Jor detecting Metallic Masses in the Human Body. 41 
and it became therefore desirable to do away with this source 
of resistance as much as possible. 
Return to original form of apparatus.—This led us back to the 
original form of apparatus that had first occurred to me (see 
fig. 1), in which a single pair of coils was employed. few 
other experiments, made July 29, 1881, will show the import- 
ance of the point attained. 
Fig.15. 
iW<€ 
Exp. 3. The two flat coils E F used in experiment 2 were 
arranged as in fig. 16, so as to form a balance by themselves. 
Result: Hearing distance, 7™. 
In all these experiments the battery used consisted of four 
cells (Leclanché.) 
Pig. 16. 
Exp. 4. The same coils used in Exp. 3 were tried again, as 
Shown in fig. 16, but with a battery of eight cells (Leclanché.) 
esult: Hearing distance, 8°7™, or nearly 34 inches—a re- 
Sult quite unprecedented in our experiments. 
The following are the dimensions of the coils K, F. 
Coil B.__.. Bviornsl diameter 6. 10 ™ 
Titernal diamoter 2 6 2a ec 2-5em 
Deoth oe ow dos ene ne tenon nent nee La 
Wire used, No. 23, (silk-eovered.) 
OM Pico. Retersal dametet co esi 
interhal diameter oo... ok c. - Bose ae 
Dye a eC eM ey niaeceut phan ered 1 
b si 
Wire used, No. 28, (silk-covered.) 
