ELEMENTS

OF

HYDROSTATICS.

Sect. I.

1. Def, A Fluid is a collection of very minute materialparticles, which cohere so slightly together, that they yield tothe smallest force, and by yielding are put in motion amongsteach other in every direction.

2. The extreme facility with which the particles moveamongst each other in every direction, has generally been sup-posed to arise from their spherical form, and from the repul-sive power exerted by each on all sides. But how this facilityof moving is affected under different circumstances, and underdifferent degrees of compression, cannot be ascertained.

3. That the facility with which the component particlesmove amongst each other is different in different fluids, isevident; or, that different fluids have different degrees offluidity : and hence they have sometimes been divided intoperfect and imperfect: the former of which are those, be-tween whose component particles there is no sensible cohe-sion; and the latter, such as oil, &c. where the cohesion issensible. This division, however, is arbitrary; there being nobody which possesses the character of perfect fluidity, that is,whose parts are wholly free from friction, cohesion, and tena-C1 ty* Mercury and water are reckoned amongst those whichapproach most nearly to perfect: and boiling water is nearerlo a state of perfect fluidity, than water in any other state;

A