Volume 1 — MISCELLANY. SCIENCE.

A New Kind of Mirror.—The Chemical News states that M. Dode, a French chemist, has introduced platinum mirrors, which are greatly admired, and which present this advantage, that the reflecting metal is deposited on the outer surface of the glass, and thus any defect in the latter is concealed. The process, which is patented in Paris, is described as follows: Chloride of platinum is dissolved in water, and a certain quantity of oil of lavender is added to the solution. The platinum immediately leaves the aqueous solution and passes to the oil, which holds it in suspension in a finely divided state. To the oil so charged the author adds litharge and borate of lead, and paints a thin coat of this mixture over the surface of the glass, which is then carried to a proper furnace. At a red heat the litharge and borate of lead are fused, and cause the adhesion of the platinum to the softened glass. The process is very expeditious. A single baking, M. Dode says, will furnish 200 metres of glass ready for commerce. It would take fifteen days, he says, to coat the same extent with mercury by the ordinary plan.

African Silkworm.—A silkworm before unknown in Europe has been introduced into France from Senegal, and without suffering from change of climate. It yields a richer silk than that of any other worm known to naturalists, and its cocoons are twice the ordinary weight. It is to be tried in Algiers, and if successful there, this new and rich silk may become in time an important article of commerce.

Science in a Balloon.—Mr. Glaisher has {713} given, in a lecture at the Royal Institution, a resumé of his scientific experiments in balloons. Tables recording the decline of temperature with elevation, show that when the sky was clear a more rapid decline took place than when the sky was cloudy. Under a clear sky, a fall of 1° takes place within 100 feet of the earth, but at heights exceeding 25,000 feet it is necessary to pass through 1,000 feet of vertical height to obtain a fall of 1° in temperature. At extreme elevations, in both states of the sky, the air became very dry, but as far as his experiments went, was never quite free from water. From ascents made before and after sunset, Mr. Glaisher concludes that the laws which hold good by day do not hold good by night; indeed, it seemed probable that at night, for some little distance, the temperature may increase with elevation, instead of decreasing. From experiments made on solar radiation with a blackened bulb thermometer, and with Herschel's actinometer, it was inferred that the heat rays from the sun pass through space without loss, and become effective in proportion to the density or the amount of water present in the atmosphere through which they pass. If this be so, the proportion of heat received at Mercury, Venus, Jupiter, and Saturn may be the same as that received at the earth, if the constituents of their atmospheres be the same as that of the earth, and greater if the amount of aqueous vapor be greater, so that the effective solar heat at Jupiter and Saturn may be greater than at either the inferior planets, Mercury or Venus, notwithstanding their far greater distances from the sun. This conclusion is most important as corroborating Professor Tyndall's experiments on aqueous vapor. Experiments on the wind showed that the velocity of the air at the earth's surface was very much less than at a high elevation. A comparison of the temperature of the dew point, as shown by different instruments, gave results proving that the temperatures of the dew point, as found by the use of the dry and wet bulb thermometers, and Daniell's hygrometer, are worthy of full confidence as far as the experiments went.

The Eruption of Mount Etna.—At a recent meeting of the Paris Academy of Sciences, an important letter was read from M. Fouqué to M. Saint-Claire Deville on the eruption of Etna, which has presented several phenomena of great scientific interest.

The eruption commenced at half-past ten on the evening of January 31. On the previous day two successive shakings of the earth had been noticed. Just before the eruption began a violent earthquake was felt, the wave travelling to the north-east; after this, slight oscillations continued until about 4 A.M. Large flames now rose from a point on the north-east side of Etna 5,500 feet above the snow line, and lava began to flow rapidly. In two or three days the lava traversed a space of 19,000 feet, with a width of from 10,000 to 12,000, and a variable thickness, but often reaching to the depth of 30 or 60 feet. After destroying for some distance everything in its passage, the current of lava struck one of the old craters, and then bifurcated. The stream on the west side moved very slowly, and, becoming subdivided, it nearly ceased to move; the stream on the east side fell over a deep and precipitous valley, which it soon filled, being then able to continue its progress, until finally it was stopped by a lava mound of a previous eruption.

The number of the craters is seven; of these five form a vast elliptical enclosure, the major axis of which is directed toward the north-east. A deep fissure, 1,500 feet in length, opened from the base of a former crater, Frumento, to the nearest of the present cones. This chasm, M. Fouqué shows, was probably formed by the shock at the commencement of the eruption. This fissure, and also a depression of the crater Frumento, is in a right line with the major axis of the ellipse formed by the craters. The same general fact has been several times noticed in previous eruptions.

The vapors attending an eruption have been divided into the dry, containing chiefly chloride of sodium and no water, the acid, which contain a large amount of watery vapor, the alkaline, and the carbonic. The first indicates the maximum, and the last the minimum of volcanic action. Each of these varieties of vapor, succeeding in their order, were noticed at this eruption. M. Fouqué found the dry vapor upon the still incandescent lava; the acid vapor in those parts where the temperature was over {714} 400°; the alkaline, where the temperature was lower, but generally over 100°; and finally, carbonic acid has been detected in one of the adjacent old craters, which was at the ordinary temperature. The first three varieties of vapor were thus found upon the same transverse section of the lava, less than 150 feet distant from each other. In all these vapors the atmospheric air which accompanied them was deprived of part of its oxygen, generally containing only from 18 to 19 per cent., and in some alkaline vapors the proportion was still less.

