463] Experiments to determine whether the quantity of electricity in coated plates bore the same proportion to that in other bodies whether el. was weak or strong, or whether it was positive or negative*. On the side of corks was placed plate A with circle 2 inches in diameter, containing 31 inches of electricity. On the other side there was no coated plate, but the wire was drawn out 23 inches and made to rest at further end on the sliding wooden plates. The heavy corks required more than 2° the force to make them separate than the light According to these experiments the plate should seem to contain 31 4 x 31 1 th x == part more electricity in proportion when electrified by heavy corks than light, and about th more when electrified pos. thau neg. 80 464] A plate 345 inches thick was pressed out of exper. rosin and coated with circle 3.41 inches diameter, therefore computed power = 33.7. This was compared with double plate B by help of the sliding coated plate mentioned in [Art. 442]. + [This would make the specific capacity of rosin 20 × 5·1/33-7=3. The num bers in Art. 462 make it 3.3.] 466] Plan of usual disposition of vials and bodies to be tried &ca drawn in the true proportion and shapet. 8 is the trial plate, B the body to be tried, A and a the vials, mM and rR the touching wires. rm = 83 inches, mM) TR ý = 27, MN = 41, Na = 24, AC=10. Height of body and trial plate above ground = 4·2 below horizontal bar = 3·11. All the wires were about '07 thick. [This is the heading of this bundle of the Journal, though the dates up to Art. 475 belong to 1771.] + [See Art. 240.] 467] Comparison of quantity of electricity in a tin plate one foot square, according to the different situations in which it was electrified. The trial plate was suspended on waxed glass, the plate to be tried on silk strings *. Description of the different ways in which it was tried. Fore Observation-The plate horizontal and placed as in figure, the touching wire also as in figure but extending to different distances upon the plate [called 2nd and 3rd way in Art. 266]. Bent Wire-the same as former except that the touching wire was bent into the shape rTR, the distance rR remaining as before, the arch TR being vertical and its greatest distance from the straight line rR being about 15 inches [5th way]. Cross Wire-The same except that the touching wire rR had a cross wire Ee placed horizontally fastened on within 3 inches of r, the touching wire being of the same length as before, and Ee 23 inches long. The touching wire was made to extend so much on the plate that Ee was about 1 inch distant from the edge of the plate [4th way]. Back Observation-The touching wire removed into the situation xy, the wire yzS being 13 feet 5 inches long and passing nearly perpendicularly over B and at the height of 3'. 7′′ above it [6th way]. Plate Vertical-The plate hanging in a vertical plane nearly perpendicular to the right line joining it and the vial. The touching wire touched it about the middle of the upper side [1st way]. 468] Sat. Dec. 14 [1771]. Th. 53°. S. H. 19. C. H. + 7+. Back observation. Touching wire extends 4 inches. [See Exp. 1. Art. 265.] [Th.-Fahrenheit's Thermometer: S. H.-Smeaton's Hygrometer. See 'De scription of a new Hygrometer by John Smeaton.' Phil. Trans. 1771, p. 198. C.H.-Common Hygrometer.] Th. 55. Smeaton's Hygrometer 181. Common Hygrometer + 5. 469] Monday, Dec. 16 [1771]. Trials of time in which electricity of stone square, &c. was destroyed. The squares were supported on glass, and a piece of tin foil about 1 inch square fastened on each corner. On one of these pieces was fastened a wire from which the pith balls were suspended. The square was then electrified by applying a charged vial, and then a wire communicating with the wall was applied to the other piece of tin foil. With slate the corks closed in 10" The gummed The stones had been kept in fore room for several days. glass had been kept in fore room till the gum began to crack. It was then kept in back room for about 5 hours, and then kept in fore room about 1 hour. Hygrometer corks closed in 4'. The glass being then wiped they closed in 7'. Being then suffered to stand uncovered for 2 or 3 hours, the corks closed in 5'. C. H. +9. 470] Tuesday, Dec. 17 [1771]. Th. 53. S. H. 20. Experiments of [Art. 468] continued. |