The electricity was found to break through the rosin plate when electrified with this strength, but there was no hole made in the plate, as it was found not to break through after that with the weak degree of electrification. It seemed not to pass over the surface, as no light was perceived.

552] Charge of compound plate of glass and rosin.

The rosin plate of p. 79 [Art. 548] without its coatings was included between the plates B and H of Nairne and the outside surfaces coated with circles 6.6 inc. diam. and is called Compound Plate.

Th. Mar. 11 [1773]. Th. 53. N. 17. [4 comparisons with K.] Fr. Mar. 12 [1773]. Th. 53. N. 131. [20 observations, Art. 664.] 553] Circle of 181" compared with double plates, also plate D, plate air and the two double plates compared with circles of 36" and 30".

A sliding trial plate was made of deal, with an additional piece to fit on, the breadth was 31 inches, the length when not drawn out, and without the additional piece, was 15, and the additional piece increased the length 10 inches.

The number in the 2nd column shows the number of inches by which the sliding piece is drawn out.

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. 21st [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. Do without the connecting wires.

3rd way.

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 coldt.

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.

* [So in MS.]

+ [Sce Art. 366 and Note 26.]

Tu. Mar. 23 and Wed. Mar. 24. [43 obs. Art. 649.]

557] Allowance for connecting wires in p. 86. [Art. 554.]

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 and 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.]
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 9 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

N. 9.

Sat. afternoon. Th. 60. 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

[See Art. 647.]

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 90o. The globe 3 was then removed from the conductors and its electricity communicated to the jars.

The straw electrometer separated to 2+.

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 23, 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.]