When water is converted into ice, it is lighter[83] than when in a fluid state, which is a circumstance of great importance. Galileo was the first who observed this. Ice consequently floats upon water, its specific gravity being to that of water as eight to nine. This rarefaction seems to be owing to the air-bubbles produced in water by freezing; and which, being considerably larger in proportion to the water frozen, render the body so much specifically lighter: these air-bubbles, during their production, acquire a great expansive power, so as to burst the containing vessels though ever so strong. [The specific weight of ice is known to be less than that of water. Our author assigns a reason not entirely satisfactory. We must admit that the freezing of the upper stratum of water, although it may _include_ the air which was in the water frozen, yet, _it does not expel the air from the subjacent volumes of water_. Hence the air in the water below will balance the effects of the air included in the ice. It is a singular fact, and is regarded as a deviation from the general rule, that water _expands_ in volume in proportion as its temperature is _reduced below_ 40° Fahrenheit. It also expands by raising its temperature above this degree. The _expansion_ of the volume then, and not the enclosed air bubbles, is the cause of water being specifically lighter when converted into ice. But it remains to account for its expansion by a _reduction_ of temperature. This is a difficult question. It seems most probable that this expansion is owing to a peculiar arrangement, of the particles of water, in the act of crystallization, i.e. _freezing_. M. Mairan found that the particles of water, in the act of freezing, arranged themselves constantly at an angle of 60°, and by this arrangement _increased the bulk_ of the water thus crystallized. It is obviously a mistake to attribute the “expansive power” of freezing to the force of the inclosed air-bubbles: because the reduction of temperature would reduce this supposed expansion of the inclosed air. The true cause of the expansion of ice is supposed above, in the arrangements of the particles of water in the process of crystallization. The _power_ which disposes these particles to arrange, _increases with the reduction of temperature_, until the disposing power becomes sufficiently great to force every impediment to the inclination to arrange. Hence the strongest vessels burst in the process of freezing.