In this eruption there was a remarkable absence of sulphur and its compounds; chemical tests as well as the sense of smell could detect no trace of them. The eruption indeed was characterized by the absence of the compounds of sulphur and the abundance of the compounds of chlorine. Hydro-chlorate of ammonia, which was found in abundance, has generally been regarded as exclusively belonging to the alkaline vapors; but here it has been discovered among the other varieties, whilst the alkaline vapors were distinguished by the carbonate rather than by the hydrochlorate of ammonia.

At the present time, M. Fouqué writes, the eruption is most active in the four lowest craters; these throw liquid lava into the air, and emit a nearly colorless smoke; the three superior craters eject solidified lava and black stones, at the same time pouring out a dense smoke charged with aqueous vapor and brown-colored ashes.

The three higher craters produce every two or three minutes a very loud report resembling the rolling of thunder; the four lower craters, on the contrary, send forth a rapid succession of ringing sounds, which it is impossible to count. These sounds follow each other without any cessation, and are only to be compared to the noise produced by a series of blows from a hammer falling on an anvil. If the ancients heard these noises in former eruptions, it is easily conceivable how they imagined a forge to exist in the centre of the volcano, with Cyclops for the master workman. The lava is black, rich in pyroxene, and strongly attracted by a magnet. Since the commencement of the eruption, the central crater of Etna has emitted white vapors, which continually cover its summit. Several good photographs of the eruption have been taken by M. Berthier, who accompanied M. Fouqué in his explorations, which were by no means unattended with danger.

M. Saint-Claire Deville then made some observations on this paper. He explained the almost entire absence of sulphur by the fact that M. Fouqué only examined the vapors from the lava. These nearly always contain chlorine for their electro-negative element, and scarcely show, and that not until later, sulphuretted and carbonic vapors. After the eruption of Vesuvius in 1861, very light deposits of sulphur were found covering the hydrochlorate of ammonia, which shows that the former body is not absent from the lava. The existence of hydrochlorate of ammonia in the emanations does not necessarily exclude that of the vapors of hydrochloric and sulphuric acids.

Magnetism of Iron-clad Ships.—Staff-Commander Evans, of the British navy, and Mr. Archibald Smith, who have devoted themselves for several years to investigations into the character of the magnetism of iron-built and armor-plated ships, have embodied the results of their studies in an interesting paper read at a recent meeting of the Royal Society. It is well known that iron ships have been very difficult to navigate because of the disturbing effect of the iron upon the compass, and serious accidents have happened in consequence. But underwriters, and the whole naval profession, will be glad to hear that the difficulty and risk are now greatly lessened, if not entirely removed. For the results established by the paper in question are—That it is no longer necessary to swing a ship in order to ascertain the compass deviation, or error, seeing that it is possible to determine the various forms of error by mathematics; that an iron ship should always be built with her head to the south; if built head north, there is such a confused amount of magnetism concentrated in the stern as to have a violent disturbing effect on the compass; that if, after building, a ship is to be armor-plated, the head, during the fixing of the plates, should be turned in the opposite direction— that is, to the north; and that especial pains should be taken while building an iron ship to provide a {715} suitable place for the standard-compass. Beside these particulars, the shot and shell stowed in the vessel, the iron water-tanks, and, indeed, all the iron used in her interior fittings, are to be taken into account; and it is satisfactory to know that the influence exerted on the compass by any one or all of these conditions can be ascertained, and allowed for, as in the other cases above mentioned.

"Gyges" Explained.—The London Reader gives the following explanation of a curious experiment in optics which has been performed at one of the London theatres under the name of "Eidos AEides," and reproduced in New York under the appellation of "Gyges." It consists in causing an actor or an inanimate object which is in full view of the audience at one moment to disappear instantly, and then to reappear with the same rapidity. The means by which this is accomplished are very simple, and are to some extent similar to those used in exhibiting "Pepper's Ghost." A sheet of plain unsilvered glass is placed upon the stage, either upright or inclined at a suitable angle, at the place where the actor or object is to disappear. This glass is not perceived by the audience, and it does not interfere with their view of the scenery, etc., behind the plate. A duplicate scene representing that part of the back of the stage covered by the glass is placed at the wing, out of sight of the spectators. With the ordinary lighting of the stage the reflection of this counterfeit scene in the glass is too faint to be observed; but when a strong light is thrown upon the scene, the stage lights being lowered at the same time, the image becomes visible. This duplicate scene being an exact fac-simile of the background of the stage, the change is not noticed by the audience, the only difference being that they now see by reflection that which they saw a moment previously by direct vision. The actor, standing a sufficient distance behind the glass, is completely hidden from view, and he is again rendered visible by turning down the light on the false scene and allowing the stage lights to predominate. When "Eidos AEides" was being performed at Her Majesty's Theatre, it was, however, possible, with a good opera-glass, to distinguish the outline of the figure behind the plate. The effects produced may of course be modified. An actor may be made to appear walking or flying in the air, or dancing on a tight-rope, by eclipsing or obscuring a raised platform on which he may be placed.