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which he writ to Dr. Lister*, tells him, that he had been informed by a friend, that some spiders threw ont, or darted, their webs from them to a considerable distance obliquely, and not strait downwards; adding, he could not conceive how that could be done, seeing their threads are very fine and soft, and not stiff like a stick. To this Dr. Lister answerst, that in the foregoing September, being a spider hunting, he first observed the urantu volucris, or flying spider, and took notice, that she turned up her tail to the wind, and darted forth a thread several yards long: the Dr's. original here is expressed by a comical simile, that is, Filumque ejaculata est quo plane modo robustissimus juvenis e distentissima vesica urinam, and this he saw afterwards confirmed by many like examples.
Some time after this, Mr. Ray informed Dr. Lister, that though he was pleased with the potices that he had given him concerning the flying spiders, he himself never doubted, but those fine cobwebs, that are seen floating in the air, were the work of spiders; and adds, that the Royal Society had received letters from the island of Bermudas, which declare, that the webs of their spiders are of a sufficient thickness and strength to entangle thrushes. But Dr. Lister, when he had read those letters from Bermudas, thought iti ridiculous to suppose (as was intimated therein) that their threads were darted from their mouths; for, according to his observations, they were ejected from the anus, and he seems to disbelieve the story of the thrushes. He says, moreover, that he is certain these tiying spiders do not traverse the expanse merely for their pleasure, but to catch gnats, and other small flies, of which there are incredible quantities in autumn in the open air. And, in another letter which Dr. Lister sent Mr. Ray, dated York, Jan. 20, 1670, be acquaints him, that, in the foregoing October, on a day when the sky was very calm and serene, he mounted to the top of the highest steeple in the Minster, and could thence discern flying spiders with their webs exceedingly high above him.
Now, though this full discovery of the flying spiders, and their operations, seems to belong to Dr. Lister, yet Dr. Hulse was the first who gave the hint to Mr. Ray of the manner of spiders shooting their threads. These observations, however, made by Dr. Lister, make it plain, I think, that the Gossamer is formed by those spiders, at a vast height in the air; and that, when it is very much rarified, or the dew falls upon their threads, they descend to the ground, or fall upon bushes, in the manner I mentioned above. Yet there remains one difficulty, which I shall be glad to see resolved, and that is, where those miilions of spiders are bred; whether they deposit their eggs on earth, or in water, or on trees, from whence they can mount to such a height in the air, to feed upon little nies, as Dr. Lister observes, that affords them such a glutinous matter for the formation of their webs, which have that sticking quality. Conjectures, in an affair of this nature, are by no means satisfactory, and I have met with no esperimental observations upon their origin.
* See Ray's Letters, p. 34.
+ P. 36--T,
I am of opinion likewise, that this phenomenon was not known to, or at least is not described by any of the Greek and Roman naturalists. I know of no name for it in either of those languages. And those, who derive Gossamer from Gossipium, are led into that inistake, I believe, from the sinilitude of the sound; one being the produce of a shrub, and the other the work of spiders. I rather take Gossamer to be of a British or Saxon original. I observe, indeed, that Mr. Dryden makes use of that word, in his translation of a passage in Virgil's first Georgic, v. 397; 'but I think he is manifestly mistaken in the thing. Virgil says,
Tenuia nec luna per cælum veltera ferri. Doubtless meaning thereby fine fleecy clouds, according to the concurrent opinion of the commentators upon that place. This Mr. Dryden incautiously renders thus;
The filmy Gossamer now flits no more. That the Gossamer was not unknown in Chaucer's time, appears from the following lines, in his Squier's Tale:
As sore wondren some on cause of thunder,
By which Chancer seems to intimate, that some naturalists, in or before his time, had assigned the cause of the Gossamer as well as of thunder, and of the flux and reflux of the sea; but what they made that cause is a doubt.
The fine contexture and appearance of the Gossamer in the air is humourously described by Shakespeare, in his Romeo and Juliet, in these words:
A lover may bestride the Gossamour,
And yet not fall, so light is vanity. Lastly, I have not observed that this curious phenomenon has been taken notice of by any of those writers, who have given us the natural history of our counties in English, which I the more wonder at, as Dr. Plot, and some others, are very circumstantial in articles of less curiosity, and perhaps of less service, because the country people have a notion, that it is injurious to their cattle, being licked up in their feeding in the lattermaths, which is a thing worthy of a further inquiry 1759, Aug.
XXIX. On the Influx of Water into the Mediterranean.
NAVIGATORS unanimously attest, that in the straits of Gibraltar, between Cape Trafalgar and Cape Spartel, a strong current carries the water of the Atlantic, or Spanish sea into the Mediterranean. This current, which is not at all times equally strong, is perceived in the Mediterranean at the distance of 20 English miles from the Straits towards the coast of Malaga. Some assure us that they have observed it at the distance of 70 miles near Cape Gaeta.
