Extract of a letter from Mr. Bowdoin of The column, being thus acted upon, be

Boston to Benjamin Franklin, concerning the crooked direction and the source of lightning, and the swiftness of the electric fire.

BOSTON, Dec. 21, 1751.

THE experiments Mr. K. has exhibited here, have been greatly pleasing to all sorts of people that have seen them; and I hope, by the time he returns to Philadelphia, his tour this way will turn to good account. His experiments are very curious, and I think prove most effectually your doctrine of electricity; that it is a real element, annexed to, and diffused among all bodies we are acquainted with; that it differs in nothing from lightning, the effects of both being similar, and their properties, so far as they are known, the same, &c.

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The remarkable effect of lightning on iron, lately discovered, in giving it the netic virtue, and the same effect produced on small needles by the electrical fire, is a further and convincing proof that they are both the same element; but, which is very unaccountable, Mr. K. tells me, it is necessary to produce this effect, that the direction of the needle and the electric fire should be north and south; from either to the other, and that just so far as they deviate therefrom, the magnetic power in the needle is less, till their direction being at right angles with the north and south, the effect entirely ceases. made at Faneuil Hall, where was Mr. K.'s apparatus, several experiments, to give some small needles the magnetic virtue; previously examining, by putting them in water, on which they will be supported, whether or not they had any of that virtue; and I think we found all of them to have some small degree of it, their points turning to the north; we had nothing to do then but to invert the poles, which accordingly was done, by sending through them the charge of two large glass jars; the eye of the needle turning to the north, as the point before had done: that end of the needle which the fire is thrown upon, Mr. K. tells me always points to the north. The electrical fire passing through air has the same crooked direction as lightning.* This appearance I endeavour to account for thus: air is an electric per se, therefore there must be a mutual repulsion betwixt air and the electrical fire. A column or cylinder of air, having the diameter of its base equal to the diameter of the electrical spark, intervenes that part of the body which the spark is taken from, and of the body it aims at. The spark acts upon this column, and is acted upon by it, more strongly than any other neighbouring portion of air.

*This is most easily observed in large strong sparks taken at some inches distance.

comes more dense, and, being more dense repels the spark more strongly; its repellency being in proportion to its density: having acquired, by being condensed, a degree of repellency greater than its natural, it turns the spark out of its straight course; the neigh bouring air, which must be less dense, and therefore has a smaller degree of repellency, giving it a more ready passage.

The spark, having taken a new direction, must now act on, or most strongly repel the column of air which lies in that direction, and consequently must condense that column in the same manner as the former, when the spark must again change its course, which course will be thus repeatedly changed, till the spark reaches the body that attracted it.

To this account one objection occurs; that as air is very fluid and elastic, and so endeavours to diffuse itself equally, the supposed accumulated air within the column aforesaid, would be immediately diffused among the contiguous air, and circulate to fill the space it was driven from: and consequently that the said column, on the greater density of which the phenomenon is supposed to depend, would not repel the spark more strongly than the neighbouring air.

This might be an objection, if the electrical fire was as sluggish and inactive as air. Air takes a sensible time to diffuse itself equally,

as

is manifest from winds which often blow

for a considerable time together from the same point, and with a velocity even in the greatest storms, not exceeding, as it is said, sixty miles an hour: but the electric fire seems propagated instantaneously, taking up no perceptible time in going very great distances. It must then be an inconceivable short time in its progress from an electrified to an unelectrified body, which, in the present case, can be but a few inches apart: but this small portion of time is not sufficient for elasticity of the air to exert itself, and therefore the column aforesaid must be in a denser state than its neighbouring air.

About the velocity of the electric fire more is said below, which perhaps may more fully obviate this objection. But let us have recourse to experiments. Experiments will obviate all objections, or confound the hypothe sis. The electric spark, if the foregoing be true, will pass through a vacuum in a right line. To try this, let a wire be fixed perpendicularly on the plate of an air pump, having a leaden ball on its upper end; let another wire, passing through the top of a receiver, have on each end a leaden ball; let the leaden balls within the receiver, when put on the air pump, be within two or three inches of each other; the receiver being exhausted, the spark given from a charged phial to the upper wire will pass through rarified air, nearly approaching to a vacuum, to the

lower wire, and I suppose in a right line, or | stroke, nor, which is more extraordinary, saw nearly so; the small portion of air remaining the light; which gave you just reason to conin the receiver, which cannot be entirely exhausted, may possibly cause it to deviate a little, but perhaps not sensibly from a right line. The spark also might be made to pass through air greatly condensed, which perhaps would give a still more crooked direction. I have not had opportunity to make any experiments of this sort, not knowing of an air-pump nearer than Cambridge, but you can easily make them. If these experiments answer, I think the crooked direction of lightning will be also accounted for.

