SCIENTIFIC AND TECHNICAL LABOURS TO 1860. 231 



Universal Exhibitions of London and Paris, several 

 mechanical arrangements constructed by us for this 

 purpose, but they had at first the drawback that the 

 currents of high tension obtained were not of uniform 



o 



intensity. It was only through the construction of my 

 so-called "plate" machine that the problem of the pro- 

 duction of uniform currents of nearly constant tension 

 by voltaic induction was actually solved. 



This "'plate " machine consists essentially of a 

 large number of electro -magnets, which are grouped 

 in a circle, and the so-called "plate", a conical piece 

 of iron, whose apex lies in the centre of the circle 

 of magnets, is set rotating above their poles. The 

 magnets are furnished with double coils, of which one 

 half of the inner ones are always inserted in the circuit 

 of a battery composed of a few large elements and 

 by a suitable contact arrangement the contact being 

 always a fourth of a revolution in advance of the rolling 

 "plate" - cause the rotation of the plate, whilst the 

 outer ones are collectively united into a closed con- 

 ducting circuit. The iron cone by rolling over the 

 magnetic poles produces in the secondary coils of the 

 magnets inserted in the battery circuit an induced 

 current in one direction, but on the other hand in 

 those of the magnets outside the battery circuit an 

 induced current in the opposite direction. The two 

 induction currents would neutralise one another, and 

 no current could at all arise in the secondary circuit, 

 unless at two oppositely situated points of this circuit 

 there was a continuous contact, by which the opposed 



