The theory of the equilibrium and motion of fluids / By Thomas Webster.

  • Webster, Thomas, 1810-1875.
Date:
[1836]
Catalogue details

Licence: Public Domain Mark

Credit: The theory of the equilibrium and motion of fluids / By Thomas Webster. Source: Wellcome Collection.

    15/238 (page 3)
    Hence a pressure exerted on a fluid is transmitted equally in all directions ; thus fluids press in all direc- tions, they also press equally in all directions. 6. The preceding is also true for fluids whose parti¬ cles have sensible tenacity or viscidity, the only difference being, that the pressure is not transmitted in all directions with the same velocity with which it is transmitted in the direction of the impressed action. This deviation is how¬ ever only instantaneous, and when the equilibrium is estab¬ lished the equality of pressure obtains. 7- The action exerted on any portion of a fluid evi¬ dently depends on the number of particles which are acted on, that is, the pressure is proportional to the area pressed. An area is measured by the number of units oi area which it contains, or by the relation which it bears to that unit of area; hence the pressure at any point is most con¬ veniently measured by the pressure which is or would be exerted on a unit of area situated at that point. 1 he quan¬ tity (p) is the symbol used to denote the pressure so re¬ ferred to a unit of area, and it is called the unit of pres¬ sure, and must be carefully distinguished from the pressure which is actually exerted on any portion of the surface. The quantity p does not represent any pressure actually produced by the fluid, but that which would be produced if the pressure at the point under consideration were uni¬ formly applied to a unit of area. When the pressure at any point in a fluid is simply the transmitted action from some pressure exerted upon it as at its surface, the pressure p will be the same at every point. But when, as is generally the case, the impressed forces are different for every point, p will vary from one point to another, that is, it will be a function of a?, y, %, the co¬ ordinates of the point; and the determination of it for different impressed forces is the object of the following pages.