nursery, and its sturdy form when it has braved for centuries all the winds of heaven, and has become the monarch of the park or forest. Animals furnish other interesting illustrations of this law. How massive and clumsy are the limbs of the elephant, the rhinoceros, the heavy ox, compared with the slender forms of the stag, antelope, and greyhound! And an animal much larger than the elephant would fall to pieces from its own weight alone, unless its bones were made of much stronger materials. Many have questioned whether the mammoth, or antediluvian elephant, could have lived on dry land, or must have been amphibious, that its great body might generally be borne up by water. The whale is the largest of animals, but feels not its mighty weight because lying constantly in the liquid support of the ocean. A cat may fall with impunity where an elephant or ox would be dashed to pieces. The giants of the heathen mythology could not have existed on this earth, for the reason which we are now considering; although on our moon, where, as already stated, weight is much less, such beings might be. In the planet Jupiter, again, which is many times larger than the earth, an ordinary man from hence would be carrying, in the simple weight of his body, a load sufficient to crush the limbs which supported him. The phrase a little compact man, points to the fact that such a one is stronger in proportion to his size than a taller man. The same law limits the height and breadth of architectural structures. In the houses of fourteen stories, which formerly stood under the castle of Edinburgh, there was danger of the superincumbent wall crushing the foundation. Roofs.-Westminster hall approaches the limit of width that is possible without very inconvenient proportions or central supports; and the domes of the churches of St. Peter, in Rome, and St. Paul, in London, are in the same predicament. Arches of a Bridge.-A stone arch much larger than those of the magnificent bridges in London, would be in danger of crushing and splintering its material. Ships.-The ribs of timbers of a boat have scarcely a hundredth part of the bulk of the timbers of a ship ten times as long as the boat. A ship's yard of ninety feet contains, perhaps, twenty times as much wood as a yard of thirty feet, and, even then, is not so strong in proportion. If ten men may do the work of a three-hundred-ton ship, many more than three times that number will be required to manage a ship three times as large. Very large ships, such as the two built in Canada in the year 1825, which carried each nearly 10,000 tons, were weak from their size alone; and the loss of these two first specimens of gigantic magnitude will not encourage the building of others like them. (To be continued.) PRESERVATION OF BOOKS FROM INSECTS. THE Societé des Bibliophiles of Hainault have offered a gold medal, worth one hundred francs, to the author of the best memoir forwarded to the society, in answer to the following question : "What are the best means of totally preventing the ravages of the insects which destroy books?" The condition annexed to the success of the paper is, that the means proposed may be applied easily, and at little expense to all libraries large or small. It seems to us, that in making this proposal, the society has not reflected that it will give a very difficult task to the commission appointed to decide on the merit of the different papers sent in. Let us suppose that several persons recommend each a different process. How is the society to test the respective value of these communications; how are they to judge if they are suitable, or if they fulfil exactly the object proposed? The ravages of insects in books are never instantaneous; it is only after the lapse of some time, more or less long, that it is possible to perceive traces of them on the paper. We are convinced that essential oils and strong perfumes would preserve a book for a length of time from the cause of destruction, to which the question of the society refers; but to be assured of the continued existence of these perfumes would require an observation of many years. Amongst the means of preservation which appears to us best, we may cite the following:-1. To introduce in every volume some leaves of an herb, of small expense, and strong and penetrating smell. 2. To submit the books to the vapour of essential oils in a state of ebullition. 3. To line the interior of the covers of every book with sheets of tanned sheepskin or paper, in the preparation of which use should be made of substances of a strong odoriferous smell, and in the course of time to rebind them with materials of a similar description. As we are on the subject of the preservation of books, it appears to us, that the printers of the present day do not work for posterity; for they employ a species of paper containing a germ of destruction, which, although it acts slowly, is not the less certain in effect. We allude to the chloride of which use has been made for some years, for the purpose of whitening the pulp, which serves to prepare the different sorts of paper intended, as well for printing, as for ordinary use. This strong agent not only takes from the paper a portion of the strength which it possessed under the old process of bleaching, and which may easily be perceived by comparison of the paper of our modern books, which can be easily torn, with the tough paper of the books of the last century; but it also enters into intimate combination with the pulp, and this union will have the effect of reducing to powder in the course of twenty years the books of the present day.