respects 

 to have advantages over that which supposes the nebulae to be at very 

 high temperatures. These and other illustrations, wdiich might be 

 given did space permit, seem to render it probable that these corpuscles 

 may play an important part in cosmical as well as in terrestrial physics. 