■. With respect to your letters on electricity; your hypothesis in particular for explaining the phenomena of lightning is very ingenious. That some clouds are highly charged with electrical fire, and that their communicating it to those that have less, to mountains and other eminences, makes it visible and audible, when it is denominated lightning and thunder, is highly probable; but that the sea, which you suppose the grand source of it, can collect it, I think admits of a doubt; for though the sea be composed of salt and water, an elecL tric per se and non-electric, and though the friction of electrics per se and non-electrics, will collect that fire, yet it is only under certain circumstances which water will not admit. For it seems necessary, that the electrics per se and non-electrics rubbing one another, should be of such substances as will not adhere to, or incorporate with each other. Thus a glass or sulphur sphere turned in water, and so a friction between them, will not collect any fire; nor, I suppose, would a sphere of salt revolving in water: the water adhering to, or incorporating with those electrics per se. But granting that the friction between salt and water would collect the electrical fire; that fire, being so extremely subtle and active, would be immediately communicated, either to those lower parts of the sea from which it was drawn, and so only perform quick revolutions; or be communicated to the adjacent islands or continent, and so be diffused instantaneously through the general mass of the earth. I say instantaneously, for the greatest distances we can conceive within the limits of our globe, even that of the two most opposite points, it will take no sensible time in passing through; and therefore it seems a little difficult to conceive how there can be any accumulation of the electrical fire upon the surface of the sea, or how the vapours arising from the sea should have a greater share of that fire than other vapours. That the progress of the electrical fire is so amazingly swift, seems evident from an experiment you yourself (not out of choice) made, when two or three large glass jars were discharged through your body. You neither heard the crack, was sensible of the

clude, that it was swifter than sound, than animal sensation, and even light itself. Now light (as astronomers have demonstrated) is about six minutes passing from the sun to the earth; a distance, they say, of more than eighty millions of miles. The greatest rectilinear distance within the compass of the earth is about eight thousand miles, equal to its diameter. Supposing then, that the velocity of the electric fire be the same as that of light, it will go through a space equal to the earth's diameter in about two sixtieths of the second of a minute. It seems inconceivable then, that it should be accumulated upon the sea, in its present state, which, as it is a non-electric, must give the fire an instantaneous passage to the neighbouring shores, and they convey it to the general mass of the earth. But such accumulation seems still more inconceivable when the electrical fire has but few feet depth of water to penetrate, to return to the place from whence it is supposed to be collected.

Your thoughts upon these remarks I shall receive with a great deal of pleasure. I take notice that in the printed copies of your letters, several things are wanting which are in the manuscript you sent me. I understand by your son, that you had writ, or was writing, a paper on the effect of the electrical fire on loadstones, needles, &c. which I would ask the favour of a copy of, as well as of any other papers on electricity, written since I had the manuscript, for which I repeat my obligations to you. J. BOWDOIN.

J. Bowdoin, Boston. Observations on the subjects of the preceding letter. -Reasons for supposing the sea to be the grand source of Lightning.— Reasons for doubting this hypothesis.-Improvement in a globe for raising the Electric Fire.-Read at the Royal Society, May 27, 1756.

PHILADELPHIA, Jan. 24, 1752. I AM glad to learn, by your favour of the 21st past, that Mr. Kinnersley's lectures have been acceptable to the gentlemen of Boston, and are like to prove serviceable to himself.

I thank you for the countenance and encouragement you have so kindly afforded my fellow-citizen.

I send you enclosed an extract of a letter containing the substance of what I observed concerning the communication of magnetism to needles by electricity. The minutes I took at the time of the experiments are mislaid. I am very little acquainted with the nature of magnetism. Dr. Gawin Knight, inventor of the steel magnets, has wrote largely on that subject, but I have not yet had leisure to peruse his writings with the attention necessary to become master of his doctrine.

