Taking the maximum of pressure as a fixed quantity, or, as not being subject to increase, and assuming the degree to be not less than equal to the tenacity of steel, there must of necessity be means of mitigating the maximum, so that in the scale of descent every degree of force should be attainable; and more, to keep the equilibrium in a state of disturbance, without which all things must be, and remain in the rest of death. Were there no minus-pressure means, the solid, or perhaps aËriform state of matter would exist everywhere, and of motion there could be none. Such means for promoting motion are amply supplied, and without any addition of matter to the measured quantity sufficient for the formation of bodies and service of nature generally, in the elements themselves, of matter.

As the body which is involved in a medium of air is under less pressure than in a medium of water, and still less within a medium of elementary matter, so is elementary matter, and the elements generally, the natural means of mitigating the maximum of pressure on and within bodies. All bodies within and on the surface of the earth, possess removable elementary matter, which prevents superficial contact, and excludes medium of space proportionally from their interior; and because the medium of space is the cause of pressure, in being thus rendered discontinuous, so is its force, as it were, intercepted or lessened. For instance, a polished needle floats on water, but when wetted or smoked is precipitated, from having its electric or minus-pressure atmosphere removed; from which it is obvious that with the minus-pressure atmosphere, the needle is under less pressure than when without it; and the same atmosphere it is which makes the bed in the water so much larger every way than the needle.

The minus-pressure principle is well exemplified in the rise of water within a tube over which fire is situated. When the fire is removed, the water falls. The fire must be in the state of combustion—mere ignition does not answer. The elements forced out of the combustible, as combustion proceeds, cover the orifice of the tube, and intercept the general pressure, notwithstanding they are under the general pressure. By such minus-pressure means is the equilibrium destroyed, and by the unaltered pressure on the water outside the lower orifice of the tube, the water is forced upwards. So is it that the water of the sea is raised to the minus-pressure, elementary matter descending from a cloud in the shape of an inverted cone, and known as the water-spout. Astronomers can best say whether the sun and moon be not minus-pressure means in promoting the rise of the ocean, productive of the tides; a miniature representation of which is effected by holding a charged jar over a surface of water, to which the water rises in a small cone,—which cone follows every motion of the jar, and falls when the jar is discharged. Capillary ascent is promoted by the interposed minus-pressure electric matter which fills the caliber of the tube: the same matter prevents the horizontal flow of water through such tubes; but when the tubes are de-electrised, the flow is free and constant: boiling water, or fire de-electrises all such tubes. The electric matter on a bar of iron is a hinderance to water running down, but when removed by means of fire, the water runs down the bar freely. The atmosphere is a minus-pressure medium to the earth, and on the general principle that interposed elementary matter renders discontinuous the medium of pressure, which is the medium of space.

Minus-pressure means exist in other than the elementary form, as in blotting-paper, candle-wick, pledgets of lint. Within the cupping-glass, which is empty of air only, it is the minus-pressure matter obtained from flame which promotes the rise of blister. Within the vessels of the vascular system, as mucilaginous lining, minus-pressure matter assists the circulation of fluids, on the foregoing capillary principle. The slime on deep-water fish, seems provided to lessen the pressure of the water on the inhabitants of those seas. Minus-pressure matter on one side only of a body, destroys the equilibrium, and promotes the motion of the body; and generally, the partial action, implied by motion, of the medium of space on bodies or their parts, is promoted by interposed minus-pressure matter in every instance of physical change. Only in minus-pressure means, which serve as a partial vacuum in some cases, to disturb the equilibrium of pressure, is motion, or change of place of the elements of bodies, or of bodies themselves promoted: without such means there is nothing to promote the blowing of a wind, or to put the medium of space into action. Cause being given, the General Pressure in the production of every physical effect, the sole province of philosophy consists in tracing out the minus-pressure means which promote the occasional and partial action of the medium of pressure.