chap, xv.] PULVERMACHER'S CHAIN PILE. 



'53 



small tangent galvanometer, since in it the strength 

 of current is proportional to the tangent of the 

 angle of deflection. 



A "battery said to be the best for therapeutic 

 purposes is a modified Daniell called the BECKER- 



MUIRHEAD. 



Fig. 80 exhibits a part of Pulvermacher's 



chain pile. It consists of cylindrical pieces of wood, 



on which are coiled in a spiral manner, a copper 



and a zinc wire. Each turn of 



the wires lies in a groove in 



the wood, and is insulated from 



its neighbours. The ends of the 



zinc wire of one cylinder are 



coupled to the ends of the copper 



wire of the cylinder below. Any 



number of cylinders may be 



used. The first has the two ends 



of its copper spiral free, and they 



are united to form the positive 



pole, as seen at b in the figure. 



Similarly the free ends of the last 



zinc spiral form the negative 



pole. To put the chain into 



A ,. ., . -,. , . , ,, Fig. 80. Pulvermaclier's 



action it is dipped into a basin of chain Pile, 



acidulated water. The poles are 



connected to copper tubes, each containing a sponge 

 moistened with acidulated water. The chain, having 

 been removed from the basin, may then be applied to 

 the body by making contact with the sponges at the 

 desired places. It is not a constant pile. 



Induction apparatus is usually set up so 

 as to have cell, coil, and accessory apparatus, all 

 within the same box, which is usually of comparatively 

 small size, since induction currents of sufficient 

 strength for the human body can be generated by a 

 small cell and a small coil. One form of apparatus 