Your explication of the crooked direction of be repelled from the then generally electrilightning appears to me both ingenious and fied surface of the sea, and fly away with solid. When we can account as satisfactori- them into the air. I thought too, that possi ly for the electrification of clouds, I think that bly the great mixture of particles electric branch of natural philosophy will be nearly per se, in the ocean water, might, in some complete. degree, impede the swift motion and dissipation of the electric fluid through it to the shores, &c.-But having since found, that salt in the water of an electric phial does not lessen the shock; and having endeavoured in vain to produce that luminous appearance from a mixture of salt and water agitated; and observed, that even the sea-water will not produce it after some hours standing in a bottle; I suspect it to proceed from some principle yet unknown to us (which I would gladly make some experiments to discover, if

The air, undoubtedly, obstructs the motion of the electric fluid. Dry air prevents the dissipation of an electric atmosphere, the denser the more, as in cold weather. I question whether such an atmosphere can be retained by a body in vacuo. A common electrical phial requires a non-electric communication from the wire to every part of the charged glass; otherwise, being dry and clean, and filled with air only, it charges slowly, and discharges gradually, by sparks, without a shock: but exhausted of air, the communica- I lived near the sea) and I grow more doubttion is so open and free between the inserted wire and surface of the glass, that it charges as readily, and shocks as smartly as if filled with water and I doubt not, but that in the experiment you propose, the sparks would not only be near strait in vacuo, but strike at a greater distance than in the open air, though perhaps there would not be a loud explosion. As soon as I have a little leisure, I will make the experiment, and send you the result.

ful of my former supposition, and more ready to allow weight to that objection (drawn from the activity of the electric fluid, and the readiness of water to conduct) which you have indeed stated with great strength and clearness.

In the mean time, before we part with this hypothesis, let us think what to substitute in its place. I have sometimes queried whether the friction of the air, an electric per se, in violent winds, among trees, and against the surface of the earth, might not pump up, as so many glass globes, quantities of the electric fluid, which the rising vapours might receive from the air, and retain in the clouds they form? on which I should be glad to have your sentiments. An ingenious friend of mine supposes the land-clouds more likely to be electrified than the sea-clouds. I send his letter for your perusal, which please to return me.

My supposition, that the sea might possibly be the grand source of lightning, arose from the common observation of its luminous appearance in the night, on the least motion; an appearance never observed in fresh water. Then I knew that the electric fluid may be pumped up out of the earth, by the friction of a glass globe, on a non-electric cushion; and that notwithstanding the surprising activity and swiftness of that fluid, and the nonelectric communication between all the parts I have wrote nothing lately on electricity, of the cushion and the earth, yet quantities nor observed any thing new that is material, would be snatched up by the revolving sur- my time being much taken up with other af face of the globe, thrown on the prime con- fairs. Yesterday I discharged four jars ductor, and dissipated in air. How this was through a fine wire, tied up between two done, and why that subtle active spirit did not strips of glass: the wire was in part melted, immediately return again from the globe, into and the rest broke into small pieces from half some part or other of the cushion, and so into an inch long, to half a quarter of an inch. My the earth, was difficult to conceive; but whe-globe raises the electric fire with greater ease, ther from its being opposed by a current set- in much greater quantities, by the means of ting upwards to the cushion, or from what- a wire extended from the cushion, to the iron ever other cause, that it did not so return pin of a pump handle behind my house, which was an evident fact. Then I considered the communicates by the pump spear with the separate particles of water as so many hard water in the well. spherules, capable of touching the salt only By this post I send to ****, who is curious in points, and imagined a particle of salt could in that way, some meteorological observations therefore no more be wet by a particle of wa- and conjectures, and desire him to communiter, than a globe by a cushion; that there cate them to you, as they may afford you might therefore be such a friction between some amusement, and I know you will look these originally constituent particles of salt over them with a candid eye. By throwing and water, as in a sea of globes and cushions; our occasional thoughts on paper, we more that each particle of water on the surface readily discover the defects of our opinions, or might obtain from the common mass, some we digest them better and find new arguments particles of the universally diffused much to support them. This I sometimes practise: finer, and more subtle electric fluid, and form- but such pieces are fit only to be seen by ing to itself an atmosphere of those particles, friends. B. FRANKLIN

four glass jars had upon a fine wire, tied be

J. Bowdoin to Benjamin Franklin. Effect of Lightning on Captain Waddel's Com-tween two strips of glass, puts me in mind of a pass, and the Dutch Church at New York. Read at the Royal Society, June 3, 1752. BOSTON, March 2, 1752.

