Part 77

Such a prodigious effect of expansion, almost double that of the most powerful steam-engines, and exerted in so small a mass, seemingly by the force of cold, was thought a very material argument in favour of those who supposed that cold, like heat, is a positive substance. Dr. Black's discovery of latent heat, however, has afforded a very easy and natural explication of this phenomenon. He has shewn, that, in the act of congelation, water is not cooled more than it was before, but rather grows warmer: that as much heat is discharged and passes from a latent and a sensible state, as, had it been applied to water in its fluid state, would have heated it to 135°. In this process, the expansion is occasioned by a great number of minute bubbles suddenly produced. Formerly these were supposed to be cold in the abstract, and to be so subtile, that, insinuating themselves into the substances of the fluid, they augmented its bulk, at the same time that, by impeding the motion of its particles upon each other, they changed it from a fluid to a solid. But Dr. Black shews, that these are only air extricated during the congelation; and to the extrication of this air he ascribes the prodigious expansive force exerted by freezing water. The only question, therefore, is, by what means this air comes to be extricated, and to take up more room than it naturally does in the fluid? To this it may be answered, that perhaps part of the heat, which is discharged from the freezing water, combines with air in its unelastic state, and, by restoring its elasticity, gives it that extraordinary force; as is seen in the case of air suddenly extricated in the explosion of gunpowder. The degree of expansion of water, in the state of ice, is by some authors computed at one tenth of its volume. Oil and quicksilver shrink and contract after freezing. Mr. Boyle relates several experiments of vessels made of metals, very thick and strong; in which, when filled with water, closely stopped, and exposed to the cold, the water being expanded in freezing, and not finding either room or vent, burst the vessels. A strong barrel of a gun, with water in it, close stopped and frozen, was rent the whole length. Huygens, to try the force with which it expands, filled a cannon with it, whose sides were an inch thick, and then closed up the mouth and vent, so that none could escape; the whole being exposed to a strong freezing air, the water froze in about twelve hours, and burst the piece in two places. Hence mathematicians have computed the force of the ice upon this occasion; and they say, that such a force would equal twenty-seven thousand seven hundred and twenty pounds.

Major Edward Williams, of the Royal Artillery, made many experiments on the force of freezing water, at Quebec, in 1784-1785. He filled all sizes of bomb shells with water, then plugged the fuze-hole close up, and exposed them to the strong freezing air of the winter in that climate; sometimes driving in the iron plugs as hard as possible with a sledge hammer; and yet they were all thrown out by the sudden expansion of the water in the act of freezing, like a ball shot by gunpowder, sometimes to the distance of between four and five hundred feet, though they weighed near three pounds; and when the plugs were screwed in, or furnished with hooks or barbs to lay hold of the inside of the shell by, so that they could not possibly be forced out, in this case the shell was always split in two, though the thickness of the metal of the shell was about an inch and three-quarters. Through the circular crack, round about the shells, where they burst, there stood out a thin film or sheet of ice, like a fin; and in the cases where the plugs were projected by freezing water, there suddenly issued out from the fuze-hole a bolt of ice of the same diameter, and stood over it to the height sometimes of eight inches and a half.

CHAP. LXVII.

CURIOSITIES RESPECTING VARIOUS PHENOMENA, OR APPEARANCES IN NATURE.--(_Continued._)

_Water Spout--Fata Morgana--Fairy Rings--Sheet of Phosphoric Fire--Phosphorus._

Every object of creation Can furnish hints to contemplation. _Gay._

WATER SPOUT.--This extraordinary meteor is most frequently observed at sea. It generally begins by a cloud, which appears very small, and which is called, by sailors, the Squall. This augments in a little time into an enormous cloud of a cylindrical form, or that of a cone on its apex, and produces a noise like the roaring of an agitated sea, sometimes accompanied with thunder and lightning, and also large quantities of rain or hail, sufficient to inundate large vessels; and to carry away in their course, (when they occur by land,) trees, houses, and every thing that opposes their impetuosity. Sailors, dreading the fatal consequences of water-spouts, endeavour to dissipate them by firing a cannon into them just before they approach the ship. We shall give an account of one, as described by M. Tournefort, in his Voyage to the Levant.

