The theory of expansion is of easy comprehension; it consists in previous de-electrisation, succeeded by influent medium of space, which, by acting with centrifugal pressure, produces the phenomenon of expansion. The general pressure is the expanding cause, by reason of the portion of medium of space within all bodies being continuous with the medium of pressure in general space.

A bar of iron placed within the medium of fire suffers de-electrisation; then acquires medium of space, by which the bar is expanded. When taken from the fire, it acquires electric matter similar to that of which it had suffered loss, which displaces the expanding medium, and now becomes contracted by external pressure. The olden philosophy has no contracting cause, the imputed attraction having been destroyed by the imputed heat of the fire, as the same philosophy states of the imputed attraction of magnets being destroyed by the heat of fire, which leaves the bar to contract itself.

A piece of lead on the fire becomes de-electrised and expanded. The portion of medium of space it has acquired separates the atoms of the lead by which the state of solidity is subverted; it remains as one of the constituents of the lead, and is as a menstruum to the metal, and the atoms of the metal may be said to swim in it as the globules of blood in the serum. Further de-electrisation and additional increments of medium of space are productive of complete dispersion of the atoms of the metal, and of a kind of efflorescent result, which is a subsequent formation. The air in a corked bottle before the fire loses electric matter to the medium of fire; and by the medium of space which enters the vacated interstices, the cork is exploded. In the partially exhausted air-pump receiver, that decrease in the quantity of air should increase the expansive power of the remainder, and that the atoms should fly asunder with exploding force, is most unreasonable and impossible. The physical fact is, the more the air is reduced, the greater is the quantity of influent medium of space, consequently of expanding and exploding force. In the condensing of air, as is the expression, by the piston of the syringe, the quantity is reduced from being forced out through the pores of the syringe; and pressure on the bottom of the piston springs it up when the depressing power is removed. Under the general pressure the atoms of air must be in contact; and the volume being reduced, implies reduction of quantity: hard unalterable atoms are incompressible beyond contact; and as to their being elastic, it is physically impossible; medium of space being forced out and re-entering, is what makes the air be considered elastic. Let the syringe be worked under water, and the matter displaced appears escaping as air-bubbles, and as air-beads on the outside of the syringe.