170 Professor TyndsWs further Researches 



doubt that the bismutli cylinders produce the motion of the mag- 

 nets in virtue of their excitement by the voltaic current ; for it 

 is not certain that these cylinders would not produce the same 

 motion wholly independent of the current. Something of this 

 kind has occurred to M. Leyser * in his experiments, and why 

 not here ? 



In answer to this, I reply, that if the case be as here suggested, 

 the motion of the magnet will not be changed when the cun'ent 

 surrounding the bismuth cylinders flows in the opposite direction. 

 Here is the experiment. 



III. 



Position 1. 761 Position 2. 742 Position 3. 701 



We observe here that in passing from position 2 to position 1 

 the motion is from smaller to larger numbers ; while in passing 

 from position 2 to position 3 the motion is from larger to smaller 

 numbers. This is the opposite result to that obtained when the 

 current flowed in the opposite direction ; and it proves that the 

 polarity of the bismuth cylinders depends upon the direction of 

 the current, changing as the latter changes. It was pleasant to 

 observe the prompt and steady march of the magnet as the cylin- 

 ders were shifted in the helices. When the magnets, operated 

 on by the bars of bismuth, were moving in any direction, by 

 bringing the two opposite ends of the bismuth bars into action, 

 the motion could be promptly checked; the magnets could be 

 brought to rest, or their movement converted into one in the 

 opposite direction. 



I may add to the above a series of results obtained some days 

 subsequently in the presence of Professors Faraday, De la Rive 

 and Marcet. 



IV. 

 Bismuth cylinders. 



Position 1. 670 Position 2. 650 Position 3. 630 



The difference between positions 1 and 3 amounts here to forty 

 divisions of the scale; subsequent experience enabled me to 

 make it still greater. 



It was found by experiment, that when the motion was from 

 lower to higher numbers it denoted that the poles NN', fig. 4, 

 were repelled from the spirals, and the poles SS' attracted towards 

 them. When, on the contrary, the motion was from larger to 

 smaller numbers, it indicated that the poles NN' were attracted 

 and the poles SS' repelled. In the position fig. 1, therefore, of 

 Tables III. and IV. the poles NN' were repelled by the ends no 

 of the' bismuth cyhnders, and the poles SS' attracted ; while in 



* Scientific Memoirs, New Series, vol. i. page 184. 



