By theory [Art. 152], the proportions should be between those of 478] Comparison of different substances tried in the usual manner*. The large tin circle suspended by silk. .9323 •9053 .8827 .8926 ⚫8597 .8353 [See Arts. 653, 654, 682.] + Double plate ground glass A, thickness 3, diam. coating 1.82, comp. power 11.04. B, 31 A tin cylinder 35.9 inches long and 2·53 in diameter, on do. B-7 A 21 14.73 3.83 16.64 A tin cylinder 54.2 long and 73 in diameter, on do. [8] Brass wire 72 inches long and 185 in diameter, on do. 479] According to the 5th and 6th article of last page, the quantity of electricity in the square is to that in a circle of the same area as 1.08 to 1, and that in square to that in oblong of the same area as '991 to 1. By comparing the 2nd article with the 3 last, the quantity of elec(thick cylinder tricity in thin cylinder may be to that in a globe whose diameter (wire equals the length of cylinder as wire -939 length thickness Therefore, if we suppose that the real quantity of electricity in any cylinder is to that in the globe whose diameter equals the length of the cylinder as 1 to N. L. 2ce length it will agree very well both with theory and experiment. 2e length thickness' Or by comparing this with the first article, the quantity of electricity in any cylinder is to that in a circle whose diameter is equal to 2ce length the length of the cylinder as 759 to tab. log thickness Comparative charges of bodies tried in the former experiment. By means of this experiment and that of 1771. [Arts. 455, 456.] If the charge of the globe is called 1, that of the circle will be 992, therefore, by comparing 6th and 7th articles with 5th, the charges of the square and oblong will be 957 and 965. By comparing arts. 1 and 5, the charge of circle on waxed glass is greater than on silk strings in ratio 1.042 to 1, and therefore if charge of cylinders and wire on waxed glass are supposed greater than on strings in the ratio 1.021 to 1,* the charges of thick cylinder, thin cylinder and wire will be 980 and 966. 480] Sat. Jan. 1.028 Th. 53. S. H. 23. C. H. 111. Comparison of different substances tried in the usual way+ except that in the first experiment the touching wire rR and the wire RS were of brass 185 thick. [The cylinders and wire were supported on waxed glass at one end only.] [Exp. iv. Art. 269.] 483] TRIALS OF CHARGES. 239 481] Result of this and Art. 471. [Same as Table, Arts. 269, 270.] TRIALS OF LEYDEN VIALS. 482] The plates from Nairne made out of the same piece of glass were coated with circles of tinfoil as below*. The plates D, E, F, G of Nairne were compared with the double plates A and B by means of the trial plates A and B and an additional wire sliding on the electrifying wire Mm. of the same thickness. The wire Bb is 9 inches long. [See Art. 315. The computed power as given in this part of the Journal is the square of the diameter divided by the thickness, which is eight times the computed power as defined in Art. 311, and calculated in Art. 315.] 484] Two of the old ground glass plates H, I, K, L of Nuremberg glasst, were coated with oblong squares to serve for trial plates to the plates I, K, L, M of Nairne, but the observations were found to be so irregular that nothing could be made of them, owing, as was supposed, to the spreading of the electricity on the surface of the glass. To prevent this, all the four plates H, I, K and L were coated with oblong squares, and cased in cement composed of 2 parts rosin, 1 of bees' wax, and 3 of brick dustt. In making it the bees' wax was first melted and imperfectly dephlegmated, the rosin was then added and melted with as little heat as possible, and then the brick dust, previously heated so as to be very dry, was added. By this means the cement is more safe and sticky than if more heat is used in making it. In some of the mixtures also a small part of the rosin, never exceeding 1th of the whole, was exchanged for as much pitch, which was added after the rest was melted and mixed. The plates E, F, G, and I, K, L of Nairne were cased in the same cement, about 165 thick. A plate of the same cement was also cast by pouring it out on a tin plate. This was coated with circles about 2-2 in diameter. 485] The spreading of the electricity on the surface of the trial plates seemed not to be prevented by casing them in cement, for putting the plate L of Nairne on the positive side, and the trial plate H on the negative, then if the apparatus was let down and drawn up again immediately, the pith balls separated about half an inch negatively, but if the apparatus was suffered to rest at the bottom about half a minute, and then drawn up immediately, they separated considerably more than 1 inch, and if it was suffered to rest at the bottom but a very short time, [See Art. 302.] [See Art. 655.] + [See Art. 303.] |