594 



COMPARATIVE ELECTRO-PHYSIOLOGY 



electro-motive method. According to the former of these, 

 the magnetising coil, c, is placed broadside on, in reference 



FIG. 361. Experimental Arrangement 

 for Magnetometric Method of Record 



M, magnetometer ; c, magnetising coil ; 

 B, balancing coil; A, ammeter; R, 

 rheostat ; K, key actuated by metro- 

 nome. 



FlG. 362. Photographic 

 Record of Uniform 

 Magnetic Responses 

 of Iron 



to a freely suspended magnetic needle with its attached 

 mirror (fig. 361). A second balancing coil, B, is placed on 

 the other side, and so adjusted as to 

 nullify any disturbance of the needle 

 by the magnetising coil. The experi- 

 mental rod of iron is then introduced 

 inside C, and the responsive molecular 

 action induced by the exciting current 

 is recorded in the usual manner by the 

 deflected spot of light from the mag- 

 netometer, M, thrown on a revolving 

 drum. The intensity of the exciting 

 current, measured by the ammeter, A, 



FIG. 363. Photographic ' 



Record of Periodic is capable of adjustment by means of 



n e Uc P R n efponses Mag " the rheostat > R - The Cation of appli- 

 cation of the exciting current is deter- 

 mined by a metronome, and thus kept uniform in successive 

 experiments. In fig. 362 is seen a series of records obtained 

 in this manner, employing stimulation of moderate intensity. 

 In fig. 363 is seen a curious instance of periodic groupings 



