This anomaly, with respect to the expansion of water by the abstraction of heat, was one of the discoveries of the Florentine academicians, about the middle of the 17th cen tury ; but it was not much attended to, until it was again brought into view by Deluc. He repeated the experi ment with more accuracy, and lie attempted to ascertain the exact degree at which the expansion commences. This lie fixed at 41°; and he farther discovered, that the expan sion is nearly equal when water is either heated, or cooled, the same number of degrees above or below : (Recher ches, t. i. p. 225.) Some circumstances, which were not sufficiently attended to by Deluc, particularly the expan sion of the glass in which the water is contained, were after wards carefully noticed by Sir C. Blagden, and in conse quence of these corrections, he fixed the point of greatest density at 39°. (Phil. Trans. 1788, p. 125, et seq.) Le Fevre-Gineau came to the same conclusion respecting this anomaly in the expansive power of water, by a very differ ent process. He weighed a cylinder of copper in water at various temperatures, and thus obtained the weight of a cy linder of water exactly equal to that of the metal which he employed. The result of this process was to fix the maxi
mum of the density of water at the 40th degree. Dr Hope adopted another method of arriving at the same conclusion, which we ha•e fully explained in our article ExrAorsioN. Rumford has since performed a set of experiments upon the same principle, and with nearly the same results. There have been some objections made against these experiments, although they appear so correct, and were so much varied; but, upon the whole, we conceive the conclusion to be thoroughly established, that the greatest density of water is at about 8 or 9 degrees above its freezing point. The cause of this peculiarity with respect to water is involved in considerable obscurity. It appears to be connected with the increased space, which water, as well as many other substances, occupy, when they assume the crystalline form; and we may conjecture, that some tendency to this state takes place in water before its actual occurrence. Sec Ex