"The first of these (says this traveller) that we saw, was about a musket-shot from our ship. There we perceived the water begin to boil, and to rise about a foot above its level. The water was agitated, and whitish; and above its surface there seemed to stand a smoke, such as might be imagined to come from wet straw before it begins to blaze. It made a sort of a murmuring sound, like that of a torrent heard at a distance, mixed, at the same time, with a hissing noise, like that of a serpent: shortly after we perceived a column of this smoke rise up to the clouds, at the same time whirling about with great rapidity. It appeared to be as thick as one's finger; and the former sound still continued. When this disappeared, after lasting for about eight minutes, upon turning to the opposite quarter of the sky, we perceived another, which began in the manner of the former; presently after, a third appeared in the west; and instantly beside it, still another arose. The most distant of these three could not be above a musket-shot from the ship. They all appeared like so many heaps of wet straw set on fire, and continued to smoke, and to make the same noise as before. We soon after perceived each, with its respective canal, mounting up in the clouds; and spreading, where it touched the cloud, like the mouth of a trumpet; making a figure (to express it intelligibly) as if the tail of an animal was pulled at one end by a weight. These canals were of a whitish colour, and so tinged, as I suppose, by the water which was contained in them; for, previous to this, they were apparently empty, and of the colour of transparent glass. These canals were not straight, but bent in some parts, and far from being perpendicular, by rising in their clouds with a very inclined ascent.

"But what is very remarkable, the spouts crossed each other, in the form of a St. Andrew's cross. In the beginning they were all about as thick as one's finger, except at the top, where they were broader, and two of them disappeared; but shortly after, the last of the three increased considerably, and its canal, which was at first so small, soon became as thick as a man's arm, then as his leg, and at last thicker than his whole body. We saw distinctly, through this transparent body, the water, which rose up with a kind of spiral motion; and it sometimes diminished a little of its thickness, and again resumed the same, sometimes widening at top, and sometimes at the bottom, exactly resembling a gut filled with water, pressed with the fingers to make the fluid rise or fall; and I am well convinced that this alteration in the spout was caused by the wind, which pressed the cloud, and compelled it to give up its contents. After some time its bulk was so diminished as to be no thicker than a man's arm again, and thus swelling and diminishing, it at last became very small. In the end, I observed the sea which was raised about it to resume its level by degrees, and the end of the canal that touched it to become as small as if it had been tied round with a cord; and this continued till the light, striking through the cloud, took away the view. I still, however, continued to look, expecting that its parts would join again, as I had before seen in one of the others, in which the spout was more than once broken, and yet the parts again came together; but I was disappointed, for the spout appeared no more."

In the Philosophical Transactions, (volume xxii. and xxiii.) we have descriptions of several of these phenomena: their effects, in some instances, are probably much exaggerated. One at Topsham is said to have cut down an apple-tree, several inches in diameter: another, we are told, seemed to be produced by a concourse of winds, turning like a screw, the clouds dropping into it: it threw trees and branches about with a gyratory motion.--One in Deeping Fen, Lincolnshire, was first seen moving across the land and water of the fen: it raised the dust, broke some gates, and destroyed a field of turnips: it vanished with an appearance of fire.--Dr. Franklin supposes that a vacuum is made by the rotatory motion of the ascending air, as when water is running through a funnel, and that the water of the sea is thus raised. But Dr. Young says, no such cause could do more than produce a slight rarefaction of the air, much less raise the water to the height of thirty or forty feet, or more.

Professor Wolke describes a water-spout, which passed immediately over the ship in which he was sailing, in the gulf of Finland: it appeared to be twenty-five feet in diameter, consisting of drops about the size of cherries. The sea was agitated round its base, through a space of about one hundred and thirty feet in diameter. One of the latest accounts of the phenomenon of a water-spout, is that read to the Royal Society in the year 1803, from a letter written to Sir Joseph Banks, by Captain Ricketts, of the royal navy. In the month of July, 1800, Captain Ricketts was called on deck, on account of the rapid approach of a water-spout, among the Lipari islands. It had the appearance of a viscid fluid, tapering in its descent, proceeding from the cloud to join the sea. It moved at the rate of about two miles an hour, with a loud sound of rain. It passed the stern of the ship, and wetted the afterpart of the main-sail: hence it was inferred, that water-spouts are not continuous columns of water; and subsequent observations confirmed the opinion. In November, 1801, about twenty miles from Trieste, a water-spout was seen eight miles to the south; round its lower extremity was a mist, about twelve feet high, somewhat in the form of an Ionian capital, with very large volutes, the spout resting obliquely on its crown. At some distance from this spout the sea began to be agitated, and a mist rose to the height of about four feet; then a projection descended from the black cloud that was impending, and met the ascending mist about twenty feet above the sea; the last ten yards of the distance were described with very great rapidity. A cloud of a light colour appeared to ascend in this spout, something like quicksilver in a tube. The first spout then snapped at about one-third of its height, the inferior part subsiding gradually, and the superior curling upwards. Several other projections from the cloud appeared, with corresponding agitations of the water below, but not always in spots vertically under them: seven spouts in all were formed; two other projections being re-absorbed. Some of the spouts were not only oblique, but curved: the ascending cloud moved most rapidly in those which were vertical: they lasted from three to five minutes, and their dissipation was attended by no fall of rain.

