VARIOUS GENERATORS OF ELECTRIC LIGHT. 87 



ring of the Gramme machines are added to those produced 

 in the ordinary magneto-electric machines. 



In order that it may be understood, let us imagine a 

 Gramme ring (Fig. 24) divided, for example, into four sec- 

 tions, magnetically insulated from each other, and therefore 

 forming four curved electro-magnets placed end to end. Let 

 us imagine that the iron core of each of these sections is ter- 

 minated at its two extremities by a piece of iron, A B, form- 

 ing an expansion of its poles; and let us suppose that all 

 these pieces, connected by means of a piece of copper, c D 9 

 constitute a solid ring, round which are placed the permanent 

 magnets, N s N s, with their poles alternating. Let us 

 examine what will happen when this ring completes a rotary 

 movement on itself; and let us first observe the effect that 

 will result, for example, from the approach of the expanded 

 pole B, as when moving from left to right it approaches N. 

 At this moment there will be developed in the electro- 

 magnetic coil of A B an induced current of magnetization, as 

 in Clarke's machine. This current will be instantaneous, 

 and in the reverse direction from Ampere's particular cur- 

 rents of the inducing magnet. It will be very energetic, on 

 account of the nearness of B to the pole N ; but the ring in 

 advancing sets up between the pole N and the core A B a 

 series of magnetic displacements which will give rise to a set of 

 currents of reversed polarity showing themselves from B to 

 A. These currents will be direct, as compared with the par- 

 ticular current of N, but they are not instantaneous, and go 

 on increasing in energy from B to A. To these are at the 

 same time united the currents of dynamical induction result- 

 ing from the passage of the spires of the coil before the pole 

 N. When A leaves N a current of demagnetization is pro- 

 duced equal in strength to, and in the same direction as, the 

 induction current resulting from the approach of the expan- 

 sion B to the pole N. The effect is, in fact, then produced 

 at the other end of the magnetic core, and the coil is pre- 

 sented to the inductive action in the reverse way. There 



