Изображения страниц
PDF
EPUB
[merged small][merged small][merged small][ocr errors][merged small][merged small]

BB

C C D

Fig. 1. Longitudinal section of the Vacuum Pipe, and side view of the Driving Carriage attached to the Piston. YES, it was the rush of the experimental train on the Dalkey Atmospheric Railway, in its up-hill flight! for we must acknowledge that sixty miles an hour, inclusive of the time allowed for the pipe, and the passengers, to recover their breath, is at least a little like flying; more especially when, as in this case, there is no apparent mechanical motive power. But we can assure the reader that if his ideas of railway travelling have been confined to twenty or thirty miles an hour, with a groaning, hissing, locomotive, it is now time for him to look out for the schoolmaster, abroad or at home, and to take some lessons in aërial philosophy. He has perhaps seen a rope of wire-may have been attached to a rope of hemp-has heard at least of a rope of sandbut if he will pass over to the green Sister Isle of the ocean, he shall be drawn from Kingstown to Dalkey by a rope of air. 'Tis a veritable fact, and no Irish bull; and we hope events will soon prove that it is no Irish blunder.

Some of our readers may recollect the ingenious project, devised some eighteen or twenty years ago, for connecting the great metropolis with that summer resort of fashionable metropolitans, Brighton, by means of an air-tight pipe or tunnel, sufficiently capacious to admit. passenger-carriages. This tunnel being made smooth internally, and the first vehicle fitting tolerably close; supposing the pipe was partially exhausted of air, in front of the train of carriages; supposing, secondly, that the tunnel was of sufficient strength to withstand the external pressure of the atmosphere; and supposing, thirdly, that the public were willing to patronize so novel a mode of transit, why then it was quite clear, (to the mind of the projector,) that his imprisoned Londoners might very easily slide along through this capacious tube or tunnel, and would soon be liberated on the shores of Brighton.

To evince the feasibility of such a scheme, by experiments on a lilliputian scale, was a task of very easy accomplishment. In this case, however, as in thousands of others, the public were not able to reciprocate the views entertained by the projector, of its practical utility, or its unnumbered advantages.

accomplishment of that which has assumed a practicable shape under the hands of Clegg and Samuda.

It is well understood that near the earth's surface the atmosphere exerts a pressure equal to about fourteen or fifteen pounds on the square inch, varying of course with the varied weight indicated by the mercurial column of the barometer; and that the pressure is equally exerted in all directions. It is this force that raises the water in a common pump, and supports the mercury in the tube of a barometer. And the schoolboy who places his moistened leather sucker upon a stone, is but calling into exercise the same power, that power which propelled the liquid aliment from its source, when, entering upon the stage of life, and untaught save by an innate philosophy, he first applied his little vacuum engine to his mother's breast.

When, in the now so oft repeated pneumatic experiment, we place the hand on the exhausted receiver of an air-pump, it is this same pressure which prevents our removing it; and were we, for the ordinary glass receiver, to substitute an iron pipe with a moveable piston, we should find that the piston would be forcibly drawn or propelled into the pipe. Now as the air presses equally in all directions, upwards, downwards, and laterally, the piston would pass along the pipe, whether it were a vertical or a horizontal one.

The unscientific reader will by this time perceive that if an air-tight pipe of sufficient capacity were laid down on a road (say a mile in length), and at one end of this pipe was a large air-pump capable of rapidly withdrawing the air, and at the opposite end was a piston working in the pipe, with a rope a mile in length attached to the piston at one extremity, and at the other to a train of carriages, which would of course be a mile from the pipe; if the air was then pumped out of the pipe, the atmospheric pressure upon the piston would drive it along the tube, and the carriages would be drawn after it. But in practice this plan would not be available.

It still remained for some one to overcome the difficulty, and to discover a plan by which the piston and the carriages might be made to travel in company, as the small tube or socket inside a common pencil-case, into which we fasten the cedar pencil, moves with the fingers that slide the pencil backwards and forwards along the case.

