246 LOCALIZED ELECTRIZATION. 



The apparatus is set in action by a battery composed of three 

 pairs of elements. These are enclosed within the drawers, U and 

 U' (iig. 52). There are two pairs in the upper drawer, and one in 

 the lower (fig. 54.) 



Each pair is composed of a carbon plate, C C (fig. 53), fixed to a 

 cell of hard caoutchouc, and of a zinc plate, ZZ', of the same 

 surface as the carbon, and separated from it by a cloth dia- 

 phragm. 



The platinum wires which form the carbon contacts are arranged 

 as in the small instrument (p. 267), while the zinc contacts differ 

 in each of the pairs: — 1, in the lower drawer, U (fig. 52), a strip of 

 iron, h (fig. 54), rivetted and soldered to the zinc Z, is bent 

 upwards at a right angle at its anterior extremity, in such a way 

 that, when the drawer is closed, the iron comes in contact with 

 a small plate of platinum fixed in the front of the apparatus on a 

 level with the knob L ; 2, in the further compartment of the upper 

 drawer, the zinc Z (fig. 53) is also prolonged by a strip of iron, h. 

 This strip is also bent upwards at a right angle at its anterior 

 extremity, and, when the drawer is closed, can be brought in 

 contact with another small plate of platinum fixed in the front of 

 the ajiparatus on a level with the knob G ; 3, lastly, the zinc Z' 

 (fig. 53), of the pair in the front compartment of the upper drawer, 

 rests on a platinum wire whicli winds over the posterior wall of the 

 cell, and comes in contact with a double spring, a, fixed to the 

 partition of the drawer, which spring, in the farther compartment, 

 rests by a platinized surface upon the carbon C. The left-side 

 drawer is absent in the figure, in order to display the arrangement 

 of the parts forming the two pairs. 



2. The two supei-posed coils forming the system of induction are 

 composed of two copper wires, differing in diameter and in length, 

 and covered with silk. 



The thicker and shorter of the two wires (half a millimetre in 

 diameter, and 200 metres in length) is rolled around a bundle of 

 soft iron wire, so as to form a coil. The extremities of this copper 

 wire, which produces the current of the first coil (the extra- 

 current of authors), terminate upon two small plates of platinum, 

 fixed to the apparatus at the level of the knobs E, L (fig. 52), 

 which are the positive and negative poles of the battery enclosed 

 in the drawers U and XT'. 



The finer and longer wire (one tenth of a millimetre in diameter, 

 and 1000 metres in length) is rolled around the one preceding. It 

 gives origin to the current of the second coil (current of the first 

 order, of authors) ; its extremities terminate at the two springs of 

 the commutator of the coils. 



