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of distilled water in tube 5, was [greater than when it was discharged

less

through 23 of the above-mentioned mixed water in tube 8.

By a former experiment, the shock passed through

water was

(greater

less than through 23 of the mixed.

1.8
2.0

By the mean, the resistance of 1.3 of distilled water = of mixed.

of distilled

that of 23

10.9 inches of tube 5 in the place where used holds 120 grains of, or 37 inches holds 408 grains, which is the same as tube 8: therefore the resistance of distilled water is 18 times greater than that of mixed, or 702 times greater than that of a saturated solution of sea salt.

578] Whether the electricity is resisted in passing out of one medium into another in perfect contact with it.

The 9th tube of P. 126 [Art. 575] was filled with 8* columns of saturated solution of sea salt inclosed between columns of, the end columns being. The tube 7 was filled with one short column of at the bent end, and a long column of saturated solution of sea salt.

inches long, was rather (more

less

It was found that the shock of one jar, charged till the straw electrometer separated to 101, passed through a column of the salt water in tube 7, 27.71 diminished than in passing 21-2 through the mixed column in tube 9, the wires used in tube 9 being immersed in the end columns of, and those used in tube 7 being immersed one in the short column of at the end and the other in the column of salt water.

The length of the mixed column in tube 9 was 43.5 inches, its weight was 10.5, the weight of a column of of the same length was 18.10, therefore the sum of the lengths of all the columns of salt water was 21.8 inches, and by the experiment the shock was as much diminished by passing through 244 inches of salt water in tube 7 as through this. But as the bore of tube 7 in that part which was used was greater than tube 9 in the ratio

24.4 36

X = 1.06 to 1 nearly, the 22.3 37.4

shock should be as much diminished in passing through a column 22.94 long in tube 9 as through one of 24.4 in this. Therefore the shock is as much diminished in passing through a mixed column, in which the length of salt water is 218 inches, as through a single column of the same size whose length is 22.94 inches.

The difference is much less than what might proceed from the error of the experiment.

579] A slip of tin was made consisting of 40 bits soldered together, all inch broad and all about inch long. They were made to lap

* [8% in MS. Perhaps 80.]

580]

HENLY'S AND LANE'S ELECTROMETERS.

297

about inch over each other in soldering. I could not perceive that the shock of a jar was sensibly less when received through this than through a slip of tin of same length and breadth of one single piece.

If the jar were charged pretty high and a double circuit made for it, namely through this piece of tin and my body, I could not perceive the least sensation.

580] Made at Nairne's with his large machine.

A long conductor was applied to the electrical machine and a smaller conductor to its end, a Henly's electrometer was placed on the middle of the long conductor, and a small jar with a Lane's electrometer fastened to it was made to touch the short one. When Henly's stood at

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The jar was then changed for one of rather more coated surface and a much smaller knob. When Henly's stood at 30 or 35, Lane's discharged at 177 = 650, so that Lane's discharged at nearly the same distance with the same charge, whichever jar was used.

Henly's electrometer was then placed on an upright rod, touching the long conductor near the furthest end, Lane's electrometer with the first jar being placed as before.

Henly then rose to 55 or 60 before Lane discharged at 17·55 = ·681 inch. Henly being then lifted higher it rose to 65, Lane remaining as before. It was then lifted still higher, when it rose to

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Lane's being then separated to 27.55 1.060, the jar once discharged over surface of glass and once to the electrometer, but there seemed reason to think that Henly's rose no higher than before, namely 65.

My Henly's electrometer usually rose to 90 when Lane's discharged at 12.20 467 inches.

Therefore the distance at which Lane's discharges, answering to different numbers on Henly's, is as follows:

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The distance at which Lane's discharges with a given jar is nearly proportional to the quantity of electricity in the jar, for if a jar is charged to a degree at which Lane is found to discharge at a given distance, and its electricity is communicated to another jar of the same size, so as to contain only as much electricity as before, Lane will then discharge at nearly the former distance.