With this object it was proposed to employ pipes with lateral openings, by means of which a connecting-rod might be attached to the piston and the carriages: and it was thought that, with a rope for a cover to this opening, a sufficient rarefaction of the air in the tube could be obtained for practical purposes. This also was a failure; and it was reserved for the present patentees, Messrs. Clegg and Samuda, to bring into practical operation as a railway motive power, that atmospheric pressure, with the existence and the force of which we had so long been familiar.

We believe the experiment was first tried, some three or four years ago, on a portion of the West London Railway at Wormwood Scrubbs. A series of cast-iron pipes, nine inches in diameter, and extending half a mile in length, was laid down; and though neither the pipe nor the rails were in good order, yet on a gradient of about 1 in 115, and with an exhaustion that indicated a pressure on the piston of about nine pounds to the square inch, a load of goods weighing several tons was pro

was attained, during some of the experiments, of thirty to forty miles, with a steam-engine to work the pump that was quite inadequate to the work.

But the idea of making use of the pressure of the atmosphere as a motive power for the transit of passen-pelled at more than twenty miles an hour; and a speed gers on railways has never been abandoned. To the sister Island belongs the merit of having reduced it to practice; and though our Irish neighbours are not to be whirled through an air-tight tunnel, yet the impelling power on the Dalkey Railway is the same as that alluded to above, namely, the rushing of the air into a partially exhausted pipe: and however improbable Vallance's Brighton tunnel may now appear, we must yet concede to it the merit of ingenuity: it was a step towards the

These experiments were decidedly encouraging; and eventually the Government agreed to advance a loan to the Dublin and Kingstown Railway Company, for enabling them to construct a line on the pneumatic principle from Kingstown to Dalkey, a distance of about a mile and three-quarters. The various opposing diffi

culties have been overcome; and the line was ready for the transit of passengers at the end of last year.

Referring again to our illustration of the pencil-case, the small socket may be called the piston, and the finger may be considered as the drawing carriage-with this difference, that the fingers in the one case move the socket; in the other case the power is reversed, and the piston (or socket) moves the carriage (or fingers).

The vacuum pipe, which is the distinguishing characteristic of this railway, is about fifteen inches internal diameter: it is of cast-iron, united in the same manner as the gas or water pipes in our streets, and is laid in the centre between the two rails. A simple cutter is passed through the pipes when they come out of the foundry sand; and being raised to the temperature of melting tallow, a mop dipped in this material is passed through them, and being followed by a wooden piston, the inside becomes coated with a thin surface of tallow, which soon acquires considerable hardness; so that practically the travelling piston moves in a tube of tallow, and this method is found very effectual in preventing atmospheric leakage. On the top of the tube is a narrow opening, extending the whole length, which is closed with a valve for the purpose of rendering the tube air-tight when required. This valve is a continuous flap of leather, on the upper and under sides of which are riveted plates of iron, the inner surface of the lower plate being so shaped as to form, when the valve is closed, a portion of the circumference of the pipe; the upper plate and the leather being both a little wider than the opening or "slot," and made to extend over it on each side. This continuous valve is hinged on one side to a projecting rib; and the other edge falls into a groove containing a mixture of wax and tallow, which, when melted, seals up the pipe, and makes it sufficiently air-tight for practical working. There is also a contrivance, called the weather-valve, for protecting the apparatus from the weather.

A reference to fig. 2, which is a cross section of the pipe when closed, will assist the reader in comprehending its structure.

B

A

A

ON HOSPITALS. IV.

AMONG the subjects which arrest our attention in considering the Continental Hospitals are those of them in which patients are admitted by paying a sum of money. There are several institutions of this kind at Paris; and it is said that great benefit has resulted from them to the classes of the community for which they were instituted. Of these, St. Perine, containing 175 beds, instituted in 1801, is the most important. Persons of either sex, who have reached the age of sixty, are admitted at the annual sum of twenty-four pounds. It is an excellent resource for small proprietors, employés, and others of limited means, who do not wish to become a burden to their friends. They may commence paying the subscription by advance at the age of forty, or may purchase the annuity for a fixed sum. The Hospice de Rochefoucauld is for a lower degree of persons, where they pay from eight to ten pounds. The Hospice des Menages admits 682 persons. The best chambers are reserved for married couples, at a hundred and twenty pounds per annum. Eighty beds are reserved for the destitute who can prove they have lived man and wife for twenty years. One hundred small chambers are appropriated to widows or widowers, at sixty pounds per annum; while others are received for forty pounds. In Paris there are also two Maisons de Santé, where persons of too limited means to remain in lodgings during their illness, and yet not willing to resort to a common hospital, are received. The number accommodated is 200. A daily sum is required from all; namely, for a bed in the public room, two shillings per diem, and for a private room four shillings or five shillings per day. This includes diet, medical attendance, and other expenses.

