450 A. G. Compton—Method of obtaining Autographic 
one second. In this way, after several. adjustments, the dura- 
tion of the armature-excursion and that of the siren were made 
very nearly equal and each equal to about 0°009 second. 
ith this adjustment, the ‘‘ frequency” of the fork as found 
by counting the number N of revolutions of the siren and the 
number n of beats in a number N’ of seconds, would be, if the 
siren was higher than the fork and if the number of holes in 
j 1oN—n ‘ nee 
the siren was 10, —,—-; and this determination would be 
exact, if the two coincidences were exact. As the error in the 
coincidences is + (a—b +1) the possible error in the frequency 
of the fork would be, neglecting 4, or 
5 were nearly equal and N’, as was frequently the case, was as 
great as ten or twelve seconds, the method would seem to 
promise a high degree of precision. 
e following table shows the results obtained with one of 
Koenig’s vowel-sound forks (marked OU) : 
) so that when a and 
Vibration No. of Vibrations Time Vibrations 
Exp. of siren, beats. of fork. seconds. per second. 
i Oe 8 1730 25 1705 5 341-0 
gAuvmi te 3100 30 3070 9 34171 
3 “10 1040 16 024 3 341°33 
Pee | 3100 316 3068-4 9 340°93 
Meas Sete 8 2770 43 272 8 340°9 
& oy 1390 25 1365 4 341°25 
igo it 2060 15 2045 6 340°83 
$2 MOE 4470 415 28°5 13 340°66 
Qoi2% Sy 1040 16°7 1023°3 3 34171 
16,9" 8 49 2071 26°6 2044°4 6 340°73 
tL. te 00 115 8 sh 341°2 
19: 4 %.48 3099 29°6 3069°4 9 341-04 
4092°07 
Mean, 341° 
The temperature during the experiments varied from 68° to 
73° F. and the rate of beating from 14 to 6 beats a second. _ 
Nine selected experiments on October 20, 27 and 30, being 
experiments in which the coincidences were the most perfect 
and the records the clearest, gave the following results: 
Repos eae sheala: Nae oe Seana 
1 3780 29°25 3750°75 340 
2 1730 25-6 1704 5 340°88 
3 3460 51-6 2408 10 340°84 
4 2410 23°5 2386 7 340°93 
5 1030 725 1022-75 3 340°92 
6 5 1023°5 3 341-17 
q 4130 38°45 4091-55 12 340°96 
8 2750 22-98 2727-72 8 340°96 
9 5540 8 515552 340°97 
T=173° Mean. 0°96 
