Electro-Motive Force and Current Curves. 



157 



The Electrometer can be alternatively connected to the 

 terminals of the lamp, for the E.M.F. curve, or to the 

 terminals of a resistance of 5 ohms for the current curves. 

 This is done by the key k. 



The Lamp used was a simple hand regulating one, and 

 therefore had no series coils and no self-induction. 



Two curves were taken at the poles of the alternator, 

 one with the lamp direct to the dynamo, the other with a 

 resistance of 1 ohm in series. 



On the same sheet, the current and E.M.F. curves of 

 the lamp with 5 ohms in series are shown. 



W 



Fig. 



Blondil. — It is interesting to compare these curves with 

 some obtained by the French electrician Blondil. — The 

 Electrician, December 15, 1893. Some of these curves 

 almost exactly agree with the ones drawn on Plate VII. 



Surging of Lines. — Plate VIII. shows the surging of the 

 lines of force of the field magnets. This was measured by 

 fitting over one of the field coils a light wooden frame which 

 carried 155 wires stretched radially across the face of the 

 pole, in the air gap between the fields and the armature. 

 The surging of the lines past these induced in them an 

 E.M.F, which was measured in the usual way by the electro- 

 meter through the intermittent contact apparatus. The 

 induced E.M.F. is proportional to the rate of motion of 

 the magnetic field. This motion must in a large degree 

 account for the deviation of the electro-motive force 

 and current curves from simple sine curves. 

 L 



