541] Crown and H with slits compared with white cylinder; also on the excitation of electricity by separating a brass plate from a glass one. Wed. Feb. 17 [1773]. Th. 55. N. 21. [6 observations, Art. 660.] Fr. Feb. 19 [1773]. Th. 53. N. 181. A plate of glass 11 inches square, coated with tinfoil 8 inc. in diameter, was supported on waxed glass. A brass plate 8 inc. in diameter was supported over it by silk strings in such manner as to lye on the plate perpendicularly over the tinfoil, and to be drawn up till it touched a piece of wire supported on waxed glass with the middle sized cork balls suspended from it. This was done in order to see how much of the charge of the plate was contained in the coating. It was found that though the plate was not electrified, yet on lifting up the brass plate the balls separated some inches if the tinfoil communicated with the ground, but if it did not communicate, the balls, as well as I remember, separated considerably less. Some bits of thin silk thread were placed between the glass and brass plate. In the afternoon. Th. 54. N. 171. The experiment repeated with bits of card between the glass plate and brass. When there was nothing between the glass and brass plate, they sep. 1.4 inc. whether the tinfoil communicated with the ground or not. In all these cases the brass plate was negative. The glass plate was found to be pos. if the tinfoil did not communicate with the ground, but I could not perceive it to be at all electrified if it did communicate. The next morning the experiment was repeated, but the balls separated much less than before. The temper. of the air was much the same. 542] It was tried whether when three tin plates 1 foot square were placed near to and parallel to each other, the line joining their centers being perpendicular to their planes, the middle plate would receive much electricity on electrifying the plates*. The experiment was tried with the same apparatus and nearly in the same manner as the experiment with the globet, except that the two outer plates were suspended by two sticks of waxed glass turning on hinges. The wire too by which the plates were electrified was made so as to touch all three plates at the same time. Four bits of sealing [Exp. VIII., Art. 288 and Note 23.] + [Art. 218.] wax were stuck to the middle plate, two on each side, to prevent the outer plates coming too near. Sun. Feb. 21. Th. supposed about 55. N. 201. If the bits of sealing wax were of such size that the distances of the the middle-sized cork balls separated 5 outer plates were about about (1.15 The light paper electrometer was used in this experiment. If the globe 2 was electrified in the same degree, and its electricity communi(the 4 jars cated to and the middle tin plate electrified by one of 1, 2 & 4 jars these jars (the two outer being drawn aside) and the cork balls then drawn up against the plate, they separated about 1st In the case the electricity of the globe was diminished {[times], and therefore when the outside plates were at (1.15 the quantity of elec of what it would have received tricity in the middle plate was about 543] Charge of A, B, and C laid on each other without any coatings between; also charge of 1st thermometer tube. The coatings were taken from the 3 plates A, B and C of Nairne, and the plates cleaned and placed one on the other without anything between them, and stuck together by dropping some melted wax on the edges. The outside surfaces were then coated with circles 6.6 inc. diam. This is called Triple Plate*. A thermometer tube was coated with coatings 11 inch long, the inside being filled with , with wire let into one end, and the ends stopped with cement. The tube was 12.7 inc. long; weighed 1..3..0, and the bore held 22 gra. of water, the specific gravity of a piece of the same tube weighed twice over was 11.7 3.15121 = 3.1. N.B. The comp. pow. of this tube is about 901. This is called Tube 1†. Mon. Feb. 22 [1773]. Th. 53. N. 201. [8 observations. Art. 675.] 544] Lane's electrometer compared with straw and paper electrometer; also charge of plate rosin with brass coating made to prevent spreading of electricity. A plate of rosin and bees wax of the same proportions as for exper. rosin was cast of the shape of figure, ABDC and abcd being brass plates 2.45 in. diam. their distance before the rosin was poured in being about 12 inc. Tu. Feb. 23 [1773] in afternoon, the rosin plate being cast that morning, the hygrom. as well as I remember being about 22. [4 observations, comparison with E.] Wed. Feb. 24 [1773]. Th. 54. N. 20. [4 observations.] Rosin closed in about 7", sep. again in 35. E was irregular. 