510 Proceedings of Societies . [July, 
position, because its maximum effedt overbalances its eledtrical 
effect. Two pieces of iron may therefore neutralise each other 
as cores in an indudfion coil. Steel is easy to balance compared 
with soft iron. Zinc disturbs most when placed along the sides 
of each pair of coils ; iron when in centre. A certain length of 
metal laid along the outsides of the coils produces silence. The 
maximum line of indudlive force is midway between the coils, and 
there is a line of minimum force at half the thickness of each coil ; 
a metal placed at these lines of minimum force has no disturbing 
effedt on the balance. Pressure, torsion, heat, magnetism, strain, 
and in fadt all imponderable forces, are indicated, and their effedts 
may be measured. 
Prof. W. G. Adams believed that one result of Prof. Hughes’s 
experiments will be the determination of the way in which the 
law of eledtro-dynamic indudtion depends on density. He also 
imagined that the metal when in the maximum line between the 
coils gathered the lines of force to itself, whereas when on the 
minimum lines it could not thus divert them. 
Prof. Ayrton cited the early experiment of Faraday with a sheet 
of copper oscillating to rest between two opposite magnetic poles. 
The copper took a long time to stop ; but a sheet of iron placed 
between two like poles was soon stopped, owing to its becoming 
imbued with an opposite polarity, and defledting the lines of force. 
He also suggested that the divergence of the results for conduc- 
tivity of metals got by the indudtion balance from those got by 
the Wheatstone balance might be due to that eledtric inertia sus- 
pected by Sir William Thomson. 
Prof. Guthrie thought that the indudtion balance pointed to the 
conclusion that the disturbing effedt of a condudting mass applied 
in this way is proportional to the quantity of eledtricity generated 
in it under certain conditions of temperature, &c. The deter- 
mination of the condudtivity of liquids would be a useful applica- 
tion of the balance. 
Mr. Chandler Roberts gave some results which he had obtained 
from an examination of certain alloys by means of the indudtion 
balance. He had been able to detedt a difference of i part in 1000 
in the amount of silver present in two shillings of equal weight. 
He also pointed out that Matthiessen divided alloys into three 
classes : — (i) Solidified solutions of one metal in another ; (2) 
Solidified solutions of one metal in an allotropic modification of 
another metal ; (3) Solidified solutions of allotropic modifications 
of both metals. For the first class the curve of eledtric conduc- 
tivity is a straight line ; for the second, a parabolic curve ; for 
the third, a bent line. Mr. Roberts found that the balance gave 
the charadteristic curve for the first class with an alloy of lead 
and tin, and for the second with an alloy of gold and silver. With 
a copper-tin alloy, which is a good example of the third class, he 
found the curve given by the balance to be intermediate between 
Alfred Rich’s curve of density and Matthiessen’s curve of conduc- 
