a solid, transparent, and brittle body, formed of some fluid, particularly water, by means of cold.

M. Lemery observes, that ice is only a re-establishment of the parts of water in their natural state; that the mere absence of fire is sufficient to account for this re-establishment; and that the fluidity of water is a real fusion, like that of metals exposed to the fire; differing only in this, that a greater quantity of fire is necessary to the one than the other. Galileo was the first who observed that ice was lighter than the water which composed it; and hence it happens that ice floats upon water, its specific gravity being to that of water as eight to nine. This rarefaction of ice seems to be owing to the air-bubbles produced in water by freezing, and which, being considerably large 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.

M. Mairan, in a dissertation on ice, attributes the increase of its bulk chiefly to a different arrangement of the parts of the water from which it is formed; the icy skin on the water being composed of filaments, which, according to him, are found to be constantly and regularly joined at an angle of 60°; and which, by this angular disposition, occupy a greater volume than if they were parallel. He found the augmentation of the volume of water by freezing, in different trials, a fourteenth, an eighteenth, a nineteenth, and, when the water was previously purged of air, only a twenty-second part; that ice, even after its formation, continues to expand by cold; for, after water had been frozen to some thickness, the fluid part being let out by a hole in the bottom of the vessel, a continuance of the cold made the ice convex; and a piece of ice which was at first only a fourteenth part specifically lighter than water, on being exposed some days to the frost, be- came a twelfth part lighter. To this cause he attributes the bursting of ice on ponds.

Though it has been generally supposed that the natural crystals of ice are stars of six rays, forming angles of 60° with each other, yet this crystallization of water, as it may properly be called, seems to be as much affected by circumstances as that of salts. Hence we find a considerable difference in the accounts of those who have undertaken to describe these crystals. M. Mairan informs us that they are stars with six radii; and his opinion is confirmed by observing the figure of frost on glass. M. Romé de l'Isle determines the form of the solid crystal to be an equilateral octahedron; M. Hasselbrant found it to be a prismatic hexahedron; but M. d'Antic found a method of reconciling these seemingly opposite opinions. In a violent hail-storm, where the hailstones were very large, he found that they had sharp wedge-like angles of more than half an inch; and in these he supposed it impossible to see two pyramidal tetrahedra joined laterally, and not to conclude that each grain was composed of octahedrons converging to a centre. Some had a cavity in the middle; and he saw the opposite extremities of two opposite pyramids, which constitute the octahedron; he likewise saw the octahedron entire united in the middle; all of them were therefore similar to the crystals formed upon a thread immersed in a saline solution. On these principles M. d'Antic constructed an artificial octahedron resembling one of the largest hailstones, and found that the angle at the summit of the pyramid was 45°, but that of the junction of the two pyramids 145°. It is not, however, easy to procure regular crystals in hailstones, where the operation is conducted with such rapidity; in snow and hoar-frost, where the crystallization goes on more slowly, our author is of opinion that the rudiments of octahedra may be discovered. (See the section on Congelation, in the article Cold.)

Blink of the Ice, is a name given by the pilots to a bright appearance near the horizon, occasioned by the ice, and observed before the ice itself is seen.

Ice-Boats, boats so constructed as to sail upon ice, and which are very common in Holland. They go with incredible swiftness, sometimes so quickly as to affect the breath, and are found very useful in conveying goods and passengers over lakes and great rivers. Boats of different sizes are placed in a transverse form upon a two-and-a-half or three-inch deal board. At the extremity of each end are fixed irons, which turn up in the form of skates. Upon this plank the boat rests, and the two ends serve as out-riggers to prevent oversetting; whence ropes are fastened that lead to the head of the mast in the nature of shrouds, and others passed through a block across the bowsprit. The rudder is made somewhat like a hatchet with the head placed downwards, which being pressed down, cuts the ice, and serves all the purposes of a rudder in the water, by enabling the helmsman to steer.