62 FKAGMENTS OF SCIENCE. 



Into a vessel containing acidulated water I dip 

 two strips of metal, the one being zinc and the other 

 platinum, not permitting them to touch each other 

 in the liquid. I connect the two upper ends of the 

 strips by a piece of copper wire. The wire is now the 

 channel of what, for want of a better name, we call an 

 6 electric current.' What the inner change of the wire 

 is we do not know, but we do know that a change has 

 occurred, by the external effects produced by the wire. 

 Let me show you one or two of these effects. 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. The ar- 

 rangement is called a voltaic battery. I plunge a piece 

 of copper wire among these iron filings ; they refuse to 

 cling to it. I employ the selfsame wire to connect the 

 two ends of the battery, and subject it to the same test. 

 The iron filings now crowd round the wire and cling to 

 it. I interrupt the current, and the filings immediately 

 fall; the power of attraction continues only so long 

 as the wire connects the two ends of the battery. 



Here is a piece of similar wire, overspun with 

 cotton, to prevent the contact of its various parts, and 

 formed into a coil. I make the coil part of the wire 

 which connects the two ends of the voltaic battery. By 

 the attractive force with which it has become suddenly 

 endowed, it now empties this tool-box of its iron nails. 

 I twist a covered copper wire round this common poker; 

 connecting the wire with the two ends of the voltaic 

 battery, the poker is instantly transformed into a strong 

 magnet. Two flat spirals are here suspended facing 

 each other, about six inches apart. Sending a current 

 through both spirals, they clash suddenly together ; re- 

 versing what is called the direction of the current in 

 one of the spirals, they fly asunder. All these effects 

 are due to the power which we name an electric current, 



