720 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



adopted. Figs. 464 and 465 show now this battery is made and how 

 it is used. Each element is composed of a cylinder of wood whose 

 surface is hollowed by helicoid grooves. Two metallic wires, one of 

 copper and the other of zinc, are rolled round these grooves without 

 touching each other and their ends are united, each to each the zinc 

 with the next copper, and so on. The form of the whole is a sort 

 of chain ending in two armatures which the patient holds in his 

 hand, as shown in Fig. 465. 



In using Pulvermaeher's chain, it is plunged in a vessel containing 



PIG 464. Elements of Pulvermacher's FIG. 465. Palvermacher's galvanic chain 



battery or chain. in use. 



weak vinegar and water ; the wood imbibes the liquid, and the 

 chemical action of the acid on the zinc produces the current the cir- 

 cuit of which is completed by the arms and body of the experimenter 

 When shocks are to be obtained the current must be interrupted. 

 An ingenious arrangement allows of successive interruptions. One 

 of the armatures contains, in the inside, some clockwork which turns 

 a wheel, one tooth of which at each revolution presses on a spring 

 The contact of the battery with the sides of the armature then ceases 

 and the current is interrupted. The rapidity of the interruptions 



