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.
FIRE.
Fire is not hot, although it burns the flesh and promotes pain. Matter, which is unalterable, cannot be made hot or cold, neither is there anything to make it so. If a limb be made rigid, or the nerves of sensation be removed, or the function of the nervous fluid be obstructed, the limb may be burned off unconsciously. Heat is a sensation effected through excitement of the brain; out of the brain there is neither excitement nor heat. The fire does not excite the brain, but the nervous fluid; and although the sensation is not hot, it is imagined that the cause must be hot, which is false reasoning. The chymist finds heat creviced in all things, even those which he admits are destroyed by heat—gunpowder and ice. How can flame be hot, when just obtained from the gases of decomposed ice water? or, if hot, sui generis, it must have been hot frozen flame in the original ice.
Modern philosophy adopts different kinds of heat,—animal, culinary, and latent heat. The first is our own feeling excited by means of fire in the sensitive centre, the brain; also by exercise and disease, in the absence of fire. How is the spark from the flint or from the steel to saturate a bushel of coal with heat? How, again, does "heat come to an equilibrium in all surrounding bodies," when some portion of the coal may be black cold, and others red hot—using the popular terms—in the fire-place, at the same time, and while the air in the chamber is indexing zero? Latent heat is of the philosopher's own peculiar making; and on the "great discovery" the most unbounded praise is still bestowed. Latent heat, "which all bodies possess without being heated," which, "heats nothing," and is not hot, is cold heat, and should be nomenclatured such, or, absurd heat. Are not Instructors less than half-reasoners and unnatural philosophers, who abide by and teach such consummate nonsense: on a par with which is the discovery of "latent dark light"—"of black being formed by the intermixture of two luminous rays at the point of intersection in the spectrum," which is the same as feelable darkness; after which, there only remains for "new discovery," latent sound, for inking on, thence vibrating from, a sheet of music-paper; and latent motion, to keep a stone at rest, the quantity of motion in the world having been already ascertained arithmetically to a fraction; the last-day discovery, the quantity of right reason, is the small remaining trifle to be discovered. Radiation of heat and cold by fire and ice, being inconsistent with the inertia of matter, is an erroneous and greatly-misleading assumption, although proved through the nicest experiments, according to the experimenter's ideas.
Instead of fire communicating anything to bodies, fire promotes loss to everything in its neighbourhood. The bars of stoves, iron pokers, steam-boilers; all culinary vessels; coal, wood, candles, paper, linen, all suffer loss by means of fire; cinders, charcoal, tinder, are but remains: to which it is no exception that some bodies acquire substance and weight in becoming oxydes; because, previous to acquiring oxygen from the air, they must have lost elementary matter to the fire to make spaces for the oxygen to enter, otherwise the open air should oxydize equally, in the absence of fire.
The loss, or matter of loss which fire promotes to fluids, appears as air-beads on the sides and bottom within the vessel on the fire, before the water comes to ebullition: these beads cannot be made to rise in the water by any manner of agitation, which is proof they have not come from the fire, and through the rigid bottom, or ascent and escape are inevitable. When the bottom has been sufficiently de-electrised by the fire, they are pressed through it to the fire; or if the vessel be removed and placed on the ground, they become dispersed through the water insensibly. The like spherules collect on an egg while boiling, which cannot be anything issued from the fire to the surface of the water, then precipitated on the egg. On the bottom of a glass-retort suspended over a lamp, the like spherules collect, from which it is supposed that water never touches the bottom of any containing vessel; it must touch that which it wets.
That air suffers loss to fire, is made evident by the air being deprived of, or losing its oxygen during combustion; and from both fire and flame becoming extinguished in a limited quantity of respirable air, in consequence of having lost its oxygen to the combustible, while in the state of fire.