1884.] on Volta- Electric and Magneto- Electric Induction. 129 



increase is very small, the current produced by the two metals being 

 as 1 to 7, at a speed of about 1300 revolutions per minute. The 

 higher the specific conductivity of the diamagnetic metal, the greater 

 the " drag," and consequently the less the current at the poles, this 

 being more manifest at the high speeds, which does not, however, 

 agree with the results obtained by Faraday, for he found that the 

 currents were proportionate in strength to the conducting power of 

 the bodies experimented with, or, in other words, that the higher the 

 conductivity the greater the current, whereas I find the reverse to be 

 the case, as shown on the diagram before you. 



Faraday also obtained much better results from copper than from 

 iron, and thus he recommended copper for his new magneto-electric 

 machine. Here, again, my results do not agree with his, for I find 

 that iron gives much better results than copper, as shown on the 

 diagram ; and also that iron has the advantage that the current in- 

 creases almost in direct proportion to the speed, whereas copper does 

 not ; in fact, as already stated, a speed might be obtained at which 

 copper would give no current. 



Faraday, in summing up the results of his experiments on Arago's 

 phenomenon, says : " Nothing can be more clear, therefore, than that 

 with iron and bodies admitting of ordinary magnetic induction, 

 opposite poles on opposite sides of the edge of the plate neutralise 

 each other's effects, while similar poles exalt the action. But with 

 copper, and substances not sensible to ordinary magnetic impressions, 

 similar poles on opposite sides of the plate neutralise each other, and 

 opposite poles exalt the action." Perhaps you will more readily grasp 

 the subject by reference to the diagram marked 4, in which P repre- 

 sents the plates of metal, and the other letters the respective poles of 

 the magnet and their position. 



Plate 4. 

 faraday. results of my experiments. 



nIs nIn sis si nI n|s n|n s|s s| n| 



IRON I I I I I IRON 



NIL MAXIMUM ^ ' 624 192 L 192 R 



nIs nIn sis si nI nIs nIn sis 



COPPER I i I I I COPPER III 



MAXIMUM ^""HiC^ ^ GOOD*^ '30 48L 48R 



Here again it will be seen that the results obtained by me are opposed 

 to those given by Faraday. I have given the actual figures obtained 

 in my experiments, and it will be seen that the only difference between 

 Vol. XI. (No. 78.) k 



