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 14th, an 18th, a 19th, and when the water was previously purged of air, only a 22d part: that ice, 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 14th part specifically lighter than water, on being exposed some days to the frost, became a 12th part lighter. To this cause he attributes the bursting of ice on ponds. Several philosophers have been very desirous to experience how far the expansive force of freezing water might be carried. “An iron gun of an inch thickness,” says M. Haüy, “filled with water and exactly closed, having been exposed by Buot to a strong frost, was found to be burst in two places at the end of twelve hours. The Florentine philosophers were able, by means of the same cause, to burst a sphere of very thick copper; and Musschenbroek, having calculated the effort which would occasion the rupture, found that it would be capable of raising a weight of 27,720 pounds.” “Colonel E. Williams, of the Royal Artillery, when at Quebec, in the years 1794 and 1795,” says Dr. O. Gregory, “made many experiments. He filled all sizes of iron bomb-shells with water, then plugged the fusee-hole close up, and exposed them to the strong freezing air of the winter in that climate; sometimes driving in the iron plugs as hard as possible with a sledge-hammer: and yet, though they weighed near three pounds, they were always forced out by a sudden expansion of the water in the act of freezing, like a ball impelled by gunpowder, sometimes to the distance of between 400 and 500 feet: and when the plugs were screwed in, or furnished with hooks and barbs, by which to lay hold of the inside of the shell, so that they could not possibly be forced out; in that case the shell was always split in two, though its thickness of metal was about an inch and three quarters. It is further remarkable, that through the circular crack, round about the shells where they burst, there stood out a thin film or sheet of ice, like a fin; and in the cases where the plugs were projected by freezing water, there suddenly issued from the fusee-hole a bolt of ice of the same diameter, and stood over it sometimes to the height of eight inches and a half. Hence we need not be surprised that excessive frost should cause the ice to split rocks, and other solid substances.”[85]