which is excited by a current that is made to traverse the iron while in a state of fusion. Numerous gas bubbles are produced, and the resulting iron is harder and more tenacious than what is manufactured in the ordinary way.

APPLICATION OF SULPHURET OF CARBON TO THE EXTRACTION OF OLEAGINOUS MATTERS ON THE LARGE SCALE.-In France there are two great sources of waste of oleaginous and fatty substances. Vast quantities of oil remain in the olives, however much they may be pressed; and enormous quantities of soap, after having been used in the silk manufactories, pass off into the rivers and are lost. Both these sources of waste are now about to cease, on account of the industrial applications of sulphuret of carbon-a substance which possesses an extraordinary power of taking up fatty matters, from which it is separated with great facility by distillation. As long as it was dear, its application in this way was impossible; from improved methods of manufacture it is now become extremely cheap; and almost none of it is lost during its application even on the large scale. The sulphuret of carbon is allowed to flow through the olives, partially exhausted by pressure, to a still, whence it passes to a new quantity of olives; the process being continuous, and so perfect that the very presence of the sulphuret is not to be perceived in the establishment. The olives, completely exhausted by the sulphuret, are far more effective as manure than those from which the oil has been only imperfectly separated. Applied to a saving of the soap refuse of the silk manufactories, several thousands of tons of that valuable material will be recovered annually. Large quantities of the regenerated soap have already come into use.

FURTHER UTILIZATION OF ALUMINIUM BRONZE.-Bronze containing ten per cent. aluminium and ninety per cent. copper, has been found to possess the invaluable property of being almost indestructible in the working parts of machinery exposed to great wear and tear. This is illustrated by a purpose to which it has recently been applied in France. Paper, and especially when coated with dried gum, is rapidly destructive of the best cutting instruments, and the parts of the machine connected with them. Holes for rendering French postage-stamps easily separable, one from another, are made by an instrument having three hundred needles, that descend through the five layers of postage-stamps lying under them into holes which have been carefully made in a steel plate placed beneath. In one day, the steel plate is worn to such a degree that afterwards, instead of the holes being punched in the paper, the latter is merely crumpled into the holes in the plate, and more or less injured. A plate of aluminium bronze having been substituted for the steel plate, it was found to last for fifteen hundred days without requiring any repair, having received daily one hundred and twenty thousand blows. Hitherto the utility of aluminium bronze was limited by the difficulty with which it was soldered; ordinary solder does not answer for the purpose. It has, however, been found, that one piece of aluminium bronze may be easily and firmly united to another, or to iron, either cast or malleable, by means of

a mixture of common tin solder and an amalgam of zinc and mercury. The proportions may vary from equal weights of tin solder and amalgam to one part amalgam and three parts tin solder.

PRESERVATION OF LIQUORS CONTAINING ALCOHOL.-Liquors, such as beer, containing comparatively small quantities of alcohol, have a great tendency to natural fermentation. It has been found that this tendency may be lessened, and even destroyed, by a judicious application of heat. The higher the temperature, the more effective it is; but unless kept within certain limits, the flavour will be deteriorated, or even destroyed-a disagreeable one supervening. It is enough if a temperature at all higher than 45 Cent. is reached; but that between 28' and 58° must be allowed to continue for as short a time as possible, since the various temperatures between these points are exactly those most favourable to the development of natural fermentation. The temperature should be raised as rapidly as possible to between 48° and 58', which should be maintained for at least twenty, and at most sixty, minutes; after which the cooling should be rapid, and the liquor should then be transmitted to barrels which have been previously filled with carbonic acid.

NEW APPLICATION OF ELECTRICITY. It is necessary that the person attending on a power-loom should carefully watch and remedy the breaking of a thread; and as several looms may be in charge of one attendant, it would be very useful that his attention should be directed to a broken thread. This is now done with great simplicity and certainty in the case of the stocking-machine, by means of electricity; and there is no reason why the same contrivance should not be applicable in other cases. A small lever rests on the thread, and retains its position as long as the thread is whole. But the instant the thread breaks, the lever falls, and completes connection between the poles of a galvanic battery, which excites a small electro-magnet, and sets a bell-ringing apparatus in action. This attracts the notice of the attendant, so that the broken thread is instantly made whole again.

