The various processes commonly employed for the observation of bodies
in motion (intermittent light or vision) greatly fatigue the observer,
and, as a general thing, give only images, that are difficult to
examine. We are going to show how Prof. Marc Thury, upon making
researches in a new direction, has succeeded in constructing an
apparatus that permits of the continuous observation of a body having
a rapid rotary motion. The principle of the method is of extreme
simplicity.
[Illustration: FIGS. 1, 2, AND 3.--DIAGRAMS EXPLANATORY OF THE
PRINCIPLE OF THE CYCLOSTAT.]
Let us consider (Fig. 1) a mirror, A B, reflecting an object, C D, and
revolving around it: when the mirror will have made a half revolution,
the image, C' D', of the object will have made an entire one. The
figure represents three successive positions of the mirror, distant by
an eighth of a revolution. The structure of the image shows that it
has made a quarter revolution in an opposite direction in each of its
positions. But if (Fig. 2) the body itself has revolved in the same
direction with an angular velocity double that of the mirror, its
image will have described a circle in remaining constantly parallel
with itself. The image will be just as insensible as the object
itself; but it is very easy to bring it back to a state of rest.
Let us suppose (Fig. 3a) the observer placed at O, the revolving
object at T, the axis of rotation being this time the line O F. Let us
place a mirror at A B and cause it to revolve around the same axis;
but, instead of looking at the image directly in the mirror, let us
receive it, before and after its reflection upon A B, upon two
mirrors, C D and D E, inclined 30° upon the axis of rotation of the
system; the image, instead of being observed directly in the mirror, A
B, will always be seen in the axis, O F, and will consequently appear
immovable.
The same result may be obtained (Fig. 3b) with a rectangular isosceles
prism whose face, A B, serves as a mirror, while the faces, A C and B
D, break the ray--the first deflecting it from the axis to throw it on
the mirror, and the second throwing it back to the axis of rotation,
which is at the same time the line of direction of the sight.
The principle of the instrument, then, consists in causing the
revolution, around the axis of rotation of the object to be observed,
of a mirror parallel with such axis, and in observing it in the axis
itself after sending the image to it by two reflections or two
refractions. In reality, the entire instrument is contained in the
small prism above, properly mounted upon a wheel that may be revolved
at will; and, in this form, it may serve, for example, to determine
the rotary velocity of an inaccessible axis. For this it will suffice
to modify its velocity until the axis appears to be at rest, and to
apply the revolution counter to the wheel upon which the prism is
mounted, or to another wheel controlling the mechanism.
But Mr. Thury has constructed a completer apparatus, the _cyclostat_
(Fig. 4), which, opposite the prism, has a second plate whose
actuating wheel is mounted upon the same axis as the first, the
gearing being so calculated that the prism shall revolve with twice
less velocity than the second plate. This latter, observed through the
prism, will be always seen at rest, and be able to serve as a support
for the object that it is desired to examine.
[Illustration: FIG. 4.--THE CYCLOSTAT.
1. General view of the apparatus.
2. Section of the ocular, O.]
The applications are multitudinous. In the first place, in certain
difficult cases, it may serve for the observation of a swinging
thermometer, which is then read during its motion. Then it may be
employed for the continuous observation of a body submitted to
centrifugal force. Apropos of this, we desire to add a few words. Most
of the forces at our disposal, applied to a body, are transmitted from
molecule to molecule, and produce tension, crushing, etc. Gravity and
magnetic attraction form an exception; their point of application is
found in all the molecules of the body, and they produce pressures and
slidings of a peculiar kind. But these forces are of a very limited
magnitude; but it might nevertheless be of great interest to amplify
them in a strong measure. Let us, for example, suppose that a magician
has found a means of increasing the intensity of gravity tenfold in
his laboratory. All the conditions of life would be modified to the
extent of being unrecognizable. A living being borne in this space
would remain small and squat. All objects would be stocky and be
spread out in width or else be shattered. Viscid or semi-solid bodies,
such as pitch, would rapidly spread out and take on a surface as
plane and smooth as water under the conditions of gravity upon the
earth. On still further increasing the gravity, we would see the soft
metals behaving in the same way, and lead, copper and silver would in
turn flow away. These metals, in fact, are perfectly moulded under a
strong pressure, just like liquids, through the simple effect of the
attraction of the earth applied to all their molecules. Upon causing
an adequate attractive force to act upon the molecules of metals they
will be placed under conditions analogous to those to which they are
submitted in strong presses or in the mills that serve for coining
money. The sole difference consists in the fact that the action of
gravity is infinitely more regular, and purer, from a physical
standpoint, than that of the press or coining mill. Through very
simple considerations, we thus reach the principle which was
enunciated, we believe, by the illustrious Stokes, that our idea of
solid and liquid bodies is a necessary consequence of the intensity of
gravity upon the earth. Upon a larger or smaller planet, a certain
number of solid bodies would pass to a liquid state, or inversely. Let
us return to the cyclostat. In default of gravity, centrifugal force
gives us a means of realizing certain conditions that we would find in
the laboratory of our magician. The cyclostat permits us to observe
what is going on in that laboratory without submitting ourselves to
forces that might cause us great annoyance. We have hitherto been
content to put poor frogs therein and study upon them the effect of
the central anæmia and peripheral congestion produced on their
organism by the unrestrained motion of the liquids carried along by
centrifugal force. The results, it seems, have proved very
curious.--_La Nature_.
* * * * *