Return to Physics of the Ether

79. Mode of the Development and Absorption of Heat in Expansion and Contraction. — It is a known fact that by the compression or contraction of matter heat is generated, and by the expansion of matter heat is absorbed; but the mode or physical process by which this result is attained, or the cause why a mere movement of translation of the molecules of a substance in a particular direction should cause the molecules to vibrate with increased energy, and a movement of translation in the opposite direction should cause the molecules to vibrate with reduced energy, requires explanation.

This may be shown to be another of the necessary consequences resulting from the fact of the existence of stationary vibrations in the medium between opposed vibrating masses and molecules. The character of a stationary vibration consisting simply in an oscillation of the intervening column of the medium, either as a whole or in parts, the extremities of the column abutting against and rebounding from the two opposed vibrating masses or molecules; it follows, therefore, that an approach of the two masses or molecules in which act each is driven against the oscillating column, must cause the column to rebound with greater energy, just as an elastic sphere will rebound with greater energy when the surface from which it rebounds

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is driven against it. Hence it follows, necessarily from this, that the act of approach of the opposed masses, such as the approach of two vibrating molecules, will be necessarily attended by an increase in the energy of the stationary vibration (oscillation) of the intervening ether column. It is, however, important to observe that the period of vibration (oscillation) of the column coincides precisely with the period of vibration of the molecules, since the column is itself put in vibration by the molecules. Hence the increase in the energy of vibration of the ether column, due to the movement of approach of the molecules, must be necessarily attended by an increase in the energy of vibration of the molecules themselves, which vibrate in synchronism with the column, and against which the oscillating column abuts, just as, conversely, any artificial increase of the vibrating energy of the molecules would affect the column. Thus it follows that a movement of translation of two molecules towards each other, as takes place by the compression of matter, will necessarily be attended by an increase in the vibrating energy of the molecules (development of heat); precisely analogous but converse considerations applying in the case of the recession of the molecules (expansion).

80. The interchange of motion between two gaseous molecules in the normal state of a gas would afford an illustration of both processes, the vibrating energy of the molecules being increased at their approach, and reduced at their recession; or the two molecules in their interchange of motion are alternately heated and chilled. If we regard the state of the case at the point when the rebound of the two vibrating molecules commences, then the intercepted pulsating ether column which does the work of urging the molecules apart, loses an amount of energy equivalent to the work done; or, in other words, the pulsations of the column are reduced by an amount represented by the translatory motion imparted to the molecules. This loss of vibrating energy by the column necessarily reacts upon the molecules, i. e. the vibrating energy of the column is, in the readjustment of the equilibrium of motion, partly made good at the expense of the vibrating energy of the molecules, the receding molecules thereby losing a certain, portion of their vibrating energy, or the molecules are chilled.

The loss of vibratory motion ( u absorption of heat") which accompanies expansion is beautifully illustrated by the known experiment by which carbonic acid is produced in the solid form by the free evaporation of the acid in the liquid form. In this case, when the vapour is allowed to escape freely, the vibrating molecules are driven apart with such velocity that the energy of vibration of the ether column intercepted between any pair of receding molecules is so reduced by the work it performs, and con- sequently the vibrating energy of the molecules themselves is reduced to such a degree that the molecules become fitted to take up the solid state.

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81. The converse case of the augmentation of vibrating energy (" development of heat ") in the approach of molecules (con- traction) is well illustrated by the simple apparatus known as the " fire syringe," by which a piece of tinder is ignited by the sudden compression of the air by a forcible blow struck upon a piston. In this case the velocity with which the air molecules are driven together is such as to augment their vibrating energy almost up to that of flame.

82. It may be observed, that however great the energy with which the molecules are urged together, and consequently how- ever forcibly the intercepted ether column may be acted upon, this need not necessarily disturb the synchronism of the oscillation of the column, for the column can adapt itself to a more energetic movement by oscillating through a greater amplitude, without necessarily changing its oscillating period, and therefore without detracting from the power which its synchronism gives it of reacting upon the molecules.

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