soda, instead of eight per cent. sulphuric acid is used. And if, after the potatoes have been macerated in the solution of soda, they are boiled in a solution containing nineteen per cent. soda, a substance resembling stags horn, and which may be used for knife handles, etc., will be formed. Turnips may be used instead of potatoes in the production of the artificial horn; and if carrots are substituted for the potatoes, a very excellent artificial coral will be obtained.

RAILWAY SAFETY SWITCH. It is of the utmost importance that the points on railways should be in the proper position. If they are not, a train may run on the wrong line, and thus destructive collisions ensue. Such has been but too often the cause of serious accidents, and great mischief to both life and property. The pointsman may be neglectful, or over-fatigue may cause him to forget his duty. Hitherto there were no effective means of discovering the circumstance until it was too late. A very ingenious and simple application of electricity now renders it extremely easy. The switch is so arranged that, whenever it is not in a proper position, it completes the electric circuit of a galvanic battery, and the current thus set in motion operates on an electro-magnetic apparatus, which keeps an alarm bell ringing where it cannot but draw the attention of responsible persons to the pointsman's neglect, so that the switch may be put in its proper position before any injury is done.

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MANUFACTURE OF STARCH.-An improvement of considerable importance has recently been made in the manufacture of starch. is founded on the fact that, although the specific gravities of the starch and of the substances associated with it in the grain, etc., from which it is extracted are very nearly, they are not quite the same; and the improvements, which is due to M. L. Maighe, consists in an ingenious application of centrifugal force. Water is added to the crude starch in the proportion of two parts of the former to one of the latter, and the mixture is introduced into a copper drum which is capable of making some hundreds of revolutions per minute. As soon as the proper velocity has been reached, the starch, having a greater specific gravity than the water, and therefore being more affected by centrifugal force, is driven with such violence against the circumference of the drum that it forms a solid mass of great whiteness and purity, being entirely separated from the other substances, which remain suspended in the water. This method of obtaining pure starch has peculiar advantages: it requires only a few minutes, while the ordinary process takes several weeks; it is more economical, since with it the yield is twenty per cent. greater, and hence starch may be profitably manufactured from other matters besides wheat, which from its nutritious qualities should be as far as possible kept for food; and, finally the cellular tissue, gluten, etc., which are very valuable, but by the ordinary modes of manufacture almost entirely go to waste, may be utilized. It is not improbable that a similar application of centrifugal force might be advantageously applied to the separation of other substances differing but little in specific gravity.

A NEW BLASTING POWDER.-Vast quantities of explosive material are now used in the operation of blasting; and hence numerous attempts have been made to discover new and better explosive compounds than gunpowder. The efforts which have been made in this direction have not, as the discovery of nitro-glycerine attests, been without success. The dangerous nature of that substance, however greatly limits its utility. Wilhelm and Ernst Fehleisen have formed a compound which is in several respects superior to any of the explosive materials hitherto used. It cleaves, rather than blows into atoms: an important quality, especially when it is employed in the coal mine. It does not ignite spontaneously, nor is it set on fire by friction or percussion. Its combustion gives rise to no opaque, nor suffocating gases, which makes it very valuable in the operations of tunnelling. It has but one disadvantage: weight for weight, it is twice as bulky as gunpowder; but even this is in a great measure compensated by the fact that it is one-half more powerful. It is formed by thoroughly mixing nine parts by weight saw-dust obtained from a light and non-resinous wood, or wood from which the resin has been extracted, from three to five parts charcoal, and forty-five parts salt petre, and, if required to be quick, one part ferrocyanide of potassium; the mixture being moistened. with one quart of water to every hundred weight. It is granulated by stamping or crushing, and the grains may be polished in the ordinary way; this, however, will merely improve the appearance without increasing the explosive power. This compound has been termed Haloxylin.

THE COLOURS OF THE STARS.-The determination of the precise tints of the stars is not only a matter of interest but importance; and an instrument for this purpose has recently been invented. The object proposed by the inventor was to compare the tint of the star to be examined with that of a solution, the colour of which is known. For this purpose, a platinum wire is rendered incandescent by means of two elements of a Smee's battery; and the rays of the artificial star, thus produced, are made to pass through small phials, filled with solutions of known tints, and attached to a drum which has radial openings, and is capable of revolving, after which, they pass into the objective of a small telescope. The artificial and the real star are compared; the drum being turned until the rays from the incandescent platinum appear of the same tint as those from the star. When the tints are the same, it is known that the proper solution has been used, and the tint of this solution being known, the colour of the star is found.

