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yet not absolutely true, because they ought to flow with a uniform and uninterrupted motion; he therefore cautiously guards against critical remarks on it in the following paragraph:
"In this table, it was thought sufficient to use such exactness, as that thereby (in drawing the lineaments of the nautical planisphere) sensible error might be avoided. He that listeth to be more precise, may make the like table to decades, or tens of seconds, out of Joachimus Rheticus his Canon Magnus Triangulorum: notwithstanding the geometrician that desireth exact truth, cannot be so satisfied neither; for whose sake and further satisfaction, I thouht good to adjoin also this geometrical conceit of dividing a meridian of the nautical planisphere. Let the equinoctial and a meridian be drawn upon a globe: let the meridian, divided into degrees, minutes, seconds, &c. roll upon a straight line, beginning at the equinoctial, the globe swelling in the mean time in such sort, that the semi-diameter thereof may be always equal to the secant of the angle, or arch contained between the equinoctial and semidiameter insisting at right angles upon the foresaid straight line: the degrees, minutes, seconds, &c. of the meridian, noted in the straight line, as they come to touch the same, are the divisions of the meridian in the nautical planisphere : and this conceit of dividing the meridian of the nautical planisphere may satisfy the curious exactness of the geometrician; but for mechanical use, the table before mentioned may suffice."
I have carefully endeavoured, says Mr. M., not to mistake the true sense and meaning of Mr. West's proposition in any part of it; if I have not, I cannot pronounce what kind of chart may be formed from his tangent line being made the line of latitudes, or that meridian line on which the tangents are to determine the sections of their respective parallels: I shall only observe, that if the meridians be right lines, and parallel to each other, the rhumbs must be right lines also; but by this tangential projection, these will be deflected from their true bearings, or make the angles of the courses too great, unless some expedient be devised to accommodate this error; and if the rhumbs be not right lines, such chart will then be embarrassed with more difficulties in practice than Mr. Wright's.
XXI. Of a Species of Ophrys, supposed to be the Plant which is mentioned by Gronovius in the Flora Virginica, p. 185, under the Name of Ophrys scapo nudo foliis radicalibus ovato-oblongis, dimidii scapi longitudine.* By George Dionysius Ehret, F. R. S. p. 81.
The root of this plant, from which many fleshy fibres branch, is composed of
Ophrys lilifolia. Lin. ?
the foot stalks of the leaves, which envelope each other in such a manner, that they form a kind of bulbous root. From this bulb proceed two oval-shaped, nervous, smooth leaves, having nembraneous convolute petioli or footstalks. These encompass a triquetrous scapus, or a single stalk arising from the centre of this root, which produces many flowers of a singular construction. These flowers are supported by small pedunculi, or flower stalks, of a bloody-red colour, which swell into seed-vessels, having at their base an acute denticle. This very singular plant blowed, for the first time in England, in the year 1758, in the curious exotic garden of Mr. Peter Collinson; who received it from Mr. Bertram of Philadelphia.
Mr. Clayton has described a plant, in the Flora Virginica, page 185, under the name of " Bifolium scapo e medio duorum foliorum nudo, aphyllo, ad exortum tenui, paulatim versus apicem accrescente, sex vel septem capsulas sustinente: radice fibrosa carnosa viridi, foliis obvolutâ, humi jacente; fibras paucas emittente, cui radix anni superioris contigua et integumentis marcidis evoluta pellucida adhæret." This description seemingly corresponds with the present plant; but yet Mr. Clayton's character of the several parts of the flower is very different from those here observed; and though it may be thought to come near to an epidendrum, yet it is neither an epidendrum nor a bifolium. This plant, however, should be ranged among the first order of Linnæus's class of gynandria diandria, which consists of several genera.
XXII. New Experiments in Electricity: In a Letter from Mr. Ebenezer Kinnersley, to B. Franklin, LL.D., F. R. S. Dated Philadelphia, Mar. 12, 1761. p. 84.
Exp. 1. Mr. K. placed himself on an electric stand, and, being well electrized, threw his hat to an unelectrized person, at a considerable distance, on another stand; and found that the hat carried some of the electricity with it; for, on going immediately to the person who received it, and holding a flaxen thread near him, he was found electrized sufficiently to attract the thread.
Exp. 2. He then suspended, by silk, a broad plate of metal, and electrized some boiling water under it, at about 4 feet distance, expecting that the which ascended plentifully to the plate, would, on the principle of the foregoing experiment, carry up some of the electricity with it; but was at length fully convinced, by several repeated trials, that it left all its share of it
Exp. 3. He put boiling water into a coated Florence flask, and found that the heat so enlarged the pores of the glass, that it could not be charged. The electricity passed through as readily, to all appearance, as through metal; the charge of a three-pint bottle went freely through without injuring the flask in
theleast. When it became almost cold, he could charge it as usual. Would not this experiment convince the Abbé Nollet of his egregious mistake? For, while the electricity went fairly through the glass, as he contends it always does, the glass could not be charged at all.
Exp. 4. He took a slender piece of cedar, about 18 inches long, fixed a brass cap in the middle, thrust a pin horizontally and at right angles, through each end, (the points in contrary directions) and hung it, nicely balanced like the needle of a compass, on a pin about 6 inches long, fixed in the centre of an electric stand. Then electrizing the stand, he had the pleasure of seeing what he expected; the wooden needle turned round, carrying the pins with their heads foremost. He then electrized the stand negatively, expecting the needle to turn the contrary way; but was extremely disappointed, for it went still the same way as before.
