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Proceedings of Societies. 
319 
maintain equal loudness of sound, must diminish one-half in 
amplitude as it rises. This instrument enabled the authors to 
form synthetically all the curves produced by vowel tones, and to 
show how these tones are compounded of primes and harmonic 
upper partials. It shows how simple tones can be produced by 
simple harmonic curves, and compound tones by the simultaneous 
adtion of several simple tones. The authors then determined to 
try to reproduce the vowels by sounding a prime and one of its 
partials alone. This was done by means of an eledtro-magnet 
vibrating an armature with a movable spring attached to it in 
such a way that the vibrations of the armature could produce a 
given prime, while the vibrations of the spring, by varying its 
length, could also be adjusted to any particular partial. The 
effedl not being by any means perfecft, a machine was made on 
the principle of the synthetic curve machine, which would, in- 
stead of drawing curves on paper, reproduce eight partials by 
transferring the vibrations of the intermediate wheels to a vi- 
brating diaphragm. Here, again, though the vowels were fairly 
reproduced, something was wanting in their clearness. Another 
machine was now made upon which disks were fitted, whose 
peripheries were cut in exadt copy of the curve produced by the 
synthetic curve machine. These curves were transmitted by 
vibration to the receiving diaphragm of a phonograph, and really 
formed an “ automatic phonograph.” With this instrument the 
sounds most resembling the vowel sounds of the human voice 
were easily recognised. But although the reproduction of vowels 
was good, it was imperfect, and it follows from this investigation, 
as far as it has gone, that vowels cannot be reproduced exactly 
by mechanical means. Something is always missing — probably 
the noises due to the rush of air through the teeth, and against 
the tongue and lips. One very curious result arising from the 
experiments with the automatic phonograph was to show that, 
by varying the pitch, the vowel sounds could be shifted, — i.e., the 
curve which produced 00 at a low velocity becomes approximately 
at O a higher velocity. O similarly becomes ah, ah becomes a, 
and a, ee. The curves arrived at synthetically do not differ very 
materially from those arrived at analytically by Helmholtz ; they 
principally differ in the prominence of the prime. But curves 
produced by the synthetic machine, compounded of the different 
partials without their prime, show that there exist heats or re- 
sultant sounds. A vowel sound of the pitch of the prime may 
be produced by certain partials alone, without sounding the prime 
at all. The beat in fadf becomes the prime. This point is 
clearly illustrated, orally, by the automatic phonograph, and 
graphically by the sketch drawn by the synthetic curve machine. 
The authors are investigating the true theory of the loudness of 
sound. They think that loudness does not depend upon ampli- 
tude of vibration only, but also upon the quantity of air put into 
vibration ; and, therefore, there exists an absolutely physical unit 
VOL. IX. (N.S.) Y 
