THE CONQUEST OF NATURE 



is far less intangible than gravitation. Not merely may 

 electricity be felt, but it may be generated through trans- 

 formation of other forms of energy; it may be stored 

 away and measured; may be conducted at will through 

 tortuous channels, or obstructed in its flight by the in- 

 tervention of non-conductors. But gravitation submits 

 to no such restrictions. It eludes all of our senses, and it 

 absolutely disregards all barriers. To its catholic taste 

 all substances are alike. It holds in bondage every 

 particle of matter in the universe, and can enforce its 

 influence over every kind of atom with an impartiality 

 that is as astounding as it is inexorable. Moreover, 

 this weird force, gravitation, has thus far evaded all 

 man's efforts to classify or label it. No man has the 

 slightest inkling as to what gravitation really is. If, 

 as you glance at these lines, you should chance to release 

 your hold and allow the volume to drop to the floor, you 

 will have performed a miracle which no scientist in the 

 world can even vaguely explain. 



As regards our electric train, then, the fact that it 

 stands there firmly, held fast to the rails by gravitation, 

 is in reality as great and as inexplicable a marvel as the 

 fact that the electric current gives it propulsion. Not 

 only so, but the fact that the train goes forward of its 

 own inertia, as we say, for a time after the current is 

 shut off, presents to us yet another inexplicable marvel. 

 It is a fundamental property of matter, we say, when 

 once in motion to continue in motion until stopped by 

 some counter-force ; but that phrasing, expressive though 

 it be of a fact upon which so many physical phenomena 

 depend, is in no proper sense of the word an explanation. 



