soul-like powers in nature. We would venture, then, to say to the artist: wait and labor till you have found and framed a thought sufficiently great to be worthy of expression. A noble office devolves upon you; it is required that you shall teach, elevate, and advance your age; but before you can wield a power thus to move, you must be the like power be moved yourself. of the scene, the terror of the theme and has yet to appropriate and make her own. action, so completely fill the thoughts, that Nature has thoughts of grandeur, waiting minor facts and incidents are not merely only for commensurate genius to mold. mentally subordinate they are, indeed, It is the power of thought in man that wholly unheeded. Do the kings and can alone enable art efficiently to work bondsmen, who call in terror upon those out and manifest the latent yet vital and falling rocks, mark or care whether they be of granite or of mountain limestone? Minor detail in such scenes of tragedy is worse than useless; it is indeed hostile to, if not wholly incompatible with, the power and intensity which, in works of this import, constitute the very essence of the sublime. Minor trivial accessories, unless they involve some deep meaning, and thus cease to be trivial, are only marked by the Men in sufficient numbers will eye, remembered by the mind, when the always be found to perform the subordithoughts are vacant of weightier matters. nate work their generation may require; Do you think that the Virgin Mary noted but you, feeling within yourself the prothe texture of the robes in which the mise of greatness, arrest the too easy deangel Gabriel came to announce his mes- scent into those minor topics about which sage? In like manner it was not till later the multitude is ever busied ; stifle in their and declining days that art learned that first rise the trivialities of purposeless deangels brought not their wings from tail; and, instead thereof, foster and maheaven, but stole them from the sides of ture master and moving thoughts in nahawks; thenceforth painters began to ture-watch for their rising in your own count feathers, and instead of pennons mind-studiously gather together all the dipped in rainbow radiance, the mundane forms and phases of beauty and of granddetails of a vulture's plumage were given eur which the life of man and the ways of as a substitute for forms and colors which nature present for your using; and thus the imagination had fitly chosen, because having made your own life a poem, your not belonging to earth. An angel of this nineteenth century would, doubtless, come clothed in Manchester cottons, or Lyons silks, and his mission be unheeded, and his heaven-abode forgotten, in our admiration of the material, texture, and quality of his atire. own mind a temple whereunto all high and beauteous thoughts are flocking, then, in the fullness and overflow of your heart, take canvas, and, in the language of forms, light, shade, and color, express thoughts worthy of a great mind discoursing with a high intent. Your works will then move We have discoursed thus much of power mankind by the power of thought they in many of its aspects, because, in an age thus contain. To apply once more the eminently powerful, art, as we have said, words of Milton to our subject, there will is comparatively weak. We know, how- be found "a progeny of life in them to ever, no reason why she should not regain be as active as that soul was whose proin new directions that influence which, geny they are; nay, they will preserve, since the Middle Ages, she has lost. Na- as in a vial, the purest efficacy and exture, we have seen, contains within her traction of that living intellect that bred realms, manifestations of power which art them.” From the Westminster Review. BOILING WATER-THE BOILING SPRINGS OF ICELAND. WE live, and move, and have our being | float for a considerable time upon the at the bottom of an atmospheric ocean whose lower strata are pressed upon by all above them. Unlike the waters of the common sea, the atmosphere yields considerably to this superincumbent pressure. It shrinks like a compressed spring, and, like it, exercises an elastic force proportioned to the weight which it has to bear. A pillar of air, with a base of one square inch resting upon the surface of the sea, and reaching to the top of the atmosphere, weighs, in round numbers, fifteen pounds; and this, therefore, is the pressure exerted by the atmosphere on each square inch of the sea's surface. It varies within narrow limits, according as the pressure is that of the warm, light air of the south, or of the cool, dense air of the north: in the former case the barometer falls, in the latter it rises. We have heard an intelligent youth ask the following question: "Suppose a room containing people to be shut up, and every chink and cranny closed, so that all communication shall be cut away between the air within and that without. Here, although the ceiling and walls interpose to shield the people in the room from the pressure of the atmosphere, still each of them bears the same pressure as a per. son outside the room; and a barometric column will stand as high within the room as without it. What is the reason?" The reason is, that the air within the room possesses the full elastic force which the pressure of the atmosphere can give to it; the spring was compressed before the room was closed, and its power of lifting the barometric column is therefore