Mon. evening. Th. 53. N. 15. [25 observations. Art. 655.]

534] Charge of the triple plate-the three plates A, B and C placed over each other, with bits of lead between coatings*.

The three plates A, B and C were placed over one another with the coatings nearly perpendicularly over each other, with bits of lead between them, so as to keep them at the distance of † inches from each other.

This compound plate was tried in the usual manner.

Tu. Feb. 2 [1773]. Th. 50. N. 17. [9 observations. Art. 677.]

535] Whether the charge of plate D bears the same proportion to that of another body whether the charge is strong or weak: tried with machine for Leyden vials‡. [Art. 664.]

Th. Feb. 4 [1773]. Th. 481. N. 13.

Tried with smallest cork balls and the light straw balls as electrometers.

The plate D placed on the neg. side and the sliding tin plates at 231 inc. dist. from wire.

5361 H with slits and a crown glass with oblong coating compared with white cylinder; also A and C with slits compared with B.

The coatings were taken off from the plates A, C and H, and oblong coatings with slits put in their room; an oblong coating without slits was also put to a piece of crown glass, vide Measures [Art. 593].

Tu. Feb. 9 [1773]. Th. 50. N. 12. 50 observations. Art. 660. These plates were tried with middle cork balls.

Spreading of el. on surf.

A & C. Balls at first sep. wider. Closed in about 10".

B.

Do, but rather sooner. As it was supposed that this proceeded from the wires not conducting ready enough, the machine was moved slower, there was then but little of this and B was a great while before it closed, C about 5", H a great while.

It was suspected that this increase of separation of the balls before they closed was owing to the wire designed to carry off el. to earth* not conducting fast enough. To try this, the next evening a long wire was insulated, and the cork balls hung to it. It was electrified sufficiently to make them sep. about an inch. They closed instantly on touching the wire with a bit of iron either communicating with wire for carrying off el. to ground, or whether it was only held in the hand. The air was as dry as the night before.

537] Crown with slits and H with Do compared with white cylinder; and A and C with oblongs compared with B†.

The coatings were taken off from the plates A and C and oblong coatings without slits put in their room. The coatings were also taken from the crown glass, and oblong coatings with slits like those put to C put in their room.

Fr. Feb. 12 [1773]. Th. 49. N.

[34 observations, Art. 660.]

538] Experiment of p. 61 [Art. 535] tried with small ball blown to the end of a thermometer tube.

A ball rather less than inch diam. was blown at end of glass tube and was coated on outside with tinfoil, the inside being filled with. This was used instead of plate D in exper. to see whether charge of Leyden vial bore the same proportion to that of another body whatever force it was electrified with. It was found that 12 inches of this tube when coated contained as much el. as K+D, and therefore the spreading of the el. inch on surface of this tube increases its charge by D, whereas the spreading of el. on surface of D increases its

charge by

1

51

Th. 49. N. 131. Tin plates at 17 inches from wire.

With electrometer at 1 + 3.

It was found on looking at the plate of crown glass that there were narrow fringed rings of dirt all round the edges of the coatings, the space between these rings and the coating being clean. This was supposed to be done by the explosions.

The distance of these rings from the edge of the coating seemed nearly the same both within the slits and without, but of the 2 seemed less within the slits. The mean distance seemed about 105 inc. which seems to shew that the electricity spreads pretty nearly the same both within the slits and without.

Something of this kind has been frequently observed in the sliding trial plate 1 and sometimes I believe in some of the coated glass plates.

Sun. Feb. 14 [1773]. Th. 49. N. 17. Last exper. repeated. [At 1+ 3, Sum = 296, at 3+1, Sum = 28.3. 27.5 respectively. See Art. 664.]

Plate D gave 26 and

539] Experiment to determine whether the charge of a Leyden vial bears the same proportion to that of another body when elect. is very weak as when it is strong.

AB' is a tin cylinder 14 feet 8.7 inches long and 17.1 inches in circumference. DC is a brass wire 37.1 inches long and 15 in diameter; both supported by non conductors; with the middle sized cork balls hung at D.

FE communicates with the prime conductor and is charged till light paper electrometer separates. A brass wire is suspended by silk, so as to be made alternately to touch E and DC.

Mon. Feb. 15 [1773]. Th. 55. N. 22.

The cylinder AB and wire DC were electrified negatively till the balls separated about 1 diameter. On touching DC twice with the wire, the corks separated about as much positively.

The wire was 27.6 inches long and 15 in diameter.

* [Art. 308.]

+ [See Arts. 358, 666, and Note 25.]

D

Ow

B

The cylinder AB was then taken away and the plates D and E placed under the wire DC. The wire was obliged to be changed for one 20.8 inches long to exhibit the same phenomenon. [See Art. 666.]

Tu. Feb. 16 [1773]. Th. 57. N. 20.

Same exper. repeated.

Cylinder touched twice with wire 31 inches long; changed from about 1 diam. neg. to Do pos.

D and E with wire 24

cyl. with wire 31

cyl. with 27

inches D°.

Do.

did not. [See Art. 666.]

540] Lane's electrometer compared with straw and paper electro

meters.

In the afternoon. Th. 56. N. 19. I tried the distance to which the spark would fly by Lane's electrometer.

*

[Revolutions and 60th parts of a revolution. One revolution = 038 inch.]

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. 14 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 globe †, 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.]