"AN ATTEMPT TO EXPLAIN SOME OF THE PRINCIPAL PHENOMENA OF ELECTRICITY,

BY MEANS OF AN ELASTIC FLUID." From the Philosophical Transactions

for 1771 (p. 1-50).

Charges of similar bodies as the n-1 power of their corresponding diame-

ters, and independent of the material of which they are made

67-72

Equilibrium of electricity in bodies communicating by a canal is in-
dependent of the form of the canal

84-93

Whether the conditions of equilibrium are the same for two bodies com.

municating by a conducting wire as if they communicated by a canal

of incompressible fluid.

Molecular constitution of air

PART II.

Containing a comparison of the foregoing theory with Experiment.

§ 3. On the cases in which bodies receive electricity from, or part with it
to the air.

§ 5. Canton's and Franklin's experiments.

§ 7. Wilcke and Epinus's experiment of electrifying a plate of air

§ 6. On the Leyden vial

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PRELIMINARY PROPOSITIONS.

From the MS. in the possession of the Duke of Devonshire, No. 4.

ARTICLES

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Prop. XXIX (Fig. 1). If the fluid uniformly spread on a circular plate is

to that collected in the circumference as p to 1 the capacity of the

plate is to that of the globe as p+1 to 2p+1

Prop. XXX. Capacity of two disks at a finite distance

Cor. 1. Capacity in terms of p

Cor. 2. Capacity when the density is supposed uniform

Cor. 3. The place in which the canal meets the disk is indifferent only

when the fluid is in equilibrium

Lemma xii (Fig. 2). Repulsion of a particle on a column

Lemma xi. Repulsion of two columns

Lemma xiv.

Lemma xv (Fig. 3). Action of a uniform cylinder on an external point .

Cor. Potential of middle and end.

Prop. XXXI (Fig. 3). Charge of cylinder compared with that of globe

Cor. Upper and lower limits of charge

Prop. XXXII (Fig. 4). Charge of two equal cylinders at a finite distance .

Prop. XXXIII. Ratio of charges of B and b may be deduced from the

ratios of B and b to C.

Lemma xv (Fig. 5). Repulsion on a short column close to an electrified

plate

Lemma xvi (Fig. 6). Two equidistant concave plates

Cor. 1. Definition of corresponding points, &c.

Cor. 2. Density increasing towards the circumference

Lemma xvii (Fig. 7). Concave plate compared with flat one

Cor.

Prop. XXXIV (Fig. 8). Theory of a coated plate

Cor. 1. Flat coated plate of any form

Cor. 2. Flat circular plate

Cor. 3. Plate not flat but of uniform thickness

Cor. 4. Density increasing towards the circumference

Cor. 5. General conclusion

Cor. 6. Comparison with globe
Cor. 7. Form of plate indifferent .
Cor. 8. Charge directly as surface and inversely as thickness
Prop. xxxv (Fig. 9). Theory of conducting strata in the glass plate
Prop. XXXVI (Fig. 10). Penetration of glass by fluid
Cor. 1. Equivalent thickness of plate if there were no penetration
Cor. 2. Thickness of coatings indifferent.
Prop. XXXVII. Density more nearly uniform than if there had been no

penetration
Cor. Distribution probably nearly the same as in plate of air of equiva-

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APPENDIX.

From MS. No. 5.

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Prop. 1. Charge of a condenser little affected by the presence of an over-

charged body

Cor.

Prop. II.

Part 1. A stricter demonstration, applicable to case of penetration

Part II.

Cor. 1

Cor. 2

Cor. 3

Cor. 4. Effect of an overcharged body

Cor. 5.

Cor. 6 (Fig. 11). Two coated plates in communication little affected by

an overcharged body

Cor. 7. Canals may be curved as well as straight
Lemma. Potential of two equal particles compared with that of their

sum at their centre of mass
Applied to case of two parallel disks
Mutual action of large circle and trial plate in Experiment v.
Mutual action of small circles and trial plate in Experiment v.

