WITH MAGNETISM AND ELECTRICITY. 183 



bar is again suffered to descend; the magnetic needle then 

 moves back with increased velocity. When the maximum elon- 

 gation on this side has been attained, the bismuth bar is again 

 raised, and so on. Between every two elongations let the posi- 

 tion of the bismuth during the intervening time be noted. If 

 the bismuth bar be exchanged for an iron bar of equal length, 

 but very thin, the experimenter can convince himself that when 

 the positions of the bars are the same, the deflections of the 

 needle produced by the iron and the bismuth are opposite in 

 direction. 



M. Leyser of Leipzig has constructed this instrument in the 

 simplest and most convenient manner (for 25 dollars without 

 the telescope) ; it deserves to be particularly recommended for 

 its applicability to this fundamental experiment on diamagnetic 

 polarity. In connexion with the results of certain experiments 

 made by him and Prof. Hankel, M. Leyser communicates to me 

 as follows : — 



"A current of four elements of Grove was made use of, and 

 by means of a multiplier the magnet was retained in its former 

 position. The bismuth was chemically pure, and was so sus- 

 pended that it could be moved up and down by means of a 

 string, without shaking the magnet in the slightest degree. 



Observations of Leyser : — 



Position of magnet without current 492-0. 



With current, bismuth in the middle . . 493*5 



„ bismuth above .... 490*8 



„ bismuth below .... 499*8 



„ bismuth above . . . . 491*1 



,j bismuth in the middle . . 493*8 



We here observe, in coincidence with all other experiments 

 executed in a similar manner, that in drawing up the bismuth 

 (from the middle to the top) the position of rest for the magnet 

 moved to smaller numbers, and by permitting it to descend 

 (from the middle to the bottom) the position of rest moved to 

 higher numbers. The difference between top and bottom 



amounts to 



+ 8*9 divisions of the scale. 



o 2 



