Henly's placed on the conductor in the usual manner, everything else being the same as before, and compared with Lane's as before.

N.B. In both trials the cork ball of Henly's was turned from the globe *.

Hence it appears that when Henly's [electrometer] is fixed on the rod it is more sensible towards the beginning of its motion than afterwards, whereas when put in the usual way it is the contrary.

570] Result of P. 70, 75, & 95 [Arts. 540, 544, 559], being a comparison of the different electrometers.

The three last columns are the distances at which Lane's electrometer discharged, expressed in divisions, or 60th parts of a revolution of the screw.

the

By

P. 94

[Art. 551] the distance at which Lane's discharges is as P. 95

(1.228

1.226 power of the quantity of electricity in the jar, and the quantity of electricity when the straw electrometer is at 2+ 3, id est the usual charge is to that when Henly's is at 90° as 1 to

*[Of the electrical machine.]

(6-53

16.38.

A

571] Comparison of Lane's electrometer with light straw electrometer in different weather.

Lane's electrometer was compared with the light straw electrometer by the apparatus represented above. A being the globe, B a conductor, CD a wooden rod supported on two waxed glass pillars, having a pin at D almost in contact with the conductor, the straw electrometer being hung to C. E is a jar with Lane's electrometer fastened to it, supported on a bracket fixed to glass pillars, the wire of which touches CD.

The distance of C from the globe is 54 inches and from the nearest glass pillar 32 inches. The height of the pith balls above the floor is 36 inches.

A small board with divisions on it, not represented in the figure, supported on an upright wooden rod, is placed behind the straw electrometer 25 inches from it, and a bit of tin with a narrow notch in it for an eye sight is placed at the same distance before the electrometer.

The outward divisions on the board, or those called the 4th, are at 5 inches asunder, the 3rd at 4 inches, the 2nd at 3 inches, and the 1st at 2.

As I found it impracticable looking attentively at both balls of the electrometer, I looked only at one, which, as my eye was guided by a narrow slit, was sufficient, and when I had made the experiment looking at one ball I repeated it looking at the other, so that the mean would be right though the slit was not right placed.

A wire was continued from the coating of the jar to the earth.

Wed. Aug. 18, 1773.

Th. 63°. N. 19. Bar. 29.64.

With two more jars communicating with E by wire.

With only one jar; straw at 3rd division, Lane discharged at 2-27. A slip of tinfoil was then pasted on CD the whole length so as to touch the wire of the jar and the frame of the straw electrometer. The result with only one jar was then as follows.

Wed. Sep. 8th. Th. 62°. N. 191. C. 18. Bar. 29-235.

Lane at

1.581

2.41

In the afternoon. Th. 62°. N. 19. C. 17. Bar. supp. 29-37.

Fr. Sept. 17. Th. 58°. N. 281. C. 29. Bar. 29-61.

572] Comparison of strength of shocks by points and blunt bodies.

The wooden rod used in P. 118 [Art. 571] was supported on waxed glass with the straw electrometer at the end, and some tinfoil wound round part of the rod. The white glass cylinder was put in contact with it, electrified in such a degree that I felt a slight shock in discharging it with a piece of brass wire with a round knob at the end. If it was then electrified in [the] same degree, and discharged [with] a like brass wire with a needle fastened to the end, I could perceive no shock, and but a very slight sensation, even though the point was approached pretty quick. The distance to which the straw electrometer separated was about 1.8 inches.

The white cylinder was then changed for one of the large jars, the shock was not very different whether it was discharged by the knob or point unless the point was approached very slow. The distance to which the electrometer separated was about 9 inch.

The wooden rod was taken away, and the white glass cylinder made to rest on the conductor with Henly's electrometer on it, and electrified till it stood at 90°, and to prevent the shock being too strong it had

its choice whether it would pass through my body or some salt water, the wires in the salt water being brought within such a distance that the shock was weak when taken by the bluut body. I then found that if I took it with the point I could scarce perceive any spark.

The experiment was tried in the same manner with a large jar. The shock was very sensibly less though the point was approached almost as fast as I could.

573] Whether shock of one jar is greater or less than that of twice that quantity of fluid spread on four jars *.

It was found that if the jars 3 and 4 were electrified in a given degree, and their electricity communicated to the jars 1 and 2, the shock produced by discharging them was nearly the same, or of the two rather more, than that produced by discharging the jar 1 or 2 by itself. The shock of the jar 3 was found to be very sensibly greater than that of jar 4.

It was tried with the wooden rod, the jars to be electrified being placed in contact with the tinfoil thereon, and when they were sufficiently electrified those to which the electricity was to be communicated being approached till they touched the rod, all four standing on the same tin plate. The jars were electrified till the straws separated 9 inch.

The

N.B. The jars 1 and 2 contain pretty nearly the same quantity of electricity and their sum is nearly equal to the sum of jars 3 and 4. quantity of electricity in jar 3 exceeds that in jar 4 in the ratio of 37 to 27, or of 4 to 3 nearly †.

574] Comparison of the diminution which the shock receives by passing through water in tubes of different bores, and whether it is as much diminished in passing through 9 small tubes as through the same length of one large tube the area of whose bore is equal to that of the 9 small ones‡.

Nov. 1773. It was tried whether a shock was as much diminished by passing through a glass tube filled with water, 37 inches of which held 250 grains of water, as in passing through 9 tubes, 37 inches of all which together held 258 grains of water, the length of water which it passed through being the same in both cases, namely about 40 inches.

Two jars were used, and charged till the straw electrometer separated to 30. The water in the tubes was mixed with a very little salt, and the shock just enough to be perceived.

I could not be certain that there was any difference, but if any, that with the single tube seemed greatest. The shock was then made to pass through 7 of the small tubes, 37 inches of which hold about 200 grains of water. The shock was then sensibly less than with the large tube.

* [Art. 406 and Note 31.]

+ [Art. 685.]

[See Art. 506.]

It was afterwards tried through what length of a tube, 37 inches of which held 44 grains, the shock must pass, so as to be as much diminished as in passing through 441 of the large one.

It was found that when it passed through 5.2 inches the shock was sensibly greater, and when it passed through 8-4 sensibly less than with the large one, so that it is supposed it would be equal if it passed through 6.8.

so that the resistance should seem as the 1.08 power of the velocity. N.B. The quantity of water which the tubes held was not measured very exactly.

575] The tubes used in p. 123 [Art. 574] were measured by and are as follows:

37 inches of the 9 first tubes, which are what was used in p. 123 [Art. 574], held together 3373 grains, therefore the shock was very nearly the same, but if anything rather greater when it passed through one tube, 37 inches of which held 3480 grains of, than when it passed through 9 tubes, 37 inches of all which together held 3373 grains.

By p. 124 the shock is as much diminished in passing through 6-8 inches of a tube, 37 inches of which hold 567 grains, as through 441 of one, 37 inches of which hold 3480, so that resistance should seem as the 1.03 power of the velocity.

576] Comparison of diminution of shock by passing through iron wire or through salt water*.

In order to compare the conducting power of iron wire and salt water, the shock of two jars had its choice whether it would pass through