Mr. Cahill's great organ looks like a large machine shop with many counter shafts geared so as to run at different speeds. On each shaft are a large number of little dynamos whose armatures have various numbers of coils. The organist, who may be far removed from this "machine shop," fingers an ordinary keyboard. Each key opens and closes a switch, thus bringing into action its own dynamo. If the key which is known as _C_, one octave below middle _C_, is pressed down, a switch closes the circuit between the telephone and a dynamo which gives 128 double alternations of current. The tone which is produced by 128 vibrations per second is the one most often heard from a man's voice in ordinary conversation. Another key brings into action upon the same telephone receiver--and at the same time if desired--a dynamo which gives twice as many alternations per second and produces the tone most often heard in female conversation. It is middle _C_. 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 C´´--1024 (= 16 × 64) Middle C G´ -- 768 (= 12 × 64) E´ -- 640 (= 10 × 64)[A] 1st octave above C´ -- 512 (= 8 × 64) Middle C G -- 384 (= 6 × 64) E -- 320 (= 5 × 64) Middle C C -- 256 (= 4 × 64)[B] 1st octave below G -- 196 (= 3 × 64) Middle C C, -- 128 (= 2 × 64)[C] 2nd octave below C,,-- 64 (= 1 × 64) Middle C [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.