LAKGE DOUBLE-CURKENT VOLTA-FAEADIC APPARATUS. 251 



the latter, if the apparatus will not be required again for some 

 hours. It will be observed, after being wiped, that the zinc has 

 become amalgamated by the action of the battery itself. 



A battery of sulphate of mercury, thus charged, will last for two 

 or three weeks, and may be used for several hours a day, without 

 any other care than to renew the moisture of the cloth, and to 

 move a little, every day before use, the paste of mercury upon the 

 carbon. It is also desirable to maintain the platinum connections 

 in a state of cleanliness. 



When the mercurial paste is quite decomposed (its colour, ori- 

 ginally yellow, will then be green) the carbon and the cloth must 

 be washed, and the battery charged with fresh deuto-sulphate as 

 before. If the battery belonging to the apparatus has undergone 

 deterioration, or is in need of repair, the coil may be put in action 

 by any other (either a Daniell's, a Bunsen's, or a sulphate of lead). 

 It is only necessary to connect the poles of the substituted battery 

 with the knobs E' and L' (fig. 52), which receive the terminations 

 of the wire of the primary coil. 



§ III. — Theory of the authors volta-faradic a^^aratus. 



If the battery be inclosed in the apparatus, with no interruption 

 either by the pedal or the trembler, the battery current, which is 

 transmitted by the buttons, L, E (fig. 52), to the wire of the central 

 bobbin, is continuous, and occasions none of the phenomena of 

 inckiction, althou2:h it magnetises the central core of soft iron. 



In this state of things, if we set at liberty the plate A of the 

 trembler, by turning back the screw C, that plate is attracted by 

 the magnet of the bobbin. At the same instant, the current being 

 interrupted, the magnetization ceases, the soft iron of the trembler 

 is driven back against the platinum point of the screw S, by a 

 spring, and restores the current, which produces a fresh magnetiza- 

 tion. These temporary magnetizations, and these breaks in the 

 current, succeed each other with extreme rapidity, in the covered 

 (fig. 52) apparatus ; and with more or less rapidity, at the pleasure 

 of the operator, in the uncovered apparatus (fig. 55). Although 

 the theory of the trembler is well known, it is desirable briefly to 

 state it, in order to explain the mechanism of its several portions. 



At the moment when the current of the primary coil is inter- 

 rupted, we may observe the physical and physiological phenomena 

 that are produced by virtue of two combined forces ; namely, the 

 inductive action of the current upon itself, by the mutual influence 

 of its coils, and by the reciprocal influence of the current and of 

 the magnetized soft iron of the bobbin. 



If the extremities of the fine wire, that forms the outer coil, are 



