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and then kept mid way for minute, and then drawn up, the balls at first separated positively but closed very soon, and after a long time separated negatively.

If a sliding plate containing about part of the electricity in the plate L was put on the positive side as an additional plate, and the apparatus was let down and drawn up immediately, the balls separated about 1 diameter negatively, but if it rested at the bottom a minute and was then drawn up immediately they separated about I inch negatively.

486] In order to see how fast the electricity spread on the surface of the glass, the heavy paper cylinders* were placed in the usual place, and the light ones on the wire Bb, the wires Gg and Ff were detached from Cc and rested at bottom, and a coated plate on the positive side. The wire Cc was suffered to rest on Aa and Bb while the jars were charging, and the wire V drawn up so as not to rest on the coated platet.

When the heavy cylinders, and a fortiori the light ones separated, the wire was let down on the plate and the wire Ce immediately drawn up, and the time elapsed till the closing of the light cylinders counted, which was as follows:

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487] Another way was taken to try the same thing, namely, the wire Ff was taken off and Gg placed so as to lye below the wire Dd and to be drawn up against it by a string. The coated plate to be tried was placed on the negative side, the wire & touching its bottom coating, The jars were then charged, the wire Ce resting all the while on Aa and Bb, and Gg drawn against Dd, and ẞ drawn up so as not to rest on the plate. When the jars were sufficiently charged ẞ was let down on the plate, and the wire Gg dropt immediately after, so as to take away the communication between Dd and the ground, so that the pith balls which were hung to D shewed whether much electricity passed round to under side of plate or spread on the surface.

When the pith balls communicated with the ground they separated about of an inch negatively by the repulsion of the wires on them.

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Plate of closed almost instantly, separated again in about 10".

cement

488] Three sliding coated plates were made, each covered all over with tinfoil on one side, with a slip of tinfoil 18 by 9 in. on the other. Two flat pieces of brass were also prepared, one 1.8 by 9 and the other 1.8 square.

The tinfoil was divided in breadth into 6 equal parts, and the breadth of the coated surface is expressed in those divisions or in 6th parts of the breadth*.

The first plate was one of exper, rosin 345 thick.
The 2nd, 2 plates of glass with rosin between.

The 3rd, a bit of the large piece of whitish plate glass.

The rosin sliding plate when the breadth of coating

2nd

as much electricity as the double plate A.

24)

contains

= 12)

The 3rd sliding plate when its breadth = 103 contains as much electricity as plate F of Nairne.

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electricity in plate D, E, F, or G of Nairne.

7 inches of additional wire answers to 1 inch of computed power in plates of Nairne.

2 trial plates were made for the plates I, K, L and M of Nairne out of 2 of the ground plates first got from Nairne. The dimensious of the coating of the small one was about 3.3 by 3·1, and that of the large one 37 by 3-4, the thickness of glass unknown.

Two trial plates were also made for the plates A, B and C of Nairne out of the old ground plates E and F. F, the smallest, was 5·7 square, and E was 6.3 by 6 nearly.

Two trial plates were made of crown glass for the plate H of Nairne, the small one 5-7 by 5.1, the other 6 by 5.9.

S. H. 17. C. H. – 5.

489] Tuesday, Feb. 4 [1772]. Th. 47°. Trial of plates D, E, F and G of Nairne, and of the 2 double plates, the plates E, F and G being cased with cement: tried by means of additional wire t.

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490] Feb. 4 continued. Comparison of the three plates E, F and G together with the plates I, K, L and M, tried by the two above-mentioned trial plates and the 1st and 2nd sliding plate*.

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491] Trials of the same kind as those in [Art. 487].

Large trial plate for the experiments of this page-balls closed in 13′′

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492] Wed. Feb. 5 [1772]. Th. 49. S. H. 17. C. H. 41.

Comparison of I, K, and L together, with A, B and C by means of the trial plates E and F, and of A, B and C together, with H by means of the two crown glass trial plates*.

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493] Comparison of A, B, C together, with H *.

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EXPERIMENTS, 1773 t.

494] Spreading of electricity on surface of glass plates.

4 plates of English glass were cut out of same piece and coated with bits of tinfoil of the same size. One of these plates was covered at different times with thick solution of lac, which ran into heaps in drying, another with transparent varnish which also ran into heaps, another with solution of lac and vermillion which lay smooth, and the other left as it was.

They were all done in the end of the summer and suffered to dry in the open air. The spreading of the electricity on their surface was tried in the manner described 1772, p. 22 [Art. 486].

Tu. Oct. 13 [1772]. Th. 63. N. 203. C.-7.

D of Nairne, corks closed immediately.

G do. in cem.

in 3" or 4".

Plate with lac closed immediately, sep. again in 3" or 4".

Lac and verm. D°, but much more.

Transparent varnish same as lacquer.

Plate not varnished closed immediately, sep. again in 5′′ or 6′′.

*[See Art. 658.]

+ [This is the heading of this bundle of the Journal, though many of the dates belong to 1772.]

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