586 



THE POPULAR SCIENCE MONTHLY. 



Submit this annular electro-magnet simultaneously to the influence 

 of the two poles of the permanent horseshoe magnet, N S, and at the 

 same time imagine it to revolve on its axis in the direction shown by 

 the arrows. 



Fig. 2. 



The south pole, S, of the horseshoe magnet, will produce in that 

 portion of the ring, E, which is near it, an electric current in a partic- 

 ular direction, as may be inferred from what we have said respecting 

 the straight bar, Fig. 1. But the north pole, N, of the magnet, will 

 likewise produce in the part of the ring which is in its neighborhood, 

 E", an electric current flowing in the opposite direction ; and it is 

 easily conceived that, in the two portions of the ring, E', and E'", 

 which are in what may be called the mean position, there is no cur- 

 rent at all. If, therefore, we wish to collect the two contrary currents 

 produced simultaneously in the wire surrounding the electro-magnet, 

 we have only to connect the wires at the mean position to two con- 

 ductors by friction-contacts, F F', when the current can be carried 

 away to a galvanometer, G, and rendered sensible. 



The principle of the arrangement being thus understood, the con- 

 struction of the machine itself will be readily intelligible. 



It consists of a permanent horseshoe magnet, S, O, N, Fig. 3, be- 

 tween the poles of which revolves an electro-magnet. This electro- 

 magnet consists of a ring of soft iron, round which is wound an insu- 

 lated conducting wire, presenting no solution of continuity. It may 

 be conceived as being an ordinary straight electro-magnet bent round 

 in a circle, and the two ends of the conducting wire soldered together 

 to establish continuity. 



In Figs. 4 and V the electro-magnet is represented at A in section, 

 while in Figs. 3 and 5 it is shown at A with the covering wire on it. 

 It revolves round its axis on an axle to which movement is communi- 

 cated either by means of belting, or with toothed gearing, shown in 

 Figs. 3 and 4, worked by a handle, M. 



The current is generated and collected in the following way : The 

 wire surrounding the electro-magnet is, as we have said, continuous, 

 but it is disposed in 40 sections or elements, each consisting, say, of 



