302 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



4 different trials in the temperature of 64°; that mean differing from the extremes 

 only by .0003 inch. 



By this examination, if I have not verified, I have at least preserved, Mr. White- 

 hurst's standard; and, for the present, I shall consider this measure of the difference 

 of the length of the two pendulums, vibrating 42 and 84 times in a minute of 

 mean time, as correct. On this presumption, I shall proceed to the examination 

 of weight. 



From the opinion of different skilful persons, with whom I have conferred, as 

 well as from the result of my own considerations, I am inclined to believe there is 

 hardly any body in nature, with which we are familiarly acquainted, that is of so 

 simple and homogeneous a quality as pure distilled water, or so fit for the purposes 

 of this inquiry ; and I have concluded, that if the weight of any quantity of water, 

 whose bulk had been previously measured by the above-mentioned scale, could be 

 obtained, under a known pressure* and temperature of the atmosphere, we should 

 be in possession of a general standard of weight. 



With this view, I directed Mr. Troughton to make, in addition to the very sen- 

 sible hydrostatic balance before-mentioned, a solid cube of brass, whose sides should 

 be 5 inches ; and also a cylinder of the same metal, 4 inches in diameter, and 6 

 high. From St. Thomas's hospital, by the favour of Dr. Fordyce, I procured 3 

 gallons of distilled water. With these I made the following observations; but, 

 before I relate the experiments, I will describe the apparatus. Here Sir G. S. adds, 

 the description of his instruments: these were, a beam-compass, or divided scale 

 of equal parts, and a hydrostatic balance. A hollow sphere of brass, of 6 inches 

 diameter, was also provided. Sir G. gives a minute detail of the curious experi- 

 ments and observations he made to ascertain the exact figures, measures, dimen- 

 sions, weights, and specific gravities of all these bodies; the results of all of these 

 being as follow : 



Of the brass cube, he measured very nicely the length of all the ] 2 linear edges; 

 viz. as it stood on one end as a base, all the 4 linear sides of the top, all those of 

 the bottom, and all the 4 upright edges: the medium of the first 4 was 4.98882; 

 of the 2d, 4.g8955; and of the 3d, 4.98925; all rather below the intended mea- 

 sure, 5 inches. The 3 mean dimensions multiplied all together, gave 124.1 891 7 

 cubic inches, for the solid content of the cube. 



In like manner, of the cylinder, the mean of several diameters taken at one 

 end, was 3-99745 inches; at the other end, 3-99785; and the medium of several 

 measures of length was 5.99502; which 3 dimensions multiplied all together, and 

 by the circular factor -7854, gave 74.94823 cubic inches, for the solid content of 

 the cylinder. 



The diameter of the sphere was, by a medium of many measurements, found to 



* I do not here mean to infer any opinion respecting the compressibility of water; but only to say, 

 that where water, or any thing else, is weighed in air, the density of that medium, as shown by the 

 barometer and thermometer, must be known, in order to make allowances for it, if necessary. — Orig. 