In the various provincial hospitals of France and Germany, those of the patients who are in a condition to pay a small sum towards their maintenance, do so; at Strasburgh, about sixty out of five hundred thus contribute, and at Lyons a better class of patients are admitted on the same conditions. At Berne, those who can pay a small sum are received into an adjoining building, which also contains a department for lodging mechanics and strangers on their passage through the town, of whom sometimes three hundred have been accommodated on one night. There is another ward reserved for servants who can pay a certain sum.

In the general hospital of Vienna there are also two classes of patients-gratuitous and paying. For a florin a day an individual has a room to himself; and if the accommodation be less the price is much diminished. At Milan and Naples, wards are reserved where the patients pay two francs a day; and at St. Petersburgh the nobles pay a certain sum for each serf while in the

Fig. 2. Transverse section of the upper part of the Vacuum hospital. An institution has been established near the

Pipe when the valves are closed.

A A is the air-tight valve;

B the weather valve; and

[blocks in formation]

Regent's Park, London, upon the plan of the Maisons de Santé, at Paris; and judging from the great good these have effected in the latter city, it is probable it will supply a want felt to exist among some respectable, though not wealthy classes of society.

At the French hospitals another arrangement exists, which we could wish to see introduced into our own, namely, the establishment of convalescent wards; or still better, if, as at the general hospital of Vienna, a separate building for the convalescent patients could be erected.

If we find something to admire, and even to imitate, in the foreign establishments, we cannot bestow our approval when speaking of their Foundling Hospitals. Some of these institutions are of immense extent, as those of Paris, Milan, Moscow, and St. Petersburgh; this last containing four or five thousand infants. The two extremes have been tried; for, in ancient times, the barbarous abandonment of children was not punishable, and in modern times all brought to the doors of the

hospitals have been received. It is difficult to say which of these proceedings is the most injurious, although the motives influencing them are widely different. This ready reception of foundlings has produced a lax morality, by encouraging the reckless incurring, and heartless abandonment, of maternal responsibility-to the severing of those ties between mother and child, which the very brute creation teaches us to respect; while, by the congregation of young children which it renders unavoidable, it has become itself a frightful source for the generation of infantile disease and mortality. M. Benoiston de Chateauneuf states (Annales d'Hygèine, Vol. XXI.), that between the years 1824 and 1833 there were received into the French foundling hospitals 452,000 infants. During the ten years there died in the hospital 46,000, and at nurse 151,750-in all 198,505. There were 127,000 received in 1837, at an expense, as he calculates, of eleven million francs. Since that period we believe the French government have determined on abolishing this indiscriminate admission.

One important feature connected with hospitals is entirely of modern origin; we mean, the attaching medical schools to them. This is of such vital importance to the community, that even were hospitals worthless on every other ground they should be sustained on this account alone. Yet, let it not be supposed that the interests or comforts of the occupants suffer for the sake of this advantage which society at large derives from these institutions. No one, at all acquainted with hospitals, is ignorant that the superintendence by the medical students insures a much more satisfactory carrying out of the views of the medical officers than would otherwise take place; while these latter, acting in the presence of a body of persons, able and willing to criticize their proceedings, receive the highest stimulus possible to the due discharge of their duty. J. C.

SINCE, of desires, some are natural and necessary; others natural, but not necessary; and others neither natural nor necessary, but the offspring of a wrong judgment; it must be the office of temperance to gratify the first class, as far as nature requires; to restrain the second within the bounds of moderation; and as to the third, resolutely to oppose, and if possible entirely repress them.-History of Philosophy.

