11 
at the beginning and at the end of the experiments, and the 
results were found to agree with each other and with the 
calculated values of resistance, thus showing that no short 
circuiting had occurred. 
The apparatus and the method employed were similar to 
Rowland’s, a ballistic galvanometer (made by Elliott Bros., 
of about 4,000 ohms resistance, and time of vibration about 
five seconds) being used to measure the induction kicks, 
which were brought within the range of the galvanometer 
(1) by using various combinations of the three secondary 
coils, and (2) by introducing resistance into the secondary 
circuit. The earth inductor was made in the Owens College 
workshop, and was wound with three coils, the first con- 
sisting of 20 turns of No. 20 copper wire, the second of 
863 turns of No. 28 copper wire, and the third of 3 turns of 
No. 20 copper wire. The area of induction of the first coil 
{ = mr^ 9 ^ is 67699 sq. cm., of the second coil is 1248500 sq. 
cm., and of the third is 10512 sq. cm. The ring was sus- 
pended in a tinned iron cylindrical vessel, which was 
surrounded by water contained in an outer vessel. The 
battery was insulated from the earth, and care was taken to 
avoid leakage between different parts of the apparatus. 
Test of Demagnetization Method . — The apparatus being 
connected, a medium current was sent through the primary 
coil, and the kick of the ballistic galvanometer needle on 
breaking the current was observed. (This kick gives a 
measure of the temporary induction, and it was found 
necessary, in order that successive kicks should be equal, 
that the current in the primary winding should be alter- 
nated a few times between each observation. If this was 
not done, the successive kicks gradually diminished for a 
time.) The maximum current was now sent through the 
primary coil, and then gradually diminishing alternate cur- 
rents until they became evanescent, the ring being agitated 
