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as often to make it greater than the striking every help to obtain, even from broken partial distance. Turning the blunt end of a wire metalline conductors. uppermost (which represents the unpointed bar) it appears that the same good effect is not from that to be expected. A long pointed rod, it is therefore imagined, may prevent some strokes; as well as conduct others that fall upon it, when a great body of cloud comes on so heavily that the above repelling operation on fragments cannot take place.

EXPERIMENT VI.

Opposite the side of the prime conductor, place separately isolated by wax stems, Mr. Canton's two boxes with pith balls suspended by fine linen threads. On each box, lay a wire six inches long and one fifth of an inch thick, tapering to a sharp point; but so laid as that four inches of the pointed end of one wire, and an equal length of the blunt end of the other, may project beyond the ends of the boxes; and both at eighteen inches distance from the prime conductor. Then charging the prime conductor by a turn or two of the globe, the balls of each pair will separate; those of the box, whence the point projects most, considerably; the others less. Touch the prime conductor, and those of the box with the blunt point will collapse, and join. Those connected with the point will at the same time approach cach other, till within about an inch, and there remain.

OBSERVATION.

This seems a proof, that though the small sharpened part of the wire must have had a less natural quantity in it, before the operation, than the thick blunt part; yet a greater quantity was driven down from it to the balls. Thence it is again inferred, that the pointed rod is rendered more negative: and farther, that if a stroke must fall from the cloud over a building, furnished with such a rod, it is more likely to be drawn to that pointed rod, than to a blunt one; as being more strongly negative, and of course its attraction stronger. And it seems more eligible, that the lightning should fall on the point of the conductor (provided to convey it into the earth) than on any other part of the building, thence to proceed to such conductor: which end is also more likely to be obtained by the length and loftiness of the rod; as protecting more extensively the building under it.

It has been objected, that erecting pointed rods upon edifices, is to invite and draw the lightning into them; and therefore dangerous. Were such rods to be erected on buildings, without continuing the communication quite down into the moist earth, this objection might then have weight; but when such complete conductors are made, the lightning is invited not into the building, but into the earth, the situation it aims at, and which it always seizes

It has also been suggested, that from such electric experiments nothing certain can be concluded as to the great operations of nature; since it is often seen, that experiments which have succeeded in small, in large have failed. It is true that in mechanics this has sometimes happened. But when it is considered that we owe our first knowledge of the nature and operations of lightning, to observations on such small experiments; and that on carefully comparing the most accurate accounts of former facts, and the exactest relations of those that have occurred since, the effects have surprisingly agreed with the theory; it is humbly conceived that in natural philosophy, in this branch of it at least, the suggestion has not so much weight; and that the farther new experiments now adduced in recommendation of long sharp-pointed rods, may have some claim to credit and consideration.

It has been urged too, that though points may have considerable effects on a small prime conductor at small distances; yet on great clouds and at great distances, nothing is to be expected from them. To this it is answered, that in those small experiments it is evident the points act at a greater than the striking distance; and in the large way, their service is only expected where there is such nearness of the cloud, as to endanger a stroke; and there, it cannot be doubted the points must have some effect. And if the quantity discharged by a single pointed rod may be so considerable as I have shown it; the quantity discharged by a number will be proportionably greater.

But this part of the theory does not depend alone on small experiments. Since the practice of erecting pointed rods in America (now near twenty years) five of them have been struck by lightning, viz. Mr. Raven's and Mr. Maine's, in South Carolina; Mr. Tucker's, in Virginia; Mr. West's and Mr. Moulder's, in Philadelphia. Possibly there may have been more that have not come to my knowledge. But in every one of these, the lightning did not fall upon the body of the house, but precisely on the several points of the rods; and, though the conductors were sometimes not sufficiently large and complete, was conveyed into the earth, without any material damage to the buildings. Facts then in great, as far as we have them authenticated, justify the opinion that is drawn from the experiments in small as above related.

