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and west. Perhaps if the force was still greater, the south end, entered by the fire (when the needle lies north and south) might become the north, otherwise it puzzles us to account for the inverting of compasses by lightning ; since their needles must always be found in that situation, and by our little experiments, whether the blast entered the north and went out at the south end of the needle, or the contrary, still the end that lay to the north should continue to point north.
In these experiments the ends of the needle are sometimes finely blued, like a watch-spring, by the electric flame. This color, given by the flash from two jars only, will wipe off; but four jars fix it, and frequently melt the needles. I send you some, that have had their heads and points melted off by our mimic lightning; and a pin, that had its point melted off, and some part of its head and neck run. Sometimes the surface on the body of the needle is also run, and appears blistered when examined by a magnifying-glass. The jars I make use of hold seven or eight gallons, and are coated and lined with tin-foil; each of them takes a thousand turns * of a globe nine inches diameter to charge it.
I send you two specimens of tin-foil melted between glass, by the 'force of two jars only.'
I have not heard that any of your European electricians have ever been able to fire gunpowder by the electric flame. We do it here in this manner; a small cartridge is filled with dry powder, hard rammed, so as to bruise some of the grains; two pointed wires are then thrust in, one at each end, the points approaching
* The cushion being afterwards covered with a long flap of buckskin, which might cling to the globe, and care being taken to keep that flap of a due temperature, between too dry and too moist, we found so much more of the electric fuid was obtained, as that one hundred and fifty turns were sufficient. 1753. VOL. V.
each other in the middle of the cartridge till within the distance of half an inch ; then, the cartridge being placed in the circuit, when the four jars are discharged, the electric flame leaping from the point of one wire to the point of the other, within the cartridge amongst the powder, fires it, and the explosion of the powder is at the same instant with the crack of the discharge. Yours, &c.
TO PETER COLLINSON.
Introductory Letter to some additional Papers.
Philadelphia, 29 July, 1750.
As you first putus on electrical experiments, by sending to our Library Company a tube, with directions how to use it; and as our honorable Proprietary enabled us to carry those experiments to a greater height, by his generous present of a complete electrical apparatus; it is fit that both should know, from time to time, what progress we make. It was in this view I wrote and sent you my former papers on this subject, desiring, that, as I had not the honor of a direct correspondence with that bountiful benefactor to our library, they might be communicated to him through your hands. In the same view I write and send you this additional paper. If it happens to bring you nothing new, (which may well be, considering the number of ingenious men in Europe, continually engaged in the same researches,) at least it will show, that the instruments put into our hands are not neglected; and that, if no valuable discoveries are made by us, whatever the cause may be, it is not want of industry and application. I am, Sir, your much obliged humble servant,
Opinions and Conjectures concerning the Properties
and Effects of the Electrical Matter, and the Means of preserving Buildings, Ships, &c. from Lightning, arising from Experiments and Observations made at Philadelphia, 1749. — Golden Fish. — Extraction of Efluvial Virtues by Electricity impracticable.
§ 1. 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.
2. 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.
3. Electrical matter differs from common matter in this, that the parts of the latter mutually attract, those of the former mutually repel each other. Hence the appearing divergency in a stream of electrified effluvia.
4. But, though the particles of electrical matter do repel each other, they are strongly attracted by all other matter. *
5. From these three things, 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 hath not already got its quantity,) it is immediately and equally diffused through the whole.
6. Thus, common matter is a kind of sponge to the
* See the ingenious Essays on Electricity, in the 'Transactions, by Mr. Ellicot.
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 were 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.
7. But in common matter 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, and forms what we call an electrical atmosphere; and then the body is said to be electrified.
8. It is supposed, that all kinds of common matter do not attract and retain the electrical, with equal strength and force, for reasons to be given hereafter. And that those called electrics per se, as glass, &c., attract and retain it strongest, and contain the greatest quantity.
9. We know, that the electrical fluid is in common matter, because we can pump it out by the globe or tube. We know 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 common matter has not (generally) more than it can contain, otherwise all loose portions of it would repel each other, as they constantly do when they have electric atmospheres.
10. The beneficial uses of this electric fluid in the creation we are not yet well acquainted with, though doubtless such there are, and those very considerable; but we may see some pernicious consequences that would attend a much greater proportion of it. For, had this globe we live on, as much of it in proportion as we can give to a globe of iron, wood, or the like, the particles of dust and other light matters that get loose from it, would, by virtue of their separate electrical atmospheres, not only repel each other, but be repelled from the earth, and not easily be brought to unite with it again; whence our air would continually be more and more clogged with foreign matter, and grow unfit for respiration. This affords another occasion of adoring that wisdom which has made all things by weight and measure !
11. If a piece of common matter be supposed entirely free from electrical matter, and a single particle of the latter be brought nigh, it will be attracted, and enter the body, and take place in the centre, or where the attraction is every way equal. If more particles enter, they take their places where the balance is equal between the attraction of the common matter, and their own mutual repulsion. It is supposed they form triangles, whose sides shorten as their number increases, till the common matter has drawn in so many, that its whole power of compressing those triangles by attraction is equal to their whole power of expanding themselves by repulsion ; and then will such a piece of matter receive no more.
12. When part of this natural proportion of electrical fluid is taken out of a piece of common matter, the triangles formed by the remainder are supposed to widen by the mutual repulsion of the parts, until they occupy the whole piece.
13. When the quantity of electrical Auid, taken from a piece of common matter, is restored again, it enters the expanded triangles, being again compressed till there is room for the whole.