The afternoon when these were tried, hygrometer corks closed in about 20 seconds. The trial plates being inlarged, tried with large trial plate. These experiments were tried in the morning. In the afternoon hygrometer corks closed in about 30 seconds. 460] The plate B was coated with a circle 2.79 inches diameter, computed power 40, and the plate D was coated with a circle 2·73, = computed power = 46. A piece of the white glass was also coated with a circle 2.85 in. diameter where the thickness was 182, computed power 44.6. White 18 nearly same as B. + 24 sep. supposed nearly same as 1st time. +27 sep. very little. + 30 nearly same or rather more than W at 24 with large plate. + 14 sep. a little neg. N N W +10 do. 461] The plate A was coated with a circle 2·16 inches diameter, computed power = 22·6; a plate of rosin also, the first which was pressed out after hardening, was coated with a circle 2.51, thickness 102, computed power 2-51*; they were tried with the trial plates described in p. 16 [Art. 457]. = 462] Hence it appears that A contains as much electricity as the two double plates. The rosin plate required the wire to be drawn out 18 inches less than them, therefore rosin plate contains 40.7 inches of electricity, and therefore quantity of electricity therein comp. power × †. = A contains 36.7 inches of electricity, and therefore as A and B are of the same kind of glass, the quantity of electricity in them = computed power x 1.6221056, and B contains 64.96 inches of electricity. The whitish glass plate required the wire to be drawn out 27 inches less than B, D requires 33 less and N requires 14 less; P requires 3 more than N, O 21 less, and Q 37 less than Ñ, therefore W contains 71.2 of electricity, D 72-5, N 68-2, P 67-5, O 73 and Q 76·7. [The "real charges" here given are in "circular inches," and the computed power is 8 times the true value, so that the numbers here given must be multiplied by 8/1.57 5.1 to compare them with those given in Art. 370. The diameters of the coatings in these experiments are not the same as those in Art. 370 which are taken from Arts. 508-515 and 672.] 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 2o the force to make them separate than the light 31 Tried with the usual corks. with the electricity neg. L-2 sep. a little. pos. L-35 neg. L-21 do. do. According to these experiments the plate should seem to contain 1 th 27 x== part more electricity in proportion when elec 4 x 31 60 more when electrified 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. mM) TR=2, RS = 61, 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 ry, 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. Fore observation. Touching wire extends 9 inches over. D-5 very little, rather doubtful 9.84 + [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.] |