THE beauty of sunset, in a fine autumnal evening, seems almost incapable of addition from any circumstance. The various and radiant colouring of the clouds, the soft light of the sun, that gives so rich a glow to every object on which it falls, the long but mellow shades with which it is contrasted, and the calm and deep repose that seems to steal over universal nature, form altogether a scene, which serves, perhaps better than any other in the world, to satiate the imagination with delight; yet there is no man who does not know how great an addition this fine scene is capable of receiving from the circumstance of the evening bell. In what, however, does the effect of this most picturesque circumstance consist? Is it not in the additional images which are thus suggested to the imagination? images, indeed, of melancholy and sadness, but which still are pleasing, and which serve most wonderfnlly to accord with that solemn and pensive state of the mind, which is almost irresistibly produced by this fascinating scene.-ALISON.

THOSE who devote themselves to the peaceful study of nature (observed a philosopher who confirmed his opinion by his example) have but little temptation to launch out upon the tempestuous sea of ambition; they will scarcely be hurried away by the more violent or cruel passions, the ordinary failings of those ardent persons who do not controul their conduct: but, pure as the objects of their researches, they will feel for everything about them the same benevolence which they see nature display towards all her productions.-CUVIER.

CONSTANT pain is a sad grievance, whatever part is affected; but patience is an anodyne of God's own preparation, and of that He gives largely to those who seek it.-CowPER.

GROUND-ICE. II.

IN a late article we gave some instances in which it has been observed that in several rivers of our own country, ice begins to form at the bottom, instead of at the surface of the water. Evidence of the same fact has been also furnished in the rivers of other countries; and M. Arago has collected this evidence with a view to the explanation of the phenomenon. He remarks, that if the formation of ice in the beds of rivers has only appeared recently as an established fact in scientific works, it is because their authors generally copy from each other, each neglecting what his predecessor neglected; and because academical collections, in which many treasures remained concealed, are very seldom consulted.

It appears that, in many cases, those large bodies of ice which are carried down by rivers towards the sea, and in their passage become arrested by bridges, or other obstacles (thus often causing fatal accidents), are actually formed at the bottom of the stream, though they afterwards become disengaged from it and rise to the surface. Evidence of this has been furnished from so many quarters, that it will be difficult any longer to doubt that this phenomenon, strange though it be, is not of common occurrence.

M. Beaun, a bailiff at Weld Wilhelmsburgh, on the Elbe, published in 1788, many dissertations, in which the existence of ice on the bottom of a river is established, either by his own observations or by the unanimous declarations of fishermen, procured after a most careful investigation. The fishermen asserted that during the cold days in autumn, long before the appearance of ice on the surface of the river, the nets which were at the bottom of the water were covered with such a quantity of grund-eis that they drew them up with great difficulty; also, that the baskets which are used for catching eels, on being brought up to the surface, were often encrusted with ice; that anchors which had been lost during the summer, again appeared in the following winter, being raised up by the ascensive force of the ice at the bottom which had covered them; that this ice raised up the large stones to which the buoys were attached by chains, and occasioned the greatest inconvenience by displacing these useful signals.

These various observations were confirmed by Beaun on his own authority. He discovered experimentally, that hemp, wool, hair, moss in particular, and the bark of trees, are bodies which on being placed at the bottom of water, are very speedily covered with ice. He states that various metals do not possess this property in the same degree; that tin occupies the first rank,—iron the last.

Some interesting observations on the ground-ice of the Siberian rivers were made by Mr. Weitz, superior officer of the Imperial Russian Mining Corps, and communicated to the Royal Geographical Society. We find them in the sixth volume of their Journal. It appears that in traversing the rapid rivers of the north at the beginning of winter, this gentleman was led particularly to notice the formation of ground-ice. These rivers flow with great rapidity over a sandy or stony bed, and notwithstanding the duration and intensity of the cold, and the abundance of snow, they continue to flow, bearing along vast quantities of floating ice brought from their source, and augmented by what is detached from the sides, as also by what rises from the bottom.

