OF CRYSTALS BY THE POLES OF A MAGNET, 355 



light bodies immediately in a double loop of a single or double 

 silkworm thread, from 60 to 300 millim. in length, and fastened 

 with a little wax to the end of the thick thread which passes over 

 the arm of the torsion-balance. The suspensions are best made 

 in the glass case itself, because the single silkworm thread is 

 more readily seen there ; and after a little practice it is easy to 

 make twenty or thirty different suspensions of such a thread in 

 an hour. Moreover, in this manner we can test as to their mag- 

 netism or diamagnetism, bodies which are not greater or heavier 

 than a single stamen of a cherry-tree flower. 



To excite the magnetism in the electro-magnet, I used through- 

 out the following experiments merely three or four small Groves's 

 elements, combined to form a battery. The platinum was im- 

 mersed in commercial nitric acid, the zinc in a mixture of 1 part 

 of concentrated sulphuric acid and 9 of water. 



3. During the month of May I made a large number of expe- 

 riments, which appear to yield the general result, that in each 

 individual plant (and perhaps animal) constant magnetic and 

 diamagnetic counteractions are in play, and are in connexion 

 with their physiological development. I shall reserve the de- 

 tails for a future communication, and merely remark, that these 

 experiments led me to examine whether the arrangement of the 

 fibre exerted any influence upon the position assumed by vege- 

 table structures suspended between the two poles of the magnet ; 

 and here the question incidentally occurred to me, whether the 

 crystallographic structure of a ciystal suspended in the same 

 manner exerted any influence. The very first experiment decided 

 this positively. 



4. I took, for instance, a green plate of tourmaline, as prepared 

 by M. Soleil, for the polarization of light. It was 3 raillira. in 

 thickness; its largest surfaces were nearly square, being 12 millim. 

 in length and 9 in breadth. The longitudinal direction of 

 the plate corresponded with the direction of its optic axis. On 

 suspending this plate by a silk thread, so that the direction of 

 the thread coincided with the direction of the optic axis, it assumed 

 the same position as any other magnetic body of the same form 

 would have done, i. e. so that the direction of its breadth coin- 

 cided with a straight line connecting the two apices of the poles, 

 and the plate maintained this position decidedly, even after the 

 polar apices were removed. This result 1 had anticipated, be- 

 cause the plate of tourmaline was so strongly magnetic, that 



2 B 2 



