46 A. G. Bell—An Induction Balance 
(being arranged, as formerly, in fig. 17), a balance could not be 
obtained, and the hearing distance was only about 4™. The 
defect was thus definitely located in the coils ee 
Figt9 
Upon close examination it was noticed that the outside con- 
volutions of the primary coil were slightly frayed at one part, 
but it appeared hardly possible that so great a Dard could be 
due to so apparently slight a cause. However, to test the mat- 
ter, I removed the outside layer of wires and he tested the 
coils again. 
Result: The defect had vanished—a aes balance was ob- 
tained, ‘and the hearing distance was again 
* These experiments have revealed the cause of the extreme difficulty always 
} 
veloc fatal to the success of an Induction Balance. Indeed, so 
required i respect that it is jestreeicly difficult to obtain coils that are per- 
fectly suitable — an apparatus intended to search out a bullet imbedded in the 
body. tie e it a rule to test every helix used in Induction Balance ex- 
perim by b ringin g it up om a system of balanced coils like that shown in fig. 19. 
RR Lg rf the helix is perfect the balance is not disturbed until the terminals of the 
coil are connected. 
2. If there is a break in any of the convolutions the balance i is not disturbed, 
ag when the terminals are co 
. If a convolution is short-circuited the balance is disturbed, even though 