It has also been objected, that unless we knew the quantity that might possibly be discharged at one stroke from the clouds, we cannot be sure we have provided sufficient conductors; and therefore cannot depend on

B. F.

To Professor Landriani, Italy. On the Utility of Electrical Conductors. PHILADELPHIA, Oct. 14, 1787. the Utility of Electrical Conductors, which I HAVE received the excellent work upon I read it you had the goodness to send me. sincere thanks for it. with great pleasure, and beg you to accept my

the number of conductors much increased, Upon my return to this country, I found many proofs of their efficacy in preserving their utility. Among other instances, my buildings from lightning having demonstrated which occasioned the neighbours to run in to own house was one day attacked by lightning, give assistance, in case of its being on fire. only found a good deal frightened with the vioBut no damage was done, and my family was lence of the explosion.

their conveying away all that may fall on | power in the clouds of collecting it; yet an their points. Indeed we have nothing to form accumulation and force beyond what mankind a judgment by in this but past facts; and we has hitherto been acquainted with is scarce to know of no instance where a complete con- be expected.* ductor to the moist earth has been insuffi- August 27, 1772. cient, if half an inch diameter. It is probable that many strokes of lightning have been conveyed through the common leaden pipes affixed to houses to carry down the water from the roof to the ground: and there is no account of such pipes being melted and destroyed, as must sometimes have happened if they had been insufficient. We can then only judge of the dimensions proper for a conductor of lightning, as we do of those proper for a conductor of rain, by past observation. And as we think a pipe of three inches bore sufficient to carry off the rain that falls on a square of 20 feet, because we never saw such a pipe glutted by any shower; so we may judge a conductor of an inch diameter, more than sufficient for any stroke of lightning that will fall on its point. It is true, that if another deluge should happen wherein the windows of heaven are to be opened, such pipes may be unequal to the falling quantity; and if God for our sins should think fit to rain fire upon us, as upon some cities of old, it is not expected that our conductors of whatever size, should secure our houses against a miracle. Probably as water drawn up into the air and there forming clouds, is disposed to fall again in rain by its natural gravity, as soon as a number of particles sufficient to make a drop can get together; so when the clouds are (by whatever means) over or undercharged with the electric fluid, to a degree sufficient to attract them towards the earth, the equilibrium is restored, before the difference becomes great beyond that degree. Mr. Lane's electrometer, for limiting precise-formed me, that having observed with his Mr. Rittenhouse, our astronomer, has inly the quantity of a shock that is to be administered in a medical view, may serve to make this more easily intelligible. The discharging knob does by a screw approach the conductor to the distance intended, but there remains fixed. Whatever power there may be in the glass globe to collect the fulminating fluid, and whatever capacity of receiving and accumulating it there may be in the bottle or glass jar; yet neither the accumulation nor the discharge ever exceeds the destined quantity. Thus, were the clouds always at a certain fixed distance from the earth, all discharges would be made when the quantity accumulated was equal to the distance: but there is a circumstance which by occasionally lessening the distance, lessens the discharge; to wit, the moveableness of the clouds, and their being drawn nearer to the earth by attraction when electrified; so that discharges are thereby rendered more frequent and of course less violent. Hence whatever the quantity may be in nature, and whatever the

conductor was obliged to be taken down. I Last year, my house being enlarged, the found, upon examination, that the pointed termination of copper, which, was originally inch in diameter in its thickest part, had nine inches long, and about one third of an been almost entirely melted; and that its connexion with the rod of iron below was this invention has proved of use to the auvery slight. Thus, in the course of time, thor of it, and has added this personal advantage to the pleasure he before received, from having been useful to others.

within the field of his view, he has remarkexcellent telescope, many conductors that are ed in various instances, that the points were of a house, provided with a perfect conductmelted in like manner. There is no example

*The immediate occasion of the dispute concerning the preference between pointed and blunt conductors of lightning, arose as follows:-A powder-mill having blown up at Brescia, in consequence of its being struck with lightning, the English board of ordinance applied to their painter, Mr. Wilson, then of some note as an electrician, for a method to prevent the like accident to their magazines at Purfleet. Mr. Wilson having advised a blunt conductor, and it being understood that Dr. Franklin's opinion formed upon the spot, was for a Royal Society, and by them as usual, to a committee, pointed one; the matter was referred in 1772, to the who, after consultation, prescribed a method conform lightning, having under particular circumstances, fallen able to Dr. Franklin's theory. But a harmless stroke of upon one of the buildings and its apparatus in May 1777; the subject came again into violent agitation, again referred to a new committee, which committee and was again referred to the society, and by the society confirmed the decision of the first committee; it produced an acrimonious controversy in the Royal Society, and a series of pamphlets; which, however, ended in the triumph of the Franklinian theory.

or, which has suffered any considerable da- | been accompanied with proper medicine and mage; and even those which are without regimen, under the direction of a skilful phythem have suffered little, since conductors have become common in this city.

