534 
MR. J. S. TOWNSEND ON MAGNETIZATION OF LIQUIDS. 
The connections were so made that (a) and (/3) almost cancelled one another, so 
that when the commutator revolved, and contact was made in the primary circuit 
with the battery, the deflection of the galvanometer in the secondary circuit could be 
reduced to zero by adjusting y, thus making M = 0. 
Let 
A = internal area of the section of the solenoid tube. 
N = number of turns in the primary coil. 
.N' = number of turns in the secondary coil. 
2 1 = length of primary. 
The mutual induction 
TttNITA 
21 
is changed to (1 -f- ink) 
4ttMN'A . . 
——— by introducing 
a liquid into the solenoid whose coefficient of magnetization is k. M is no longer 
zero, as the deflection of the galvanometer indicates, and if m is the amount bv which 
y must be diminished so as to reduce this deflection to zero we have 
ink . 
47rMN A 
21 
= m 
The balance M = 0 being again restored. 
We have thus a means of measuring k in terms of quantities which are easily 
found without involving in the formula the rate of rotation of the commutator or the 
value of the primary current. 
The method is therefore very easily adapted to determine whether k varies with 
the force, since the latter can be changed by altering the resistance of the primary 
circuit. 
The general plan of the arrangements is shown in fig. 1. The continuous line 
denoting the primary and the dotted line the secondary circuit. The solenoid A is 
connected with the other parts of the apparatus as shown. The two circular coils B 
are separated by ail ebonite sheet; the upper one belonging to the secondary circuit 
could be moved about till the mutual induction of the pair cancelled the mutual 
induction of the two coils A. The adjustable induction y is represented at C (and also 
in fig. 2), the primary circuit leading to the mercury cups at E by which the 
required changes in induction are made. D and G represent the commutator and 
galvanometer. The sensitiveness is not much diminished by increasing R the re¬ 
sistance of the primary, as it will be shown that in this case the rate at which the 
commutator revolves can also be increased without any danger of the Foucault 
current generated in the liquid having any efl’ect on the secondary current, as far as 
its effect on the galvanometer is concerned. 
It is convenient to have a key, K, in the primary circuit by means of which the 
current can be sent in either direction to the terminals, T, so as to reverse the 
