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but when x is nothing, d2+2ax, or be2 = d3, and when x = af, or s+d, its, therefore the whole fluent generated while b moves from a to f is

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but the repulsion of all the fluid collected in the center on b

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therefore the repulsion of the surface of the globe is to that of the same quantity of fluid collected in the center as

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[EXPERIMENTS ON THE CHARGES OF BODIES.]

236] The intention of the remaining experiments was to find out the proportion which the quantity of redundant fluid in bodies of several different shapes and sizes would bear to each other if placed at a considerable distance from each other and connected together by a slender wire, or, which comes to the same thing, to find the proportion which the quantity of redundant fluid in them would bear to each other if they were successively connected by a slender wire to a third body placed at a great distance from them, supposing the quantity of redundant fluid in the third body to be the same each time; and to examine how far that proportion agrees with what it should be by theory if the bodies were connected by canals of incompressible fluid.

237] To avoid circumlocution I shall frequently in the following pages make use of a term the meaning of which is given in the following definition.

DEF. When in relating any experiment in which two bodies B and b were successively connected to a third body and overcharged, I say that the charge of B was found to be to that of b as P to 1, I mean that the quantity of redundant fluid in B would have been to that in b in the above proportion, provided the quantity of redundant fluid in the third body was exactly the same each time, everything else being exactly the same as in the experiment, that is, the bodies being situated exactly as in the experiment. But when I say simply that the charge of one body is to that of another in any particular proportion, for instance, when I say that the charge of a thin circular plate is to that of a globe of the same diameter as 1 to 157, I would be understood to mean that if the circular plate and globe are successively

239]

EXPERIMENTS ON THE CHARGES OF BODIES.

115

connected to a third body by a thin wire the redundant fluid in the plate would be to that in the globe in that proportion, provided they were placed at a very great distance both from the third body and from any other over- or undercharged matter, and that the quantity of redundant fluid in the third body was exactly the same each time.

238] The method I took in making these experiments was by comparing each of the two bodies I wanted to examine, or B and b as I shall call them, one after another with a third body, which I shall call the trial plate, in this manner. I took two Leyden vials and charged both of them from the same conductor; I then electrified B positively by the inside of one of the vials, and at the same time electrified the trial plate negatively by the coating of the other vial. Having done this I tried whether the redundant fluid in B was more or less than sufficient to saturate the redundant matter in the trial plate, by making a communication between them by a piece of wire; for if the redundant fluid in B was more than sufficient to saturate the redundant matter in the trial plate, they would both be overcharged after the communication was made between them; if, on the other hand, the redundant fluid in B was not sufficient to saturate the redundant matter in the trial plate, they would be undercharged. Having by these means found what size the trial plate must be made so that the redundant matter in it should be just sufficient to saturate the redundant fluid in B, I tried the body b in the same manner, and if I found that it required the trial plate to be of the same size in order that the redundant matter in it should be just sufficient to saturate the redundant fluid in b, I was well assured that if B and b were successively made to communicate with a third body and positively electrified they would each of them contain the same quantity of fluid, supposing the quantity of redundant fluid in the third body to be the same each time; that is, that the charge of B was equal to that of b.

Having thus given a general idea of the method I used, I proceed to describe it more particularly.

239] The trial plates I made use of consisted of two flat tin plates ABCD and abcd (Fig. 15), made to slide one upon the other, so that by making the side bc of one plate extend more or

less beyond the side BC of the other it formed a plate of a greater or less size, and which consequently contained more

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or less

Fig.15

240] The apparatus used in making these experiments is represented in Fig. 14, where the parallelogram T represents the trial plate and B one of the bodies to be compared together, each supported on non-conductors. dD8 is the wire for making a communication between them, having a joint in it at D, where it is supported by a non-conductor, and where are also hung two small pith balls to show whether B and T are over- or undercharged after the communication is made between them. A and a are the two vials; Ee is a wire communicating with the inside coating of A, aCc a wire communicating with the same coating of a; and Ff and Gg are wires fastened to the outside coating of a; RrSs is a wire for making a communication between B and the vial A, having joints in it at R and S, where it is supported by nonconductors, and mMNn is another wire of the same kind for making a communication between T and the vial a.†

241] In order to try the experiment I proceed in this manner: the wires Dd and DƐ are lifted off from the plates B and T so as not to touch them, and consequently so that there is no communication between B and T: the wires Rr and Mm are suffered to rest on B and T, and the wires Ss and Nn are lifted up so as not to touch Ee and Ff. The vials are then charged by means of the wire bt which rests on Ee and Cc, and communicates by the wire [See table for trial plate at Art. 468.]

*

+ [See plan, Fig. 17, p. 128.]

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