THE LATENT IMAGE. The photographer had long been surprised at, but unable to explain, the existence of the latent image; and its development has never failed to astonish the uninitiatedits appearance being something resembling the effects of magic. Its nature, thanks to Mr. Carey Lea, is no longer a mystery; and its existence is shown to be due to well-known optical principles. There are certain substances which, in contact with organic matters (thus, iodide of silver), undergo a marked chemical change when exposed to the action of light. It was considered that the presence of the luminous body itself was required to produce this effect, which is not, however, the case. It has long been known that certain substances are capable of absorbing light and again emitting it-some in a few seconds, some during a much longer period. It is true that this fact was remarked only regarding the luminous rays; but we might infer it from analogy with regard to the actinic rays also; and there is no question of it regarding the calorific. It explains, indeed, the fact, that an engraving exposed for a few

minutes to light, and then placed in contact with sensitized paper in the dark, will give rise, on development, to an image. Applying this principle, we shall find that a latent image must result when iodide of silver, for example, is exposed to light along with some substance capable of absorbing light, and retaining it for a sufficient length of time, and is then, before the light has been all emitted, placed in contact with the requisite organic matter. The conditions necessary for the production of the chemical changes indispensable to the obtaining a picture are fulfilled; since the iodide of silver and the organic matter are simultaneously in presence of light, though not of the luminous body.

ELECTRIC CONDITION OF DIFFERENT PARTS OF THE EARTH.—It has been found that, if one extremity of a long wire is inserted in the earth at one place, and the other in the earth at another place which is higher than the former, a current of electricity will constantly traverse the wire from the lower to the higher level. This fact has been recently explained by M. Matteucci, and his explanation has been experimentally illustrated by him. It is a consequence of the positive electricity constantly carried towards the poles by the wind, and the inductive action of this electricity on the earth. The stratum of air near the earth, especially over seas and lakes, is continually being neutralized, but the neutralization goes on more slowly and imperfectly in mountainous and even slightly elevated regions. Hence the mountain and the air in contact with it are in opposite electrical states of greater intensity, and thus it is that clouds are so strongly attracted by mountains. The mountain and the plains are negatively electrified, but not in an equal degree; and if their electricity is not in a static condition, a conductor must lead a current from one to the other. They are not in a statical condition; for neutralization of the air in contact with the earth is constantly taking place, and electrical equilibrium is therefore constantly being disturbed. This is illustrated by M. Matteucci by a very simple and satisfactory experiment. He places a globe, made of porous earth or of wood, covered with moistened blotting-paper, on an insulating stand; fixes a small metallic disk on the highest part of the globe, and in contact with the moistened blotting-paper, and a similar disk from fifty to ninety degrees from the first; then, having connected the plates with a galvanometer, he electrifies the globe. No current is, under these circumstances, indicated by the galvanometer; for the electricity of the globe is in a static condition. He next suspends, by an insulator, a small, slightly concave metallic plate over the higher disk, and about an inch from it. This concave plate represents the atmosphere; and if it is placed in connection with one conductor of the electrifying machine, and the globe with the other conductor, so as to oppositely electrify the globe and the plate, the galvanometer will, on turning the electrifying machine, at once indicate the presence of a current. The electric condition of the globe is different at different parts; and it is no longer static, for the electricity of the globe is constantly passing to and neutralizing that of the plate. It is not always necessary that the extremities of a long insulated wire, in

serted in the earth, should be at different levels, in order that a current should be developed in it, since the positive electricity of the air increases as the poles are approached; and hence, in a similar way, the negative electricity of the earth produced by inductions. There is, therefore, usually a difference of intensity between the earth at the poles and at the equator; and as the electric state is not static, a wire in a direction from the equator to either pole should indicate a current, which experiment shows actually to take place.

