THE NATURE OF ELECTRICITY. 33 



pansion of our atmosphere conflict at all with the 

 theory of the universal existence of ether, since 

 the theory of ether is that it permeates all material 

 substances. 



The wave theory assumes that radiant energy is 

 transmitted by the undulations of some medium ; that 

 an impulse originating at any center of energy, as the 

 sun, produces a wave which traverses this medium with 

 inconceivable velocity, till it reaches some distant 

 point, as the earth ; and that the constancy of such im- 

 pulses at every point on the sun gives rise to the phe- 

 nomena of solar light, heat, and electricity. 



In like manner we may assume any other center of 

 energy, as a red-hot metal ball, radiating light and 

 heat; a stick of ebonite, excited by friction, radiating 

 electricity. 



It is also assumed that the impulses radiate in straight 

 lines, while the undulations occur at right angles to 

 those lines. 



To illustrate : Drop a pebble on a smooth sheet of 

 water ; the impulse creates waves which radiate out- 

 ward in widening circles. The pebble has depressed 

 the water at the point where it struck, forcing the ad- 

 jacent water outward, and causing it to rise above the 

 general level ; then the downward impulse of this 

 wave, cinking under the force of gravity, raises the 

 original center, and also produces, by its outward im- 

 pulse, another wave beyond, as it descends by its inertia 

 below the general level. 



As the water oscillates vertically above and below the 

 level, each successive impulse produces a new wave, 

 while the same process goes on in the outward waves, 

 creating new waves beyond, in ever widening circles, 



