50 A. G. Bell—Ezxploring for an imbedded bullet. 
effect.* I was unable to continue experiments with the steel 
mattress, as just at this time I was obliged to leave Washington 
on account of illness in my family. ‘Although I was unable 
or a long time Stern erde to carry on eieaeergd induction 
_ ment of Mr. Ch arles Williams, Jr., 
Haperiments continued in Boston. Mn Tainter forwarded from 
Washington drawings of an improved apparatus he had designed 
to remedy the defects of the instrument shown in fig. 18, in 
which the case, adjusting screws, etc., were all to be composed 
of ebonite. 
Mr. Gleason constructed for me a number of such ebonite in- 
struments differing slightly from one another in detail, and the 
apparatus shown in fig. 20 combined the different points that 
had been approved. 
he two coils A B were eccentrically arranged in two cir- 
cular disks of ebonite, © D, and the adjustment was obtained 
by means of an ebonite key O, like the key used for ge 
pianos, which turned a cam pivoted in the upper disk an 
wore ing | in a slot N in the lower disk. 
order to prevent any movement of the coils, eae 
oe Sede by the adjusting-key O, each coil was placed in 
a recess turned out in its ebonite disk, the edges of ich were 
bevelled as shown at R. Paraffine was then poured in so as 
to fill up each recess. But this alone did not prevent a slight 
pulsation of sound when the instrument was swayed from side 
to side, and a very slight pressure of the finger on the thin 
portion of the ebonite plate under the coil B was sufficient to 
aes the balance. 
an amit thumb-secrew H. thie ceil increased the 
difficulties of adjustment. When the coils were adjusted to 
silence, then the tightening of the thumb-screw H disturbed 
*The death of President Garfield and the subsequent post-mortem Se. 
however, proved that the bullet was at too great a distance from the 
have our apparatus, 
