Jor detecting Metallic Masses in the Human Body. 27 
“60 Irvine Pracr, Brooxtyn, July 16, 188). 
“Mr. J. Stantey Brown: 
“Dear Sir: I have made two new instruments on plans differ- 
ing from that _— but they yield no better results. The first 
consisted of tw o oblong coils arranged at right angles to each 
other, thus : 
Pig. 8. 
ifefufet 
“The outer coil ere: BE conn wire (No. 18) placed in con 
primary circuit, the inne 1 being of very fine wire (No. 36) 
and connected with a jelaphcia The parallel currents travers- 
ing the wires iret each other, and no audible effects are 
wire (Se. oo aced upon opposite sides of a coil of coarse wire 
fo coil tos une eon so that the induced cur- 
rents oritidiie each other, 
_ -1 am sorry to be obliged to say of this as of the other, ae: 
it is no more sensitive than the one sent. To produce the 
effects from the instrument which you have it will be ace 
to use all the batter y power possible without burning the coils, 
a two receiving telephones of the best constrnetion must be 
se 
“As I stated in the first instance, if the ball is more than two 
inches deep, I think it cannot be located by this wees : 
wad larger coils were used the stitrdtanilt might erative 
at a greater distance, but the area indicated as sonkaiiia the ball 
ag be so large that the result would be indefinite and without 
2 SHoping that hte Bell will be able to succeed, I remain, 
oe ae “Gro. M. Hopxrs,” 