-Le Fanal. ATMOSPHERIC REFRACTION AND REFLECTION. NOT only every thing we hear, but all we see, is through the medium of the atmosphere. Without some knowledge of its action upon light, it would be impossible to ascertain the position of the heavenly bodies, or even to determine the exact place of very distant objects upon the surface of the earth; for, in consequence of the refractive power of the air, no distant object is seen in its true position. All the celestial bodies appear to be more elevated than they really are; because the rays of light, instead of moving through the atmosphere in straight lines, are continually inflected towards the earth. Light passing obliquely out of a rare into a denser medium, as from vacuum into air, or from air into water, is bent or refracted from its course towards a perpendicular to that point of the denser surface where the light enters it. In the same medium, the sine of the angle contained between the incident ray and the perpendicular is in a constant ratio to the sine of the angle contained by the refracted ray and the same perpendicular; but [this ratio varies with the refracting medium. The denser the medium, the more the ray is bent. The barometer shows, that the density of the atmosphere decreases as the height above the earth increases. Direct experiments prove, that the refractive power of the air increases with its density. It follows, therefore, that if the temperature be uniform, the refractive power of the air is greatest at the earth's surface and diminishes upwards. A ray of light from a celestial object falling obliquely on this variable atmosphere, instead of being refracted at once from its course, is gradually more and more bent during its passage through it, so as to move in a vertical curved line, in the same manner as if the atmosphere consisted of an infinite number of strata of different densities. The object is seen in the direction of a tangent to that part of the curve which meets the eye, consequently the apparent altitude of the heavenly bodies is always greater than their true altitude. Owing to this circumstance, the stars are seen above the horizon after they are set, and the day is lengthened from a part of the sun being visible, though he really is behind the rotundity of the earth. It would be easy to determine the direction of a ray of light through the atmosphere, if the law of the density were known; but as this law is perpetually varying with the temperature, the case is very complicated. When rays pass perpendicularly from one medium into another, they are not bent; and experience shows, that in the same surface, though the sines of the angles of incidence and refraction retain the same ratio, the refraction increases with the obliquity of incidence. Hence it appears, that the refraction is greatest at the horizon, and at the zenith there is none. But it is proved that at all heights above ten degrees, refraction varies nearly as the tangent of the angular distance of the object from the zenith, and wholly depends upon the heights of the barometer and thermometer. the quantity of refraction at the same distance from the zenith, varies nearly as the height of the barometer, the temperature being constant; and the effect of the variation of temperature is to diminish the quantity of refraction by about its 480th part for every degree in the rise of Fahrenheit's thermometer. Not much reliance can be placed on celestial observations within less than ten or twelve degrees of the horizon, on account of irregular variations in the density of the air near the surface of the earth, which are sometimes the cause of very singular phenomena. The humidity of the air produces no sensible effect on its refractive power. For Bodies, whether luminous or not, are only visible by the rays which proceed from them. As the rays must pass through strata of different densities in coming to us, it follows that, with the exception of stars in the zenith, no object either in or beyond our atmosphere is seen in its true place. But the deviation is so small in ordinary cases, that it causes no inconvenience, though in astronomical and trigonometrical observations due allowance must be made for the effects of refraction. Dr. Bradley's tables of refraction were formed by observing the zenith distances of the sun at his greatest declinations, and the zenith distances of the pole-star above and below the pole. The sum of these four quantities is equal to 180°, diminished by the sum of the four refractions, whence the sum of the four refrac tions was obtained; and from the law of the varia. tion of refraction determined by theory, he assigned the quantity due to each altitude. The mean hori. zontal refraction is about 35′ 6′′, and at the height of forty-five degrees it is 58".36. The effect of refraction upon the same star above and below the pole was noticed by Alhazen, a Saracen astronomer of Spain, in the ninth century, but its existence was known to Ptolemy in the second, though he was ignorant of its quantity. The refraction of a terrestrial object is estimated differently from that of a celestial body. It is measured by the angle contained between the tangent to the curvilineal path of the ray, where it meets the eye, and the straight line joining the eye and the object. Near the earth's surface, the path of the ray may be supposed to be