THE SPIRIT-RAPPERS 



Langley's wonderful bolometer and told that it 

 will measure the heat of a candle a mile or more 

 away, he would be sure you were making game of 

 the old man. 



Newton invented a new electrical machine and 

 performed many interesting electrical experiments ; 

 but his knowledge of electricity and magnetism 

 was necessarily of the most meagre sort. He did 

 not know of any relation between an electrified 

 body and a loadstone; he did not know of such a 

 thing as an electrical current ; and if he were shown 

 a common Morse telegraph instrument, and told 

 that a current sent round a piece of soft iron makes 

 this a magnet and pulls down a key, and that this 

 can be done at a distance of thousands of miles, he 

 would not understand what you were talking about. 

 He did not know that zinc and copper plates dipped 

 in a salt or acid water may generate a current, so 

 he could not explain a common voltaic battery. 

 As no one before Faraday had any idea of electrical 

 induction, if Newton were shown a bar of soft iron 

 whirling in front of a magnet he would not know 

 that it could produce an electrical current strong 

 enough to kill a man. He could make no mental 

 picture whatever of an ordinary dynamo. 



Not knowing that a vibrating iron plate can, 

 under proper conditions, vary the character of an 

 electrical current in its vicinity, Newton would be 



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