OF ARTS AND SCIENCES. 21 



waves of water are radiated in all directions until they reach the 

 shore. Waves are likewise radiated downward to the bottom of 

 the lake, and fishes have organs, like our ears, that enable them to 

 take cognizance of these vibrations. 



In the case of waves of water, or waves of sound, or waves of 

 light, we know there is no bodily transference of a particle of 

 water, or air, or ether, from the centre of disturbance to the shore, 

 or ear, or eye. Each particle moves at the most only through a 

 minute fraction'of an inch; but each pushes the next, and this the 

 next, so that motion, and not matter, is what is transmitted to a 

 distance. Indeed, this propagation of motion, in contradistinction 

 to propagation of matter, is the essential characteristic of wave 

 motion. 



Who has not seen a wave pass over a field of grain? Each par- 

 ticle bows its head but for a few inches, yet the wave passes on to 

 the utmost limit of the field. 



Sound, then, is a wave motion transmitted through the air. 

 Light is a wave motion transmitted through the ether. But both 

 of these media are also capable of having set up in them currents 

 in which there is an actual bodily transference of the medium from 

 place to place through considerable distance. 



In the case of air, we call this motion the wind. In the case of 

 the ether, I propose to show that it is a current of electricity. 



As wind is the bodily forward motion of the medium whose 

 vibratory motion we call sound, so a current of electricity is the 

 bodily forward motion of the medium whose vibratory motion we 

 call light. 



A current of electricity is a breeze of light. 



We may, perhaps, best get a realistic conception of electric cur- 

 rents, whether flowing through open space, or confined to a spe- 

 cially provided metallic conducting path, by first picturing to 

 ourselves the phenomena of air currents, with which we are more 

 familiar, and then mentally transferring these phenomena from the 

 air to the more subtle medium, the ether. The analogies are very 

 striking, and will materially aid the imagination in picturing 

 electrical phenomena. 



In the islands of the Pacific Ocean there is almost always a 

 breeze, either from the land to the water, or from the water to the 

 land. In the daytime the island is heated by the sun, its air is 

 rarefied and rises, and the cooler breeze rushes in from the ocean 

 to take its place. At night the island cools, the air descends, and 



