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dent; and he further observes, that all needles constructed after this manner are liable to be rendered useless, not only by the lightning's destroying their virtue, but also by its placing it in a particular direction ; ex. gr. if the lightning struck the needle in the direction of either of the two parallel sides of the lozenge, it must strike the other two sides very obliquely; by which the first two sides may have their polarity destroyed, and a very strong one given them in the contrary direction ; while that of the other sides, if it be inverted, will be very weak; but it is probable that the virtue would be placed obliquely in the direction of the stroke ; in either case, these two sides can contribute but very little, if any thing, in directing the card ; and if the first two sides only be ca. pable of acting on it, it will point in the direction of those sides, which will produce a variation of about four points.
It may further be observed that a needle would not continue long in this state, but would every day grow more regular; because if the virtue be placed obliquely, it generally turns itself in the di. rection of any piece of steel that is long and slender; and that may be the reason why this card is now become regular, except that it is inverted.
The wires that join the box seem weaker than when first exa. mined ; which makes it very probable that they might be rastly stronger when first struck with the lightning; and the same may be likewise true, in regard to the nails in the binacle; which may account for the experiments not answering exactly the same as at first.
From what has been said it appears, that this form of needles is very improper, and ought to be changed for that of one straight piece of steel ; and then if a needle should be inverted, it might still be used. It also she ws the absurdity of permitting iron of any kind about the compass.box, or the binacle. Whoever considers the whole description here given of this compass, will esteem it a most despicable instrument; how then must any one be shocked to hear, that almost all the compasses, made use of by our trading vessels are of the same sort! the boxes all joined with iron wire, and the same degree of inaccuracy observed throughout the whole !
Death of Professor Richman by Lightning, with Observations
on the same.
1. Extract of a Letter from John Lining, M.D. of Charlestown, South Caro
lina, to Charles Pinkney, Esq. London, with bis Answer to several Queries sent to him concerning his Experiment of Electricity with a Kite *. Dated Charlestown, January 14, 1754.
INCLOSED are answers to the queries sent me concerning the experiment with the kite. Since making that experiment last May, I have not had an opportunity of making any more, having been confined all the summer and autumn with the gout, which perhaps prevented my meeting with the same unhappy fate with Professor Richman of Petersburg. It appears that the professor had a wire, which came down from the iron rod, erected on his house, through the gallery-ceiling, to an iron bar, which stood in a glass vessel, filled with water and filings of brass ; and that the professor stood so near that iron rod, that his face was within a foot of it. Now if there was no wire that went from that iron rod, or from any part . of the wire above it, into the earth, it is no great wonder that the professor was killed. I should be extremely glad to be informed, whether the iron rod on his house, at the time the experiment was made, bad any communication, by means of metal, with the earth. For if it had, there is then more danger attending these experi. ments than I imagined. It is likewise said in the account, that from the electrical needle, which he observed, there was no danger. I am at a loss to know what that electrical needle was, and should be glad to be informed. I know that a magnetic needle placed on a sharp point on the prime conductor, as soon as the conductor is sufficiently electrified, will move round with so great rapidity, that in the dark the electricity, thrown off from both poles of the needle, will appear like a circle of fire.
Answers of Dr. Lining to the Queries sent to him. Query 1. In what manner, and of what materials, was your
* See on Dr. Franklin's electrical kite, sec. II. of this chapter, VOL. IV.
kite, and the string by which you flew it, made and to what height did it rise above the earth?
Answer. The kite, which I used, was made in the common way; only, instead of paper, I covered it with a silk, called alamode. The line was a common small hempen one of three strands. A silk line, except it had been kept continually wet, would not con. duct the electricity; and a wire, besides other inconveniencies, would have been too heavy. I had not any instrument to take the height of the kite; but believe it was at least 250 feet high. It was flown in the day-time.
Query 2.-You say also, “ All the electrical fluid, or light. ning, was drawn from the cloud, and discharged in the air ; and a greater degree of serenity succeeded, and no more of the awful noise of thunder, before expected, was heard.” Now I should be glad you would inform us, whether the serenity in the air was such, as generally follows, after the clouds in the summer thunder. storms bave discharged several loud thunder-claps; and whether any flashes of lightning appeared in the skies, after you had discharged the cloud of its lightning by the kite, as commonly do after a thunder-storm is over in a summer's night? for if there were no appearance of such flashes, then I think your assertion, that all the electric fluid, or lightning, was drawn from the cloud, stands full proved; but if there were such flashes after, I con. ceive there must have been some of the electrical matter left behind.