After the above experiments with the wooden needle, he formed a cross of 2 pieces of wood of equal length, intersecting each other at right angles in the middle; hung it, horizontally, on a central pin, and set a light horse, with his rider, on each extremity; on which the whole being nicely balanced, and each courser urged on by an electrized point, instead of a pair of spurs, he was entertained with an electrical horse-race,
Exp. 5. Let a person in the negative state, out of doors, in the dark, when the air is dry, hold, with his arm extended, a long sharp needle, pointing upwards; and he will soon be convinced that electricity may be drawn out of the air; not very plentifully, for being a bad conductor, it seems loth to part with it; but yet some will evidently be collected. The air near the person's body having less than its natural quantity, will have none to spare; but, his arm being extended as above, some will be collected from the remoter air, and will appear luminous as it converges to the point of the needle. Let a person electrized negatively present the point of a needle, horizontally, to a cork ball suspended by silk, and the ball will be attracted towards the point, till it has parted with so much of its natural quantity of electricity as to be in the negative state, in the same degree with the person who holds the needle: then it will recede. from the point; being it seems attracted the contrary way by the electricity of greater density in the air behind it.
Exp. 6. He set the thermometer on an electric stand, and kept it well electrized a considerable time; but this produced no sensible effect, Which shows that the electric fire, when in a state of rest, has no more heat than the air and other matter in which it resides.
Exp. 7. A large charge of electricity sent through wires in contact, even that of a case of 35 bottles, containing above 30 square feet of coated glass, will
produce no rarefaction of the air included in a tube. wires are not heated by the fires passing through them.
Which shows that the
Exp. 8. When the wires are about 2 inches apart, the charge of a threepint bottle darting from one to the other, rarefies the air very evidently. Which shows that the electric fire must produce heat in itself, as well as in the air, by its rapid motion. The charge of the case of bottles sent through the brass wire consumed great part of it into smoke. The thermometer appeared quite opaque with it.
Exp. 9. He suspended a piece of brass wire, about 24 inches long, with a pound weight at the lower end; and, by sending the 'charge of the case of bottles through it, discovered a new method of wire-drawing. The wire was red hot, the whole length well anealed, and above an inch longer than before. A 2d charge melted it; it parted near the middle, and measured when the ends were put together, 4 inches longer than at first.
Exp. 10. That he might have no doubt of the wire's being hot as well as red, he repeated the experiment on another piece of the same wire, encompassed with a goose-quill filled with loose grains of gunpowder; which took fire as readily as if it had been touched with a red hot poker. Also tinder, tied to another piece of the wire, kindled by it. He tried a wire about twice as thick, but could produce no such effects as that. Hence it appears, that the electric fire, though it has no sensible heat when in a state of rest, will, by its violent motion, and the resistance it meets with, produce heat in other bodies when passing through them, provided they be small enough. A large quantity will pass through a large wire without producing any sensible heat; when the same quantity passing through a very small one, being there confined to a narrower passage, the particles crowding closer together, and meeting with greater resistance, will make it red hot, and even melt it. And hence lightning does not melt metal by a cold fusion, as we formerly supposed. But when it passes through the blade of a sword, if the quantity be not very great, it may heat the point so as to melt it, while the broadest and thickest part may not be sensibly warmer than before. And when trees or houses are set on fire by the dreadful quantity which a cloud, or the earth sometimes discharges, must not the heat by which the wood is first kindled, be generated by the lightning's violent motion through the resisting combustible matter.
Mr. K. then adds a dissertation, showing, from experience, the usefulness of pointed conductors to houses, in securing them from a stroke of lightning.
XXIII. Observations on Electricity, and on a Thunder-storm. By Mr. Torbern Bergman, F. R. S. Acad. Reg. Upsal. Soc. From the Latin, p. 97. With regard to the electrical experiments with island crystal, given by Mr. Delaval, in the Philos. Trans., vol. 52, p. 355, Mr. B. here states, that after often repeating those experiments, he always found a contrary result. Thus, he exposed various pieces of this crystal to 12 degrees of cold of the Swedish thermometer, filled with quicksilver, being the degrees of cold below the freezing point of water, of which there are 100 between the freezing and boiling points of water. He then rubbed it after the space of some hours, but without producing any except a very small degree of electricity. Next day he repeated the experiment with a greater degree of cold, but with still less success. He next heated a small piece, hoping thus to eradicate its whole force; but unexpectedly he found its electric virtue not at all destroyed, but much increased. This being found to be the case with all the specimens he could collect, he suspects there are different kinds of this crystal, endued with such different properties. And indeed Mr. Delaval had said as much in his paper.
The thunder-storm happened at Upsal, Aug. 24, 1760; but there is nothing very remarkable in the account.
XXIV. Remarks on Swallows on the Rhine: in a Letter from Mr. Achard, in Privy-Garden, to Mr. Peter Collinson, F.R. S. p. 101.
In the latter end of March I took my passage down the Rhine to Rotterdam: a little below Basil the south bank of the river was very high and steep, of a sandy soil, 60 or 80 feet above the water. I was surprized at seeing near the top of the cliff, some boys, tied with ropes, hanging down, and searching, as we were informed, the holes in the cliff for swallows, or martins, which took refuge in them, and lodged there all the winter, until warm weather, and then they came abroad again.
The boys being let down by their comrades to the holes, put in a long rammer with a screw at the end, as is used to unload guns, and, twisting it about, drew out the birds. For a trifle I procured some of them. When I first had them they seemed stiff and lifeless. I put one in my bosom, between my skin and shirt, and laid another on a board, the sun shining full and warm upon it. That in my bosom revived in about of an hour; feeling it move, I took it out to look at it, and saw it stretch itself on my hand, but perceiving it not sufficiently come to itself, I put it in again: in about another quarter, feeling it flutter pretty briskly, I took it out and admired it. Being now perfectly recovered, before I was aware, it took its flight, but the covering of the boat prevented me from seeing where it went: the bird on the board, though exposed to 4X