The Kann is a river of this kind; it takes its rise in a branch of the Siansk mountains, and empties itself into the Jeneseï, forty versts from Kranojarsk. Mr. Weitz traversed this river in November, after much hard frost, and had an opportunity of observing the formation of ice at the bottom. The ice was in long prismatic and pyramidal crystals, collected some

[ocr errors]

times into large masses, reposing on the bottom. The great transparency of these rivers made the ice at the depth of fourteen feet quite evident. It had a greenish tinge, and looked not unlike moss. Sometimes it became detached from the bottom, and on rising to the surface it soon grew more compact by contact with the cold air, and floated away with the other flakes. It frequently happens that these pieces, in rising from the bottom, bring up with them sand and stones, which are thus transported by the current. Arrived at those parts of the river where, from the very little slope of the bed, the motion of the water is slow, and where the surface is sometimes frozen over, these floating masses collect, rub against each other, and get fixed; whence the inhabitants affirm that the river first freezes towards the lower part of the stream, and that from thence the congelation proceeds upwards till it reaches the higher and most rapid parts. Others assert that, where the water is shallow the ice begins to form at the bottom, and increases upwards by degrees till it gains the surface; thus forming a barrier to the ice-meers that come down, and contributing by this means to the congelation of the surface of the whole river. When the thaw sets in, the ice becoming rotten, lets fall the gravel and stones in places far distant from those whence they came.

Á striking example of the formation of ground-ice is mentioned by the Commander Steenk, of Pillau. On the 9th of February, 1806, during a strong south-east wind, and a temperature a little exceeding 34° Fahr., a long iron chain, to which the buoys of the fair-way are fastened, and which had been lost sight of at Schappelswrack in a depth of from fifteen to eighteen feet, suddenly made its appearance at the surface of the water, and swam there; it was, however, completely encrusted with ice to the thickness of several feet. Stones, also, of from three to six pounds' weight, rose to the surface; they were surrounded with a thick coat of ice. A cable, also, three and a half inches thick, and about thirty fathoms long, which had been lost the preceding summer in a depth of thirty feet, again made its appearance by swimming to the surface; but it was enveloped in ice to the thickness of two feet. On the same day it was necessary to warp the ship into harbour in face of an east wind; the anchor used for the purpose, after it had rested an hour at the bottom, became so encrusted with ice, that it required not more than half of the usual power to heave it up.

On the 11th of February, 1816, the engineers of bridges and roads, residing at Strasburg, saw above the bridge of Kehl, that many parts of the bed of the Rhine were covered with ice. About ten o'clock, A.M. this ice became loose, rose to the surface, and floated. The thermometer in the open air stood at 10° Fahr.; the water in the river at every depth was at 32°. The ice at the bottom was only formed in places, however, where there were stones and angular projections. It was spongy, and formed of ice spicula. The overseers of the bridge stated that it never appeared on the surface until after ten or eleven o'clock in the morning.

During the winter of 1823, Professor Merian carefully examined the bed of the canal of St. Alban, which conveys the waters of the Birse through the town of Bale. The stream is very limpid and flows rapidly. The bed is generally covered with pebbles. The Professor noticed that wherever the bottom exhibited any projections, there was a small piece of ice, which might have been supposed at a distance to be a re-uniting of tufts of cotton. This ice became disengaged from the bottom from time to time, and floated on the surface. It had all the appearance of the grund-eis of the Ger

man watermen.

M. Hugi, president of the Society of Natural History at Soleure, observed in February, 1827, a multitude of large icy tables on the river Aar. These were continu

ally rising from the bottom, over a surface of four hundred and fifty square feet, and the phenomenon lasted for a couple of hours. Two years afterwards he witnessed a similar occurrence. On the 12th of February, 1829, at sun-rise, and after a sudden fall in the temperature, the river began to exhibit numerous pieces of floating ice, although there was no sign of freezing on the surface, either along the banks, or in shady places where the water was calm. Therefore it could not be said that the floating masses were detached from the banks. Nor could they have proceeded from any large sheet of ice farther up the river, because, higher up, the river exhibited hardly any ice. Besides, flakes of ice commenced soon to rise up above the bridge; towards mid-day, islands of ice were seen forming in the centre of the river; and by the next day these were twenty-three in number; the largest being upwards of two hundred feet in diameter. They were surrounded with open water, resisting a current which flowed at the rate of nearly two hundred feet in a minute, and extended over a space of one-eighth of a league. M. Hugi visited them in a small boat. He landed, examined them in every direction, and discovered that there was a layer of compact ice on their surface a few inches in thickness, resting on a mass having the shape of an inverted cone, of a vertical height of twelve or thirteen feet, and fixed to the bed of the river. These cones consisted of half-melted ice, gelatinous, and much like the spawn of a frog. It was softer at the bottom than at the top, and was easily pierced in all directions with poles. Exposed to the open air, the substance of the cones became quickly granulated, like the ice that is formed at the bottom of rivers.