B. FRANKLIN.

John Pringle, M. D.

sician. It may be, too, that a few great strokes, as given in my method, may not be so proper as many small ones; since by the account from Scotland of a case, in which two hundred shocks from a phial were given daily, it seems, that a perfect cure has been made. As to any uncommon strength supposed to be in the machine used in that case, I imagine it In compliance with your request, I send could have no share in the effect produced; you the following account of what I can at since the strength of the shock from charged present recollect relating to the effects of elec-glass, is in proportion to the quantity of surtricity in paralytic cases, which have fallen under my observation.

On the Effects of Electricity in Paralytic Cases.
CRAVEN-STREET, Dec. 21, 1757.

face of the glass coated: so that my shock from those large jars, must have been much greater than any that could be received from a phial held in the hand.

B. FRANKLIN.

Electrical Experiments on Amber.

Saturday, July 3, 1762.

Some years since, when the newspapers made mention of great cures performed in Italy and Germany, by means of electricity, a number of paralytics were brought to me from different parts of Pennsylvania, and the neighbouring provinces, to be electrised, which I did for them at their request. My method was, to place the patient first in a chair, on an electric stool, and draw a number of large strong sparks from all parts of the affected limb or side. Then I fully charged two sixgallon glass jars, each of which had about three square feet of surface coated; and sent the united shock of these through the affected limb or limbs, repeating the stroke commonly three times each day. The first thing observed, was an immediate greater sensible warmth in the lame limbs that had received the stroke, than in the others; and the next morning the patients usually related, that they had in the night felt a pricking sensation in the flesh of the paralytic limbs; and would sometimes show a number of small red spots, which they supposed were occasioned by those prickings. The limbs, too, were found more capable of voluntary motion, and seemed to receive strength. A man, for instance, who could not the first day lift the lame hand from off his knee, would the next day raise it four or five inches, the third day higher; and on the fifth day was able, but with a feeble languid motion, to take off his hat. These appearances gave great spirits to the patients, and made them hope a perfect cure; but I do not remember that I ever saw any amendment after the fifth day; which the patients perceiving, and finding the shocks pretty severe, they became discouraged, went home, and in a short time relapsed; so that I never knew any advantage from electricity in palsies that That I might better see the effect on the was permanent. And how far the apparent amber, I made the next experiment in a tube temporary advantage might arise from the ex- formed of a card rolled up and bound strongly ercise in the patients' journey, and coming with packthread. Its bore was about one daily to my house, or from the spirits given eighth of an inch diameter. I rammed powby the hope of success, enabling them to ex-der of amber into this as I had done in the ert more strength in moving their limbs, I will not pretend to say.

To try, at the request of a friend, whether amber finely powdered might be melted and run together again by means of the electric fluid, I took a piece of small glass tube, about two inches and a half long, the bore about one twelfth of an inch diameter, the glass itself about the same thickness; I introduced into this tube some powder of amber, and with two pieces of wire nearly fitting the bore, one inserted at one end, the other at the other, I rammed the powder hard between them in the middle of the tube, where it stuck fast, and was in length about half an inch. Then leaving the wires in the tube, I made them part of the electric circuit, and discharged through them three rows of my case of bottles. The event was, that the glass was broke into very small pieces, and those dispersed with violence in all directions. As I did not expect this, I had not, as in other experiments, laid thick paper over the glass to save my eyes, so several of the pieces struck my face smartly, and one of them cut my lip a little so as to make it bleed. I could find no part of the amber; but the table where the tube lay was stained very black in spots, such as might be made by a thick smoke forced on it by a blast, and the air was filled with a strong smell, somewhat like that from burnt gunpowder. Whence I imagined, that the amber was burnt, and had exploded as gunpowder would have done in the same circumstances.