PHOTOGRAPHIC MARINERS' COMPASS.-A simple means of registering a ship's course by photography has recently been invented. The instrument employed is the compass by which the vessel is steered, modified for the purpose. A small aperture is made in the line representing the north on the card, and in it is placed a lens. Under the card is sensitized paper, which is made, by clockwork, to pass along with a regulated speed. Were the vessel constantly to move in the plane of the magnetic meridian, the paper, after development, would show a straight line, of a length dependent on the time of the voyage; but every deviation to the east or west will be marked, by the light which illuminates the compass, on the paper, which moves under the aperture in the card, the latter being immovable. If the paper is divided by transverse lines, the length of time during which the vessel was steered in any particular direction will be indicated by the corresponding deviations from a line corresponding with the intersection of the planes of the magnetic meridian and the horizon.

LITERARY NOTICES.

OUTLINE LUNAR MAP. Zones II. and IV. Areas IV. a and IV. §, with Catalogue of two hundred and three objects, the whole deduced from Photographs, Observations, and Measurement, by W. R. BIRT, F.R.A.S. Under the direction of the Lunar Committee of the British Association. (From the Report of the British Association for the Advancement of Science, for 1866.) (Printed for private circulation.) -Mr. Birt, the Secretary of the British Association Moon Committee has evidently made his arduous and laborious task a labour of love, and the positions of the great map comprised in Zones II. and IV., areas ÍV. a and IV. I, now issued together with the elaborate, accompanying, and explanatory, pamphlet, bear ample testimony to the value of his work. The pamphlet states that "the scale of two hundred inches in the moon's diameter appears to be the smallest that can be used with advantage in the present state of selenography." This dictum embodies the deliberate opinion of the distinguished astronomers who form the committee, and must therefore be received with great respect. No doubt much may be said for it; but as few observers have any opportunity of seeing portions of the moon on anything like so large a

scale, and as the majority of observations are necessarily made under a magnification which is only a small fraction of that supposed by a map of the lunar disk nearly seventeen feet in diameter, the scale selected is not without serious difficulties. It certainly gives plenty of room for "inserting synonyms" and "numerical data," but renders objects seen under moderate powers difficult of identification, and tends to induce observers to draw them on a scale disproportionate to the amount of detail actually seen. The "best possible scale," for the purpose will be estimated differently by various observers; but all agree in appreciating Mr. Birt's work, which is to supply a series of lunar map sections, carefully drawn to scale, and exhibiting contour lines of the various formations.

The nature of each object is indicated by a symbol which is explained in the Report of the Moon Committee for 1865, and there is no attempt at a minute exactness not possible until a much larger accumulation of facts has been made. Mr. Birt rightly describes his charts as "a guide to observers in obtaining data for the construction of a complete map." He adds, "at present the engraved portions of the map are in outline, and will doubtless require considerable modification, as observers work at the subzones which they may select." Mr. Birt also recommends observers to tint or colour their subzones, so as to make craters and other objects more conspicuous than they are in the simple red outlines which he provides, and which are printed in that colour to distinguish them readily from any corrections or additions which observers may make in black ink. It would require a series of elaborate notices to do justice to the numerous suggestions and important bits of information which Mr. Birt supplies concerning the zones and areas comprised in his map, and we can only observe that they are calculated to render most valuable aid to lunar students.

It will be very interesting to compare the physical geography of the earth and moon, and to notice how the distribution of hollows, elevations, etc., vary in the two bodies whose surfaces have assumed their existing forms under such different conditions as are expressed by the presence, and absence, of water and air, and numerous observations will be found in Mr. Birt's pamphlet, which will materially facilitate researches of this kind. We would take this opportunity of urging the British Association Committee to lose no time in providing Mr. Birt with a telescope of suitable dimensions. The small instrument which he is at present using is not half the diameter of that which he ought to have to justify his drawing his contour lines on so large a scale, and can supply no means of testing the observations of difficult objects that may be communicated to him by other observers.

AUVERGNE: ITS THERMO-MINERAL SPRINGS, CLIMATE, AND SCENERY. A Salutary Retreat for Invalids. By ROBERT CROSS, M.D., Edin. and Heidel, F.R.C.P., Ed., and M.R.C.S.E., Author of " Physiology of Human Nature. (Hardwicke.)-Geologists have long been familiar with the Auvergne as a district remarkable for its illustration of volcanic action, and for the numerous extinct craters which