the same as that of the free atmosphere. A vessel of water with its surface exposed yields up vapor at all temperatures, and the water will finally disappear; but the elastic force of this vapor will depend on the temperature at which it is generated, being greater the higher the temperature. If the heat be sufficient to boil the water, bubbles rise, and sometimes surface. Let us consider the case of such a bubble, whose area is one square inch. The fragile thing bears the atmospheric pressure of fifteen pounds. Why, then, does not the film burst? Simply because the elastic force of the steam within the bubble is exactly equal to the elastic force of the air without it; so that the film is in reality placed between two gaseous cushions, which press upon it equally, in opposite directions, and therefore neutralize each other. Until the water is hot enough to produce steam of this tension, it cannot boil; the tendency to ebullition is subdued by the atmospheric pressure. Under the full atmospheric pressure of fifteen pounds per square inch, water boils at a temperature of 212o Fahr.; and hence steam generated at this temperature is said to have an elastic force equal to one atmosphere. But if a portion of the atmospheric pressure be removed, water will boil before it reaches 212o. Take the case of a bubble floating on the surface of water at the top of a mountain. We have seen that the existence of the thin film which constitutes the bubble, depends on the pressure against it from within being the same as the pressure upon it from without. But the pressure without the bubble on the summit of the mountain is less than at the surface of the sea, and hence the elastic force of the steam must be less in the former position than in the latter. This is the case; and to produce this feebly elastic steam less heat is required; or, in other words, the boiling point of water on the mountain is lower than at the sea level. At 18,000 feet, on Donkia mountain, in the Himalaya, Dr. Hooker found that water boiled at 180°; so that tea, soup, and chocolate, which require to be made with water of nearly a temperature of 212°F., would be of very inferior quality in this mountain region. It is not, however, necessary to ascend a mountain to satisfy ourselves that the boiling point sinks as the atmospheric but will cling to the upper portion of the pressure is diminished. If water at 1800 tube. This experiment shows that the be placed under the receiver of an air- adhesion between the liquid and the glass pump, and the air be removed until the is enormously increased by the expulsion pressure becomes as low as it is on Donkia, of the air, for no such effect could be prothe water will boil. It is not even ne- duced with ordinary water; but it also cessary to heat the more volatile liquids teaches that the cohesion among the parto produce this effect. A beaker of alco- ticles of the liquid itself is very great; hol placed under the receiver of an air- for there is nothing to prevent the central pump, at the ordinary temperature of our portion of the liquid column from detachclimate, will boil violently when the re- ing itself from the portion in contact with ceiver is sufficiently exhausted. Revers- the tube, except the cohesion between the ing the conditions, we can, by increasing liquid particles themselves. Now here the pressure upon its surface, enable water we have a force which tends to resist the to attain a far higher temperature than separation of the particles; how will it 212° without boiling. Thus, as is natural affect the boiling point of the liquid? to expect, an external force which resists Most remarkably. Water thus purged of the tendency of heat to tear asunder the its air may be heated to a temperature of particles of a liquid, and convert it into 275° Fahr. without boiling; and when it vapor, elevates the boiling point of the does boil, it is not with the gentle ebulliliquid. tion of ordinary water. The particles snap suddenly asunder like a broken spring, and ebullition is converted into explosion. The boiling point depends also on the nature of the vessel in which the liquid is placed. Any thing that resists the separation of the particles produces the same effect as an increase of external pressure. Water adheres to certain surfaces much more strongly than to others; thus, it clings to glass more tenaciously than to metal; so that, to make water boil in a glass vessel, requires more heat than is necessary if it be contained in a metallic vessel. It is possible that this property of water may sometimes act disastrously in the case of steam-boilers. For if the water in a boiler be deprived of its air by long boiling, it may assume the condition described, and become heated to a degree far beyond that which corresponds to the pressure upon its surface, as indicated by the gauge. Explosions very often occur at the precise In boiling their solutions in glass vessels, moment when the engineer turns on the chemists have to be very careful, for the steam; an act which would be calculated adhesion between glass and liquid is over- to rupture the cohesion of a mass of water come by jerks; instead of the amicable in the state referred to, and to cause it ebullition exhibited in a metallic vessel, instantly to apply its excess of heat to the the solution boils by starts; and this in generation of steam of enormous tension. sometimes so energetic a manner as to No man practically acquainted with exproject