Bodies are repelled from the Poles of a Magnet. 281 



Now it is not to be imagined that even in Coulomb's experi- 

 ments with the iron filings the molecular induction was abso- 

 lutely nothing, but simply that it was so enfeebled by the sepa- 

 ration of the particles that it was insensible in the experiments. 

 This remark ajiplies with still greater force to M. Matteucci's 

 experiments with the bismuth powder; for the enfeeblement of 

 a force already so weak, by the division of the diamagnetic mass 

 into powder, must of course practically extinguish all reciprocal 

 action of the particles, even supposing a weak action of the kind 

 to exist when the mass is compact. 



I will not here refer to my own experiments on compressed 

 bismuth, but will take a result arrived at by M. Matteucci him- 

 self while repeating and corroborating these experiments. "I 

 made," says JM. Matteucci, "two cylinders of bismuth precisely 

 of the same dimensions, the one compressed, the other in its 

 natural state, and found that the compressed mass had a diamag- 

 netic power distincthj superior to that of natural bismuth*.'" 

 Now M. Matteucci, in his Coiirs Special, has made his own 

 choice of a test of recipi'ocal molecular action ; he assumes that 

 if cylinders of the same length, but of different masses, have 

 equal times of oscillation, it is a conclusive proof that there is no 

 action of the kind referi-ed to. This necessarily implies the 

 assumption, that were the times of oscillation different, a x*eci- 

 procal action would be demonstrated. Now, according to his 

 experiments described in the Association Report, the times of 

 oscillation are diffei'ent; the diamaguetism of the compressed 

 cylinder is "distincthj superior" to that of the uncompressed 

 one : the diamagnetic effect increases in a greater proportion than 

 the quantity of matter ; and hence, on M. Matteucci's own pria- 

 ciples, the result negatived by his experiments on powdered bis- 

 muth is fairly established by those which he has made with the 

 compressed substance. 



APPENDIxf. 



Reflecting further on the subject of diamagnetic polarity, an 

 experiment occurred to me which constitutes a kind of crucial 

 test to which the conclusions arrived at in the foregoing memoir 

 may be submitted. 



Two square prisms of bismuth, 0"43 of an inch long and 0*2 

 of an inch wide, were laid across the ends of a thin plate of cedar 

 wood, and fastened there by white wax. Another similar plate 

 of wood was laid over the prisms, and also attached to them by 



* Report of British Association for 1852, Transactions of Sections, p. 7. 

 t llcceived December 21, 1854, 

 Phil. May. S. 4. Vol. 10. No. 66. Oct. 1855. U 