In the same year the pebbles in a creek of shallow water near a very rapid current of the Rhine, were observed to be covered with a sort of transparent mass, an inch or two in thickness, and which, on examination, was found to consist of icy spicula, crossing each other in every direction. Large masses of spongy ice were also seen in the bed of the stream, at a depth of between six or seven feet. The watermen's poles entered these with ease, and often bore them to the surface. This kind of ice forms most quickly in rivers whose bed is impeded with stones and other foreign bodies.

It is unnecessary to give further instances of the recurrence of ground-ice; but it is time that we inquire concerning the cause of its formation. It may first be desirable to have a clear idea of the process of freezing, under the ordinary circumstances, and where the surface of still water becomes ice.

Every one knows that if liquids of different densities be poured into a vessel, the heavy will sink to the bottom, and the light will remain at the top. This applies equally to different kinds of liquids, and also to one and the same liquid under varying temperatures. Liquids, like all other bodies, become more dense as their temperature diminishes. But there is a certain point in the temperature of water which presents a very singular exception to this rule. If water is taken at 50° Fahr. and gradually cooled, it becomes successively denser and heavier, until it reaches a temperature of about 39°, when it attains its greatest amount of contraction by cold. After this point it is a very curious fact that any further increase of cold causes it to expand, and consequently to become lighter, until it attains the freezing point, i. e., 32°, when a further and sudden expansion takes place, and it becomes ice. Were it not for this beautiful provision in the case of water, our lakes and rivers, instead of freezing gradually, would become almost in a moment a solid mass of ice, from which it is evident that the most serious evils would result. But under the law which thus providentially regulates the congelation of water, the freezing of a lake or pond, or other body of still water, proceeds as follows. The first effect of the diminishing temperature of the air is to

cool the particles of water on the surface, and thus make them denser and heavier than the particles below. It naturally follows that the upper particles sink, and the lower rise to take their place. These in their turn become cooler and heavier, and sink likewise, being replaced by others. This successive cooling of the different layers of water goes on until the whole mass has attained the point spoken of above, i. e., about 394°, when it is at its greatest condensation. The continuance of the cold after this point, therefore, does not, as before, make the upper layer of water heavier, and cause it to sink, but on the contrary it makes it lighter, and thus keeps it at the surface. The expansion and consequent lightness of this upper portion of the water thus increases as the cold becomes greater, until it reaches the temperature of 32°, or freezing-point, when under ordinary circumstances, a layer of ice is formed. This coat of ice is in some measure a barrier to the effect of the atmosphere on the water beneath, so as to make it remain longer in a liquid state. But if the condensation of water went on regularly increasing up to freezing-point, the continual sinking of the colder portions would so affect the whole mass, that the whole would become, as we have already observed, a solid mass of ice. Surely there is ground for admiration and thankfulness in this exception to the rule by which all other liquids are governed; an exception which bears the stamp of beneficence, and affects in a very high degree the well-being of men and animals.

Such is the process of freezing as regards still water: let us now consider the modifications which the motion of the water is likely to produce.

The effect of this motion when it is rather rapid, when it forms eddies and flows over a rocky or unequal channel, is perpetually to mix all the layers. The law which regulates the congelation of still water, no longer applies. The water which is lightest does not always float on the surface. The currents are precipitated into the general mass, which is thereby cooled, and the temperature therefore soon becomes equal throughout.

In a deep mass of still water the temperature of the lowest part can never descend below 39°; but when this mass is in a state of agitation, the surface, the middle, and the bottom, may be found at the freezing-point, or 32°, simultaneously. It becomes therefore necessary to inquire, why when this uniformity of temperature exists, and when the entire mass of liquid is at the freezing-point, congelation commences at the bottom, and not at the surface.

