MATTER AND FORCE. 79 



single vessel of acidulated water. Before you is a series of 

 ten vessels, each with its pair of metals, and I wish to get 

 the added force of all ten. This arrangement is called a 

 voltaic battery. I take a piece of copper wire in my hand, 

 and plunge it among these iron filings ; they refuse to cling 

 to it ; the wire has no power over the filings. J now em- 

 ploy the self-same wire to connect the two ends of the bat- 

 tery, and subject it to the same test. The iron filings now 

 crowd round the wire and cling to it. This is one of the 

 effects of the electric current now traversing the wire. I 

 interrupt the current, and the filings immediately fall ; the 

 power of attraction continues only so long as the wire con- 

 nects the two ends of the battery. 



Here is a piece of similar wire, overspun with cotton, to 

 prevent the contact of its various parts. It is formed into 

 a coil, which at present has no power over these iron nails ; 

 but I now make the coil part of the wire which connects 

 the two ends of the voltaic battery. No visible change has 

 occurred in the coil, but it is no longer what it was. By 

 the attractive force with which it has become suddenly en- 

 dowed, it now empties this tool-box of its nails. I twist a 

 covered copper wire round this common poker. At present 

 the poker is powerless over these iron nails ; but when we 

 connect with the wire surrounding the poker the two ends 

 of the voltaic battery, the poker is instantly transformed 

 into a strong magnet. Here, again, are two flat spirals sus- 

 pended facing each other. They are about six inches 

 apart. By turning this handle in a certain direction a cur- 

 rent is sent through both spirals. When this is done they 

 clash suddenly together, being drawn together by their mu- 

 tual attraction. By turning the handle in another direction, 

 I reverse what is called the direction of the current in one 

 of the spirals, and now they fly asunder, being driven apart 

 by their mutual repulsion. All these effects are due to the 

 power which we name an electric current, and which we 



