Sun. Dec. 6 [1772]. Th. 54. N. 20.

[19 observations. Art. 655.]

[Result.] By these exper. the two double plates should contain about 1.13 inc. el. more than D, that thick white contained same as D, that the 2nd rosin contained 2.26 less, that the thin white contained 45 less than D+ E, and that N contained 1.81 less.

Sunday evening. Th. 57. N. 171.

[18 observations.]

510] Crown A and C compared with A, B and C of Nairne. Mon. Dec. 7 [1772]. Th. 55. N. 18.

[10 observations.

21 observations of spreading of electricity on the different plates.]

By the above exper. Crown A and C should contain 15 inc. el. less than A.

511] Whether the shock from the plate air was diminished by changing the air between them by moving them horizontally*.

Sat. Dec. 18 [1773+]. Th. 60°. N. 231.

It was tried whether shock in charging plate air was sensibly diminished by moving the 2 plates horizontally, and thereby changing the air between them in the manner represented in figure, where AB represents the two 8-inch brass plates with sealing wax between them suspended by the silk strings AC and BD.

AE and BF are silk strings fastened to the frame on which lower plate rests, and passing over wire hooks E and F, and stretched by

weights so that the plates would move from E towards F and rest in any position.

The electrifying wire was suspended by the string G with a counterpoise.

The plates were electrified, holding my finger to bottom plate, they were then moved 24 inches by lifting up the weight M, and then discharged by holding my little finger to lower plate and touching upper plate with brass knob held in the other hand. I could feel a small pulse in little finger, having tried this I electrified and discharged the plates in same manner only without moving them first and endeavouring to preserve the same distance of time between the electrification and discharge. I was not able to perceive any difference in the feel. I endeavoured to ascertain the time by the vibrations of a pendulum, but without much success. It seemed needless, however, as I could perceive scarce any difference in the sensation whether I discharged it immediately or waited as long as when the plates were moved. The usual time between the electrification and discharge was about 21′′.

The experiment was also made by Richard, who did not perceive any difference.

The heavy paper electrometer was used. The bits of sealing wax between the plates were those made in 1771 [Art. 457].

512] Whether globe included within hollow globe is overcharged by electrifying outer globe*.

It was tried whether the globe enclosed within hollow paper globe was overcharged when the outer globe was electrified.

This was first tried by making the 2 hemispheres slide on 2 sticks of glass by means of 2 tin hooks and a stick of glass fixed to the back of the hemisphere.

The wire by which it was elect. was suspended about 4 inches above the hemispheres while the vials were charging. It was then let down, and it was so contrived that the same motion of the hand which lifted up again the elect. wire, lifted up the wire which connected the inner globe with the outer, drew back the hemispheres, and drew up the pith balls fastened to a stick of glass till they touched the inner globe.

It was found that if the elect. of the hemispheres was discharged before they were separated, but after the communication between them and the inner globe was taken away, that the pith balls did not sep., but if they were separated before their elect. was discharged, then the pith balls would at first sep. about an inch or so, but quickly closed, whereas if the inner globe was electrified after the hemispheres were separated, it was found to be a great while before the pith balls closed. It was found that this was owing to the sticks of glass on which the hemispheres slid being electrified thereby, as the same phenomena were produced by electrifying those sticks when the hemispheres were taken off.

[See Exp. 1. Art. 218.]

N.B. These sticks were not covered with sealing wax, and as appeared by this exper. suffered the electric. to run along them pretty readily. The stick of glass run through the globe had all that part without the globe covered with sealing wax.

513] The same thing tried by a better machine.

Wed. Dec. 23 [1772]. Th. 52°. N. 183.

The exper. was tried in a different manner, the hemispheres being fastened by sticks of glass covered with sealing wax within wooden frames turning on hinges.

If the pith balls were made to sep. pos. about 1 inch before the globe was elect. they separated 1 or two diameters on touching the globe. If they separated only 1 inch before touching, they did not sep. at all on touching the globe. If they separated negatively 1 or 2 inches before touching, they did not sep. at all after touching.

The event was just the same whether the wires for discharging the elect. of the globes when separated were placed so as to touch the hemispheres as soon as they were sep. an inch from each other, or whether they were placed so as not to touch them till they were scparated almost the whole distance.

N.B. Each hemisphere was drawn back about 11 inches from its first situation.

It appears from hence that the inner globe was a small matter overcharged, but not enough so to make the balls sep. unless they were before positively electrified, so that the redundant fluid in it could hardly be of that which it would have received by the same degree of electrification if the outer hemispheres had been taken away, and probably not more than as much.

[Exper. rosin*.]

514] These rosin plates were made out of a mixture of 4 parts rosin and 1 of bees wax mixed together with a considerable heat, towards the beginning of the year 1771. Towards end of 1772 some round plates were cast out of this by gentle heat, which were pared to a proper size and shape and then pressed out between brass plates heated in wooden box over furnace (the tin lining being not then made), the bits of tinfoil were at first fastened on by just wetting it in a few places with gum water and sticking it on, but as this was found not to do well, the bits of tinfoil were afterwards rubbed with melted wax and fastened on by keeping them some time pressed with slight weights with flannel between them.

515]

1 and 2nd sliding plates compared with double plate B, also P, Q and O and thin rosin. Old G and whitish plate compared with D, E, F, and M.

The 1st and 2nd sliding coated plates were compared with double plate B [6 observations]. The 25 div[isions] on sliding] pl[ate] 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.

[19 observations, and 3 on insulation. Art. 656.]

By this exper. with large trial plate Q contains

7.3 11.7

(small

inc. el. less

.7

less, O less, old G less, whitish plate

4.4

9.5

than D, E & F, Р 14.7 less, and thin rosin

17.2

less.

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 Ce 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.

冬

[See Arts. 344, 511.]

↑ [Art. 295.]

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. 171.

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. means the thickness of these plates of air were as follows:

By this

M.