by a succession of bubbles, till the spirit is above it. From the foot of this rod, a wire (the thickness of a goose-quill) came through a covered glass tube in the roof, and down through the well of the staircase; the lower end connected with the iron spear of a pump. On the staircase opposite to my chamber door, the wire was divided; the ends separated about six inches, a little bell on each end; and between the bells a little brass ball suspended by a silk thread, to play between and strike the bells when clouds passed with electricity in them. After having frequently drawn sparks and charged bottles from the bell of the upper wire, I was one night awaked by loud cracks on the staircase. Starting up and opening the door, I perceived that the brass ball instead of vibrating as usual between the bells, was repelled and kept at a distance from both; while the fire passed sometimes in very large quick cracks from bell to bell; and sometimes in a continued dense white stream, seemingly as large as my finger, whereby the whole staircase was enlighted as with sunshine, so that one might see to pick up a pin.* And from the Experiments, Observations, and Facts, tending to support the Opinion of the utility but conceive that a number of such conducapparent quantity thus discharged, I cannot of long pointed Rods, for securing Build-tors must considerably lessen that of any apings from Damage by Strokes of Light-proaching cloud, before it comes so near as to ning. Read at the committee appointed deliver its contents in a general stroke:—an to consider the erection of conductors to effect not to be expected from bars unpointsecure the magazines at Purfleet, Aug. 27, ed; if the above experiment with the blunt end of the wire is deemed pertinent to the case. 1772. B. FRANKLIN. EXPERIMENT I. THE prime conductor of an electric machine, A, B (See the plate) being supported about 10 inches and a half above the table by a wax-stand, and under it erected a pointed wire 7 inches and a half high, and one fifth of an inch thick, and tapering to a sharp point, and communicating with the table; when the point (being uppermost) is covered by the end of a finger, the conductor may be full charged, and the electrometer, c, (Mr. Henley's) will rise to the height indicating a full charge: but the moment the point is uncovered, the ball of the electrometer drops, showing the prime conductor to be instantly discharged and nearly emptied of its electricity. Turn the wire its blunt end upwards (which represents an unpointed bar) and no such effect follows, the electrometer remain ing at its usual height when the prime conductor is charged. OBSERVATION. What quantity of lightning, a high pointed rod well communicating with the earth may be expected to discharge from the clouds silently in a short time, is yet unknown; but I have reason from a particular fact to think it may at some times be very great. In Philadelphia I had such a rod fixed to the top of my chimney, and extending about nine feet EXPERIMENT II. The pointed wire under the prime conductor continuing of the same height, pinch it between the thumb and finger near the top, so as just to conceal the point; then turning the globe, the electrometer will rise and mark the full charge. Slip the fingers down so as to discover about half an inch of the wire, then another half inch, and then another; at every one of these motions discovering more and more of the pointed wire; you will see the electrometer fall quick and proportionably, stopping when you stop. If you slip down the whole distance at once, the ball falls instantly down to the stem. OBSERVATION. From this experiment it seems that a greater effect in drawing off the lightning * Mr. de Romas saw still greater quantities of lightning brought down by the wire of his kite. He had "explosions from it, the noise of which greatly resembled that of thunder, and were heard (from without) into the heart of the city, notwithstanding the various noises there. The fire seen at the instant of the explosion from the clouds may be expected from long | conductor therefore shows, that a quantity of pointed rods, than from short ones; I mean from such as show the greatest length, above the building they are fixed on. EXPERIMENT III. Instead of pinching the point between the thumb and finger, as in the last experiment, keep the thumb and finger each at near an inch distance from it, but at the same height, the point between them. In this situation, though the point is fairly exposed to the prime conductor, it has little or no effect; the electrometer rises to the height of a full charge. But the moment the fingers are taken away, the ball falls quick to the stem. OBSERVATION. To explain this, it is supposed, that one reason of the sudden effect produced by a long naked pointed wire is, that (by the repulsive power of the positive charge in the prime conductor) the natural quantity of electricity contained in the pointed wire is driven down into the earth, and the point of the wire made strongly negative; whence it attracts the electricity of the prime conductor more strongly than bodies in their natural state would do; the small quantity of common matter in the point, not being able by its attractive force to retain its natural quantity of the electric fluid, against the force of that repulsion. But the finger and thumb being substantial and blunt bodies, though as near the prime conductor, hold up better their own natural quantity against the force of that repulsion; and so, continuing nearly in their natural state, they jointly operate on the electric fluid in the point, opposing its descent and aiding the point to retain it; contrary to the repelling power of the prime conductor, which would drive it down.-And this may also serve to explain the different powers of the point in the preceding experiment, on the slipping down the finger and thumb to different dis tances. Hence is collected, that a pointed rod erected between two tall chimnies, and very little higher (an instance of which I have seen) cannot have so good an effect, as if it had been erected on one of the chimnies, its whole length above it. EXPERIMENT IV If, instead of a long pointed wire, a large solid body (to represent a building without a point) be brought under and as near the prime conductor, when charged; the ball of the electrometer will fall a little; and on taking away the large body, will rise again. OBSERVATION. Its rising again shows that the prime conductor lost little or none of its electric charge, as it had done through the point: the falling of the ball while the large body was under the VOL II.... 2 S its atmosphere was drawn from the end where the electrometer is placed to the part immediately over the large body, and there accumulated ready to strike into it with its whole undiminished force, as soon as within the striking distance; and, were the prime conductor moveable like a cloud, it would approach the body by attraction till within that distance. The swift motion of clouds, as driven by the winds, probably prevents this happening so often as otherwise it might do: for, though parts of the cloud may stoop towards a building as they pass, in consequence of such attraction, yet they are carried forward beyond the striking distance, before they could by their