CHAP, in.] ELECTRICITY AND MAGNETISM. 183 



able displacement of the drop. The direction of the 

 displacement varies with that of the current. 



226. Physiological Actions. Currents of elec- 

 tricity passed through the limbs affect the nerves with 

 certain painful sensations, and cause the muscles to 

 undergo involuntary contractions. The sudden rush of 

 even a small charge of electricity from a Leyden jar 

 charged to a high potential, or from an induction coil 

 (see Fig. 148), gives a sharp and painful shock to the 

 system. The current from a few strong Grove's cells, 

 conveyed through the* body by grasping the terminals 

 with moistened hands, gives a very different kind of 

 sensation, not at all agreeable, of a prickling in the joints 

 of the arms and shoulders, but not producing any 

 spasmodic contractions, except it be in nervous or 

 weakly persons, at the sudden making or breaking of 

 the circuit. The difference between the two cases lies 

 in the fact that the tissues of the body offer a very con- 

 siderable resistance, and that the difference of potential 

 in the former case may be many thousands of volts ; 

 hence, though the actual quantity stored up in the 

 Leyden jar is very small, its very high E.M.F. enables 

 it at once to overcome the resistance. The battery, 

 although it might, when working through a good con- 

 ductor, afford in one second a thousand times as much 

 electricity, cannot, when working through the high re- 

 sistance of the body, transmit more than a small fraction, 

 owing to its limited E.M.F. 



After the discovery of the shock of the Leyden jar by 

 Cunaeus in 1745 many experiments were tried. Louis 

 XV. of France caused an electric shock from a battery of 

 Leyden jars to be administered to 700 Carthusian monks 

 joined hand in hand, with prodigious effect. Franklin 

 killed a turkey by a shock from a Leyden jar. 



227. In 1752 Sulzer remarked that " if you join two 

 pieces of lead and silver, and then lay them upon the 

 tongue, you will notice a certain taste resembling that of 



