Chap. VII.] 



THE METRONOME. 



commutator c, with cross, being interposed. The only 

 advantage of c over a key is, that by simply inclining 

 the bridge from one side to the other, Ei-m are demag-. 

 netised for an instant, and so the hammer falls, anclE -m 

 are immediately reinagnetised ; so that, to repeat the 

 experiment, one requires only to raise the head again. 

 El is the element for the primary coil I, and is so 

 connected with s and s' through the medium of L, that, 

 as already explained, the fall of the hammer-head 

 breaks the circuit. II represents the secondary coil, 

 whose wires can be led to muscle telegraph or elec- 

 trodes, as in former experiments. The second circuit 

 at H and ax is not represented, for the sake of 

 simplicity. It is simply a repetition of EI s s', so 

 arranged that the fall of H closes the primary circuit. 



Pflueger's hammer 

 can thus be arranged so 

 as to yield only an 

 opening induction shock, 

 or only a closing one, 

 according to the two 

 binding screws used. 



The metronome. 

 By using the ordinary 

 interrupter of the in- 

 duction coil, it is not 

 possible to estimate the 

 number of shocks given 

 to a muscle in a given 

 time. This it is desir- 

 able to do, to determine 

 what rapidity is neces- 

 sary for the production 

 of tetanus. By an 

 adaptation of the instrument used in music for 

 beating time, the metronome, this can be done, and 

 the rate of speed at which the shocks follow one 



Fig. 39. The Metronome. 



