WITH THE CAVENDISH APPARATUS. 
227 
The two last examples are taken from the 25th series, 2-inch lead balls with single 
copper wire, diam. *0219 inch ; and what is very remarkable is, that the time of vibra- 
tion remains throughout nearly the same, 253 seconds. And since 
7r 2 £E ia TiNUc 
T * =m p p 5 
• Jc^JLic 
this circumstance shows two things, first that the term -p— must be exceedingly 
small, and therefore c very small ; and also that m 2 , and therefore the force of torsion 
is not sensibly changed. 
I have therefore, I conceive, satisfactorily shown that the masses and balls do exert 
influences on each other independent of the action of gravitation, and that such in- 
fluences are of a very fluctuating nature, and the action arising from them is either 
positive or negative ; and changes as to sign when the masses are turned round a 
vertical axis through 180°, or thereabouts. Moreover, that such action may either 
fall short of that arising from gravitation, or exceed it many times. 
It is inconceivable that this disturbing force can arise from anything but magnetic 
influence, and in this we must remember there are three distinct modifying causes at 
work, — first, terrestrial influence ; second, mutual influence of masses and balls ; and 
third, the alternate motion of the masses changing from one position to the other. 
I am of opinion that ordinary magnetic influence is inadequate to the explanation of 
the motions, or rather of the disturbing force demonstrated to have an existence, and 
that, as all the substances used are such as are classed by Dr. Faraday amongst the 
diamagnetic , that new magnetic condition discovered by this illustrious experimen- 
talist is also greatly concerned as a cause. It will probably be found that both spe- 
cies of magnetism combine in producing such very extraordinary results. The cir- 
cumstance of the numbers proportional to the gravitating influence not exactly agree- 
ing is easily explained. The simple condition M+M'=0, which we have assumed, is 
of course not accurate, and the wonder is that it answers so well. 
But we now come to the question how future experiments with the torsion balance 
are to be conducted so as to arrive at a satisfactory conclusion as to the mean den- 
sity A. It has occurred to me that, instead of using diamagnetic substances, we 
should have hard iron balls possessing the ordinary magnetic state in sufficient in- 
tensity to render their magnetic effect sensible, so that we may with precision ascer- 
tain the magnetic axes of each iron mass and ball. Suppose the balls placed on the 
rod so that their magnetic axes shall be in the direction of the rod and therefore 
horizontal. Let the rod be suspended in the magnetic meridian, and let the masses 
be placed with their magnetic axes vertical, and centres in the same horizontal plane 
with those of the balls. The contiguous masses and balls would exert no magnetic 
force on each other perpendicular to the length of the rod, and the resolvent of mag- 
netic force of a further mass on a nearer ball, or a further ball on a nearer mass per- 
2 g 2 
