Music Trade Review

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THE MUSIC TRADE REVIEW
11
Being a Continuation of a Talk on the Fundamentals of Player Design,
Discussed Last Month, in Which the Aim Then as Now is to Enable the
Reader to Get Basic Facts so as to Talk Intelligently About a Player-Action
In the first of these articles, published last
month, we spoke of the foundational facts re-
quired to be understood before one can talk in-
telligently about a player action. We arrived at
the conclusion that weight and velocity are the
principal elements in the problem of applying
pneumatic power to the piano action. We likewise
spoke in general terms, about the apparatus em-
ployed for the purpose of propagating power—an
apparatus for reducing the pressure of internally-
contained air, usually called "the bellows system."
It will now be in order to speak more particu-
larly of the bellows system and to explain in quite
simple language some of its peculiarities of con-
struction and operation.
Everybody who has been to high school will re-
member the physics room, with its apparatus of all
kinds mysteriously attractive, wherewith the in-
structor used to demonstrate the laws of mechan-
ics. Of all this apparatus, none perhaps would be
more generally interesting than the air-pump. One
remembers seeing a mercury gauge attached to the
pump and observing how the mercury column
would rise in the tube as the air was exhausted
from the bell of the pump. Now, when we deal
with the player bellows, we are simply dealing with
a different sort of air-pump. And when we under-
stand the air-pump we understand all that is neces-
sary fundamentally to know about the production
of power in the player mechanism.
What. Is Power?
Power is energy applied to doing work. Ma-
chines are means for converting energy into use-
ful power. What energy is, neither you nor any-
one else knows; at least from the physical point
of view, which is our only concern here. All we
can know is that we are able to apply energy to
work and get results. Rut we do not create energy
by means of any machine. We do not get out of
a machine, that is to say, any more than we put
into it in another way. A machine, therefore, ij
not a creator of energy, but a transformer of
energy latent into energy positive. It is highly im-
portant to remember this point clearly.
The bellows system of the player mechanism is
a producer of power, to use the ordinary language
of the street. What is the nature of the power it
produces and how is the production brought about?
The Weight and Pressure of Air.
Of course we all know, in a general way, that
the player action works through what is called
"suction," that is to say, through the displacement
of air from a closed box. The atmosphere of
which we are conscious in our daily life and which
we are constantly inspiring and expiring, is a com-
pound of oxygen, nitrogen, and other gases in-
cluding some hydrogen and some carbonic acid
gas. It is itself, therefore, like all gases and com-
pounds of gases—invisible, intangible, exceedingly
thin and exceedingly elastic. The latter two qual-
ities are th.e most important from our present point
of view. The air is so thin and so elastic that, in
common with all gases, it is capable of being almost
indefinitely compressed and also almost indefin-
itely thinned.
What Is Compression?
Suppose I take in my hands a lump of dough
from the baking table. By squeezing this up in my
hands and pressing it tightly together I can cause
it to become smaller in bulk. At the same time,
however, its weight remains as great as before,
while it becomes considerably denser. Really,
what happens is that I have pressed together the
atoms or particles or molecules (for our purpose
the differences between the meanings of these
terms may be disregarded), and have thus reduced
the extension of the lump in space. Now, just
this can also be done with air. If we have an
apparatus whereby air can be forced into a box,
the latter can be made to contain much more air
than would otherwise ordinarily flow into it with-
out assistance, but the box does not stretch. On
the other hand, the air is compressed, that is, be-
comes pressed tightly together, so that it is much
denser than ordinarily and exerts on all sides a
much greater pressure than is usual with it. That
is compression.
What Is Tension?
Suppose you stretch a rubber band. It will
stretch out under a pull until it is considerably
longer than it normally would be. But at the
same time it is thinner and under a state of high
tension. That is to say, its particles are kept arti-
ficially stretched apart from each other and will
return to their normal state as soon as permitted.
That is what we call stretching. And its result
is to make thin at the same time. Now, air can
be stretched this way when certain things are done
first. And the more it is stretched, the thinner
any part of it becomes.
