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.
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.