Page:Philosophical Transactions - Volume 095.djvu/86

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72
Dr. Young's Essay

in Taylor's well known experiment the weight required was 50 grains. But when the solid employed is small, the curvature of the horizontal section of the water, which is convex externally, will tend to counteract the vertical curvature, and to diminish the height of separation; thus if a disc of an inch in diameter were employed, the curvature in this direction would perhaps be equivalent to the pressure of about one-hundredth of an inch, and might reduce the height from .2 to about .19, and the weight in the same proportion. There is however as great, a diversity in the results of different experiments on the force required to elevate a solid from the surface of a fluid; as in those of the experiments in capillary tubes: and indeed the sources of error appear to be here more numerous. Mr. Achard found that a disc of glass, 11/2 inch French in diameter, required, at 69° of Fahrenheit, a weight of 91 French grains to raise it from the surface of water; this is only 37 English grains for each square inch; at 441/2° the force was 1/14 greater, or 391/2 grains; the difference being 1/343 for each degree of Fahrenheit. It might be inferred from these experiments, that the height of ascent in a tube of a given bore, which varies in the duplicate ratio of the height of adhesion, is diminished about 1/180 for every degree of Fahrenheit that the temperature is raised above 50°; there was however probably some considerable source of error in Achard's experiments, for I find tliat this diminution does not exceed 1/1000. The experiments of Mr. Dutour make the quantity of water raised equal to 44.1 grains for each square inch. Mr. Achard found the force of adhesion of sulfuric acid to glass, at 69° of Fahrenheit, 1.26, that of water being 1, hence the height was as .69 to 1, and its square as .47 to 1, which is the