Abbildungen der Seite

The following is an extract from the Preface to the first edition of the pamphlet published by Cave, as above mentioned.

“ It may be necessary to acquaint the reader, that the following observations and experiments were not drawn up with a view to their being made public, but were communicated at different times, and most of them in letters, written on various topics, as matters only of private amusement.

“But some persons, to whom they were read, and who had themselves been conversant in electrical disquisitions, were of opinion, they contained so many curious and interesting particulars relative to this affair, that it would be doing a kind of injustice to the public, to confine them solely to the limits of a private acquaintance.

“ The editor was therefore prevailed upon to commit such extracts of letters and other detached pieces as were in his hands to the press, without waiting for the ingenious author's permission so to do; and this was done with the less hesitation, as it was apprehended the author's engagements in other affairs would scarce afford him leisure to give the public his reflections and experiments on the subject, finished with that care and precision, of which the treatise before us shows he is alike studious and capable.”,

Dr. Priestley, in his History of Electricity, published in the year 1767, gives a full account of Franklin's experiments and discoveries.

“Nothing was ever written upon the subject of electricity," he says, “ which was more generally read and admired in all parts of Europe, thán these letters. There is hardly any European language into which they have not been translated ; and, as if this were not sufficient to make them properly known, a translation of them has lately been made into Latin. It is not easy to say, whether we are most pleased with the simplicity and perspicuity with which these letters are written, the modesty with which the author proposes every hypothesis of his own, or the noble frankness with which he relates his mistakes, when they were corrected by subsequent experiments.

• Though the English have not been backward in acknowledging the great merit of this philosopher, he has had the singular good fortune to be, perhaps, even more celebrated abroad than at home; so that, to form a just idea of the great and deserved reputation of Dr. Franklin, we must read the foreign publications on the subject of electricity; in many of which the terms Franklinism, Franklinist, and the Franklinian system, occur in almost every page. In consequence of this, Dr. Franklin's principles bid fair to be handed down to posterity as equally expressive of the true principles of

[ocr errors]
[ocr errors]

electricity, as the Newtonian philosophy is of the true system of nature in general."

The observations and theories of Franklin, met with high favor in France, where his experiments were repeated, and the results verified to the admiration of the scientific world. In the

year 1753, his friend, Peter Collinson, wrote to him from London ; " The King of France strictly commands the Abbé Mazéas to write a letter in the politest terms to the Royal Society, to return the King's thanks and compliments, in an express manner, to Mr. Franklin of Pennsylvania, for his useful discoveries in electricity, and the application of pointed rods to prevent the terrible effects of thunder-storms." And the same Mr. Collinson wrote as follows to the Reverend Jared Eliot, of Connecticut, in a letter dated, London, November 22d, 1753. “ Our friend Franklin will be honored on St. Andrew's day, the 30th instant, the anniversary of the Royal Society, when the Right Honorable the Earl of Macclesfield will make an oration on Mr. Franklin's new discoveries in electricity, and, as a reward and encouragement, will bestow on him a gold medal.” This ceremony accordingly took place, and the medal was conferred.

The best translation of Franklin's papers on electricity is that in French by M. Dubourg, published at Paris in two elegant quarto volumes, in the year 1773. Several of his other philosophical writings, and some of his political pieces, are also included in these volumes, with valuable additions and remarks by the learned translator. Letters and other original papers were transmitted by Dr. Franklin to M. Dubourg, and appeared for the first time in his translation. — EDITOR.


Introductory Letter.

Philadelphia, 28 March, 1747. SIR, Your kind present of an electric tube, with directions for using it, has put several of us on making electrical experiments, in which we have observed some particular phenomena, that we look upon to be new. I shall therefore communicate them to you in my next, though possibly they may not be new to you; as, among the numbers daily employed in those experiments on your side the water, it is probable some one or other has hit on the same observations. For my own part, I never was before engaged in any study that so totally engrossed my attention and my time, as this has lately done; for what with making experiments when I can be alone, and repeating them to my friends and acquaintance, who, from the novelty of the thing, come continually in crowds to see them, I have, during some months past, had little leisure for any thing else.

I am, &c.



