HYDROSTATICS 



17 



fig. 18. 



less, which bears a considerably smaller 

 proportion to its former weight of 3415 

 grs. The comparative trials are gene- 

 rally made at a temperature of 60, at 

 which rain-water weighs 1000 ounces 

 avoirdupois, or 62i pounds, by the 

 cubic foot, or -2.33 UTS. by the cubic inch. 

 Spirits expand and become lighter 

 by means of heat, in a greater pro- 

 portion ; consequently they are heaviest 

 in winter. A cubic inch of brandy has 

 been found by many trials to weisrh 10 

 UTS. more in winter than in summer, 

 the difference bein? between 4 clrs. 32 

 grs. and 4 drs. 42 grs. Of this, liquor- 

 merchants are often found to take ad- 

 vantage, making their purchases in 

 winter rather than in summer, because 

 they set in reality a greater quantity 

 in the same bulk, buying by measure. 



If two liquids of 

 different specific 

 gravities are poured 

 into a bent tube, 

 so as to meet at the 

 bottom or middle 

 point, they will ba- 

 lance each other, 

 and each keep its 

 own side of the tube, 

 if they are in height 

 inversely as their 

 specific gravity; the 

 heaviest bein^ the 

 lowest. Thus mer- 

 cury, being thirteen 

 times and a half 

 heavier than water, 

 if you pour in so 

 much mercury as 

 will stand 2 in. high, 

 and so much wafer 

 as will stand 27, 

 they will balance 

 each other,and meet 

 at the bottom : thus, 

 in the tube' A B, i 

 (Jig. 18.) D I being a "7 

 the mercury, and 

 E I the water, and 

 C the middle point, 

 if E G, the per- 

 pendicular from the surface of the 

 water to the level at G is thirteen 

 and a half times D F, the perpendi- 

 cular from the surface of the mercury 

 to the horizontal line F G, passing 

 through the contiguous surfaces of the 

 water and mercury, the water will ba- 

 lance the mercury. Nor will this de- 

 pend at all upon the figure of the 



tube, or the quantity of the two 

 fluids : for whatever be the shape or 

 inclination of the branches A C and 

 B C, the balance will be kept, pro- 

 vided the heights E G and F D are in 

 the same proportion. Thus, the part 

 E C K in the tube A C D, (fig. 1 9.) 



-at 



may contain as much or more mer- 

 cury than K F does water ; still the 

 water will balance the mercury, the 

 height F H of its surface being thirteen 

 times and a half the height E G of the 

 mercury. Nor is it at all necessary 

 that the branches of the tube should 

 be of the same bore ; for the one with 

 the mercury (fig. 20.) may be much 

 wider than the one with the water; 



fiff. 20. 



21. 



and the smaller weight of water will 

 balance the greater weight of mer- 

 cury, provided the water stand thirteen 

 times and a half higher than the mer- 

 ciny. But if the tube has both branches 

 perpendicular, an easy method is fur- 

 nished of comparing the specific gra- 

 vity of liquids. We have r- 

 only to divide the upright /c t 

 branches into equal parts, t 

 and observe at what height r 

 above the common level 

 the two fluids stand in 

 them when they are ba- 

 lanced (fig.l 1 .) ; their spe- 

 cific gravities are inversely 

 as the heights: if oil, for v -^ 



instance, stands at 10 in one branch, 

 while water stands at nine in the other, 

 we infer that the specific gravity of the 

 c 