FATA MORGANA.--This is a very remarkable aërial phenomenon, which is sometimes observed from the harbour of Messina, and adjacent places, at a certain height in the atmosphere. The name, which signifies the _Fairy Morgana_, is derived from an opinion of the superstitious Sicilians, that the whole spectacle is produced by fairies, or such like visionary invisible beings. The populace are delighted whenever it appears; and run about the streets shouting for joy, calling every body out to partake of the glorious sight. This singular meteor has been described by various authors; but the first who mentioned it with any degree of precision was Father Angelucci, whose account is thus quoted by Mr. Swinburne in his Tour through Sicily: "On the 15th of August, 1643, as I stood at my window, I was surprised with a most wonderful delectable vision. The sea that washes the Sicilian shore swelled up, and became, for ten miles in length, like a chain of dark mountains; while the waters near our Calabrian coast grew quite smooth, and in an instant appeared as one clear polished mirror, reclining against the aforesaid ridge. On this glass was depicted, in _chairo scuro_, a string of several thousands of pilasters, all equal in altitude, distance, and degree of light and shade. In a moment they lost half their height, and bent into arcades, like Roman aqueducts. A long cornice was next formed on the top, and above it arose castles innumerable, all perfectly alike. These soon split into towers, which were shortly after lost in colonnades, then windows, and at last ended in pines, cypresses, and other trees, even and similar. This is the Fata Morgana, which for twenty-six years I had thought a mere fable." To produce this pleasing deception, many circumstances must concur, which are not known to exist in any other situation. The spectator must stand with his back to the east, in some elevated place behind the city, that he may command a view of the whole bay; beyond which the mountains of Messina rise like a wall, and darken the back ground of the picture. The winds must be hushed, the surface quite smoothed, the tide at its height, and the waters pressed up by currents to a great elevation in the middle of the channel. All these events coinciding, as soon as the sun surmounts the eastern hills behind Reggio, and rises high enough to form an angle of forty-five degrees on the water before the city, every object existing or moving at Reggio, will be repeated one thousand-fold upon this marine looking-glass, which, by its tremulous motion, is as it were cut into facets. Each image will pass rapidly off in succession, as the day advances, and the stream carries down the wave on which it appeared. Thus the parts of this moving picture will vanish in the twinkling of an eye. Sometimes the air is at that moment so impregnated with vapours, and undisturbed by winds, as to reflect objects in a kind of aërial screen, rising about thirty feet above the level of the sea. In cloudy heavy weather, they are drawn on the surface of the water, bordered with fine prismatical colours.

To the above account we shall add the following, given by M. Houel, whose judgment and veracity render his authority highly respectable.

"In fine summer days, when the weather is calm, there rises above the great current a vapour, which acquires a certain density, so as to form in the atmosphere horizontal prisms, whose sides are disposed in such a manner, that when they come to their proper degree of perfection, they reflect and represent successively, for some time, (like a moveable mirror,) the objects on the coast, or in the adjacent country. They exhibit by turns, the city and suburbs of Messina, trees, animals, men, and mountains. They are certainly beautiful aërial moving pictures. There are sometimes two or three prisms, equally perfect; and they continue in this state eight or ten minutes. After this, some shining inequalities are observed upon the surface of the prism, which render confused to the eye, the objects which had been before so accurately delineated, and the picture vanishes. The vapour forms other combinations, and is dispersed in the air. Different accounts have been given of this singular appearance; which for my part I attribute to a bitumen that issues from certain rocks at the bottom of the sea, and which is often seen to cover a part of its surface in the canal of Messina. The subtile parts of this bitumen being attenuated, combined, and exhaled with the aqueous globules that are raised by the air, and formed into bodies of vapour, give to this condensed vapour more consistence; and contribute, by their smooth and polished particles, to the formation of a kind of aërial crystal, which receives the light, reflects it to the eye, and transmits to it all the luminous points which colour the objects exhibited in this phenomenon, and render them visible."