the solution quite out of the glass perimental investigation, and the numbervessel. But the most remarkable influ-less chances that arise to modify and deence upon the boiling point of water is exercised by the air which it holds in solution. When water is exposed to air, a certain amount of the latter is absorbed by the liquid, the magnitude of the absorption being proportional to the pressure exerted by the air on the surface of the liquid. It is extremely difficult to expel this air, but it may be done by continual boiling. Imagine a glass tube, which has been exhausted by the air-pump, to be half filled with water which has been purged of its air by boiling, and hermetically closed at both ends. This water adheres so closely to the sides of the tube, that when the latter is turned upside down, the liquid will not fall downward, feat the most probable conjectures, will be inclined to express himself dogmatically upon the point in question. But one thing is certain, that we ought to know whether this cause, or the other causes, with which conjecture alone now deals, can practically affect the question of boiler-explosions. We know nothing; but we ought to know a great deal, for the whole subject is clearly within the range of experimental investigation. Instead of being reduced to vague surmises, certain experimental results ought to be before us as the basis on which to found a rational opinion. But such results are wanting, not on account of the insuperable difficulty of the subject, but simply because there is no person with sufficient | same as that exhibited by a drop of mercash, leisure, ability, and inclination to un-cury; that the heating of the metal estadertake the investigation. We now turn to the examination of another interesting point connected with the boiling of water. To a person unacquainted with the facts of the case, nothing can appear more manifestly true than the statement that the hotter a vessel is into which water is poured, the sooner the liquid will boil. But this statement is diametrically opposed to. fact. Let a silver basin be heated to redness, and let a small quantity of water be poured into it. The water, instead of flashing into steam, as might be expected, will gather itself into a globule, and roll upon the hot surface as a drop of mercury upon a table, or as a rain-drop upon a cabbage-leaf. The liquid is in a state of incessant motion: sometimes it elongates itself into an oval in one direction; then, drawing itself up, it becomes elongated in a direction perpendicular to the former; and these changes take place so rapidly that a star-shaped figure is often the result. Sometimes rosettes of surpassing beauty are thus formed. While the drop is in this spheroidal condition, as it called, let the lamp which heats it be withdrawn; the basin gradually cools, and after a short time the drop loses its spheroidal shape, spreads out on the surface of the basin, and is instantaneously thrown into violent ebullition. Throughout the Continent, this is known as the experiment of Leidenfrost, who described the phenomenon in a work published toward the close of the last century. Water is not the only liquid which is capable of exhibiting this effect: it is obtained more easily with alcohol, and still more easily with ether. In fact, the more volatile the liquid, the more readily it as sumes the spheroidal condition. In the place of a metallic basin, water near its boiling-point may be made use of to support a drop of ether. Instead of mixing with the hot water, the ether gathers itself up into a globule, and rolls about upon the surface of the other liquid. With regard to the cause of this singular phenomenon, differences of opinion still exist among men of science; but we imagine, that those who have studied it aright will be found to be tolerably unanimous. M. Boutigny propounded a theory which had no scientific basis, and therefore never made a convert. M. Buff considers the action to be precisely the blishes the same relation between it and a drop of water as that which ordinarily exists between mercury and a surface of glass or porcelain. The very appearance of the drop on the heated surface suggests the idea that the liquid and metal are not in contact with each other. At an early period of railway history it was proposed by that original genius, George Stephenson, to substitute for ordinary steel springs, in the case of locomotives, springs of elastic steam. It was proposed to convey the steam into cylinders, in which pistons should move steamtight; these pistons, supported by the steam beneath them, were to bear the weight of the locomotive. Now, what the great engineer proposed for the locomotive, the spheroidal drop effects for itself—it is borne upon a cushion of its own steam. The surface must be hot enough to generate steam of sufficient tension to lift the drop. The body which bears the drop must be of such a nature as to yield up readily a supply of heat; for the drop evaporates and becomes gradually smaller, and to make good the heat absorbed by the vapor, the substance on which the drop rests must yield heat freely in other words, it must be a good conductor of heat. This is why a silver basin was recommended for the experiment, for silver stands at the head of conductors. Again, a cushion of vapor being required, the liquid must be of such a nature as to furnish this. Hence it is that the most volatile liquids—those which are most readily