The 1st and 2nd sliding coated plates were compared with double plate B [6 observations]. The 25 divisions] on sliding] plate] were measured by using brass plate 3 inc. by 1 and 9 div. of the tinfoil. 2 trial plates were made for plates M &c. out of a white glass hemisphere [8 observations. Art. 656.] Fr. Dec. 25 [1772]. Th. 49. N. 20. 3 on insulation. Art. 656.] (0 [19 observations, and By this exper. with small large trial plate Q contains inc. el. less 7.3 less, whitish plate By mean P contains 9.5 less, O 5·8 less, old G 5·1 less, whitish plate 7 less, thin rosin 16 less, and Q 3 less. The wires used in the machine were all cleaned between this experiment and the next. 516] Whether the charge of plate air is diminished by changing the air between them by lifting up the upper plate*. In order to try whether in electrifying plate air the electricity was lodged in the air or in the plates, the two brass 8-inch plates were placed on each other with supports of sealing wax to keep them at about 4 inc. distance from each other and placed on the machine† with the end M of the wire Mm resting on it; the uppermost plate being fastened by a stick of waxed glass and 3 pieces of silk to the end of a lever so that it could be lifted up and down. It was also contrived so that in lifting up the plate the wire Mm was first lifted up from it about inch, for fear that if Mm rested on the plate when lifted from the under one, some electricity might escape from the ends of the wire Bb, &c. The third sliding trial plate was put on the negative side. If the wire Ce was let down and up immediately without lifting up the upper plate, the pith balls separated negatively very little with 18 divisions of sliding plate. If the wire Cc was let down and immediately drawn up half way, but not drawn quite up till the upper plate had been drawn up and let down again, the balls separated very little more. The event was the same also if the trial plate was drawn out so that the balls should separate a little positively. The upper plate was lifted up 2 or 3 inches. The sliding plate was let out to 12 divisions that the balls should separate positively. * [See Arts. 311, 511.] + [Art. 295.] 517] PLATES OF AIR. 257 517] Trials of plate air 1, 2, 3 and 4. [See Arts. 341 and 668.] Two plates of glass 11 inches square were coated with tinfoil about 11.4 inches diam. a slip of tinfoil extending from the coating to the other side. These plates were placed upon each other with coated sides to[wards] each other and kept asunder by 3 supports of sealing wax, the supports being placed a little on outside of coated part and tried in the usual manner. Sun. Dec. 27 [1772]. Th. 50. N. 18. [4 observations.] Mon. Dec. 28 [1772]. Th. 53. N. 17. The exper. tried in same manner except that only 1 corner of the under plate rested on machine, the rest being supported by 2 wooden pillars, the places where it was supported being nearly under wax supports. [15 observations. Art. 668.] By this exper., plate air 1 contains 1 inc. el. more than D, plate air 2, 1 inc. el. less than D+ E, and plate air 3, 10 inc. less than D+E+ F. Wed. Dec. 30 [1772]. Th. 55. N. 15. The supports of plate air 3 altered and called plate air 4. [12 observations.] One of the pith balls was destroyed by accident, and another put in its room. The plate air 1 was made to rest intirely on machine. [3 observations.] By this exper., plate air 4 contains 1 inc. el. less than D + E + F, plate air 2, 1 inch less than E + F, and plate air 1, 1 inch more than E. It should seem also that the wire Mm contained 2 inches less el. when the plate rested intirely on the machine than when it rested on it only by one corner. The thickness of these plates of air was found by laying these plates on bracket fastened to dividing machine* with or without wax supports between them, and finding the division at which the new machine stood right, the knob of the new machine resting on the middle of upper plate, and the under plate being supported under the wax supports. By this means the thickness of these plates of air were as follows: Some experiments were made by putting bits of tinfoil between the plates whether the glasses were flat, and consequently whether the measures thus found were true. It seemed as if when the plates lay on each other the middle of the coatings could not want more than 002 or 004 of touching, but it did not appear that it wanted so much, and it seemed as if the outside did not want anything of touching, so that the above measures seem pretty just. The diameter of the coating was 11.4. The above coatings were taken off from these plates of glass, and coatings 6.254 in diameter put in their room, these with the small wax supports placed between them is called plate air 5. N.B. 8 folds of the tinfoil used for these coatings was found to be To inch thinner than the same number of folds of that used for former coatings, so that this plate air is about 003 thicker than plate air 4. The coatings were also taken from thin rosin and coatings 4.525 put in their room. A plate of pure lac was also pressed out 125 thick, and the coatings used before for thin rosin put on, which were found at a medium 4.23 in diameter. Two plates of dephlegmated* bees wax pressed out the year before were also coated. N.B. The bees wax was heated very hot in dephlegmating, and melted with gentle heat when cast into plates. 