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three in wooden boxes. The hanging compass in the cabin was not quite so much disabled as the rest ; they were at first very Dear reversed, the north to the south; and after a little while ram. bled about so as to be of no service. The storm lasted five days; they lost the mainmast and mizenmast, and almost all the sails; and arrived at Cowes the 21ts of January in a very shattered condition.
(Phil. Trans. 1749.
19. Examination of the preceding Mariner's Compass; and the Explanation of the Cause of its reversed polarity.
By Gowin Kuight, M.B. F.R.S. On examining the compass struck with lightning, it appeared that the outward case was joined together with pieces of iron wire, sir. teen of which were found in the sides of the box, and ten in the bottom. Mr. K. applied a small needle to each of these wires, and immediately perceived that the lightning had made them strongly magnetical ; particularly those that joined the sides. All the heads of the wires on one side of the box attracted the north point of the needle and repelled the south ; while all the heads on the other side attracted the south and repelled the north; the wires at the bottom attracted the south and repelled the north; but it is not certain whether this polarity was any wise owing to the lightning; since it might be acquired by their continuing long in an erect position.
On examining the card, he found the needle was vigorous enough in performing its vibrations, but that its polarity was inverted; the north point turning contrary to the south. He then tried to take out the card, to examine the state and structure of the needle : but the junctures, every where were well secured with putty, be. come so hard, that he was obliged to use some violence, and at last broke the glass. The needle consisted of two pieces of steel wire, each bent in the middle, so as to make an obtuse angle; and the ends of these wires applied together, forming an acute one, the whole appearing in the shape of a lozenge; in the centre of which was placed a brass cap on which the card turned. And so far was it from being made with any tolerable degree of exactness, that there was not the least care taken either to bend the wires in the middle, or to fix the cap exactly in the centre of the lozenge. The pin on which it turned, was made of a slip of plate brass, sharpened to a point.
Besides the particulars already communicated to the Society, the captain informed him, that he was obliged to sail above 300 leagues, after this accident happened, without a compass, till he arrived at Cowes in the Isle of Wight; where being provided with one, he placed it in the binacle, but was much surprised to find that it va. ried from the direction it stood at when out of the binacle nearly two points. He removed the binacle to different parts of the deck, but found that it always made the needle to vary after the same manner when placed in it. He repeated the same experiment lately, in the river, with the like success; only that he observed, that the variation of the needle, when placed in the binacle, was rather less than at first. It was natural to inquire if there was any iron about the binacle ; but the Captain said he had given strict charge to the maker not to put so much as a single nail in it; and that he firmly believed that there was not the least bit of iron about it.
Being willing to be satisfied of the truth of a circumstance so very extraordinary, the captain was desired to send the binacle to a house in the city ; where, in company with the Captain, Mr. Elli. cot, and another gentleman, Mr. K. tried it with a large compass touched by his bars; but finding no sensible variation, they at that time desisted, thinking the fact quite improbable; but having discovered the effect which the lightning had produced on the wires which fastened the sides of the compass box, he was induced to ex. amine the binacle a second time; which he did with a small compass, and with great care, in every part; and at last, about the middle of the binacie, he found it to vary very sensibly, but could not discover any nails or iron thereabouts ; till turning it up to ex• amine the bottom, he there found three or four large nails, or rather spikes, driven through it to fasten the upright partitions in the middle of the binacle,
It would not be difficult to explain why any needles, under such circumstances, should be rendered useless by lightning, though the needles themselves had remained unhurt. So many iron wires made strongly magnetical would doubtless have effected it; and three or four large nails in the binacle, if made magnetical, would alone have been sufficient to have done it. But it has always been noticed that the polarity of the needle was inverted by this acci.
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 direction 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 shews 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 his 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 mapper, 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 Auid, 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 dis. charged 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 er. tracted 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 filashes 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, which had passed the town, at too great a distance to be acted on by the kite.