converted into vapor-show the phenomenon most readily. It is to the escape of steam in regular pulses from beneath the drop that the beautiful figures which it sometimes exhibits are to be referred. By using a very flat basin, over which the spheroidal drop spreads itself widely, we render it difficult for the vapor to escape from the center to the edges of the drop; and this resistance may be increased till the vapor finds it easier to break in bubbles through the middle of the drop than to escape laterally. All the facts are in perfect harmony with the explanation, that it is the development and incessant renewal of a steam spring at the lower surface of the drop which keeps the liquid from contact with the metal, and shields it from the communication of heat by contact. Owing to It has been stated that the water in the red-hot metallic capsule does not reach its boiling point: the existence of an intensely cold liquid in such a vessel is also possible. It is well known that carbonic acid gas can be rendered liquid by great pressure. It is needless to observe that this gas is one of the products of respiration; that its escape causes the effervescence of champagne and soda-water; and that if marble, or chalk, which is a carbonate of lime, be acted upon by sulphuric or any other acid, this gas is liberated in abundance. The liquid carbonic acid is preserved in strong iron bottles, which are closed by perfectly-fitting taps. When one of these is opened, the substance being relieved from the pressure which held it in the liquid condition, flashes into gas-but not all of it. It is well known that a body, in passing from the liquid to the gaseous condition, absorbs an enormous quantity of heat. So great is the amount of heat absorbed in the case now before us, and so intense is the cold produced by this absorption, that a great portion of the carbonic acid is actually frozen, and may be collected as a pure white snow. this, indeed, the liquid in the spheroidal | over his naked body. He escaped uncondition never reaches its boiling tem- harmed, and the heretics were all conperature. If you plunge a thermometer verted. into a spheroid of water in a red-hot vessel, its temperature will be found to be some degrees under 212°. When the lamp is withdrawn and the basin cools, the tension of the steam underneath the drop becomes gradually feebler. The spring loses its force, the drop sinks, and finally comes in contact with the metal. Heat is then suddenly imparted to the liquid, which immediately bursts into ebullition. It is a common experiment, and one which may be made in any smithy, to rub the tongue against a bar of white-hot iron. The tenderest lady who chances to read this article may make the experiment with perfect impunity, provided the bar be sufficiently heated. In this case, the layer of vapor developed between the hot metal and the moist tongue, effectually shields the latter from harm. And this brings us to those remarkable experiments, the performance of which, by M. Boutigny, excited so much interest a few years ago. At the meeting of the British Association at Ipswich, in 1851, many of the visitors had an opportunity of seeing M. Boutigny pass his hand through a stream of molten iron. Previous to doing so, the experimenter dipped his hand in a bucket of water. He afterwards scooped, with his Not only does a body in passing from fingers, the liquid metal out of a crucible, the liquid to the gaseous condition aband scattered its drops around like those sorb a large amount of heat; in passing of water. A similar experiment may be from the solid to the liquid state, a similar made with molten lead, care being taken absorption, and a corresponding producto skim the oxide from the surface, and tion of cold, takes place. If the solid carrender it clean. The fingers, moistened bonic acid obtained in the manner above by water, or by liquid ammonia, may be described, be mixed with ether, the sodipped into the lead with impunity. Here, lid melts, and the cold produced is the also, the hotter the metal, the less will be most intense known to man. Fahrenheit the danger. Pondering upon these results, thought that the lowest temperature posthe miraculous disappears from the follow-sible was at 32° below the freezing-point ing experiment, made by a holy man of antiquity. In the year 241, Sapor gave orders to his wise men to do all in their power to convert certain of his subjects who had backslidden from the faith, of their ancestors. To effect this, one of the priests of the dominant sect, Abdurabad Mabrasphaud by name, offered to submit to what he called the fiery ordeal. He proposed that a quantity of molten copper should be poured over his body, on condition that, if he remained uninjured, the dissidents should return to their ancient belief. This was agreed to; and eighteen pounds of the molten metal were poured of water, and hence chose this point is the zero of his scale; but with a mixture of carbonic acid and ether, Thilorier obtained a temperature 152° below the freezing point of water, and Mitchell one 178° below the same point. If a quantity of the mixture be placed in a red-hot metallic crucible, the elastic force of the ether-vapor shields the substance from contact with the vessel, the heat imparted by the latter is absorbed by the vapor, and the mixture remains intensely cold. If a spoon containing water be plunged into the mixture, the water is instantly converted into ice. If |