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Effect of floor and walls of the room
Effect of earth connexion the same as if it were infinitely long

THOUGHTS CONCERNING ELECTRICITY.

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From MS. No. 18. (Probably an early draft of the theory.)
Hypothesis of an electric fluid
The fluid acts at a distance but does not itself extend to any perceptible

distance from electrified bodies

Proof of this, and objections to the hypothesis of electric atmospheres

On the hypothesis of electric atmospheres .

Condition of electric equilibrium between conductors in electric com-

munication

Illustration from the equilibrium of air

Definitions of positive and negative electrification, and of over and under

charge

Four hypotheses

Cor. 1, 2. Effect of two overcharged bodies approaching each other

Cor. 3, 4. Equally electrified bodies repel

Cor. 5. Electrification by induction

Theory of condensers

Shock of the Leyden vial

Fifth hypothesis, on the communication of electricity between conductor

and the surrounding air

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Effect of an overcharged body

Attraction and repulsion of electrified bodies

Electrification by induction

The electric spark.

Vacuum formed by the spark

Statement of the theory of one electric fluid

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ACCOUNT OF THE EXPERIMENTS.

(1) INVESTIGATION OF THE LAW OF FORCE.

From the MS. No. 7 (apparently prepared for publication).

217

The electricity of glass is here taken to be positive

First experiment. A globe within a hollow globe and in communication

with it does not become over or undercharged when the whole is

electrified (Fig. 12).

General description of the apparatus

General plan of the experiment

The apparatus actually used

Mechanism for performing the required operations

The charging jar

The gauge electrometer

Reason for using the jar

Theory of the experiment

Result of the experiment

Second method of trying the experiment

Advantages of the second method .

Estimation of the degree of accuracy of the result

The charge of the inner globe is less than to of that of the outer globe

Hence the electric force is inversely as the square of the distance

Demonstration of this by Lemma 4 (Fig. 13)

Limits between which the law of force must lie, n=2+76

Second experiment—A piece of wood within a vessel formed of two

wooden drawers

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(2) EXPERIMENTS ON THE COMPARISON OF CHARGES.
From the MS. Nos, 9 and 10 (apparently prepared for publication).

Intention of the experiments

Definition of the ratio of the charges of two bodies, illustrated by the

comparison of a disk with a sphere

Method of the experiment

The Trial-plate. (Fig. 13).

Arrangement of the apparatus

Method of operation. (Fig. 14)

Theory of the experiment

Interpretation of the result

The testing electrometer

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Method of testing

Advantages of the method

Capacity of the trial plate

The gauge electrometer

Form of electrometer used in the later experiments. (Fig. 30)

Estimation of error arising from unequal electrification in the two trials

Comparison of the capacities of two bodies

Demonstration

Why the electrification is tested by the gauge electrometer

The bodies to be tested were chosen of nearly equal capacity

Measurements of the apparatus

The insulating supports of waxed glass. (Fig. 16)

Electrification of air

Effects of the electrification of the air

The earth-connexions

The electrometer threads salted

Leakage of the Leyden vials

Estimate of the accuracy of the experiments

Probable cause of error

Weak charges always used

Reason for this

Third experiment. On the effect of variations in the arrangement of the

apparatus in testing capacities. (Fig. 17)

Six different arrangements

Results of the six arrangements

Conclusion.

Fourth experiment. Capacities of bodies of different substances, but of

the same shape and size

Glass coated with various substances

Method of the experiment

Effect of the thickness of a plate on its capacity

Fifth experiment. Charge of two small circles compared with that of a

large one. (Fig. 18)

Results of the experiment

The experiment repeated in a different manner

Comparison with theory

Remarks on the calculation

Bearing on the theory

Sixth experiment. Charge of two short wires compared with that of one

long one

Comparison with theory

Seventh experiment. Comparison of the capacities of several bodies

Comparison of disk with sphere

Comparison of square plate with disk

Oblong plate

Cylinder

Comparison of different cylinders

Disturbing cause

Eighth experiment. Comparison of the charge of the middle plate of

three parallel plates with that of the outer ones. (Fig. 19)

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