descending come within it. EXPERIMENT V. Attach a small light lock of cotton to the underside of the prime conductor, so that it may hang down towards the pointed wire mentioned in the first experiment. Cover the point with your finger, and the globe being turned, the cotton will extend itself, stretching down towards the finger, as at a; but on uncovering the point, it instantly flies up to the prime conductor, as at b, and continues there as long as the point is uncovered. The moment you cover it again, the cotton flies down again, extending itself towards the finger; and the same happens in degree, if (instead of the finger) you use, uncovered, the blunt end of the wire uppermost. OBSERVATION. To explain this, it is supposed that the cotton, by its connexion with the prime conductor, receives from it a quantity of its electricity; which occasions its being attracted by the finger that remains still in nearly its natural state. But when a point is opposed to the cotton, its electricity is thereby taken from it, faster than it can at a distance be supplied with a fresh quantity from the conductor. Therefore being reduced nearer to the natural state, it is attracted up to the electrified prime conductor; rather than down, as before, to the finger. Supposing farther that the prime conductor represents a cloud charged with the electric fluid; the cotton, a ragged fragment of cloud (of which the underside of great thunderchimney or highest part of a building.-We clouds are seen to have many) the finger, a then may conceive that when such a cloud passes over a building, some one of its ragged by the chimney or other high part of the ediunder-hanging fragments may be drawn down fice; creating thereby a more easy communication between it and the great cloud.-But a long pointed rod being presented to this fragment, may occasion its receding, like the cotton, up to the great cloud; and thereby increase, instead of lessening the distance, su 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 power in the clouds of collecting it; yet an August 27, 1772. To Professor Landriani, Italy. the Utility of Electrical Conductors, which Own their conveying away all that may fall on their points. Indeed we have nothing to form a judgment by in this but past facts; and we know of no instance where complete conductor to the moist earth has been insufficient, 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 suf- the number of conductors much increased, Upon my return to this country, I found ficient to carry off the rain that falls on a square of 20 feet, because we never saw such buildings from lightning having demonstrated many proofs of their efficacy in preserving a pipe glutted by any shower; so we may their utility. Among other instances, my judge a conductor of an inch diameter, more than sufficient for any stroke of lightning that which occasioned the neighbours to run in to house was one day attacked by lightning, will fall on its point. It is true, that if another deluge should happen wherein the win-But no damage was done, and my family was give assistance, in case of its being on fire. dows of heaven are to be opened, such pipes only found a good deal frightened with the viomay be unequal to the falling quantity; and lence of the explosion. 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 formning 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. Rittenhouse, our astronomer, has inMr. Lane's electrometer, for limiting precise- formed me, that having observed with his ly the quantity of a shock that is to be administered in a medical view, may serve to within the field of his view, he has remarkexcellent telescope, many conductors that are nake this more easily intelligible. The dis-ed in various instances, that the points were charging knob does by a screw approach the melted in like manner. There is no example conductor to the distance intended, but there of a house, provided with a perfect conductremains 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 at-1777; the subject came again into violent agitation, traction 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 heen 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. *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 pointed one: the matter was referred in 1772, to the Dr. Franklin's opinion formed upon the spot, was for a Royal Society, and by them as usual, to a committee, who, after consultation, prescribed a method conformable to Dr. Franklin's theory. But a harmless stroke of lightning, having under particular circumstances, fallen upon one of the buildings and its apparatus in May and was again, referred to the society, and by the society again referred to a new committee, which committee 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 sician. It may be, too, that a few great strokes, have become common in this city. B. FRANKLIN. John Pringle, M. D. On the Effects of Electricity in Paralytic Cases. In compliance with your request, I send you the following account of what I can at present recollect relating to the effects of electricity in paralytic cases, which have fallen under my observation. as given in my method, may not be so proper 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 To try, at the request of a friend, whether was, to place the patient first in a chair, on amber finely powdered might be melted and an electric stool, and draw a number of large run together again by means of the electric strong sparks from all parts of the affected fluid, I took a piece of small glass tube, about limb or side. Then I fully charged two six- two inches and a half long, the bore about one gallon glass jars, each of which had about twelfth of an inch diameter, the glass itself three square feet of surface coated; and sent about the same thickness; I introduced into this the united shock of these through the affect- tube some powder of amber, and with two ed limb or limbs, repeating the stroke com- pieces of wire nearly fitting the bore, one inmonly three times each day. The first thing serted at one end, the other at the other, I observed, was an immediate greater sensible rammed the powder hard between them in warmth in the lame limbs that had received the middle of the tube, where it stuck fast, the stroke, than in the others; and the next and was in length about half an inch. Then morning the patients usually related, that leaving the wires in the tube, I made them they had in the night felt a pricking sensa- part of the electric circuit, and discharged tion in the flesh of the paralytic limbs; and through them three rows of my case of botwould sometimes show a number of small tles. The event was, that the glass was red spots, which they supposed were occasion- broke into very small pieces, and those dised by those prickings. The limbs, too, were persed with violence in all directions. As I found more capable of voluntary motion, and did not expect this, I had not, as in other exseemed to receive strength. A man, for in-periments, laid thick paper over the glass to stance, 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. Perhaps some permanent advantage might have been obtained, if the electric shocks had 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. 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 |