HYDROGRAPHICAL SUIIVEY. 199 



The following Table exhibits the results of this 

 experiment *. 



• It may not be amiss to explain the method by Avhich the 

 calculations, in the annexed Table, were made. I shall take 

 the first line as an example. A cube of ash, weighing in air 

 157 grains, weighed in snow-water, temperature 60°, with a 

 load of 880 grains attached, 797 grains, (col. v.) Hence 880 — ■ 

 797 = 83 + 157, (col. iv.) — 240, (col. vi.) Then, as 252^} 

 grains, (the weight of a cubic inch of water, at temperature 60*,) 

 is to 1 cubic inch, so is 240 grains, (col. vi.) to 0.951, (col. vii.) 

 And as 240 grains, (col. vi.) is to 1.000, (the unit of specific 

 gravity,) so is 157, (col. iv.) to 0.654, (col. viii.) The diffe- 

 rence between col. x. and xi. gives col. xii. Then, as 252^ 

 grains, is to 1 cubic inch, so is 238 grains to 0.943, (col. xiii.) 

 And as 238 grains, (col. xii.) is to 1.000, so is 278 grains, 

 (col. X.) to 1.168, (col. xiv.) The difference between cols. iv. 

 and X. gives col. xv. And, finally, as 0.943, (col. xiii.) is to 

 121 (col. XV.), so is 1.000 to 128 (col. xvi.) 



All the results in columns iv, v, x, and xi, were found by 

 means of an excellent hydrostatical balance, sensible to the 

 twentieth of a grain. The scale-beam, Avhich was made under 

 my own inspection, and after a new plan, by an excellent 

 workman, has two adjustments, derived from a perpendicular 

 motion in the centre of the beam, and a horizontal motion in 

 the centre of one of the ends. The former moving up and down 

 by two opposite screws, adjusts the centre of gravity of the 

 beam, in any way that may be required, either for a quick or 

 a slow motion : and the latter, moving horizontally, adjusts the 

 two arms to the same length. With this balance, most of the 

 specific gravities, and other weights of any consequence, given 

 in these volumes, were determined. 



