The central Presbyterian. [volume] (Richmond, Va.) 1856-1908, 1881-05-11


Possibly he bubbles on the word "per-
feet" If SO, it is too small to deserve
notice. AS to the teaching of the wave
theory, that a vibrating prong sends off
air-waves at the velocity l state, no one
doubts, save perhaps some one who will
not waste" his time to investigate the
matter.
l cannot take time or space to reply to
all his misconceptions. But one other
point is important to your readers, as 1T
involves principle of science fundamen-
tai in physics, and especially acoustics;
and that is his criticism of my argument
based on Prof. Tyndall's assumption that
the loudness of sound diminishes as the
square of the distance from the sounding
body the same as the quantity of AR an
creases. He approaches this criticism by
announcing the most statpeado1s 6latnde'
have ever seen in any book" and then
adds it is elaborated in a manner which
would Justify one in believing that the
author stands prepared to maintain that
1877 was in the seventh decade of the
nineteenth century" Yet my objection
to Prof. Tyndalls position is one of the
plainest truths in natural philosophy,
Notwithstanding all this shouting in adj
vance about my "stupendous blunder,
and will now prove it in single para
graph to the intelligence of every reader
of the Central Presbyterian.
Prof Tyndall teaches correctly, that
the quantity of air increases as the square
of the distance from central point. And
then, as sound, according to his theory is
nothing but the wave-motion of the air,
he was obliged to teach that the amount
of this motion representing sound inten-
sity) decreased in the same ratio I took
exception to this view in my book, and
here is my argument. The maximum in
tensity of any sound is of course at the
centre, or right at the sounding body.
Now it depends entirely upon the original
loudness Of given sound as to its ratio
of decrease, or as to what unit of meas
urement that decrease may be approx
mately expressed by. For example ::
while you can correctly express the in
crease of the quantity of air by using any
unit of measurement, foot furlong, mile,
league, 1T is utterly absurd to say that
the intensity of sound can be measured
in the same way. How could you use
miles as unit of measuring the decrease
comes wholly inaudible within a.distance
of foot from the insect? By using sac
teenths of an inch as the unit the ratio
of decrease in the gnat's sound might
nearly be estimated. But suppose you
employ sirteenthS of an inch as the unit
to determine the proportionate decrease
in the intensity of the sound of steam
siren, which can be distinctly heard a
distance of ten miles, you will utter in
your figures the most "stupendous blum
der" ever seen recorded. Here it is, ac-
cording to Prof. Tyndall's law quoted by
me and discussed in the Problem of Hu-
man Life, p. 1872 At radius of one
sixteenth of an inch from the mouth of
the siren, the calculation commences.
At one eighth of an inch the sound, of
course, is but one fourth as loud as with
in the. one sixteenth, because the quantity
of air within the second sixteenth. radius
is four times that in the first. This is
undoubtedly the teaching of the wave
theory. Then at quarter of am inch
radius the sound will be but one six
teenth as loud At one inch it will be
but one 256th as loud as within the first
sixteenth inch radius Who believes, or
can believe, such nonsense as this? Why,
every man must believe it who believes
in the wave-theory. Carry it a little
further and behold it's enormity At one
foot from the siren the sound is but one
36,894th as loud, and at ten feet from the
instrument, where no observable differ
ence in loudness occurs, this scientific %
theory assures us that there is but one
1855, 400th the intensity as within the
first unit This most stupendous blum
der" has thus, like certain chickens we
read about, come home to roost" Be-
fore my reviewer aOaSteS his time in hunt
ing for other objections to my book let
him try his mathematical skill upon this
decrease of the sirens sound for dis
tance of ten miles, " as the square of the
distance" with the sirteentH of an inch
as the unit of measure, and he will no
doubt wish he had been one Of the cable
men, Of his acquaintance who resolved
to let the book alone as ga sort of hoax
and "as unworthy of serious attention. y
A. WILFoRD HALL.
No. 26 E. 9th street, New York, April
28th, 1881.