circular; and the angle at the centre of the earth corresponding to this path is called the horizontal angle. The quantity of terrestrial refraction is obtained, by measuring contemporaneously the elevation of the top of a mountain above a point in the plain at its base, and the depression of that point below the top of the mountain. The distance between these two stations is the chord of the horizontal angle; and it is easy to prove that double the refraction is equal to the horizontal angle, increased by the difference between the apparent elevation and the apparent depression. Whence it appears that, in the usual state of the atmosphere, the refraction is about the fourteenth part of the horizontal angle. (To be continued.) APPARATUS FOR INCREASING THE ILLUMINATING POWER OF COAL GAS. BY J. W. TAYLOR. CARBURETTED hydrogen it is well known owes nearly all its illuminative power to the accidental admix. ture of a certain oily vapour, which is given off during the decomposition of the coal in the retorts: being aware of this, it occurred to me, that if the gas could be more strongly impregnated with a similar compound, the flame would be increased in intensity, which I afterwards found to be the case. The apparatus consists of a brass reservoir, or chamber, attached to the end of the gas pipe, near the burner; this reservoir may be in the shape of an oil-flask, made air-tight with a screw joint, or other means of supplying any highly volatile oil, turpentine or mineral naphtha, and should be kept about half full; into this reservoir the gas pipe ascends a little above the surface of the oil; a very small jet pipe of gas regulated by a stopcock, is branched off below this chamber, so as to cause a sufficient evaporation of the oil to unite with the gas in the flask receiver: the whole is, of course, surmounted with the usual burner and lamp glass. By employing this apparatus for burning coal gas, the intensity of the flame will be very considerably augmented, consequently the same degree of light may be obtained with a far less consumption of gas, a point which I consider of some importance. It may also be employed for burning those varieties of gas, by the decomposition of several of the anthracites, bituminous earths, woods, &c., which would not be otherwise employed with any advantage for the purpose of illumination. The apparatus might be manufactured at a very trifling cost, being very compact and neat in appearance.-Chemist. LONDON.-Printed by D. FRANCIS, 6, White Horse Lane, Mile End.-Published by W. BRITTAIN, 11, Paternoster Row. Edinburgh, J. MENZIES.-Glasgow, D. BRICE and J. BARNES.—Liverpool, G. PHILIP. IMPREGNATING WATER WITH CARBONIC ACID GAS. We have already, in Volume II, given several contrivances for this purpose as used among us; we give the present as the French method of accomplishing the same purpose. A mere description and reference to the apparatus will be all that is sufficient to render it intelligible. The two bottles A and A, seen on the sides of the apparatus, contain chalk and oil of vitriol. These bodies, as is well known, act chemically upon each other. The chalk, which is a carbonate of lime, becomes decomposed, parts with its carbonic acid, and its lime unites with the sulphuric acid, forming a sulphate of lime; the carbonic acid being gaseous, rises and remains in the upper part of the bottle, but as an infinitely greater quantity is liberated than can be contained in the bottle, it passes off through a tube B, and from that into a second tube D, and along it into a second bottle E, which is partly filled with water. The gas being soluble in water is rapidly absorbed by it in this vessel, until the water becomes charged with the gas, that is, until it can take up no more; when this is the case, it, instead of being absorbed, passes up the second pipe D into the lower vessel E. The same thing again occurs here as in the former vessel, and when the water in this lower vessel is in like manner charged, the gas will proceed onwards by the third tube D into the bottle F, charging this also; finally it passes along the pipe G, beneath water in the basin H, into the air-jar I, whence it may be removed for use as collected. The reason there are several jars is, that the gas before it can reach I must pass through the water of three vessels, and it becomes thereby very pure and cool. The apparatus is to be considered double, one side of the cut corresponding to the other. Also there are three safety tubes attached to various parts, marked CCJ; these are bent tubes of glass, having a few drops of mercury poured into them to prevent the passage of air inwards; their use is to prevent bursting of any part of the apparatus by too great pressure of the gas arising from its rapid formation. WALLACE'S EIDOGRAPH. Ir is a fact well known, that artists of various descriptions, who have frequent occasion to imitate original designs, have long felt the want of convenient mathematical instruments, by which a copy may be made with neatness and expedition, that shall have any given proportion to the original. The pantograph is the only instrument that has been hitherto employed; but although correct and plausible in theory, in practice it is found to be so very imperfect, that the artist hardly ever thinks of making use of it. A consideration of the essential service that would be rendered to the graphic art, by a copying instrument, which should be at once simple in its theory, and easy in its application, induced