very similar one of lightning, that I observed at New York, October, 1750, a few days af ter I left Philadelphia. In company with a number of gentlemen, I went to take a view I HAVE received your favour of the 24th of of the city from the Dutch church steeple, in January past, enclosing an extract from your which is a clock about twenty or twenty-five letter to Mr. Collinson, and *****s letter to feet below the bell. From the clock went a yourself, which I have read with a great deal wire through two floors, to the clock-hammer of pleasure, and am much obliged to you for. near the bell, the holes in the floor for the Your extract confirms a correction Mr. Kin- wire being perhaps about a quarter of an inch nersley made a few days ago, of a mistake I diameter. We were told, that in the spring of was under respecting the polarity given to 1750, the lightning struck the clock hammer, needles by electrical fire," that the end which and descended along the wire to the clock, receives the fire always points north;" and melting in its way several spots of the wire, "that the needle being situated east and west from three to nine inches long, through one will not have a polar direction." You find, third of its substance, till coming within a few however, the polarity strongest when the feet of the lower end, it melted the wire quite needle is shocked lying north and south; through, in several places, so that it fell down weakest when lying east and west; which in several pieces; which spots and pieces we makes it probable that the communicated saw. When it got to the end of the wire, it magnetism is less, as the needle varies from flew off to the hinge of a door, shattered the north and south situation. As to the needle door, and dissipated. In its passage through of captain Waddel's compass, if its polarity the holes of the floors it did not do the least was reversed by the lightning, the effect of damage, which evidences that wire is a good lightning and electricity, in regard of that, conductor of lightning (as it is of electricity) seems dissimilar; for a magnetic needle in a provided it be substantial enough, and might, north and south situation (as the compass neein this case, had it been continued to the dle was) instead of having its power revers-earth, have conducted it without damaging ed, or even diminished, would have it confirmthe building.*

a

ed or increased by the electric fire. But per- Your information about your globe's raising haps the lightning communicated to some the electric fire in greater quantities, by means nails in the binnacle (where the compass is of a wire extended from the cushion to the placed) the magnetic virtue, which might dis-earth, will enable me, I hope, to remedy a turb the compass.

This I have heard was the case; if so, the seeming dissimilarity vanishes: but this remarkable circumstance (if it took place). I should think would not be omitted in captain

Waddel's account.

I am very much pleased that the explication I sent you, of the crooked direction of lightning, meets with your approbation.

As to your supposition about the source of lightning, the luminous appearance of the sea in the night, and the similitude between the friction of the particles of salt and water, as you considered them in their original separate state, and the friction of the globe and cushion, very naturally led you to the ocean, as the grand source of lightning: but the activity of lightning, or the electric element, and the fitness of water to conduct it, together with the experiments you mention of salt and water, seem to make against it, and to prepare the way for some other hypothesis. Accordingly you propose a new one, which is very curious, and not so liable, I think, to objections as the former. But there is not, as yet, I believe, a sufficient variety of experiments to establish any theory, though this seems the most hopeful of any I have heard of. The effect which the discharge of your

lect the fire with the electrifying glass I use, great inconvenience I have been under, to colwhich is fixed in a very dry room, three stories from the ground. When you send your meteorological observations to ****, I hope I shall have the pleasure of seeing them.

J. BOWDOIN.

Proposal of an experiment to measure the time taken up by an Electric Spark in moving through any given space. By James Alexander, of New York.-Read at the Royal Society, Dec. 26, 1756.

Ir I remember right, the Royal Society made one experiment to discover the velocity

*The wire mentioned in this account was replaced by a small brass chain. In the summer of 1763, the lightning again struck that steeple, and from the clockhammer near the bell, it pursued the chain as it had be fore done the wire, went off to the same hinge, and again shattered the same door. In its passage through the same holes of the same floors, it did no damage to of the chain. But the chain itself was destroyed, being partly scattered about in fragments of two or three links melted and stuck together, and partly blown up or reduced to smoke, and dissipated. [See an account of the same effect of lightning on a wire at Newbury, p. 296.] The steeple, when repaired, was guarded by an iron spindle down the outside of the building, into the earth

the floors, nor to the building during the whole extent

conductor, or rod, extending from the foot of the vane.

