LARGE DOUBLE-CURRENT VOLTA-FARADIC APPARATUS. 261 



Fig 57. — Front view of the uncovered 

 apparatus shown in fig. 55. 



placed in front of it against the screw C, communicates with the 

 knob F. As soon as the knobs E and F are phxced in communica- 

 tion with the poles of a pile, the 

 current passes through the wire of 

 the primary coil, and magnetises 

 its core of soft iron, which attracts 

 the movable piece of soft iron G. 

 This draws with it the piece of 

 copper A, which was resting against 

 the screw C. A solution of continuity 

 is produced, demagnetising the core, 

 and causing the return of A to C. 

 The current is then re-established, 

 and the same order of events con- 

 tinues. 



So far it will be seen that the 

 trembler differs but little from that 

 of the instrument represented in fig. 

 52, from which, however, it is dis- 

 tinguished by the following modifications. The movable soft 

 iron, Gr (fig. 57), is sufficiently remote from the core to have a 

 much longer distance to travel when attracted by the temporary 

 magnetization of the latter. In this condition it will beat only 

 four times in a second; but, by gradually turning the screw C 

 from right to left, the distance is progressively diminished, and 

 consequently the rapidity of movement of the trembler can be 

 progressively increased at the pleasure of the operator, who is able, 

 by this simple means, to regulate the speed according to the effect 

 that he desires to obtain. In order tliat the magnetic force may 

 exert its attraction when the distance is at the greatest, it is 

 necessary to increase the bulk of the movable soft iron. For this 

 purpose, I have attached to the latter an additional bar of soft iron, 

 fourteen centimetres in length, and which extends over the surface 

 of the end of the coil, as shown in fig. 57. The magnetization of 

 the plate G by the iron of the core is then considerably increased, 

 since the plate forms but one mass with the piece added to it. 

 When the screw C is tightened, the spring which presses the piece 

 A against it is sufficiently tense to cause the intermissions to occur 

 without vibrations ; l^ut, when the spring is relaxed by loosening 

 the screw, each beat or intermission is followed by a vibration, the 

 special action of which upon the sensibility I have mentioned 

 above. These vibrations are such, when the spring is completely 

 relaxed, that even the slowest action of the trembler (four inter- 

 missions per second) produces muscular contractions that are 



