Jor detecting Metallic Masses in the Human Body. 35 
The final form of apparatus adopted as the result of the 
above experiments is shown in fig, 11. With this arrange- 
ment and a battery of six bichromate elements freshly set up, 
Wwe were always sure of a hearing distance of at least 5™, 
although after the battery had been in use for some time the 
hearing distance hardly exceeded 4°. 
The following are the dimensions of the coils A B (fig. 11) 
and their resistance : 
Coil a eo External diameter ne 
nternal diameter _ =i 
epth ig 
Wire used, No. 23 (cotton covered). Resistance, 2 ohms. 
Coil B____External diameter. dian oie 3:30 
Hternal Giaiheler .. eke oe a 
Depth 
The face of the coil B projected beyond the face of coil A 4™. 
he balancing coils were made as nearly as possible the 
duplicates of A and B. The resistance of the coil of the tele- 
PAone employed was 75 ohms. ; ) 
Influence of Battery Power.—The following experiments were 
made with this apparatus (fig. 11) on July 20th, 1881, to test 
the influence of battery arrangements upon the hearing distance 
Of a leaden bullet: 