M[EASURES]*.

581] M. 1. Comparative charges of jars and battery↑.

If jar 1 is electrified till straw electrometer separates to 1, and its electricity is communicated to jars 2 + 4, pith electrometer separates 5. Therefore charge required to make pith balls separate 5 is to that required to make straw electrometer separate 1 as 3184 to 8909, and that to make pith separate 51 to that to make straw separate 11⁄2 as 2920 to 8909.

Jars 1 and 2 being electrified by wire and jar 6 by coating till pith electrometer separated 11⁄2 and a communication being then made between 53 them in the manner used for trying Leyden vials, pith balls separate 5 (1316+

5

negative, therefore charge of jar 6 should be 1273.

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Jars 1 + 2 + 3 + 4 being compared in the same manner with jar 6

the pith balls did not separate at all.

M. 2. If the charge of jars 1 + 2 + 3 + 4 is called 4

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Jar 8 being electrified it was found that it must be touched 7 times by white cyl. to reduce the quantity of electricity to . The 4 jars must be touched 81⁄2 times by do. Therefore charge of jar 8=31.

A piece of crown glass 1 foot square of which weighed 10-12 was coated with tinfoil about 10 inches square.

* [These "Measures" are on a set of loose sheets of different sizes marked M. 1 to M. 21, and another set marked M. 1 to M. 12.]

+ [Art. 411.]

[These numbers are given as in the MS. They should be each multiplied by 10. See also Art. 585, where the numbers seem to be deduced from some other experiment.]

582]

JARS AND BATTERY.

299

M. 3. The charge of each row of the battery was found by charging to a given degree by electrometer and touching it repeatedly with jar 4 till the separation of electrometer was reduced to that answering the charge.

to

*The 1st, 2nd, 3rd, 4th, 5th, 6th, 7th row required to be touched 18, 19, 17, 18, 17, 17, 18 times, therefore charge

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and charge of whole battery = 180 times that of jar 4

and real charge

= 321000

and if real charge by computed of white glass = 7.5,

computed charge = 42800

which answers to 187 square feet of glass whose thickness = 1.

Therefore charge of jar 4 answers to 1.04 square feet of D° thickness. The coating is about of a square foot, and therefore the mean thickness = ·058.

582] M. 4. Let jar be touched n times† by jar which is to first as x to 1, it will be reduced in ratio of 1 to (1+x)", therefore if it is reduced to thereby

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Rule for finding ratio of charge of 2 jars, supposing the charge of first to be reduced to by touching n times by 2nd

Charge of 1st is to that of 2nd: 1444n- to 1.

*N.B. The left-hand row is supposed to be called the 1st row. [If Jar 4=2675 circ. inc. (See Art. 506) whole battery = 481500 circ. inc. or 321000 glob. inc., counting 1 glob, inc. 1.5 cire. inc., as Cavendish seems to do here.]

+ [Art. 413.]

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584] M. 6. Electricity of 1st row of old battery was reduced to by touching 11 times by crown glass of 10 inches square. Therefore charge of 1st row to that of crown glass as 153 to 1. The first row of new battery appeared by that means to contain 107, the 2nd row 11, and the 3rd 11.4 times the charge of the same plate.

5

The mean area of the convex coating of each jar seemed to be 14 × 12 = 175 inches, to which adding 5, id est of area of bottom, whole coating may be estimated at 180 square inches of same thickness as sides.

(1st

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Elect. 2 row of new battery was reduced to by touching 101 3

(13-94

(13.94

10

times by jar 1, therefore charge = jar 1 x 14-66, and charge mean row

= jar 1 × 14·18 = 45149 inc. el.

* [See Art. 506.]

[Here A seems to be the charge of one of the first 4 jars taken as unit, B that of one of the others taken as 4, and R that of the row taken as 22, the battery being 154, as in M. 2.]

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