40 A. G. Bel—An Induction Balance 
and well-marked sounds were heard in the telephone; and in 
he case of John McGill, who was supposed to carry a bullet 
n his back, no results were obtained. 
Further efforts were then prosecuted for the improvement of 
the apparatus 
Further experiments to improve apparatus.—Our attention had 
hitherto been directed chiefly to modifications of the exploring 
instrument. We now investigated the effect upon the hearing 
distance, of the coils used to obtain a balance. 
The following experiments, made July 29, 1881, bear upon 
the point: 
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Exp. (See fig. 14.) Resistance of primary A of ex- 
loving fetuaaee 2 ohms; resistance of primary C of bal- 
ancing coils, also 2 ‘ohms ; resistance of e he bee cam J B, 
140 olims; and of balancing secondary D, 120 oh 
Result : "Hearing distance of bullet from explorer A A B, 36%. 
Hearing distance from balancing coils C D, also 8°5 
xp. 2. (See fig. 15.) Same exploring coils as in Exp. 1 
but balancing son consisted of a flat primary, E—resistance, 
5°30 ohms; and flat secondary, F—resistance, 83 ohms. The 
adjustment was made by sliding the pe ene! ry coil upon the 
primary until a position of silence was obtain 
Result: Hearing distance from explorer re B, 15™. Hear- 
ing distance from EF, 3™ 
_ As a general fel of our ex eriments we found that ever 
mnerease in the rsistance of the balancing coils (especially the 
primary) reduced the reset! distance of the exploring instrument, 
