Tu. Mar. 9. [Electrometer] At inner marks. At outer marks.

Sat. Mar. 13. Th. 55. N. 12. [12 observations. See Art. 649.] Mon. Mar. 15. Th. 54. N. 14. [15 observations. See Arts. 649, 655.]

554] The same with addit. four small rosin plates.

Four plates of rosin and bees wax were cast 4 inches square and about 22 thick and coated with circles 1.8 in. diam. A tin trial plate was also made 6 inches long and 5 broad. It is called N. The plates of rosin were connected by bits of brass wire like that used for connecting the two double plates.

555] Sun. Mar. 21 [1773]. Th. about 55. N. about 15.

It was tried whether the 4 rosin plates contained the same quantity of electricity whether they were placed close together or at a distance, and what is to be allowed for the connecting wires, &c.

This was tried with the usual machine*, the rosin plates being placed on the positive side and sliding plate 3 on the negative side, the sliding plate remaining always at the same division, the small variations of the charge being found by the additional wire.

They were tried in 5 different ways.

1st way.

wires plates.

The plates placed close together near the end m, the usual resting on the plates, with the connecting wires put on the

2nd way.

3rd way.

Do without the connecting wires.

The connecting wires suffered to remain, and also one of the wires V, but the 3 others removed towards end M, placed at 4 inches

[Art. 295. See Art. 337.]

distance from each other, and supported in their usual situation by silk strings.

4th way.

away.

5th way.

The same, except that the 3 wires were taken quite

The rosin plates placed at as great a distance from each * inches with the usual wires V, but without

other as possible id est the connecting wires.

556] Whether charge of white glass thermometer tube is the same when hot as when cold.

Sun. Mar. 21 [1773] afternoon. Th. about 55. N. about 15.

A ball about 1 inch in diameter was blown at the end of a thermometer tube with a bulb 4.3 inches above. This was filled with sufficient to rise into the bulb. The tube was coated 3.4 inches from the ball with gummed paper dipped in salt water and bound on with iron wire. This ball was placed in a glass of surrounded with iron filings and placed on machine near M, and heated by a spirit lamp, the in which the ball was immersed being made to communicate with the ground, and a bit of iron wire bound round the wire Mm being dipped into the in bulb.

The crown glass plate * and the plate A of Nairne, which was coated as a sliding plate, being put on negative side.

The 1st column being the number of square inches which it was necessary to give to the coating of the sliding plate in order that the balls might sep. pos. and the 2nd column that they might sep. neg. The charge of the crown glass plate being equal to that of the sliding plate when its coated surface is 33 square inches.

The allowance to be made for the charge of the connecting wires was endeavoured to be found by suspending the two circles of 9.3 inc. horizontally by silk lines at 11 inches distance from each other aud finding their charge by means of the forked electrifying wire as in 1772 p. 7 [Art. 472], both when the plates were connected by a wire similar to that used for connecting the rosin plates, and without any connexion. The event was as follows.

Fr. Mar. 26th [1773. 8 obs. See Art. 647.]

2

Therefore the plates contain about 2 square inc., or 1·41 inc. el. more with the connecting wire than without *.

Sat. Mar. 27 [1773].

It was tried by usual machine whether the 4 rosin plates contained more el. when at a distance than near. The trial plate B id est the largest trial plate used for D & being placed on neg. side.

=

With a quantity of additional wire to 93 inc. el. the balls sep. pos. when the plates were at as great a distance as possible. When they were placed close together they seemed to require rather more additional wire, and as well as I could judge, a quantity = about inc. el.

one.

558] Excitation of electricity by separating brass plate from glass

Sat. afternoon. Th. 60. N. 9.

The experiment of p. 71 [Art. 541] was repeated. It was found that the brass plate was electrified on lifting up as before, though the plate was not electrified before. But if the plate was first charged and discharged again before the plate was lifted up, it was found to be stronger electrified.

I then took a piece of tinfoil of the same size as the brass plate, with a silk string fastened to it near the edge, and laid it on the glass and

lifted it up gently by the silk string. The tinfoil was found to be electrified thereby.

559] Comparison of Henly's, Lane's,

and straw electrometer.

Sun. Mar. 28 [1773]. Th. about 58. N. about 8.

*

The two conductors of Nairne were placed end to end, and Henly's electrometer placed on that furthest from globe parallel to conductor and the cork pointing from globe. The four jars were also joined to the usual wire with the straw electrometer hung to it, the wire and jars being placed at such a distance from the conductors that the electricity was found not to flow sensibly from them to the jars.

The globe 3+ was then applied to that conductor nearest the globe and electrified till Henly's electrometer stood at 90°. The globe 3 was then removed from the conductors and its electricity communicated to the jars.

The straw electrometer separated to 2 +1.

The experiment was repeated several times and was found to agree together pretty well.

The jars were then electrified, they and the straw electrometer standing in the same place, and it was found that Lane's electrometer fastened to one of them discharged at 0.53 with that degree of electrification, the same jar being applied to the conductor and electrified till Henly's electrometer stood at 90°, Lane's discharged at 12.15.

The conductors being then taken away and the jars and straw electrometer placed in usual position, Lane's discharged at 1·17 when straw stood at 2 +3, and at 1+2 when light paper electrometer just separated. The knobs touched at 0.4.

* [Of Nairne's electrical machine.]

+ [Globes 2 and 3 are glass globes coated as Leyden jars. See Art. 505 for their charges.]

[For the charges of these jars see Art. 506.]

Sun. eve. Th. 58. N. 8.

The globe 3 electrified till Henly stood at 90°, and its electricity communicated to 1, 2, and 3 jars, straw electrometer separated to 2+13. Lane's with that degree of electrification discharged at 1·7.

When Henly's stood at 90°, Lane's discharged at 12.20.

Jar 2 charged till straw electrometer separated to 4, and electricity communicated to jar 1, straw separated to 2+ 1.

When straw electrometer separated to

light paper just separated

4

2 + 1

2+3

Lane's discharged at 2.0

52

1.19

1.1

560] Excess of redundant fluid on positive side above deficient fluid on negative side in glass plate and plate air &c.*

Mon. Mar. 29th [1773]. Th. 58. N. 7.

The 11 inch plate coated with circles of 8 inches diameter was supported on waxed glass. I charged this by touching the top with a vial charged till the straw electrometer separated to 2+3 while I touched the bottom with a wire. At the same time an assistant stood ready with a bent wire in his hand ready to discharge it as soon as I took the jar away, the wire was fastened to a stick of waxed glass and had the pair of cork balls commonly made use of hanging to it, the cork balls separated about 1 inch.

I then charged the jar 4 to the same degree and communicated its electricity to the jars 1 & 2 and touched the upper side of the plate with one of the jars, but without touching the bottom with the wire. The corks separated very nearly the same as before, but of the 2 rather more. I then charged the jar till the straw electrometer separated to 2+2 and diminished its electricity as before, the corks now separated rather less than the first time. The experiment was repeated several times with very nearly the same event.

I could perceive no difference in the separation of the cork balls whether the wire of the jar with which I touched the plate was 17 inches long or only 23.

If the four jars were charged to 2 + 3 and its electricity communicated to globe 3, it was diminished to 2 + 2.

The plate air 4 was charged by jar charged till straw electrometer stood at 20, and if jar 4 was charged to the same degree and its electricity communicated to jar 2, the corks separated the same if bottom was not touched.

With plate air 1 the charge was obliged to be reduced by communi

[See Note 30.]