MODERN THEORIES AS TO ELECTRICITY 291 



1st. It must be able to explain electrostatic attraction. These 

 electrostatic forces are mostly rather feeble as we ordinarily see them. 

 Air breaks down and a spark passes when the tension on the ether 

 amounts to about j^-g- pound to the square inch. It is the air, how- 

 ever, that causes the break-down. Take the air entirely away, and we 

 then know no limit to this force. In a suitable liquid it may amount 

 to 500 times that in air or 5 pounds to 1 square inch, and become a 

 very strong force indeed. In* a perfect vacuum the limit is unknown, 

 but it cannot be less than in a liquid, and may thus possibly amount 

 to hundreds, if not thousands, of pounds to the square inch. 



2d. It must explain magnetic action. These actions are apparently 

 stronger than electrostatic actions, but in reality they are not neces- 

 sarily so. A tension on the ether of only a few hundred pounds on 

 the square inch will account for all magnetic attraction that we know of, 

 although we are able to fix no limit to the force the ether will sustain. 

 No signs have ever been discovered of the ether breaking down. 



Again, we must be able to account for the magnetic rotation of 

 polarized light as it passes through the magnetic field; and it can only 

 be accounted for by assuming a rotation around the lines of mag- 

 netic force. This action, however, takes place only while the lines 

 of magnetic force pass through matter, and it has never been observed 

 in the ether itself. The velocity of rotation, however, is immense, the 

 plane of polarization rotating in some cases 300,000,000 times per 

 second. 



The ether must also account for the earth's magnetism. If we 

 assume that magnetic lines of force are simply vortex filaments in the 

 ether, we have only to suppose that the ether is carried around by the 

 rotation of the earth, and we have the explanation needed. The mag- 

 netism of the earth would then be simply a whirlpool in the ether. 



3d. The ether must be able to transmit to a distance an immense 

 amount of energy either by means of electromagnetic waves as in light 

 or by the similar action which takes place in the ether surrounding a 

 wire carrying an electric current. 



The amount of energy which can be transmitted by the ether in 

 this manner is enormous, far exceeding that which can be carried by 

 anything composed of ordinary matter. Thus take the case of sun- 

 light: on the earth's surface illuminated by strong sunlight a horse- 

 power of energy falls on every 7 square feet. At the surface of the 

 sun the etherial waves carry energy outward at the rate of nearly 8000 

 horse-power per square foot! 