FAIRY RINGS,--are circles of dark green grass frequently observed in old pastures; they have long been known under the name of fairy rings, and have generally been supposed to be occasioned, in some way or other, by electricity. Dr. Wollaston has, in a late volume of the Transactions of the Royal Society, given a new and very ingenious theory, of which we shall present our readers with a brief account, premising, that Mr. Davy, in the course of his lectures at the Royal Institution, had occasion to refer to the subject, and seemed to coincide in opinion with Dr. Wollaston. That which first attracted his notice was the position of certain fungi, which are always found growing upon these circles, if examined in a proper season. The position of these fungi led him to imagine that the progressive increase from a central point was the probable mode of formation of the ring: hence he conjectured that the soil, which had once contributed to the support of the fungi, might be so exhausted of some peculiar pabulum necessary for their production, as to be rendered incapable of producing a second crop. The second year's crop would, if this theory be just, appear in a small ring surrounding the original centre of vegetation; and at every succeeding year the defect of nutriment on one side, would necessarily cause the new roots to extend themselves solely in the opposite direction, and would occasion the circle of fungi continually to proceed, by an annual enlargement, from the centre outwards. An appearance of luxuriance of the grass would follow as a natural consequence, as the soil of an interior circle would always be enriched, by the decayed roots of fungi of the year's growth. This theory is supported by some observations of Dr. Withering; and Dr. Wollaston says, by way of confirmation, that whenever two adjacent circles are found to interfere, they not only do not cross each other, but both circles are invariably obliterated between the points of contact: the exhaustion occasioned by each obstructs the progress of the other, and both are starved.--Philosophical Transactions, 1807, Part II.

Though it cannot be doubted that most fairy rings, if not all of them, have considerable relation to the running of a fungus; there, nevertheless, seems reason to conclude that electricity may likewise be concerned in their production. The electrical effect may relate to fairy rings of a different kind from those occasioned by the fungus, or it may have been antecedent to the production of the vegetable. It is a familiar effect in our experiments, that the spark proceeding from a positive conductor, breaks or radiates at about one-third of its course, and strikes the receiving conductor by a central spark surrounded by other smaller ones. The concentric rings produced upon polished metallic surfaces by the strong explosion of a battery, as first observed by Dr. Priestley, appears to be a fact of the same kind; and the forked radiations of lightning are well known. There is related, in the Philosophical Journal, volume I. 4to, some events which happened in Kensington Gardens in June, 1781, when a powerful thunder-storm passed over the western extremity of London. The explosions were very marked and distinct, and in many instances forked at the lower end, but never at the top; from which it seems proper to conclude, that the general mass of clouds, or, at least, that extremity which passed over London, was in the state called positive.

Five days afterwards, upon visiting Kensington Gardens, it was observed, that every part of that extensive piece of ground shewed marks of the agency of the lightning, chiefly by discoloration of the grass in zigzag streaks, some of which were fifty or sixty yards in length. Instances of this superficial course of the lightning along the ground, before it enters the earth, are sufficiently frequent. But the circumstance applicable to our present subject is, that several trees had been struck by the lightning. Two of them, which stood on the outside to the westward, had holes torn in the ground, close to the trunk; and round one of these trees was a space of six feet in diameter, in which the grass was very much scorched. Another tree on the west was surrounded by a faint ring of burnt or faded grass, which seemed to be occasioned by some earlier stroke, as the vegetation had begun to shoot up again. Another tree, standing on the out side to the south, was surrounded by a ring of twelve feet diameter, and eighteen inches broad. Within the ring the grass was fresh; but on the surface of the ring, the grass and the ground were much burned. To the eastward of the tree, upon the ring itself, were two holes, in which the ground had the appearance of ashes. Another tree, on the east side of the grove, had the half of a faint ring to the westward. And, lastly, a tree which stood in the middle was surrounded by a faint ring of twelve feet diameter, within which the grass was unhurt; and to the westward, at the distance of about three feet from the inner ring, was part of another similar ring, of nearly the same appearance; the verdure being unhurt in the interval between the rings.

A SHEET OF PHOSPHORIC FIRE.--A curious instance of this occurred to Monsieur Peron, in his voyage from Europe to the Isle of France. Between three and four degrees north latitude, during the obscurity of a night intensely dark, the wind blowing a hurricane, and the vessel making a rapid progress, he was struck by the sudden appearance of a vast sheet of phosphoric fire, floating before the ship, and covering a considerable space. The vessel presently made its way through this inflamed part of the sea, which enabled the observant navigator to discover that this prodigious light was occasioned entirely by an immense number of small animalcules, which swam at different depths, and appeared to assume various forms. Those which were most immersed in the water, looked like great red-hot cannon balls: whilst those on the surface resembled cylinders of red-hot iron. Some of them were soon caught, and found to vary in size, from three to seven inches. All the outside surface of the animal was bristled with thick oblong tubercles, shining like so many diamonds; and these seemed to be the principal seat of its wonderful phosphorescence. The inside, also, appeared furnished with a multitude of little, narrow, oblong glands, which possessed the phosphoric virtue in a high degree.