A. G. Bell—An Induction Balance, ete. 45 
had been obtained from coils that were simply placed upon a 
table and adjusted by hand. 
¢ immediately proceeded to the Executive Mansion with 
the apparatus shown in fig. 13, prepared to make a trial, if it 
was deemed advisable ; but upon learning of the results of our 
later experiments the surgeons resolved to postpone any further 
trial until we could arrange the coils (fig. 17) in a portable 
By forced exertions the coils were arranged that same night 
in a wooden case, as shown in fig. 18. This case consisted 
essentially of two oblong blocks AB. A shallow circular 
recess was turned out in each block for the reception of one of _ 
the coils, and the two blocks were held together by four pins 
of ebonite, C, D, E, F, which passed up through slots in the 
upper block and were secured by ebonite thumb-screws. 
_When the instrument was completed [ found to my great 
distress that a balance could not be obtained by any adjust- 
ment of the apparatus. There was a position of minimum 
sound, and the telephone responded to a bullet presented to 
the central part G of the instrument; but the bearing distance 
did not exceed 3 or 4™_ whereas we had obtained with the 
Same coils before the construction of the wooden case a perfect 
balance and a hearing distance of 13°", 
ter numerous unsuccessful experiments had been made to 
nature of the defect. ‘ 
he coils (fig. 18) were then removed from their case, but a 
cursory examination revealed no defect. Upon trial, however 
