190

EXPERIMENTS WITH

TRACT 36.

Where the numbers placed at the bottom of all the co-lumns, denote the general mean proportions of their resist-ances to one another, from the velocity 10, to each of thefollowing ones.

Note. The general mean height of the barometer was30 - l, and of the thermometer 62°; in which circumstancestherefore, the ratio of the weight of water to air, was as840 to 1, or the cubic foot of air weighed nearly 14 ozavoirdupois.

It may be repeated also, that the diameter of the smallhemisphere was 4|- inches, and consequently the area of itsbase, or great circle, was 17f square inches, or ^ of a squarefoot nearly. But the common diameter of all the other fi-gures was 6-f inches, and therefore the area of the circularbase, was just 32 square inches, or •§■ of a square foot. Also,the altitude of the cone was 64 inches ; its side is thereforeinclined to the axis in an angle of 25° 42'.

43. From the preceding table of resistances, several prac-tical inferences may be drawn ; such as the following.

( 1 ). That the resistance is nearly as the surface; the re-sistance increasing but a very little above that proportion inthe greater surfaces. Thus, by comparing together thenumbers in the 6 th and 8 th columns, for the bases of the twohemispheres, the areas of which are in the proportion ofIT- to 32, or as 5 to 9 very nearly; it appears that the num-bers in those two columns, expressing the resistances, arenearly as 1 to 2, or as 5 to 10, as far as to the velocity of12 feet; after which the resistances on the greater surfaceincrease gradually more and more above that proportion;and the mean resistances are as 140 to 288, or as 5 to 104 ,so far as these experiments have been extended. Nearlythe same proportions result from the comparison of the num-bers in other columns with similar surfaces. Now, the ratioof the surfaces being that of 5 to 9; and the ratio of the re-sistances as 5 to 104 ; it appears that the latter exceeds theformer in the ratio of 9 to lOf-, or of 1 to 1 4 ; or of 7 to 8 .Hence then, to find the resistance to any surface, from hav-