366 Locke 



, usQd, instead of the switch board above described, the double switch 

 frequently used as commutator on small spark-coils, consisting of 

 two parallel bars playing over three contacts,^ or a Pohl's rocking 

 switch with only one cross-wire. In the case of both of these also 

 the spare contact can be used for the short-circuiting of stimulating 

 electrodes in a secondary circuit. 



After devising the methods just described for connecting at will 

 two current-paths in series or parallel (in the special case in 

 question clock-contact and signal), I found that Ewald^ has 

 described and figured the special arrangement be for Pohl's 

 rocker with one cross- wire with a view to quite other practical 

 applications than the one made here. I find too that Kronecker,^ 

 in his report on chronographic methods, mentions the possibility 

 of using temporary omission of the time -record as a signal 



Fig. 5. — The terminals numbered 1,2, 3, and 4 are those of the Brodie- 

 Palmer Clock from right to left. (Cf. the figure showing the clock- 

 connections in Proc. of the Physiol. Soc., Dec. 8, 1900, Journal of 

 Physiology, xxvi., p. xii.) 



("Signal 1"). He also states that Judin^used as a signal the 

 diminution of the amplitude of the excursions of the chrono- 

 graph produced by the passage of a weak constant current 

 through its electromagnet. I believe, although I caimot now 

 recover the reference, that Kronecker has stated in a much 

 earlier publication that Dew- Smith long ago employed on 

 a continuous paper- kymograph a chronograph with polarised 

 armature, so that currents in reverse directions produced reversed 

 excursions. 



The methods of signalling described in this section were shown to 

 the Physiological Society on 1st March 1902. 



' In this case the usual permanent connection of the outer two of the three contacts 

 must be broken. Since the above was written, this form of switch has been applied to 

 general electrophysiological work by H. G. Roaf and W. G. Smith (Proc. oi the Physiol. 

 Soc, Nov. 11, 1905 ; Journal of Physiology, ixxiii., p. xiv.), wlio have made the connection 

 in question breakable at will. 



2 J. R. Ewald, Arch. f. d. ges. Physiol., xlii., p. 478, 1888. 



' H. Kronecker, Arch. Ital. de Biol., xxxvi., p. 135, 1901. 



^ A. Judin. La Physiologiste Ru.sse, v., p. 67, 1898, cited after Kronecker. 