Mr. Wallace, Professor of Mathematics, at Edinburgh, to turn his attention to the subject; and some years ago he produced a model of a copying instrument, which he denominated an eidograph. The instrument, and its application to the copying of a very great variety of subjects, having been shown to engineers, engravers, and other competent judges in London and in Edinburgh, their opinion of its utility has been such as to leave no doubt of its completely fulfilling the views of the inventor. The instrument is represented in Fig. 2. The beam A B, which is made of mahogany, slides backward and forward in a socket C: the socket turns on a vertical axis, supported by the fulcrum D, which stands on a table. There is a slit in the beam, through which the axis of the socket passes, so that when the beam slides in the socket, a portion of it passes on each side of the axis. There are two equal wheels EE below the beam, which turn on axes that pass through pipes fixed at AB, near its extremities; and a steel chain passes over the wheels as a band, by which a motion of rotation may be communicated from the one to the other. There are two arms FF, which slide in sockets along the lower face of the wheels, just under their centres at the extremity G of one arm, there is a metal tracer, with a handle attached to it, by which its points may be carried over the lines in any design; and at H, the extremity of the other arm, there is a black-lead pencil fixed in a metal tube, which is ground to fit so exactly into a pipe so as just to slide up or down. In using the instrument, the pencil in its tube is raised by a thread which passes over a pulley, and it descends again by a weight with which it is loaded. From the perfect equality of the wheels, it is easy to see, that if the arms attached to them be placed parallel in any one position, they will retain their parallelism, although one of the wheels, and consequently both, be turned on their centres. Supposing, now, that B C and A C, the parts into which the axis is divided at the centre, have any proportion whatever to each other, if the distances of the tracing point G, and pencil point H, from the centres of their wheels have the very same proportion, then it follows from the elements of geometry, that the tracing point G, the centre C, and the pencil point H, will be in a straight line; and further, that CG, and CH, the distance of these points from the centre, will have to each other the constant proportion of CB to CA, or of E G to AH. Such being the geometrical property of the eidograph, if any subject to be copied be fixed to the table on which the instrument stands, and the tracing point be carried over every line of the design, the pencil point will trace a copy in all respects similar to the original. To facilitate the adjustment of the instrument, so that the copy may have any given ratio to the original, there are scales of equal parts on the beam and the two arms. By these and verniers, both halves of the beam, and equal lengths on the arms, are each divided into one thousand equal parts, and, at certain intervals, corresponding numbers are marked on them. By means of the scales, when any ratio is assigned, the adjustment is made without the least difficulty. To avoid any derangement by the chain slipping on the wheels, there are clamps at K and K, which hold it fast to the wheels at points where it never quits them. They are slackened when the instrument is adjusted. ALLOYS OF STEEL WITH SILVER. BESIDES the various processes that have been adopted ostensibly with the design of improving the quality of pure steel, an almost equal number of attempts have been made to alloy it with other substances, with which, really or in pretence, it has been found chemically to combine. These projects have given rise to a variety of specious appellations, at the best harmless, when applied to mere supe riority in the article professedly manufactured from factitious steel, the real excellence of which, if it have any, the common refiner knows must depend entirely upon his old-fashioned operations skilfully performed. Two eminent chemists make and publish a series of experiments, by which it is demonstrated, that a small portion of various of the precious metals might be mixed, by fusion, with the substance of steel; the idea of turning the discovery to practical account is promptly caught; and silver steel, having the advantage of euphony and novelty, becomes a popular denomination in the market. But as there is some chance of this manufacture being considered as new-fangled, and diversity and competition being the body and spirit of business, another projector turns him to antiquity: every one interested in cutlery having heard of the famous oriental sabres that, while they bent like a switch, were of so stern a temper that they would themselves cut through ordinary irons; so, with tolerably good taste at least, we are greeted with the announcement of Damascus steel. Silver, however, is an ingredient within the reach of every manufacturer who chooses to put it into his melting pot; and Damascus being a somewhat equivocal epithet, at best applying rather to a mode than a material of steel-making; a third party procures from abroad a few lumps of the celebrated Indian wootz, a substance which not many persons have seen, and still fewer thoroughly understand, and under these auspices comes forth Peruvian steel. Each of these materials may be of acknowledged goodness and celebrity; but at