144 
DRS. GUY BARLOW AND H. B. KEENE ON THE ANALYSIS OF SOUND. 
When bowed 8 metres away a response 150 div. was obtained. (The magneto¬ 
phone gave 20 div. under the same conditions.) When a 512 resonance box was placed 
in front of the microphone the response was increased to over 200 div. 
Fork 2048 bowed at 2 metres gave 200 div. 
It was noticed that the overtone of a certain pipe blown gently gave abnormal dis¬ 
turbances of the microphone without the interrupter. This disturbing frequency was 
found to be about 1030/sec. Starting and stopping a 1024 fork gave violent kicks on 
the galvanometer, indicating a large increase of microphone resistance during the 
vibration. This change of resistance was shown directly on the milliammeter in the 
microphone circuit. This effect suggested that the microphone would be abnormally 
sensitive to a note of about this frequency. This was actually the case ; thus it was 
shown that the microphone as a detector was as sensitive as the ear for this particular 
frequency. E.g., fork 1024 when bowed in adjoining room with doors shut was detected 
by the galvanometer ; to the ear the note was only just audible. 
Also this instrument was extremely sensitive to taps on a fork resonator-box, and 
also in a less degree to almost any sharp taps given by wooden objects— e.g., putting 
down tool on table or walking about on wooden floor ; locomotive whistles from the 
railway near by were especially effective. 
(2) Note from Harmonica / (Ellis). —The note selected had a fundamental frequency of 
66/sec. All harmonics up to the twentieth (the analysis was not carried further) were 
observed and their amplitudes measured. The results are given in the following table :— 
Harmonic. 
Frequency. 
Resjoonse. 
Harmonic. 
Frequency 
Response. 
1 
66 
100 
11 
726 
70 
2 
132 
100 
12 
792 
10 
O 
O 
198 
50 
13 
858 
15 
4 
264 
40 
14 
924 
5 
5 
330 
60 
15 
990 
SO 
6 
396 
20 
16 
1056 
60 
7 
462 
50 
17 
1122 
60 
8 
528 
14 
18 
1188 
10 
9 
594 
25 
19 
1254 
5 
10 
660 
50 
20 
1320 
10 
It will be seen that some of the harmonics are as important as the fundamental. 
The fifteenth, sixteenth and seventeenth harmonics are probably enhanced on account 
of their frequencies being nearly in resonance with the microphone. The subharmonics 
are not recorded in the table. 
In illustration of the complexity arising from the subharmonics of strong harmonics, 
the following example from another experiment is given :— 
The harmonica! note 263/sec. contained a strong fourth harmonic of frequency 
263 X 4 = 1052. This was greatly enhanced on account of its being so nearly in 
