306- 



LOCALIZED ELECTRIZATION. 



{g). Trouves electric roll. — " The small induction coils con- 

 structed by this skilful mechanician are chefs d'oeuvre of in- 

 genuity and precision. One of these coils is 

 shown at B, in fig. 90, at half the natural 

 size. 



" We have already described the inter- 

 rupter employed by M. Trouve. 



'"' His coil is composed of a very delicate 

 plate of soft sheet-iron, rolled into a helix, 

 and surrounded by a copper graduating-tube, 

 the end of which is seen at 0; the inductive 

 wire and the induced wire are placed end- 

 wise ; the first forms six layers, the second 

 eighteen. 



" The knobs for the rheophores are placed 

 at 5 and 1 . The extra current of the two 

 layers, the complete extra current, the 

 induced current only, and the combination 

 of both currents may be obtained. 



"Single intermissions are produced by 

 interrupting with the hand the contact be- 

 tween the battery and a small knob attached 

 to the coil for the purpose. 



" The battery, which is shown at A, is a 

 box of hard caoutchouc, closed by a screw 

 lid, which carries a cylinder of zinc, a little 

 less than half the length of the box. The 

 latter is half filled with water, to which is 

 added three or four grammes of bisulphate 

 of mercury. It follows, from this arrange- 

 ment, that the battery only acts when the 

 box is placed wdth its lid downwards. Thus 

 charged, it will work for about an hour and a 

 half. 



"The effects of this small apparatus are 

 comparatively remarkable, and are to be 

 explained by the care shown in its construc- 

 tion, by the complete insulation of all its 

 parts, and by its perfect combination of the 

 conditions most favourable for producing 

 the results that are desired. 



" It is only just to add, that M. Gaiffe long since prepared the 

 wav for the manufacture of small induction coils ; but M. Trouve' 



(5) 



/m 



Fig. 90. — Trouve's electric roll. 



