218 THE ELECTRIC TELEGRAPH. 



arrange themselves with the same tension in the order 

 shown in the sketch, and the combination of the oxygen 

 atoms with the zinc is retarded. The current of such an 

 element, therefore, becomes gradually weaker from the 

 moment of closing the circuit until the maximum collection 

 of hydrogen gas on the copper plate is attained. 



2. The current of a galvanic battery manifests itself in 

 various ways, by some of which we are enabled to measure 

 its intensity and to study its relations under different con- 

 ditions. 



The most important of these manifestations are : its produc- 

 tion of light, its property of heating bodies, its physiological, 

 its* chemical, and its magnetical effects. 



At the moment when the poles of a single pair of plates 

 of large surface are separated, the experimenter observes a 

 beautiful bright spark pass between them. If the poles have 

 been amalgamated beforehand, the spark is very intense. 

 This is, on a small scale, the celebrated electric light. By 

 taking forty or fifty elements of large surface and high 

 electro-motive force, such as the platinum- zinc battery of 

 Mr. Grove, or the carbon-zinc battery of Robert Bunsen, 

 having first furnished the poles of the system with carbon 

 points, if we touch these points together for an instant and 

 then separate them, we have an electric light too brilliant 

 to be regarded, without danger, by the naked eye. By 

 separating the points steadily for a short distance, the 

 particles of carbon are built into a bridge by the current 

 through which it circulates, and keeps it incandescent with 

 a peculiar brilliancy until it is broken. 



The heating power of the current may be observed with 

 an element of large surface by inserting between its poles 

 a short piece of platinum wire, which becomes, in a few 

 moments, red hot. A battery of thirty Bunsen's elements 

 easily melts pieces of platinum and of every other metal 

 which are brought between its poles. So great indeed is 

 the heat known to be generated by the galvanic current, 

 that it has even been attempted to gasify carbon by it. 



The physiological effects of the galvanic current were first 