The existence of this current is confirmed by the chart of the Strait, published in 1700, by M. d'Ablancourt, who observes, that the constancy of the current is such in the middle of the Strait, that the tides make no variation in it; but that towards the two sides the water follows the ordinary laws of the flux and reflux in the 24 hours. This chart is the more to be depended upon as it was drawn by order of the king of Portugal, from careful observations made by the most able and experienced engineers and mariners.
Hudson adds, in the Philosophical Transactions, that in the middle of the Strait, which is about five English miles over, the current is carried towards the Mediterranean with such rapidity, that it runs at the rate of two miles an hour, and is so deep, that the longest line of a ship of war cannot reach the bottom of it. Other relations inform us that the strength of this current will carry a ship into the Mediterranean against the wind, if it be not very high. A few years ago a cele. brated admiral confirmed this fact by his own experience. But he found, at the same time, that the upper part of the water in the Strait was indeed always carried into the Mediterranean; but that the water at bottom had a directly opposite direction, and ran from the Mediterranean into the Atlantic
As the Mediterranean has no other sensible issue, but by the Straits of Gibraltar, and that, instead of emptying its water by this issue, it on the contrary, continually receives fresh supplies by it, an embarrassing problem arises. Either the Mediterranean runs off by some unknown passage; or the water it receives is carried off by some secret power in nature,
Mr. Kuhn adheres to the first of these opinions, and, in his treatise of the origin of springs, endeavours to prove that the Mediterranean hath a subterraneous gulph, by which its redundant water is discharged. But this supposition is confuted by facts; since it would be impossible for the water to run in with the rapidity we have just mentioned, if the Atlantic were not higher than the Mediterranean. If the two seas were of equal height, and the water of equal gravity, no reason could be assigned for the invariable direction of the current, which,' according to the laws of hydrostatics, demonstrates that the Atlantic is the highest, consequently no water can run out of the Mediterranean into other seas by subterraneous channels, even supposing there were such; on the contrary, those seas would supply the Mediterranean till it should obtain the requisite height and gravity.
Nevertheless, not only the Atlantic discharges itself into this
sea, bụt also many great rivers run into it, to which must be added the water which falls in rain: as, therefore, its water cannot have any subterraneous issue, nature must employ some other method. Some naturalists have thought evaporation sufficient; and this opinion hath gained great probability since Mariotte proved that all the rain that falls annually is not sufficient to cover the globe of the earth to the height of eighteen or twenty inches; whereas the annual evaporation is about thirty or thirty-two inches.
Supposing then that the rain which falls annually in the Mediterranean, bears the same proportion to that which evaporates as at Paris, this sea would lose annually ten or twelve inches of water more than it receives. But what is carried to it by the Atlantic Ocean and by rivers much exceeds that quantity: And if we should even carry the evaporation much further, it would not account for the influs in a satisfactory manner; for we may admit that the water of the Mediterranean, being in a warmer climate than that of Paris, suffers an evaporation of twelve or fourteen inches
more, that is to say, the quantity evaporated exceeds the rain that falls by twenty-four inches. The length of this sea is about a thousand leagues, of twenty-five to the degree, and its mean breadth may be about an hundred of those leagues; so that we can determine pretty exactly its surface to be 100,000 square leagues. For the rivers, then, to repair the annual diminution occasioned by evaporation, they must furnish, besides what is supplied by rain, a surface of 100,000 square leagues, with water to the height of twentyfour inches. Now according to Marriotte, the river Seine, in France, furnishes annually water enough to cover 561 square leagues the height of twelve inches. Riccioli, in his Geography Reformed, says, that the quantity of water furnished by the Po is to that of the Seine as 264.to 1; so that it would cover annually, to the height of twelve inches, a surface of 14,586 square leagues; which is about the fourteenth part of the water required to repair the evaporation of the Mediterranean. It would then only remain that we should consider the other rivers which empty themselves into it, as amounting altogether to fourteen times as much as the Po. Now as Riccioli attributes to the Nile seventeen times more water than to the Po, the Nile alone would furnish five times more water than would be necessary to supply the decrease made by evaporation. Supposing therefore that Riccioli has made the quantity of water carried by rivers to this sea too much by one half, as Sedileau proves that he hath done, there will still remain enough to make up the deficiency by evaporation.
Let us suppose the breadth of the Straits of Gibraltar to be a league of 25 to the degree, and that the water runs one such league in one hour: instead of a bottomless depth, let us take a depth of 200 feet only; the Mediterranean will then receive annually by the Straits a quantity of water, of 3,723,000 square leagues, and 24 inches in height, which will raise it annually 741 feet. But as the velocity of the current is not at all times equal, and as it is only in the middle of the Straits that the water is constantly carried towards the Mediterranean, it being subject at each side to the flux and reflux; to which must be added, what we observed before, that the water beneath follows a contrary di-1 rection, and is carried towards the Atlantic; these circumstances will oblige us to make a considerable abatement in the quantity of water which runs through the Straits. However, we may venture to assert that the water which the Mediterranean receives annually by the Straits and by the Nile increases its height at least twenty feet.