20 PROCEEDINGS OF THE AMERICAN ACADEMY 



the surface of the body feels the heat, the presence of electricity 

 cannot he detected by any of our senses. Electricity cannot be 

 seen, or heard, or felt; it is tasteless and odorless. 



Subjectively considered, then, electricity eludes our grasp. 



Objectively, however, electricity is as familiar to us as light, or 

 sound, or heat. Its phenomena have been as carefully studied, 

 and its laws are as accurately known. 



Let us for a moment recall the physical explanation of light and 

 sound. Let us picture to the eye of the imagination the mechanics 

 of a ray of light. 



When we stand out of doors on a cloudless night and look above 

 us, we see a multitude of stars. The telescope tells us that some 

 of these are suns, some are moons, and some are other worlds than 

 ours. 



The nearest of them is distant millions of miles, and yet we can 

 see them. There is a chain of something linking the star at which 

 we are gazing to the eye. This chain we call, familiarly, a ray of 

 light. Physicists tell us that along the pathway from the star to 

 our eyes there are chasing each other with enormous speed a mul- 

 titude of waves of light. 



If we turn our eyes to another star, it too sends to our eyes its 

 waves of light. If we go to a distant part of the earth, the same 

 stars send rays of light to us there. And so we find that each of 

 the multitude of stars is radiating ceaselessly in all directions mul- 

 titudes of waves of light. 



Between us and the stars, and between the stars extending 

 everywhere through visible space, is the medium that transmits 

 these waves, crossed and intercrossed continually with countless 

 waves of light, — a medium rarer than the rarest gas, — the medium 

 that is still left in space when we remove from it all solids and 

 liquids and gases, the ether. 



Objectively considered, then, light is a wave motion of the ether 

 that everywhere surrounds us and fills all space. By a similar 

 wave motion, but in a coarser medium, the air, sound is trans- 

 mitted from place to place. 



By means of his vocal organs, a public speaker moulds the cur- 

 rent of air that issues from his lungs into waves of sound. These 

 waves of sound are radiated in all directions, and fall upon the 

 various listeners' ears. 



Something analogous takes place when we drop a pebble on to 

 the surface of a placid lake. From this centre of disturbance, 



