Page:Proceedings of the Royal Society of London Vol 1.djvu/191

Rh disc, and the great inclination and eccentricity of its orbit, may also be considered as a true asteroid.

Dr. Herschel concludes by observing, that the speciﬁc diﬂ'erence between planets and asteroids appears now, by the addition of a third individual of the latter species, to be more fully established; and that circumstance, he thinks, has added more to the ornament of our system, than the discovery of another planet could have done.

Dr. Young's principal objects in this paper are to reduce the phe- nomena of the capillary action of ﬂuids to the general law of an equable tension of their surfaces; to investigate the properties of the curves resulting from this law; to determine the magnitude of the apparent adhesion of solids to ﬂuids, and the cohesion of moistened solids; and to show in what manner the law itself is probably de- rived from the fundamental properties of matter.

Dr. Young observes, that a ﬂuid which is not capable of wetting a given solid, forms with it an angle of contact which is constant in all circumstances; that the curvature of the surface of a ﬂuid, or the sum of the curvatures, where the curvature is double, is always pro- portional to the elevation or depression with respect to the general surface, and that the curve itself admits, in all cases, an approximate delineation by mechanical means, but is not always capable of being easily subjected to calculation. When, however, the mature is simple, the direction of the surface, _at any given height, admits a correct determination. Hence the elevation of a ﬂuid in contactwith a given surface, whether vertical, horizontal, or inclined, is deduced from its ascent between plates, or in a tube, of the same substance; and the result is shown to agree with experiments. Thus, taking T'Ah of an inch for the diameter of a tube, in which water rises to the height of an inch, it is inferred that the apparent adhesion of water, to a square inch of any horizontal surface capable of being wetted by it, must be 50% grains, which is only half a grain more than the result of Taylor’s experiments. The adhesion of alcohol, and of sulphuric acid, as measured by Achard, are also found to agree with the ascent of those ﬂuids in capillary tubes. Lord Charles Cavendish’s table of the depression of mercury in barometer tubes, is compared with the same principles by means of diagrams con- structed for each particular case; and the apparent adhesion of the surface of mercury to glass, as well as the depth of a portion of mer- cury spread on a plate of glass, is deduced from these measures, and is shown to agree with experiments. The observations of Morveau, on the attraction of the different metals to mercury, are also dis- cussed; and some remarks are made on the magnitude of drops of various substances.

The hydrostatic actions of these elevations and depressions of ﬂuids are such as to afford a ready explanation of the attractions