As it was found the preceding day that the straws conducted ill, they were kept ab ut 3 or 4 hours in the morning in salted paper, at about 3 they were taken out of the paper and hung up to dry. In the afternoon they were tried, a screen being placed to keep them from the fire.

566] After the additional wire had been taken from the heavy electrometer, the two electrometers were electrified and compared to

567]

COMPARISON OF ELECTROMETERS.

287

gether without the process of communicating the electricity from one globe to the other, when they stood as follows.

If globe 2 was electrified till D° electrometer separated to 17, on communicating electricity to globe 3 it separated to 91.

17

The light straw electrometer was then placed instead of the paper electrometer, and a paper with divisions placed behind it. It was found that when heavy straw electrometer separated to divisions, the light straw electrometer separated to

Large Small divisions. divisions.

91

567] As the straws seemed not to conduct well enough, they were gilt. The gilding was not perfect in several places, but it was sufficient to conduct the shock of a jar very weakly electrified.

The globe 2 electrified and communicated to globe 3.

It was found that some electricity ran from the electrifying wire to the knob of the globe to which electricity was to be communicated, on

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

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

N. 2)

N. 15

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

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 16 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 electro

meter 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,

569]

CALIBRATION OF ELECTROMETER.

289

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 experiments.

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*.

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

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

(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 (6.53

16.38'

[Of the electrical machine.]