all events they must alike be content with the common credit of an earthly origin: not so, however, with those ferruginous masses which have, at different times, fallen from the clouds. Poetry and policy unite to favor the notion that iron smelted in ether, and hardened in the north wind, must needs, like Homer's horses begotten of the latter agent, be of excellent temper; accordingly, meteoric steel has been among the discoveries which have claimed the approbation of the public. We have taken the liberty to introduce, thus playfully, four denominations of factitious steel, which, when recommended as superior to pure steel, for fine cutlery in general, deserve to be treated in no graver style: as connected, however, with metallurgic phenomena, the processes developing those peculiarities of elementary chemical combination, or mechanical structure, upon which the obvious characteristics of the above-named steels are assumed to depend, are far from being uninteresting to the experimentalist. Attempts to combine iron with silver have at various times been made. The experiments of a French chemist, M. Guyton, as published in the "Annales de Chimie," were deemed so satisfactory to the operator, that he concludes his detail in these terms: Thus the iron was here alloyed with the silver even in greater quantity than the silver with the iron. Iron can, therefore, no longer be said to refuse to mix with silver; it must, on the contrary, be acknowledged that those two metals brought into perfect fusion, contract an actual chemical union; that, whilst cooling, the heaviest, and, at the same time, the most fusible metal, separates for the greatest part; that notwithstanding each of the two metals retains a portion of the other, as is the case in every liquation; that the part which remains is not simply mixed or interlaid, but chemically united; lastly, that the alloy in these proportions possesses peculiar properties, particularly a degree of hardness that may render it extremely useful for various purposes." A few years ago, Messrs. Stodart and Faraday made a series of experiments on the alloys of iron and steel at the laboratory of the Royal Institution, the results of which are subsequently published in the "Journal of Arts and Sciences." From the account referred to it appears, that not only silver, but platinum, rhodium, gold, nickel, copper, and even tin, have an affinity for steel sufficiently strong to make them combine chemically according to the import of this notice, though only mechanically in the opinion of some persons. With respect to the alloy of silver, there are, according to the testimony of the experimentalists mentioned above, some very curious circumstances attending it. If steel and silver be kept in fusion together for a length of time, an alloy is obtained, which appears to be very perfect while the metals are in a fluid state; but on solidifying and cooling, globules of pure silver are expressed from the mass, and appear on the surface of the button. If an alloy of this kind be forged into a bar, and then dissected by the action of dilute sulphuric acid, the silver appears, not in combination with the steel, but in threads throughout the mass, so that the whole has the appearance of a bundle of fibres of silver and steel, as if they had been united by welding. The appearance of these silver fibres is very beautiful; they are sometimes one-eighth of an inch in length, and suggest the idea of giving mechanical toughness to steel, where a very perfect edge may not be required. At other times, when silver and steel have been very long in a state of perfect fusion, the sides of the crucible, and frequently the top also, are covered with a fine and beautiful dew of minute globules of silver; this effect can be produced at pleasure. At first the operators were unsuccessful in detecting, by means of chemical tests, the presence of silver in the metallic button; and considering the steel to be uniformly improved, they were disposed to attribute its excellence to the effect of the silver, or to a quantity too small to be tested. By subsequent experiments, however, they were able to detect the silver, even to less than one part in five hundred. "In making the silver alloys, the proportion first tried was 1 silver to 160 steel; the resulting buttons were uniformly steel and silver in fibres, the silver being likewise given out in globules during solidifying, and adhering to the surface of the fused button; some of these, when forged, gave out more globules of silver. In this state of mechanical mixture the little bars, when exposed to a moist atmosphere, evidently produced voltaic action; and to this we are disposed to attribute the rapid destruction of the metal by oxydation; no such destructive action taking place when the two metals are chemically combined. These results indicated the necessity of diminishing the quantity of silver, and 1 silver to 200 steel was tried. Here, again, were fibres and globules in abundance; with 1 to 300 the fibres diminished, but still were present; they were detected even when the proportion of 1 to 400 was used. The successful experiment remains to be named. When 1 of silver to 500 steel were properly fused, a very perfect button was produced; no silver appeared on its surface; when forged and dissected by an acid, no fibres were seen, although examined by a high magnifying power. The specimen forged remarkably well, although very hard; it had, in every respect, the most favor |