Answer.-During the time of my drawing the lightning from the cloud, and for some little time afterward, it rained; by which means, the body of the cloud being diminished, a greater degree of serenity necessarily succeeded; and the quantity of lightning ertracted from the cloud, or rather its atmosphere, proved sufficient to prevent any thunder in town that afternoon; though there was a great appearance of thunder before the kite was raised. But whether the same serenity succeeded, as frequently happens after a thunder-storm, and whether there were any flashes of lightning seen in the evening, I cannot now recollect. If such flashes had after. wards been seen in the skies, as is common in a summer's evening, especially after a thunder-storm, those might proceed from other clouds, wbich had passed the town, at too great a distance to be acted on by the kite.
Electrified clouds have an electrical atmosphere, as well as the prime conductor, when it is electrified; and the diameter of that atmosphere, cæteris paribus, will bear some proportion to the size of the cloud. My smallest prime conductor is 2 inches diame. ter; and when it is fully charged, its atmosphere extends to the distance of about three feet from the surface of the conductor. How great then must the extent be of the atmosphere, which sur. rounds a large cloud fully electrified? It perhaps may extend to many hundreds of feet round the cloud, and may even reach so low as to touch the surface of the earth : and when that is the case, a man, or a rod of metal, placed on a cake of resin on the ground, may be electrified, and yield sparks of fire. When a sharp point is presented to that atmosphere, it cannot deprive the cloud of its whole quantity of electricity, except the sharp point be so near, that the cloud may explode upon it; and in that case the cloud must have a communication with the ground, by means of some non-electric body. Suppose an electrified cloud to have an atmos. phere, which extends round it to the distance of ninety feet from its surface; and let that atmosphere be divided into three parts, A, B, and C, each thirty feet in diameter: now, if a sharp metalline point erected on a kite, or otherwise, be placed either vertically or horizontally in the most interior part of the atmosphere C, that point will continue to act till a quantity of the lightning is drawn off, equal to the quantity contained in that atmosphere, and no longer. For then the semidiameter of the atmosphere being reduced to 60 feet, every part of it is above, and not in contact with the sharpupoint, and consequently beyond its sphere of action. But let the sharp point be then advanced into the atmosphere B, and it will act as before, &c.
The truth of this, however contradictory it may be, to the general opinion of the action of sharp points, in drawing off the electricity or lightning*, may be illustrated by the following experi. ments on the prime conductor. Electrify the prime conductor in a dark room, and draw back the globe to a sufficient distance from the prime-conductor, to prevent its being supplied with any more electricity from the globe, while you are taking off the elec
* Mr. Franklin says, speaking of sharp points, “ At whatever distance you see the light, you may draw off the electrical fire,” page 2.-Orig.
trical atmosphere with a sharp point. Bring then a sharp point, either vertically or horizontally, or in any other direction, within two feet of the prime conductor; and the point, for some time, will appear luminous. After that light disappears advance the point three or four inches nearer to the conductor, and you will observe the same phenomena as before; and by advancing the point gradually in this manner, as the light on it disappears, the point will be alternately luminous and dark, till you have taken off the whole atmosphere in different lamina. As the point appears more and more luminous, the nearer that it approaches the prime-con. ductor, the electrical atmosphere may have different degrees of density, being perhaps denser near the prime-conductor, and rar. er at a greater distance from it. If a phial be charged on the prime-conductor, when this experiment is made, the light on the sharp point will be much greater, and continue longer.
Query 3.-Did you make any trial at what distance you could kill an animal, with a discharge of the electrical fluid from the key or the bottle suspended to it?
Answer.-I have not hitherto had an opportunity of making any such experiment with the kite. But as to the first, I appre. hend, that no animal could be killed by the discharge of any quantity of electricity accumulated on the key; as the key in that experiment answers the same end as the prime conductor ; and, like it, is capable of receiving only a certain charge of electricity, except the lightning flows down the line too fast, or the kite be so near the cloud that it may explode, when one standing on the ground approaches the key to draw sparks from it: but such an explosion would probably be fatal to the operator. When a phial is suspended to the key, after it has received its charge, if you let it continue hanging on the key, the surcharge will fly off from the hook of the phial, and the phial, when charged in that manner, will not give a greater shock than if it had been charged in the common way with the globe.