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