Thus, if A be set to
swing twice while B swings three times, an entirely new series of figures
results; and the variety is further increased by altering the respective
amplitudes of swing and phase of the pendulums.
We have now gone far enough to be able to point out why the harmonograph is
so called. In the case just mentioned the period rates of A and B are as 2:
3. Now, if the note C on the piano be struck the strings give a certain
note, because they vibrate a certain number of times per second. Strike the
G next above the C, and you get a note resulting from strings vibrating
half as many times again per second as did the C strings--that is, the
relative rates of vibration of notes C and G are the same as those of
pendulums A and B--namely, as 2 is to 3. Hence the "harmony" of the
pendulums when so adjusted is known as a "major fifth," the musical chord
produced by striking C and G simultaneously.
In like manner if A swings four times to B's five times, you get a "major
third;" if five times to B's six times, a "minor third;" and if once to B's
three times, a "perfect twelfth;" if thrice to B's five times, a "major
sixth;" if once to B's twice, an "octave;" and so on.
Pages:
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297