on the Polarity of the Diamagnetic Force* 183 



the air, it very soon becomes tarnished, even without heating. 

 A quantity of such powder was prepared, and its conducting 

 power for electricity tested. The clean ends of two copper wires 

 proceeding from a battery of Grove were immersed in the powder ; 

 but though the wires were brought as near as possible to each 

 other, short of contact, not the slightest action was observed 

 upon a galvanometer placed in the circuit. When the wires 

 touched, the needle of the galvanometer flew violently aside, thus 

 proving that the current was there, but that the powder was 

 unable to conduct it. Two glass tubes were filled with the pow- 

 der and submitted to experiment. The following results were 

 obtained : — 



XXXII. 



Cylinders of Bismuth Powder. 



Length 3 inches. Diameter 0*7. 



Current direct. Current reversed. 

 Position 1. 640 230 



Position 2. 625 245 



Position 3. 596 260 



These deflections are the same in kind as those obtained with 

 the cylinders of massive bismuth. This experiment responds 

 perfectly to the conditions proposed by Mr. Faraday. We have 

 here no cessation of action. The division of the mass does not 

 affect the result seriously or in its essential nature, and hence 

 the deportment exhibits the characteristics of " a true diamag- 

 netic polarity." 



In summing up the results of his inquiry on this subject, 

 Mr. Faraday writes thus : — " Finally, I am obliged to say that 

 I can find no experimental evidence to support the hypothetical 

 view of diamagnetic polarity, either in my own experiments, or 



in the repetition of those of Weber, Reich and others It 



appears to me also, that, as magnetic polarity conferred by iron 

 or nickel in small quantity, and in unfavourable states, is far 

 more easily indicated by its effects upon an astatic needle, or by 

 pointing between the poles of a strong horseshoe magnet, than 

 by any such arrangement as mine or Weber's or Reich's, so dia- 

 magnetic polarity would be much more easily distinguished in the 

 same way." I was struck, on reading this passage, to find how 

 accurately the surmise has been fulfilled by the instrument with 

 which the foregoing experiments were made. In illustration of 

 the powers of this instrument, as compared with that made 

 use of by Mr. Faraday, I may be permitted to quote the follow- 

 ing result from his paper on supposed diamagnetic polarity 

 so often referred to : — " A thin glass tube, 5^ inches by three- 

 quarters of an inch, was filled with a saturated solution of proto- 



