LARGE DOUBLE-CURRENT VOLTA-FARADIC APPARATUS. 249 



elements are placed in the compartments for which they are des- 

 tined ; and which are distinguished by numbers marked on the 

 sides of the caoutchouc cells (see figs, 53 and 54). Lastly, the 

 drawers must be shut (U XT', tig. 52) and the button A' turned in 

 such a manner that its bar assumes a vertical direction and pre- 

 vents them from opening. The communications of the elements 

 of the battery with each other, and with the circuit of the primary 

 coil, are then established in the following manner. 



The zinc of the pair of elements in the lower drawer, which is 

 the negative pole of the battery, corresponds to the knob L (fig. 

 52), and the platinum contact of the carbon of this pair communi- 

 cates with the spring of the piece of copper by which it is screwed 

 to the knob N. But, as the knobs N and G are opposite the two 

 small platinized plates that are seen on the right side of the front 

 of the apparatus above the drawers U U', and as these two plates 

 are connected by a copper wire, if we turn the knobs N and G 

 from left to right into contact with the plates, they connect the 

 carbon of the pair in the lower drawer with the zinc Z (fig. 53) of 

 the farther pair of the upper drawer. Lastly, the carbon of the 

 latter pair being placed, as I have said already, in communication 

 with the zinc Z' of the front pair, by means of the double spring a, 

 and the platinum wire of the carbon of this last pair being in 

 contact, through a spring, with the knob E, this becomes the posi- 

 tive pole of tlie battery. The small plates of platinum, which are 

 fixed to the front of the apparatus on the left, receive the ex- 

 tremities of the wire of the primary coil ; so that, by turning 

 the knobs E and L, which are the poles of the battery, from left 

 to right into contact, the current of the battery passes through the 

 wire of the primary coil. 



It therefore suffices to place in their respective compartments 

 the three pairs of elements, charged with bisulphate of mercury 

 as described, to shut the drawers U and U' (fig. 52), to turn the 

 knob L' from left to right (for a reason that will be declared here- 

 after), and lastly, to turn into contact the knobs E, G, L, N, in 

 order that the battery current may pass through the wire of 

 the primary coil, or, in other words, that the circuit formed by the 

 battery and the primary coil may be completed. 



The apparatus may be worked with only the two elements of 

 the upper drawer U' (fig. 52) ; when it will still possess very con- 

 siderable power, and will fulfil the ordinary requirements of practice. 

 We must then take care to turn the knob L' (fig. 52) from left to 

 right into contact, in order to su]3press the elements of the lower 

 drawer U, which may be used as a place for the rheophores and 

 the conductors. It is unnecessary to say that when we wish to 



