388 FRAGMENTS OF SCIENCE. 



means of tearing them asunder, and the agent by which 

 we accomplish this may here receive a few moments' 

 attention. 



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 cop- 

 per wire. The wire is now the channel of what, for want 

 of a better name, we call an "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 arrangement 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 con- 

 nect 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 buttery. 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 here are suspended facing each other, about six inches 

 apart. Sending a current through both spirals, they clash 

 suddenly together; reversing 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 elec- 

 tric current, and which we figure as flowing through the 

 wire when the voltaic circuit is complete. 



By the same agent we tear asunder the locked atoms of 

 a chemical compound. Into this small cell, containing 

 water, dip two thin wires. A magnified image of the cell 

 is thrown upon the screen before you, and you see plainly 

 the images of the wires. From a" small battery I send au 



