SCIENCE AXD PRACTICE. 219 



observed by Sulzer and Gralvani, and led to the discovery 

 of galvanism. The experiment published by Sulzer of putting 

 a piece of zinc under and a piece of copper upon the tongue, 

 and letting them come into contact with each other, is the 

 simplest arrangement by which we become acquainted with 

 this effect. When the poles of a battery of a number of 

 elements are taken hold of in the hands, the latter being 

 moistened, a very unpleasant sensation in the arms and chest 

 is felt whilst the current continues, and a still more un- 

 pleasant one when the circuit is interrupted and re-made. 

 This effect is said to have been often used with advantage 

 in medical cases, and has been employed in some highly 

 interesting experiments with dead bodies, members of both 

 human and brute creation. 



A use to which the practical electricians of the gutta- 

 percha factories put this property of the galvanic current is 

 in the detection of faults in insulated wires. For this purpose 

 the wire is connected at one end with one pole of a battery, 

 the other pole of which is to earth. The further end of the 

 wire is insulated. The wire is then drawn through a wet 

 sponge or cloth held in the hand of a workman. The moment 

 a bad place passes through his hand the water enters the 

 fault, closes the circuit of the battery through the man to 

 earth. Notice of the fact is given unfailingly when the 

 battery is strong enough. 



The epidermis is a little insensible to the action of the 

 current, and becomes quite so after repeated shocks ; but 

 the tongue and wounds in any part of the body are highly 

 electroscopic. 



The physiological effect of the current has, we believe, 

 only once been enlisted into the ranks of the telegraph. 

 In 1839, Yorzelmann de Heer carried out a telegraph in 

 which the operator received the signals in his fingers. Ten 

 leading wires connected the corresponding stations. At the 

 receiving end the operator placed his fingers and thumbs 

 upon the ten metallic terminals of the lines. The signals 

 were given by sending currents at the same time through 

 two of the wires, and were observed 



