Jor detecting Metallic Masses in the Human Body. 33 
Continuing the experiment, the coil B was moved a deter- 
mined distance beyond the plane of A, and the balancing coils 
again adjusted to silence. The brass ring C was once more 
caused to disturb the balance, and the new hearing distance was 
noted. ‘The results of a series of experiments made on the 19th 
of July, 1881, are tabulated on the preceding page. The battery 
employed consisted of six bichromate cells connected in series. 
These figures show that the distance from the primary coil A 
(fig. 8) at which the influence of the brass ring C became perceptible 
mereased with the diameter of the primary ring, and that the sec- 
ondary coil B required to be projected considerably beyond the plane 
of the primary in order to obtain the maximum effect 
_ The conclusion seemed a natural one that the degree of pro- 
Jection A B of the secondary coil should proportionally increase 
with the diameter of the primary ring, but the tabulated figures 
did not fully justify the inference. 
_ The experiments had necessarily occupied a considerable 
time, and I thought that the difference between the results that 
should have been observed, according to the above hypothesis, 
and those that were actually obtained, might have been due to 
the gradual exhaustion of the bichromate battery employed and 
: y- 
t will be seen by reference to the tabulated statement shown 
above that the maximum hearing distance ad been ob- 
Hearing distance. 
- Apparatus tried with 1 cell (bichromate battery). ..(B C, fig. 8) = 9™™ 
- Six cells in series 
: B 
: B es 
3. Six cells in multiple are B = 
4. Six cells in two series of 3 each B O, fig. 8) = 15™™ 
6. Same experiment repeated _- (B = 13°5™™ 
6. Same experiment repeated by Mr. Tainter.------- (B =< ig oom 
I concluded, therefore, that if the battery power had re- 
mained constant, the hearing distance might not only have been 
Proportional to the diameter of the primary ring, but, in order to 
attain the maximum effect, the projection of the secondary coil 
beyond the plane of the primary might also bave been found 
to increase in like proportion. 
AM. Jour. 8c1,—Turrp Series, Vor. XXV, No. 145,—January, 1883. 
3 
