THE HIGHEST AIM OF THE PHYSICIST 673 



And yet, however wonderful it may be, its laws are far more simple 

 than those of matter. Every wave in it, whatever its length or inten- 

 sity, proceeds onwards in it according to well known laws, all with the 

 same speed, unaltered in direction from its source in electrified matter, 

 to the confines of the universe unimpaired in energy unless it is dis- 

 turbed by the presence of matter. However the waves may cross each 

 other, each proceeds by itself without interference with the others. 



So with regard to gravitation, we have no evidence that the presence 

 of a third body affects the mutual attraction of two other bodies or 

 that the presence of a third quantity of electricity affects the mutual 

 attraction of two other quantities. The same for magnetism. 



For this reason the laws of gravitation and of electric and magnetic 

 action including radiation are the simplest of all laws when we confine 

 them to a so-called vacuum, but become more and more complicated 

 when we treat of them in space containing matter. 



Subject the ether to immense electrostatic, magnetic or gravitational 

 forces and we find absolutely no signs of its breaking down or even 

 change of properties. Set it into vibration by means of an intensely 

 hot body like that of the sun and it conveys many thousand horse-power 

 for each square foot of surface as quietly and with apparently unchanged 

 laws as if it were conveying the energy of a tallow dip. 



Again, subject a millimeter of ether to the stress of many thousand, 

 nay even a million, volts and yet we see no signs of breaking down. 



Hence the properties of the ether are of ideal simplicity and lead to 

 the simplest of natural laws. All forces which act at a distance, always 

 obey the law of the inverse square of the distance and we have also the 

 attraction of any number of parts placed near each other equal to the 

 arithmetical sum of the attractions when those parts are separated. So 

 also the simple law of ethereal waves which has been mentioned above. 



At the present time, through the labors of Maxwell supplemented by 

 those of Hertz and others, we have arrived at the great generalization 

 that all wave disturbances in the ether are electromagnetic in their 

 nature. We know of little or no ethereal disturbance which can be set 

 up by the motion of matter alone: the matter must be electrified in 

 order to have sufficient hold on the ether to communicate its motion 

 to the ether. The Zeeman effect even shows this to be the case where 

 molecules are concerned and when the period of vibration is immensely 

 great. Indeed the experiment on the magnetic action of electric con- 

 vection shows the same thing. By electrifying a disc in motion it 

 appears as if the disc holds fast to the ether and drags it with it, thus 



setting up the peculiar ethereal motion known as magnetism. 

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