ASCENT of fluids, is particularly un derstood of their rising above their own level, between the surfaces of nearly con tiguous bodies, or in slender capillary glass tubes, or in vessels filled with sand, ashes, or the like porous substances. This effect happens as well in vacuo as in the open air, and in Crooked as well as straight tubes. Some liquors, as spirit of wine and oil of turpentine, ascend with greater celerity than others ; and some rise after a different manner from others. Mercury does not ascend at all, but ra ther subsides. Upon the same principle, two smooth polished plates of glass, me tal, stone, or other matter, being so dis posed as to be almost contiguous, have the effect of several parallel capillary tubes ; and the fluid rises in them ac cordingly : the like may be said of a ves sel filled with sand, &c. the divers little interstices of which form as it were a kind of capillary tubes : so that the same prin ciple accounts for the appearance in them all. And to the same may probably be ascribed the ascent of the sap in vegeta bles. Thus Sir I. Newton says, if a large pipe of glass be filled with sifted ashes, well pressed together, and one end dipped into stagnant water, the fluid will ascend slowly in the ashes, so as in the space of a week or fortnight to reach the height of 30 or 40 inches above the stag nant water. This ascent is wholly owing to the action of those particles of the ashes which are upon the surface of the elevated water ; those within the water attracting as much downwards as up wards : it follows, that the action of such particles is very strong ; though, being less dense and close than those ofthe glass, their action is not equal to that of glass, which keeps quicksilver suspended to the height of 60 or 70 inches, and there fore acts with a force which would keep water suspended to the height of about 60feet. By the same principle a sponge
sucks in water; and the glands in the bo dies of animals, according to their several natures and dispositions, imbibe various juices from the blood. If a drop of oil, water, or other fluid, be laid on a glass plane perpendicular to the horizon, so as to stand without breaking or running off, and another plane inclined to the former, so as to meet at top, be brought to touch the drop, then will the drop break, and ascend towards the touching end of the planes ; and it will ascend the faster in proportion as it is higher, because the distance between the planes is constantly decreasing. After the same manner the drop may be brought to any part of the planes, either upward or downward, or sideways, by altering the angle of inclina tion. Lastly, if the same perpendicular planes be so placed as that two of their sides meet, and form a small angle, the other two only being kept apart by the interposition of some thin body, and thus i mmerged in a fluid tinged with some co lour, the fluid will ascend between the planes, and this the highest where the planes are nearest, so as to form a curve line which is found to be a just hyberpo la, one of the asymptotes whereof is the line ofthe fluid, the other being a line drawn along the touching sides. The physical cause in all these phenomena is the same power of attraction.