In the first place, crystals are known to form more easily on unequal or pointed surfaces, than on any other, and therefore when the whole body of water has arrived at the freezing-point, it is not to be wondered at that the crystals begin first to form on the stones or other projections at the bottom of a river. Again, it is to be recollected that the motion of the waters has much to do in modifying the effect. At the surface this motion is very rapid and irregular in all those rivers in which ground-ice has been formed; while at the bottom of the river the motion is at least considerably diminished, so that although it may be sufficient to prevent the formation of compact ice, such as we see at the surface of still water, yet it may not prevent the gradual accumulation of that spongy kind of ice described in some of the foregoing examples, which could be easily pierced by the watermen's poles.

This appears to afford the true solution of the difficulty respecting ground-ice; but there have been other theories on the subject which must not be withheld. That of Mr. Eisdale was founded on information which

he had received from country people and others, whose operations depended on water-wheels, and whose interests forced them to attend to appearances, which might pass unheeded by others. The sum of their information was that the ground-ice was never formed except after

a heavy rime, or hoar-frost. Hence Mr. Eisdale is disposed to offer the following explanation. The hoar-frost, which is congealed moisture precipitated from the atmosphere, and falling into the river when the water is cooled down to the freezing-point, cannot be dissolved. It retains in the water the very shape in which it descends from the air. When these small crystals fall on a deep unfrozen pool, the water being above the freezingpoint, the particles melt and are incorporated with the water; but in a shallow and agitated stream, almost the whole water is brought in succession into contract with the intense frost, and may thus be cooled down to the freezing-point to the very bottom of the stream, before even a pellicle of ice is formed on the stagnant pool. All the particles of hoar-frost, then, or frozen vapour, which fall on such a stream, will remain unmelted; and being tossed in all directions by the agitations of the current, will be brought into contact with the rocks or other substances projecting from the bottom, to which they will readily adhere, and form a nucleus for the ground-ice.

Mr. Weitz conceives that the intensity and long continuance of the cold may freeze the soil to the depth of the bottom of the river, particularly where it is not deep, and that there the diminished velocity of the water permits of its congelation, particularly if there be any hollows where the water remains stagnant. So long as the congealed masses continue small with regard to the volume of water immediately above them, they adhere as if rooted to the bottom, and they rise bringing with them such gravel and stones as are found attached to them; whence Mr. Weitz concludes that not only does the current occasion a change in the bed of the river, by its erosion of the looser soil which it carries from one place to another, but that the ice which forms at the bottom of rapid rivers, in very cold countries, tends also to affect a change in the beds of those rivers.

Mr. Farquharson has also a theory which is founded on the principle of the radiation of heat. Those parts of the bed of the stream which radiate most freely, become cooled most rapidly to freezing temperature, and hence ice is deposited in a manner somewhat similar to the deposition of dew, viz., the earth by radiation becoming colder than the atmosphere, condenses the vapour into drops of water; and so by the free radiation of some portions of the bed of the stream the water may become converted into particles of ice.

In concluding our notice of this interesting subject, we may remark that although the theory of the formation of ground-ice is yet involved in much obscurity, the reader will be repaid the trouble of perusing the large number of facts which we have thus brought together from various sources; and should he be able to contribute any observations of his own they will be valuable, and still more so if given entirely free from theory.

In their great designs men show themselves as they would wish to be; in small affairs they appear in their real characters.

THE fruits of toil are the sweetest pleasures.

WE should learn to think on principles in an age which cares only to remember facts.

Ir is cheaper to educate two children than to feed a single vice.

THE tricks of involuntary actions, as twitchings of the face, restless gesticulations of the limbs, biting the nails, &c., are generally at first occasioned by the want of sufficient bodily exercise to expend the superfluous animal power, but are also acquired by imitation. Hence long continued quiet, so often imposed in schools, should be avoided.— Encyclopædia.

JOHN W. PARKER, PUBLISHER WEST STRAND, LONDON,

« ПредыдущаяПродолжить »