258 
PROFESSOR TYNDALL’S FURTHER RESEARCHES 
Now when bismuth is powdered and exposed to the action of 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 slight- 
est 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 powder and submitted to experiment. The following results 
were obtained : — 
XXXII. 
Cylinders of Bismuth Powder, 
length 3 inches, 
diameter 0‘7. 
Current direct. 
Position 1 . 640 
Position 2. 625 
Position 3. 596 
Current reversed. 
230 
245 
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 ex- 
hibits the characteristics of ‘‘a true diamagnetic 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 experi- 
ments, 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 moi’e 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 diamagnetic polarity would 
he much more easily distinguished in the same wayT 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 per- 
mitted to quote the following 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 protosulphate of iron, and employed as an experi- 
mental core; the velocity given to the machine at this and all average times was 
such as to cause five or six approaches and withdrawals of the core in one second ; 