Society, Dec. 25, 1756.

SUPPOSE a tube of any length open at both ends, and containing a moveable wire of just the same length, that fills its bore. If I attempt to introduce the end of another wire into the same tube, it must be done by pushing forward the wire it already contains; and the instant I press and move one end of that wire, the other end is also moved, and introducing one inch of the same wire, I extrude, at the same time, an inch of the first, from the other end of the tube.

of the electric fire, by a wire of about four | Answer to the foregoing.-Read at the Royal miles in length, supported by silk, and by turning it forwards and backwards in a field, so that the beginning and end of the wire were at only the distance of two people, the one holding the Leyden bottle and the beginning of the wire, and the other holding the end of the wire and touching the ring of the bottle; but by this experiment no discovery was made, except that the velocity was extremely quick. As water is a conductor as well as metals, it is to be considered whether the velocity of the electric fire might not be discovered by means of water; whether a river, or lake, or sea, may not be made part of the circuit through which the electric fire passes? instead of the circuit all of wire, as in the above experiment.

Whether in a river, lake, or sea, the electric fire will not dissipate and not return to the bottle? or, will it proceed in strait lines through the water the shortest courses possible back to the bottle?

If the tube be filled with water, and I inject an additional inch of water at one end, I force out an equal quantity at the other in the very same instant.

And the water forced out at one end of the tube is not the very same water that was forced in at the other end at the same time, it was only in motion at the same time.

The long wire, made use of in the experiment to discover the velocity of the electric fluid, is itself filled with what we call its natural quantity of that fluid, before the hook of the Leyden bottle is applied to one end of it.

The outside of the bottle being at the time of such application in contact with the other end of the wire, the whole quantity of electric fluid contained in the wire is, probably, put in motion at once.

If the last, then suppose one brook that falls into Delaware doth head very near to a brook that falls into Schuylkill, and let a wire be stretched and supported as before, from the head of the one brook to the head of the other, and let the one end communicate with the water, and let one person stand in the other brook, holding the Leyden bottle, and let another person hold that end of the wire not in the water, and touch the ring of the bottle.If the electric fire will go as in the last question, then will it go down the one brook to Delaware or Schuylkill, and down one of them If such long wire contains precisely the to their meeting, and up the other brook; the quantity that the outside of the bottle de time of its doing this may possibly be observ-mands, the whole will move out of the wire able, and the further upwards the brooks are chosen, the more observable it would be.

For at the instant the hook, connected with the inside of the bottle, gives out; the coating or outside of the bottle, draws in a portion of that fluid.

to the outside of the bottle, and the over quartity which the inside of the bottle contained, being exactly equal, will flow into the wire, and remain there, in the place of the quantity the wire had just parted with to the outside of the bottle.

Should this be not observable, then suppose the two brooks falling into Susquehanna and Delaware, and proceeding as before, the electric fire may, by that means, make a circuit round the North Cape of Virginia, and go But if the wire be so long as that one tenth many hundred miles, and in doing that, it (suppose) of its natural quantity is sufficient would seem it must take some observable time. to supply what the outside of the bottle de If still no observable time is found in that mands, in such a case the outside will only reexperiment, then suppose the brooks falling ceive what is contained in one tenth of the the one into the Ohio, and the other into Sus-wire's length, from the end next to it; though quehanna, or Potowmac, in that the electric fire would have a circuit of some thousands of miles to go down the Ohio to Mississippi, to the Bay of Mexico, round Florida, and round the South Cape of Virginia; which, I think, would give some observable time, and discover exactly the velocity.

But if the electric fire dissipates, or weakens in the water, as I fear it does, these experiments will not answer.

the whole will move so as to make room at the other end for an equal quantity issuing, at the same time, from the inside of the bottle.

So that this experiment only shows the extreme facility with which the electric fluid moves in metal; it can never determine the velocity.

And, therefore, the proposed experiment (though well imagined, and very ingenious) of sending the spark round through a vast length of space, by the waters of Susquehanna, or Potowmac, and Ohio, would not afford the satisfaction desired, though we could be sure that the motion of the electric fluid would be