Perhaps some permanent advantage might have been obtained, if the electric shocks had

other, and as the quantity of amber was greater, I increased the quantity of electric fluid by discharging through it at once five rows of my bottles. On opening the tube, I

To Thomas Ronayne, Esq. Cork, Ireland.
On the Electricity of the Fogs in Ireland.

LONDON, April 20. 1766.

found that some of the powder had exploded, at about the distance of three or four inches an impression was made on the tube, though from that part which is most distant from the it was not hurt, and most of the powder re- balls, and you will see the balls separate from maining was turned black, which I suppose each other, being positively electrified by the might be by the smoke forced through it from natural portion of electricity, which was in the burned part: some of it was hard; but as the box, and which is driven to the further part it powdered again when pressed by the fingers, of it by the repulsive power of the atmosphere I suppose that hardness not to arise from melt- in the excited glass. Touch the box near the ing any parts in it, but merely from my ram- little balls (the excited glass continuing in the ming the powder when I charged the tube. same state) and the balls will again unite; B. FRANKLIN. the quantity of electricity which had been driven to this part being drawn off by your finger. Withdraw then both your finger and the glass at the same instant, and the quantity of electricity which remained in the box, uniformly diffusing itself, the balls will again be separated; being now in a negative state. While things are in this situation, begin once more to excite your glass, and hold it above the box, but not too near, and you will find, that when brought within a certain distance, the balls will at first approach each other, being then in a natural state. In proportion as the glass is brought nearer, they will ́ again separate, being positive. When the glass is moved beyond them, and at some little further distance, they will unite again, being in a natural state. When it is entirely removed, they will separate again, being then made negative. The excited glass in this experiment may represent a cloud positively charged, which you see is capable of producing in this manner all the different changes in the apparatus, without the least necessity for supposing any negative cloud.

I HAVE received your very obliging and very ingenious letter by captain Kearney. Your observations upon the electricity of fogs, and the air in Ireland, and upon different circumstances of storms, appear to me very curious, and I thank you for them. There is not, in my opinion, any part of the earth whatever, which is, or can be, naturally in a state ofnegative electricity: and though different circumstances may occasion an inequality in the distribution of the fluid, the equilibrium is immediately restored by means of its extreme subtlety, and of the excellent conductors with which the humid earth is amply provided. I am of opinion, however, that when a cloud, well charged positively, passes near the earth, it repels and forces down into the earth, that natural portion of electricity, which exists near its surface, and in buildings, trees, &c. so as actually to reduce them to a negative state before it strikes them. I am of opinion too, that the negative state in which you have frequently found the balls, which are suspended from your apparatus, is not always occasioned by clouds in a negative state; but more commonly by clouds positively electrified, which have passed over them, and which in their passage have repelled and driven off a part of the electrical matter, which naturally existed in the apparatus; so that what remained after the passing of the clouds, diffusing itself uniformly through the apparatus, the whole became reduced to a negative state.

I am nevertheless fully convinced, that there are negative clouds; because they sometimes absorb, through the medium of the apparatus, the positive electricity of a large jar, the hundredth part of which the apparatus itself would have not been able to receive or contain at once. In fact, it is not difficult to conceive, that a large cloud, highly charged positively, may reduce smaller clouds to a negative state, when it passes above or near them, by forcing a part of their natural portion of the fluid either to their inferior surfaces, whence it may strike into the earth, or to the opposite side, whence it may strike into the adjacent clouds; so that when the large If you have read my experiments made in cloud has passed off to a distance, the small continuation of those of Mr. Canton, you will clouds shall remain in a negative state, exreadily understand this; but you may easily actly like the apparatus; the former (like the make a few experiments, which will clearly latter) being frequently insulated bodies, havdemonstrate it. Let a common glass be warm- ing communication neither with the earth nor ed before the fire that it may continue very with other clouds. Upon the same principle dry for some time; set it upon a table, and it may easily be conceived, in what manner place upon it the small box made use of by a large negative cloud may render others poMr. Canton, so that the balls may hang a lit-sitive. tle beyond the edge of the table. Rub ano- The experiment which you mention, of ther glass, which has previously been warm- filling your glass, is analogous to one which ed in a similar manner, with a piece of black I made in 1751 or 1752. I had supposed in silk or silk handkerchief, in order to electrify my preceding letters, that the pores of glass it. Hold then the glass above the little box, were smaller in the interior parts than near

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the surface, and that on this account they prevented the passage of the electrical fluid. To prove whether this was actually the case or not, I ground one of my phials in a part where it was extremely thin, grinding it considerably beyond the middle, and very near to the opposite superfices, as I found, upon breaking it after the experiment. It was charged nevertheless after being ground, equally well as before, which convinced me, that my hypothesis on this subject was erroneous. It is difficult to conceive where the immense superfluous quantity of electricity on the charged side of a glass is deposited.

