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TO THE PAPERS ON ELECTRICITY.
WATSON'S ABSTRACT OF FRANKLIN'S ELECTRICAL EXPERIMENTS AND OBSERVATIONS.
An Account of Mr. Benjamin Franklin's Treatise, lately published, entitled "Experiments and Observations on Electricity, made at Philadelphia in America;" by William Watson, F. R. S.
READ AT THE ROYAL SOCIETY, JDNE Gth, 1751.
Mr. Franklin's Treatise, lately presented to the Royal Society, consists of four letters to his correspondent in England, and of another part, entitled "Opinions and - Conjectures concerning the Properties and Effects of the Electrical Matter, arising from Experiments and Observations."
The four letters, the last of which contains a new hypothesis for explaining the several phenomena of thunder-gusts, have, either in the whole or in part, been before communicated to the Royal Society. It remains, therefore, that I now only lay before the Society an account of the latter part of this treatise, as well as that of a letter intended to be added thereto by the author, but which arrived too late for publication with it, and was therefore communicated to the Society by our worthy brother, Mr. Peter Collinson.
This ingenious author, from a great variety of curious and welladapted experiments, is of opinion, that the electrical matter consists of particles extremely subtile; since it can permeate common matter, even the densest metals, with such ease and freedom, as not to receive any perceptible resistance; and that, if any one should doubt, whether the electrical matter passes through the substance of bodies, or only over and along their surfaces, a shock from an electrified large glass jar, taken through his own body, will probably convince him.
Electrical matter, according to our author, differs from common matter in this, that the parts of the latter mutually attract, and those of the former mutually repel, each other; hence the divergency in a stream of electrified effluvia.* But that, though the particles of electrical matter do repel each other, they are strongly attracted by all other matter.
From these three things, viz. the extreme subtilty of the electrical matter, the mutual repulsion of its parts, and the strong attraction between them and other matter, arises this .effect, that when a quantity of electrical matter is applied to a mass of common matter of any bigness or length within our observation (which has not already got its quantity), it is immediately and equally diffused through the whole.
Thus common matter is a kind of sponge to the electrical fluid: and, as a sponge would receive no water, if the parts of water were not smaller than the pores of the sponge; and even then but slowly, if there was not a mutual attraction between those parts and the parts of the sponge; and would still imbibe it faster, if the mutual attraction among the parts of the water did not impede, some force being required to separate them; and fastest, if, instead of attraction, there were a mutual repulsion among those parts, which would act in conjunction with the attraction of the sponge; so is the case between the electrical and common matter. In common matter, indeed, there is generally as much of the electrical as it will contain within its substance; if more is added, it lies without upon the surface.t- and forms what we call an electrical atmosphere, and then the body is said to be electrified.
It is supposed, that all kinds of common matter do not attract and retain the electrical with equal force, for reasons to be given hereafter; and that those called electrics per se, as glass, &-c, attract and retain it the strongest, and contain the greatest quantity.
We know that the electrical fluid is in common matter, because we can pump it out by the globe or tube; and that common matter has near as much as it can contain, because, when we add a little more to any portion of it, the additional quantity does not enter, but forms an electrical atmosphere; and we know, that
* As the electric stream is observed to diverge very little, when the experiment is made in vatuo, this appearance is more owing to the resistance of the atmosphere, than to any natural tendency in the electricity itself. — W. W.
f The author of this account is of opinion, that what is here added, lies not only without upon the surface, but penetrates with the same degree of density the whole mass of common matter upon which it is directed, •