Another key might bring into action a dynamo which gives 64 vibrations per second to the diaphragm of the telephone receiver. This would send forth a tone very nearly like the base note of our 60-cycle alternating current dynamo.
The following table shows a series of ten tones which might be produced by the same little piece of sheet iron in a telephone receiver played upon by ten dynamos at the same time. The whole list of ten tones would sound well when produced simultaneously. The great mystery is that the iron disc can vibrate in such a complex manner. It is important to note, however, that the number of vibrations in each of the upper tones is a multiple of that of the lowest tone:
| 2nd octave above Middle C | C´´—1024 | (= 16 × 64) |
| G´ — 768 | (= 12 × 64) | |
| E´ — 640 | (= 10 × 64) [A] | |
| 1st octave above Middle C | C´ — 512 | (= 8 × 64) |
| G — 384 | (= 6 × 64) | |
| E — 320 | (= 5 × 64) | |
| Middle C | C — 256 | (= 4 × 64) [B] |
| G — 196 | (= 3 × 64) | |
| 1st octave below Middle C | C, — 128 | (= 2 × 64) [C] |
| 2nd octave below Middle C | C,,— 64 | (= 1 × 64) |
| [C] The tone most easily reproduced by the vocal cords of a man. | ||
| [B] The tone most easily reproduced by the vocal cords of a woman. | ||
| [A] The tone which the telephone receiver responds to most readily. | ||
| The table covers the range of the human voice, male and female. | ||
All the intermediate tones, with their sharps and their flats, are produced each by its own separate dynamo.
The insignificant amount of current required to operate a telephone receiver makes it possible to furnish the music of these dynamos to many and far distant telephones. This naturally suggests the idea of having a great musician perform upon the keyboard and have many auditors scattered about the city in their private homes or even in many public halls, for the telephone receiver can readily be made audible to a good-sized audience.
XVIII
ELECTRIC BELL OUTFIT FOR THE COTTAGE
The boys asked me what arrangement of electric bells we needed at the cottage and so I gave them this problem to work out by themselves:
1. We want a bell in the kitchen to be rung by a push button at the front door. But there are times when no one is in the kitchen and hence,