156 



PHYSIOLOGICAL PHYSICS, 



[Chap. XV. 



several times with cold water. The zinc rod is kept 

 amalgamated while hanging in the liquid. 



The accessory apparatus consists of two leading 

 wires, two handles, three covered electrodes, and one 

 wire brush. 



The size of this case is only 7 inches in each 

 direction, and it weighs only a little over 2^ pounds. 

 A larger size of the same apparatus can be had, if 

 desired. 



Some manufacturers make cases containing on one 

 side a constant battery and on the other an induction 

 apparatus. 



Magneto-electric machines are also used for 

 producing induced currents. Bobbins of wire with 

 cores of soft iron are caused to rotate in the neighbour- 

 hood of the poles of a strong magnet. As each coil 

 approaches one pole an induction current is produced, 

 and another when the coil goes away from the pole, 

 so that each coil produces four induced currents in 



one rotation. Wires are 

 arranged to lead off the 

 currents, which can be 

 applied in the same way 

 as ordinary induced cur- 

 rents. Fig. 82 shows an 

 apparatus for magneto- 

 electric induction. 



Wires for making con- 

 nections should always be 

 insulated with silk or guttapercha. 



The electrodes or rheophores are of various 

 forms according to the part to which they are in- 

 tended to be applied. They consist usually of an 

 insulating handle of wood supporting a brass cup 

 from one-half to three inches in diameter, a binding 

 screw for the attachment of wires being connected. 

 The metal cup is not applied to the body, but is filled 



Fig. 82. Magneto-electric Induc- 

 tion Machine. 



