8 PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
eight cases the fibre set either oblique or axial. The whole thirty-five specimens 
were carefully rescraped with glass and tested once more; still two remained, which, 
though repelled as masses, persistently set with the fibre axial, and oscillated round 
this position so steadily as to lead to the supposition that the real deportment of the 
substance was thus exhibited. I scraped these cubes ten times successively, and 
washed them with all care, but the deportment remained unchanged. The cubes, 
for the sake of reference, had been stamped with diminutive numbers by the maker 
of them ; and I noticed at length, that in these two cases a trace of the figures 
remained : on removing the whole surface which bore the stamp from each, the cubes 
forsook the axial position, and set, like the others, with the fibre equatorial. 
The influence of the mere form of an impurity was here very prettily exhibited. 
The cubes in question had been stamped (probably by an iron tool) with the numbers 
33 and 37, which lay in the line of the fibre; the figures, being dumpy little ones, 
caused an elongation of the magnetic impurity along the said line, and the natural 
consequence of this elongation was the deportment above described. 
Of the thirty-five specimens examined one proved to be paramagnetic. Now, it 
may be asked, if the views of molecular action stated in the foregoing pages be correct, 
how is it that this paramagnetic cube sets its fibre equatorial ? The case is instructive. 
The substance (bog oak) had been evidently steeped in a liquid containing a small 
quantity of iron in solution, whence it derived its magnetism ; but here we have no 
substitution of paramagnetic molecules for diamagnetic ones, as in the cases referred 
to. The extraneous magnetic constituent is practically indifferent as to the direc- 
tion of magnetization, and it therefore accommodates itself to the directive action 
of the wood to which it is attached. 
II. ON THE ROTATION OF BODIES BETWEEN POINTED MAGNETIC POLES. 
In his experiments on charcoal, wood-bark and other substances, M. Plucker 
discovered some very curious phenomena of rotation, which occurred on removing 
the substance experimented on from one portion of the magnetic field to another. 
To account for these phenomena, he assumed, that in the substances which exhibited 
the rotation two antagonist forces were perpetually active — a repulsive force, which 
caused the substance to assume one position ; and an attractive force, which caused it 
to assume a different position : that, of these two forces, the repulsive diminished 
more quickly than the attractive, when the distance of the body from the poles was 
augmented. Thus, the former, which was predominant close to the poles, succumbed 
to the latter when a suitable distance was attained, and hence arose the observed 
rotation. 
Towards the conclusion of the memoir published in the September number of the 
Philosophical Magazine for 1851, I stated that it was my intention further to examine 
this highly ingenious theory. I shall now' endeavour to fulfil the promise then made, and 
to state, as briefly as I can, the real law which regulates these complex phenomena. 
