I find no difficulty in thinking it would be easy to arrange a mixture of water and snow in such a manner that it might be kept for hours and days without any transition of heat either to or from it; but I find great difficulty in thinking that the particles of snow, small as they may be made, would remain for the whole of the time at a lower temperature by 0°.3 F. than the particles of water intermingled with them:—still admitting for the present the possibility that Prof. Forbes's view may be correct, and also the truthfulness of Mr. Thomson's principle, and its possible action in reg elation, I wish to say a few words on the other principle already referred to, which was originally assumed by myself, which in relation with the mechanical theory of heat, has been adopted by Dr. Tyndall, and which, after all, may be the sole cause of the effect.
The principle I have in view being more distinctly expressed is this:—In all uniform bodies possessing cohesion, i. e. being in either the solid or the liquid state, particles which are surrounded by other particles having the like state with themselves tend to preserve that state, even though subject to variations of temperature, either of elevation or depression, which, if the particles were not so surrounded, would cause them instantly to change their condition. As water is the substance in which reg elation occurs, I will illustrate the principle by the phenomena which it presents. Water may be cooled many degrees below 32° Fahr.[1] and yet retain its liquid state, for as far as we know any length of time, without solidification; yet, introduce a piece of the same chemical substance, ice, at a higher temperature, and the cold water freezes and becomes warm. It is certainly not the change of temperature which causes the freezing, for the ice introduced is warmer than the water. I assume that it is the difference in the condition of cohesion existing on the different sides of the changing particles which sets them free and causes the change. The cold water particles would willingly, as to temperature, have solidified without the ice, but were held fluid by the cohesion with them of other like fluid particles on all sides.
- ↑ Water may he cooled to 22° F. It is probable that if it were perfectly freed from air it would remain fluid at a much lower temperature, for the air is excluded at the freezing-point, and the occurrence of this exclusion would break cohesion.
