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444 A. G. Compton—Method of obtaining Autographic 
_ Art. LIL—On a method of obtaining autographic records of the 
free vibrations of a tuning-fork, and on the autographic record- 
ing of beats; by ALFRED G. COMPTON. 
THE exact determination of the rate of vibration of a tuning: 
fork by means of the siren has heretofore been attended with 
errors resulting from imperfections of the recording gear, and 
difficulty of maintaining and counting the beats of the two 
tones. I have sought to remove these errors by obtaining 
autographic records of the rate of the siren and of the differ- 
ence between this rate and that of the fork. The exper 
menter, while obtaining these records, being freed from the 
“necessity of even counting the beats, no personal element enters 
‘into the observation, and the records ‘being permanent, can be 
_ studied at leisure. The following is the method of obtaining 
the autographic records. - 
A strip of chemically prepared paper, which rests on 4 metal 
wheel, beiig drawn by clock-work under three platinum pens 
placed in electric circuits, three simultaneous electro-chemical 
records are received ne of these is a line of dots made at 
the rate of one a second, by a chronometer placed in the cir- 
cuit of the same battery with one of the pens. The second 1s 
a row of dots made by the closing of the same circuit by a 
siren once in each revolution, while singing nearly in unison 
with the fork. The third is a row of dots made by the closing 
of the circuit of a second battery, once for each beat of the 
fork and the siren. 
It thus results that from the same strip of paper can be. 
counted the number of revolutions made by the siren in any 
number of seconds (from which the number of impulses pro 
same time,—which is the difference between the number. of 
Shocks imparted to the air by the siren and the number 1m 
parted by the fork. The record being made without throwing 
work upon the fork, the rate of vibration of the uncon- 
strained fork results. 
The following description will give an idea of the details of 
the method. 
A break-cireuit chronometer J and a relay W are included 
in the circuit of a battery B of one carbon cell. The arma- 
ture A is therefore freed from the magnet once a second by 
oe 
the break-cireuit mechanism of the chronometer. When the — 
armature is thus freed, a platinum point P closes the circuit of 
another battery B’, the current of which then passes thromey ee 
to 
the armature A, the platinum contact point c, the pen ee 
metallic wheel R on which the pen point rests, and so back to 
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