5451 Second thermometer tube; also comparison of charge of cylinder used in [Art. 539] with D + E. = A thermometer tube whose length was 22.1 inc., weight 2, 17, 21 and weight water which filled bore 14 gra. was coated with tinfoil 15.5 long, conseq. comp. power: *the spec. gra. of a part of the same tube being 3.243. Fr. Feb. 26 [1773]. = Th. 52. The cyl. used in [Art. 539] compared with the plates D and E, the wire Mm of machine being drawn out to 39 inches, and resting on the cylinder as in that experiment. A sliding trial plate on neg. side. [6 observations. See Art. 666.] 546] Charge of second thermometer tube; also that of rosin plate with brass coating; also that of A, B, and C laid on each other without coatings between. [10 observations. Art. 675.] The same things were tried the day before, Th. 55, N. 171, but the wire for making communication between machine and ground was forgot to be fixed. [14 observations. See Art. 666.] 547]† The quantity of electricity in Plate D compared with that in a tin circle of 36 and another of 30 inches diameter by means of the machine used for comparing simple plates*, the trial plate being a tin cylinder inches long, and + in circumference, fastened to the end of the usual sliding trial plates, with another cylinder of the same size sliding within it. Tried with elect. of usual strength and with the middle sized corks. 548] Charge of plate of experimental rosin designed for compound plate of glass and rosin; tried both when warm and when cold. A plate of experimental rosin near 8 inches square was pressed out between two glass plates with tinfoil coatings fastened on by oil, the heat being such that it required very little weight to press out the rosin. The thickness of the plate was much less toward one end than the other, varying in different parts of the coated plate from 137 to 108, but the mean thickness was 122. It was coated with circles of tinfoil 6.61 in. diameter. Its charge was compared with that of the plates K, Nairne by means of a sliding trial plate made of the plate Sat. March 6 [1773]. Th. 55. N. 17. D and E of of Nairne. The rosin plate was then warmed before the fire between two glass plates with flannel between them and the rosin till it would not support its own weight without bending. As soon as it was strong enough to bear its own weight it was compared as before. In about 2 or 3 hours after, when it was quite cold it was tried again: 549] Whether charge of glass plate is the same when warm as when cold. The same afternoon the charge of a glass plate when hot and cold was compared together in the same manner. The glass was 11 inches square, used for Æpinus experiment*, coated on one side with a circle of 8 inc. diameter, and a brass plate of same diameter used for the other coating. The glass and brass plate were both heated before the fire till almost as hot as I could bear my hand on, and then tried by the help of the 6th sliding plate, when the breadth of the sliding plate was required to be 37 in order that it should sep. pos. After the plate was cold it was tried again, the breadth of the sliding plate was obliged to be 36. Hence it would seem as if the charge both of glass and of rosin plate was the same when hot as when cold, the small difference between them being most likely owing to the electricity spreading more on the surface of the warm plate than of the cold one. 550] Crown with slit coatings and H with oblong compared with white cylinder; also second thermometer tube with D + E + F. The slit coatings were taken from H and plain coatings, 6·03 square, put in their room. Sun. March 7 [1773]. Th. 56. N. 15. Straw elect. at 2+ 3, which is equivalent to light paper electrometer [4 obs.]. Elect. at 3+1 [6 obs.]. Elect. at 1+3 [7 obs. Art. 660]. Mon. Mar 8 [1773]. Th. 54. N. 143. [4 obs.]. 551] Quantity of electricity in plate D and rosin with brass coatings compared with that of tin circle of 36" and one of 30" by machine for trying simple platest; with different degrees of electrification+ Tu. Mar. 9 [1773]. Th. 51. N. 15. The exper. of p. 78 [Art. 547] repeated, only using square tin plates of different sizes made to fasten on to sliding cylinder instead of the sliding trial plates. The tin circles and the square plates both supported on silk. Straw el. at inner marks N° 2. [Arts. 134, 341, 517.] + [Art. 240.] + [Art. 664.] |