WHAT IS ELECTRICITY ? 



AN old friend of mine, by profession a banker, who 

 spent a large portion of his life of eighty-nine years in 

 studying geology and astronomy, once put to me the 

 question : ' Whence comes the motive power of electricity ? 

 I can understand the motive power of steam, but not of 

 electricity. 5 



This led me to think on the subject ; and although there 

 is not much new in my reply, it contains, nevertheless, one 

 novel point, which contributes, I think, to clearness of 

 thought. 



The answer refers only to electricity generated by a 

 battery; not to a current made by means of a dynamo 

 machine. The answer to the question, What generates a 

 current in a dynamo ? must be left till a later oppor- 

 tunity. 



The simplest form of a battery consists of a vessel 

 containing dilute hydrochloric acid, into which dip a 

 copper and zinc plate, connected by a wire. A current 

 flows through the wire ; its presence can be demonstrated 

 by a galvanometer, or by dipping the wire from the copper 

 plate and the wire from the zinc plate into a solution of 

 iodide of potassium; a brown stain begins to appear at 

 the end of the wire connected with the zinc plate ; it is 

 caused by the iodine being set free, which dissolves in the 

 liquid with a brown colour. 



If it is desired to make the test more striking a little 

 starch may be added to the solution of iodide of potassium. 



