TRACT 36.

THE WHIRLING-MACHINE.

205

Aug. 11 , 1788 .

Barometer 30 - 0S ; Thermometer 60.

55. The occasion of this day’s experiments was as follows:On comparing the last experiments, made with the parallelo-gram inclined in various angles, with those formerly made•with the cone, the vertex foremost, the surface of which Ithought might be considered as expanded or unrolled in atriangle of an equal area, and inclined in the same angle.But the resistances not turning out to be in the proportionof the two surfaces, I imagined that the difference might re-sult from the diversity in the shape of the two figures, orsurfaces compared, the one being a plane rectangle, and theother a conical surface, or as it were a triangle rolled up.

•56. I therefore procured an equilateral triangular brassplane, nearly of the same area and weight as the parallelo-gram last used, viz, the triangle being 3l£ square inches, ornearly of a square foot, and performed the following ex-periments with it, inclining the plane to the direction of mo-tion in all angles, differing by 5° at each time, and at eachinclination turning the vertex of the triangle both lore wardsand backwards, so that it might go both foremost and hind-most ; but, as there was no difference in the resistance be-tween the two positions, the numbers are set down only forone of them, the same numbers serving for both. The mid-dle line of the plane was placed at 53^ inches from the cen-tre of motion; and therefore the velocity of that line, is tothe velocity of the actuating weight, as 51*51 to 1. Theweights, for each inclination, were gradually changed, so asto bring the plane to make 2 uniform revolutions in. every 5seconds of time, in which case the velocity of the plane was1feet per second, or rather 11'26 feet.

57. Having therefore placed the several angles in thefirst column of the following table, and the actuating weightsin the 2nd column, which gave 2 revolutions in 5 seconds, inthe 3rd column are set the differences between the firstweight, when horizontal, and each of the other following