Wonderful Effect of Points. Positive and Negative

Electricity. - Electrical Kiss. Counterfeit Spider. - Simple and commodious Electrical Machine.

Philadelphia, 11 July, 1747. SIR, In my last I informed you that, in pursuing our electrical inquiries, we had observed some particular phenomena, which we looked upon to be new, and of which I promised to give you some account, though I apprehended they might not possibly be new to you, as so many hands are daily employed in electrical experiments on your side the water, some or other of which would probably hit on the same observations.

The first is the wonderful effect of pointed bodies, both in drawing off and throwing off the electrical fire. For example,

Place an iron shot, of three or four inches diameter,

VOL. v.



on the mouth of a clean, dry glass bottle. By a fine
silken thread from the ceiling, right over the mouth of
the bottle, suspend a small cork ball, about the bigness
of a marble; the thread of such a length, as that the
cork ball may rest against the side of the shot. Elec-
trify the shot, and the ball will be repelled to the dis-
tance of four or five inches, more or less, according to
the quantity of electricity. When in this state, if you
present to the shot, the point of a long, slender, sharp
bodkin, at six or eight inches distance, the repellency
is instantly destroyed, and the cork flies to the shot.
A blunt body must be brought within an inch, and
draw a spark, to produce the same effect. To prove
that the electrical fire is drawn off by the point, if you
take the blade of the bodkin out of the wooden handle,
and fix it in a stick of sealing-wax, and then present it at
the distance aforesaid, or if you bring it very near, no
such effect follows; but sliding one finger along the
wax till you touch the blade, and the ball flies to the
shot immediately. If you present the point in the dark,
you will see, sometimes at a foot distance and more,
a light gather upon it, like that of a fire-fly, or glow-
worm; the less sharp the point, the nearer you must
bring it to observe the light; and, at whatever distance
you see the light, you may draw off the electrical fire,
and destroy the repellency. If a cork ball so suspend-
ed be repelled by the tube, and a point be presented
quick to it, though at a considerable distance, it is sur-
prising to see how suddenly it flies back to the tube..
Points of wood will do near as well as those of iron,
provided the wood is not dry; for perfectly dry wood
will no more conduct electricity than sealing-wax.

To show that points will throw off * as well as draw

* This power of points to throw off the electrical fire, was first communicated to me by my ingenious friend, Mr. Thomas Hopkinson, since

off the electrical fire; lay a long sharp needle upon the shot, and you cannot electrize the shot so as to make it repel the cork ball. Or fix a needle to the end of a suspended gun-barrel, or iron rod, so as to point beyond it like a little bayonet;* and, while it remains there, the gun-barrel, or rod, cannot by applying the tube to the other end be electrized so as to give a spark, the fire continually running out silently at the point. In the dark you may see it make the same appearance as it does in the case before mentioned.

The repellency between the cork ball and the shot is likewise destroyed; Ist, by sifting fine sand on it; this does it gradually; 2dly, by breathing on it; 3dly, by making a smoke about it from burning wood ; † 4thly, by candle-light, even though the candle is at a foot distance; these do it suddenly. The light of a bright coal from a wood fire, and the light of a red-hot iron do it likewise; but not at so great a distance. Smoke, from dry rosin dropped on hot iron, does not destroy the repellenty; but is attracted by both shot and cork ball, forming proportionable atmospheres round them, making them look beautifully, somewhat like some of the figures in Burnet's or Whiston's Theory of the Earth.

deceased, whose virtue and integrity, in every station of life, public and private, will ever make his memory dear to those who knew him, and knew how to value him.

* This was Mr. Hopkinson's experiment, made wití an expectation of drawing a more sharp and powerful spark from the point, as from a kind of focus, and he was surprised to find little or none.

† We suppose every particle of sand, moisture, or smoke, being first attracted and then repelled, carries off with it a portion of the electrical fire ; but that the same still subsists in those particles, till they communicate it to something else, and that it is never really destroyed. So, when water is thrown on common fire, we do not imagine the element is thereby destroyed or annihilated, but only dispersed, each particle of water carrying off in vapor its portion of the fire, which it had attracted and attached to itself.

« ZurückWeiter »