All gaseous bodies have the property of indefin-
itely great expansion. That is to say, they will fill
completely any space into which they are put. Sup-
pose, then, that it is possible to have a closed box
filled with air. Suppose no more air can get in
than is normally inside. Suppose, now, that some
of the air is taken out of the box without any
more getting in to replace what has been displaced.
Plainly, one of two things must happen. Either
the remaining air must stay as it wai, leaving
blank emptiness where the portion of air was taken
away, or else the remaining air must expand to fill
the space left empty. We all know that this is
what it does. But if it be expanded in this way
it is like the stretched rubber band. It is thinner.
And being thinner it exerts less pressure. Let us
see what this really means.
Air Has Weight.
The atmosphere is a great sea of air some twen-
ty-nine miles high. It has been discovered that if
we could cut out a rectangular pillar of air of one
square inch base and the height of the atmosphere,
the weight of that pillar would be about fourteen
and three-quarter pounds. But what is weight?
Only the measure of the tendency of a body to fall
toward the earth; that is to say, only the measure
of the attraction of gravitation upon a body. That
is what we call its "weight," and when we com-
pare that weight with the weight of some body
chosen as a standard we speak of "specific gravity."
So it would be fair to say that the weight of a
body is best measured in terms of the pressure it
exerts upon the surface of the earth. In the case
of the air, this attraction exerted upon it by gravi-
tation is such that we find it to measure a pressure
of fourteen and three-quarter pounds per square
inch upon the earth's surface.
This means, in other words, that the bottom of
an air column one inch square in base and the
height of the atmosphere will, if not interfered
with, exert this pressure at the earth's surface.
Now here we have a plain and tangible some-
thing. Suppose, in the manner suggested above,
we can displace some of the air that normally and
naturally will fill a box. Let us closj the box and
then expel some of the contained air into the at-
mosphere without letting any more into the box.
The remaining air will expand. But it will be thin-
ner—less air filling the same space. Hence, on
every square inch of surface inside the box the
actual bulk of air will be less, and so will exert
less pressure.
Disturbing Balance.
If, now, we can bring the normal outside air
against the outside of the box while the internally-
contained air is at lowered pressure, it is plain that
the outside air will exert on the outside of the box
a pressure effective to do work, and a pressure
measurable by the difference between the press-
ure of the normal atmosphere and the lowered
pressure inside the box.
That is the secret of the player—getting the at-
mosphere outside a box to work on the box be-
cause the air inside is artificially thinned out.
Displacement.
The work of the power plant of the player
is the work of displacing from a closed vessel or
box so much air as will, by causing the expansion
of the remainder enclosed within, lower the inter-
nal pressure and so cause the external atmosphere
to exert an effective pressure. This work is per-
formed, and performed most efficiently, for the
peculiar purposes of the case by the bellows system.
The principle of the player action, then, is not
to be loosely talked of as suction, or vacuum, or
anything so confusing. As we shall see, the oper-
ations whereby the bellows perform the work of
displacement are so simple and so intelligible when
we once understand that we are dealing with two
bodies of varying pressure, that there can no
longer be any mystery. This we shall discuss in
the next article.
The General Law of Pneumatic Machines.
Before going on to. describe the actual operation
of the bellows system, then, let us repeat in other
words what was said above as to the general laws
of mechanical power. They may be expressed, foi
our purpose, in somewhat simple language:
1. You cannot get something out of nothing.
2. There is just so much energy in the world.
All we know of it is its manifestations, how it
shows itself to us, not what it is.
3. Consequently, no machine creates energy. Ma-
chines merely transform energy latent in one form
into energy able to perform work, and thus be-
come power in another form.
4. In the pneumatic player mechanism, on these
principles we have to look for an intelligible rea-
son for the behavior of air under the stated con-
ditions of such machines.
5. On such conditions, we can suppose only the
exertion of pressure by the air and means for ren-
dering this pressure available.
G. Pneumatic machines then, arc fundamentally
contrivances for lowering normal air pressure in
one place to bring it into operative contact with
normal air in another place.
(To be continued.)
E
Pass judgment
on them all-
You will then
decide on the
Sl
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