458] The wire not drawn out is about 40 inches, and may therefore contain about 10 cyl.* inc. of electricity, id est, as much electricity as is contained in circle of 10 inches diameter. Quantity of electricity in additional wire is supposed to be equal to its length [divided] by 4.4. Both the trial plates together, whose computed power = 66, is equivalent to 2A+ 2B+ 80 inches of wire + 45 of additional wire, id est, to 73·4 +20 + 10·1 = 103.5 inches of electricity, therefore 1 inch of computed power in the glass of which trial plates are made should be equivalent to 141 inches of electricity. By the experiment marked in [457], a difference of computed power in the trial plates 3.6, which is equivalent to 508 inches of electricity, was equivalent to drawing out wire 20 inches, which is supposed = 4.54 inches of air, which is as near an agreement as can be expected. By a medium of the experiments, the plate of air 39 thick required wire to be drawn out 11 inches less than A and B, the different experiments varying from 9 to 14, therefore the plate of air contains 2.6 inches more electricity than A and B, id est, it contains 39.3 inches of electricity. The plate of air 343 seemed by 1 experiment to contain 42.7 of electricity. Therefore plate of air 39 contains 4.94 times more electricity than a circle of same diameter, therefore quantity of electricity therein is to that in circle of same diameter as radius to thickness × 2:06 or quantity of electricity = computed power × ·243. X 459] Four irregular pieces of glass, N, O, P, Q, were coated with circles. The thickness, specific gravity of glass and diameter of circles are marked in [Art. 370], the thickness of glass being found by taking thickness with calipers at center of proposed circle, and finding a part of outside of same thickness and measuring that part by Bird's instrumentt; the computed power of all being just 40. The experiments were tried with sliding wire as former[ly]. 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. They were tried with the same trial plates. White 18 nearly same as B. + 24 sep. supposed nearly same as 1st time. + 30 nearly same or rather more than W at 24 with large plate. N N + 14 sep. a little neg. 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 x t. = 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 × 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 N, 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 2° the force to make them separate than the light Tried with the usual corks. with the electricity neg. L-2 sep. a little. pos. L-31 neg. L-21 do. do. According to these experiments the plate should seem to contain 31 x=1=17th part more electricity in proportion when elec 4 x 31 27 thmore when electrified trified by heavy corks than light, and about th pos. than neg. 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) rm = 83 inches, m} = 27, MN = 41, Na = 24, AC=10. Height of body and trial plate above ground 4.2 below horizontal bar All the wires were about '07 thick. = 3.11. * [This is the heading of this bundle of the Journal, though the dates up to Art. 475 belong to 1771.] [See Art. 240.] |