518] Lac plate and 4th rosin compared with D+E+F; also thin wax with E+F; also thick wax and plate air 5 with D. Mon. Jan. 4 [1773]. Th. 51. N. 17. [23 observations.] By these exper. Lac plate contains 1 inc. el. more than D+E+F; 4th rosin from 3 inc. more to 2 inc. less, by mean much the same as D+E+F; thin wax 4 inc. less than E+ F; thick wax 2 less than D; plate air 5more, and 1st made rosin more. In the preceding experiments the plates of rosin &c. were exposed to the heat of the fire during trials, which seemed to cause an irregularity. To avoid that, in the following days' experiments the plates were laid on table at same distance from fire as the machine for some time before they were tried, and a screen was placed between all of them (except plate air) and fire while trying. 519] Lac and 4th rosin with D + E + F; also thin wax with D + E ; also thick wax, 2nd rosin and 1st made rosin and plate air 5 with F. [Art. 375.] 520] ELECTRIC STRENGTH OF LAC, ROSIN AND WAX. 259 Tu. Jan. 5 [1773]. Th. 50. N. 17. [22 observations.] By these exper. 4th rosin contains from 2 inc. more to 21 less than D+E+F; by mean, the same as D + E + F. Lac from 4 more to less, by mean 21 more than D + E + F. Thin wax from 4 less to 1 less, by mean 21 less than D + E. 2nd rosin, 13 less, plate air 5 more, and 1st made rosin same as F. N.B. The 1st made rosin was made of the same proportion of rosin and bees wax as the others, but not of the same parcel: it is uncertain how much it was heated in making the mixture. 520] Breaking of electricity through thin plates of lac, exper. rosin and dephleg. bees wax. Thin plates were pressed out of lac, experimental rosin and dephlegmated bees wax, very thin at one end and thicker at the other. The tinfoil was stript from one side of these plates but the other left on, and was fastened to a piece of glass with gum water, and a piece of tinfoil fastened to the under side of glass communicating with the other. These plates were placed on [the] negative side of the machine with wired bearing against bottom and a flat piece of brass at top on which wire was suffered to rest. The machine was electrified in usual degree, and the bit of brass shifted from thicker to thinner part, till the electricity broke through the plate and discharged the jars. A piece of the plate with the tinfoil under it was then cut out of the size of the brass plate, as near as possible to the place where the electricity broke through, and the thickness of the plate found by weighing it and also the tinfoil after the plate was separated from it. The thickness of the plates thus found was as follows †, the specific [See Art. 343. The inches of electricity are circular inches, and to reduce them to globular inches must be multiplied by 12-1, the diameter of globe, and divided by 18.8, the diameter of a circle which has the same charge. The computed power here is the square of the diameter divided by the thickness, and this must be multiplied by 8 to get the computed power as defined in Art. 311.] + [With the usual degree of electrification" Lane's electrometer discharged at 04 inch. See Art. 329. The electric strength of wax, rosin, and lac is therefore about three times that of air.] 521] The quantity of electricity in a Florence flask tried with and without a magazine. The quant. el. in a Florence flask was tried by putting it on negative side, and some of the jars &c. on the other, the battery of 6 Florence flasks being used instead of the jars. With the 1st, 2nd, 3rd jar with sliding plate 6 – 40 sep. neg. rather more than 1 diam. sep. a little pos. Th. 56. N. 19. The same thing tried again in same manner with the 4 jars and white cyl. sep. about 1 diam. pos. With 4 jars and white cyl. sep. at 1 about 1 diam, but soon closed, with 1, 2, & 3 jar sep. a good deal neg. with 1, 2, & 3 jar + wh. cyl. + gr. cyl. 2 after a time sep. near 1 diam. With 4 jars and the 2 cyl., sep at 1 a good deal, after a time sep. about 1 diam. A coating of tinfoil to a part of the Florence flask out of water. With 4 jars wh. cyl. + gr. cyl. 2 sep. rather more than 1 diam. The case was much the same whether wire was suffered to rest at bottom 2" or 3′′, or less than 1". With 4 jars sep. a little neg., increased after a time to full 1 diam. By the 1st night's experiments the flask contains 12126 inc. el. by the 2nd and by the 3rd Without magazine by 2nd night it contained 11694 11495 13205 inc. el. 11700 |