PHYSIOLOGICAL PHYSICS. 



[Chap. VII. 



as to break contact with R, and thus, by the fall of the 

 hammer, the current ivill be interrupted. Secondly, 

 let one electrode from an element be attached to c at 

 the other end of the instrument, and let the second 

 electrode be attached to the screw in connection with 

 the mercury cup. The current would pass from c up 

 the handle of the hammer to the hammer-head, and, 

 when the head fell, would pass by the hook m through 

 the mercury, and off by the wire in connection. So that 

 by the fall of the hammer this current would be es- 

 tablished. In other words, by the fall of the hammer 

 the circuit at R would be opened, and that at X closed. 

 Thus, suppose these currents to be sent round the 

 primary coil of an induction machine, the secondary 

 wires of which were connected with a muscle, by the 

 fall of the hammer an opening or a closing shock 

 would be given to the muscle, and the opening 

 or closing would be effected with the same sudden- 

 ness in each case. The magnetisation 

 magnetisation of the eleetro-magnets is 



a 



BA ' 



de- 



and 



effected 

 Daniell's 



element El, con- 

 nected with the 

 coils of wire by 

 means of bind- 

 ing screws, a key 

 or commutator, 

 with cross, being 

 interposed. A 

 Daniell is used 

 because it is just 

 sufficient to hold 

 the hammer up, 

 and consequently there is no delay in the hammer 

 dropping on interrupting the current. The arrange- 

 ment of the apparatus is shown in Fig. 38. E2 is 

 the element supplying the electro-magnets EZ-m, the. 



Fig. 38. Arrangement of Apparatus 

 Pflueger's Trip- Hammer. 



with 



