tation to the class of occult qualities. This circumstance
induced Newton and his most devoted followers to abandon the reserve
which they had hitherto considered it their duty to maintain. Those
persons were then charged with ignorance who regarded attraction as an
essential property of matter, as the mysterious indication of a sort of
charm; who supposed that two bodies may act upon each other without the
intervention of a third body. This force was then either the result of
the tendency of an ethereal fluid to move from the free regions of
space, where its density is a maximum, towards the planetary bodies
around which there exists a greater degree of rarefaction, or the
consequence of the impulsive force of some fluid medium.

Newton never expressed a definitive opinion respecting the origin of the
impulse which occasioned the attractive force of matter, at least in our
solar system. But we have strong reasons for supposing, in the present
day, that in using the word _impulse_, the great geometer was thinking
of the systematic ideas of Varignon and Fatio de Duillier, subsequently
reinvented and perfected by Lesage: these ideas, in effect, had been
communicated to him before they were published to the world.

According to Lesage, there are, in the regions of space, bodies moving
in every possible direction, and with excessive rapidity. The author
applied to these the name of ultra-mundane corpuscles. Their totality
constituted the gravitative fluid, if indeed, the designation of a fluid
be applicable to an assemblage of particles having no mutual connexion.

A single body placed in the midst of such an ocean of movable
particles, would remain at rest although it were impelled equally in
every direction. On the other hand, two bodies ought to advance towards
each other, since they would serve the purpose of mutual screens, since
the surfaces facing each other would no longer be hit in the direction
of their line of junction by the ultra-mundane particles, since there
would then exist currents, the effect of which would no longer be
neutralized by opposite currents. It will be easily seen, besides, that
two bodies plunged into the gravitative fluid, would tend to approach
each other with an intensity which would vary in the inverse proportion
of the square of the distance.

If attraction is the result of the impulse of a fluid, its action ought
to employ a finite time in traversing the immense spaces which separate