Page images
PDF
EPUB

which the knob was removed to such a distance that no sensible electricity ran from one to the other.

[blocks in formation]

N.B. The holes where the wires were put in were gilt over.

N. 2)

N. 1)

16.65

of heavy electrometer were found to weigh 19.65

The wires were then taken out, the holes stopped up with wax and gilt over. It was then found on electrifying the globe without communicating its electricity to the other, that when the heavy electrometer stood at

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

Therefore force required to separate heavy electrometer falls short of four times force required to separate light electrometer in the ratio of 296 to 303-6, or of 1 to 1.027.

568] Separation of Henly's electrometer by different strengths of electrification.

Nairne's jar being tried against the two trial plates for plate H, the pith balls separated a little after a short time the same way as the two trial plates. Therefore Nairne's jar is supposed to contain about 1 of plate H, or 16 times as much as plate M.

The two conductors of Nairne were set end to end with [Henly's] electrometer on furthest, and the jar applied to the same, the furthest conductor being without any point, and the plate M was placed near it, set on a conductor communicating with the ground. When the electrometer was raised a little above 90°, the nearest conductor was removed and the electricity of globe taken away. Then as soon as the electrometer was sunk to 90° a communication was made between conductor and plate M and immediately taken away again, and the figure to which the electrometer sunk wrote down and the electricity of plate M discharged,

after which a communication was again made between the conductor and plate M.

The results of the experiments are contained in the following Table, where the first column is the number of times that a communication has been made between the conductor and M.

The second column shows the quantity of electricity in the jar, which must diminish each time in the ratio of 15 to 16, and the other column is the number which the electrometer stood at in the different experi

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

The above experiment is supposed to have been made in the autumn of 1772.

569] Separation of Henly's electrometer when fixed in the usual way and on an upright rod.

Aug. 13, 1773. Th. about 78.

Henly's electrometer was stuck on a thin wooden rod 25 inches long, the end of which was fixed into the hole made in the conductor for receiving the electrometer, being parallel to the conductor as usual. The conductor to which this was fixed was connected to the other conductor which received the electricity from the machine by a brass wire about 10 inches long, and a jar with Lane's electrometer fastened to it was made to communicate with this last conductor, so that the rod to which the electrometer was fastened was about *inches from the globe and *inches from the jar.

Henly's electrometer was then compared with Lane's while in this situation, and when this was done the wooden rod was taken away and

* [So in MS.]

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 *.

[blocks in formation]

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.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

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.

P. 94

By P. 95 [Art. 551] the distance at which Lane's discharges is as (1.228 the 11-226 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 (6.53

* [Of the electrical machine.]

16.38'

Α

E

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.

[blocks in formation]

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.

[blocks in formation]

Wed. Sep. 8th. Th. 62°. N. 193. C. 18. Bar. 29-235.

[blocks in formation]

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

[blocks in formation]

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

[blocks in formation]

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 18 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

« PreviousContinue »