310 Magneto-Electric Illumination. [July, 



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 100 turns. The outer 

 end of the coil of one section forms the commencement of 

 the first coil of the next section, and so on. The whole of 

 the wire is therefore divided into 40 equal sections, being, 

 however, continuous throughout. 



To understand better how an uninterrupted current is 

 produced, let us imagine a line to be drawn equatorially, or 

 perpendicular to the lines of force between the poles of the 

 horseshoe magnet, and dividing the ring armature into two 

 parts ; suppose likewise that to the two ends of one of the 

 40 coils two wires are soldered, the other ends of which 

 are attached to a galvanometer. Now let the ring be 

 intermittently revolved in one direction, so as to give to 

 the said coil a succession of movements of about 10 degrees, 

 stopping each time to permit the galvanometer needle to 

 resume its normal position. It will then be seen that the 

 whole time the coil is above the equatorial line the galva- 

 nometer needle will be urged in the same direction, and the 

 currents may be called positive. But as soon as the said 

 coil crosses the equatorial position, the currents generated 

 in it will be negative, and in the opposite direction to what 

 they were at the other half of the circle. This expe- 

 riment shows that a reversal of the direction of move- 

 ment carries with it a reversal of the direction of the 

 current. 



From this insight into what is produced in one of the 

 sections, the general phenomena produced by the whole 

 circle of coils are easily understood. The 20 sections 

 which are on one side of the equatorial position are the 

 source of positive currents ; these may be of unequal in- 

 tensity among themselves, but for a uniform velocity of 

 rotation their sum is evidently constant, for as one coil 

 crosses the equatorial line from north to south an opposite 

 one comes up from south to north to take its place. On 

 the other hand, the 20 sections which are on the other side 

 of the equatorial line are the seat of negative currents, the 

 sum of whose intensities is likewise constant, and equal to 

 that of the positive currents. 



Thus the revolving armature presents two groups of coils, 

 generating two equal but opposite streams of electric force. 

 The wire being unbroken the currents neutralise each other, 