I send you my paper concerning meteors, which was lately published here in the Philosophical Transactions, immediately after a paper by Mr. Hamilton on the same subject. B. FRANKLIŃ.

plate touches the upper part of the fish, with a metal rod: then observe, if the force of the shock be the same as to all the persons forming the circle, or is stronger than before.

Repeat this experiment with this difference: let two or three of the persons forming the circle, instead of holding by the hand, hold each an uncharged electrical bottle, so that the little balls at the end of the wires may touch, and observe, after the shock, if these wires will attract and repel light bodies, and if a ball of cork, suspended by a long silk string between the wires, a little distance from the bottles, will be alternately attracted and repelled by them.

To M. Dubourg,

On the Analogy between Magnetism and Electricity.

LONDON, March 10, 1773.

As to the magnetism, which seems pro

Mode of ascertaining, whether the Power, giving a Shock to those who touch either the Surinam Eel, or the Torpedo, be elec-duced by electricity, my real opinion is, that these two powers of nature have no affinity with each other, and that the apparent production of magnetism is purely accidental. The matter may be explained thus:

trical.

1. Touch the fish with a stick of dry sealing-wax, or a glass rod, and observe if the shock be communicated by means of those bodies.

1

Touch the same fish with an iron, or other

metalline rod.

If the shock be communicated by the latter body, and not by the others, it is probably not the mechanical effect, as has been supposed, of some muscular action in the fish, but of a subtle fluid, in this respect analogous at least to the electric fluid.

2. Observe farther, whether the shock can be conveyed without the metal being actually in contact with the fish, and if it can, whether, in the space between, any light appear, and a slight noise or crackling be heard.

If so, these also are properties common to the electric fluid.

3. Lastly, touch the fish with the wire of a small Leyden bottle, and if the shock can be received across, observe whether the wire will attract and repel light bodies, and you feel a shock, while holding the bottle in one hand, and touching the wire with the other.

If so, the fluid, capable of producing such effects, seems to have all the known properties of the electric fluid.

Addition, 12th of August, 1772, In consequence of the Experiments and Discoveries made in France by Mr. Walsh, and communicated by him to Dr. Franklin.

Let several persons, standing on the floor, hold hands, and let one of them touch the fish, so as to receive a shock. If the shock be felt by all, place the fish flat on a plate of metal, and let one of the persons holding hands touch his plate, while the person farthest from the

1st, The earth is a great magnet.

2dly, There is a subtle fluid, called the magnetic fluid, which exists in all ferruginous bodies, equally attracted by all their parts, and equally diffused through their whole substance; at least where the equilibrium is not disturbed by a power superior to the attraction of the iron.

3dly, This natural quantity of the magnetic fluid, which is contained in a given piece of iron, may be put in motion so as to be more rarefied in one part and more condensed in another; but it cannot be withdrawn by any force that we are yet made acquainted with, so as to leave the whole in a negative state, at least relatively to its natural quantity; neither can it be introduced so as to put the iron into a positive state, or render it plus. In this respect, therefore, magnetism differs from electricity.

4thly, A piece of soft iron allows the magnetic fluid which it contains to be put in motion by a moderate force, so that being placed in a line with the magnetic pole of the earth, it immediately acquires the properties of a magnet; its magnetic fluid being drawn or forced from one extremity to the other; and this effect continues as long as it remains in the same position, one of its extremities becoming positively magnetised, and the other negatively. This temporary magnetism ceases as soon as the iron is turned east and west, the fluid immediately diffusing itself equally through the whole iron, as in its natural state.

5thly, The magnetic fluid in hard iron, or steel, is put in motion with more difficulty,

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