MAGNETISM AND THE METEORITES.-From the fact that meteorites consist invariably and almost exclusively of nickel and iron, it might, at first, be concluded that the small planetary bodies which are now known to circulate in such numbers in orbits intersected by the orbit of our earth, especially in August and November, consist only of these metals. But the conclusion would not be legitimate, if it be true, as there is reason to believe, that gravitation is not the only force which causes meteorites to be precipitated on our earth. It is remarkable

that the constituents of meteorites are iron and nickel, two eminently magnetic metals. And it is not improbable that gravity is aided by magnetism, in attracting these bodies to the earth. Only bodies, therefore, containing iron and nickel reach us, because gravity unassisted by magnetic attraction is unable to draw bodies otherwise constituted out of their orbits.

STEAM APPLIED TO RAILWAY BREAKS.-The safety of a train not unfrequently depends on the power of quickly bringing it to a state of rest. This can be effected only by breaks. The more rapidly, therefore, and powerfully these can be brought into action the more they contribute to the safety of the train. Manual power, to be at all effective, must be slow; and hence, independently of its being very limited in amount, an accident may occur before it has had sufficient time to come properly into play. Steam therefore is now being substituted in America for the muscular power of the breaksman, and with most excellent effect. A steam cylinder of small bore, but of considerable stroke is placed in the locomotive, under the driver's foot board. The steam is turned on or off this cylinder, by means of a handle which projects through the foot board. A chain which acts on all the breaks of the train is attached to the extremity of the piston rod. The pressure is never allowed to become so great as to cause the wheels to slide, that in the cylinder being regulated by a safety valve attached to it. The power which may be given to such a break is practically unlimited. That with which the experiments were tried was capable of exerting a force of three thousand five hundred pounds; and of stopping within a space of seven hundred feet, a train moving at the rate of fifty-six miles an hour.

NEW PRESERVATIVE COMPOUND.-Many substances have been employed for the preservation of animal matters, and with greater or less success. Most of them are, however, liable to the objection of difficult application or expense. A compound which is cheap and easily applied, and is very effective, especially in the preservation of anatomical specimens, has recently been discovered. It is made by adding to about fourteen parts glycerine, two parts brown sugar, and one part nitre; the addition of the sugar and nitre being discontinued as soon as a slight deposit begins to be formed. Immersion in this fluid for a number of days, dependent on the size of the object to be preserved, effectually preserves organic substances from putrefaction, without, at the same time, altering their appearance. When first lifted out they will indeed, be in the highest degree rigid, but on being placed for a while in a warm dry place they will become as pliant as ever.

NEW EXPLOSIVE COMPOUND.-Experiments made on the effects produced by nitrate or chlorate of potash on glue have led to the discovery of a new and extremely cheap explosive compound, which may be employed with special advantage in conjunction with ordinary gunpowder. This compound may be obtained by either of two methods. According to one of them, two parts glue are washed with cold water; then heated moderately with a small quantity of nitric acid, evaporated, again mixed with water, and freed from

acid by carbonate of baryta, not in excess: again evaporated to dryness, mixed with one part sulphur, then with water, and next with six parts nitrate of potash. According to the other method, the glue having been melted in warm water, half the nitrate of potash and then the sulphur are added to it. It is then heated until it assumes a uniform appearance, on which the rest of the nitrate is added. The compound obtained by either of these methods is neither deliquescent nor hydroscopic; but being made with nitrate instead of chlorate, unless mixed with ordinary gunpowder it burns slowly and without explosion. If mixed with five

parts gunpowder it forms a cheap and powerful explosive agent. It is applicable, advantageously, in the formation of fire-works: and when mixed with the appropriate substances, it affords brilliantly coloured fires.

NEW APPLICATION OF PHOTOGRAPHY.-Photography is now being applied to the registration of the pulsations of the heart and arteries, a purpose eminently useful to the physician. The apparatus employed consists of a glass tube, that at one end is widened out into a cone, the base of which is closed with a thin membrane of vulcanized india-rubber. The upper extremity of the tube is inserted in the slit formed in a division placed in a small camera about its middle and at right angles to its length; the slit being capable of being closed or opened at pleasure, by means of a small moveable screen. The sensitized plate is made to move with a regulated speed by clockwork. When an experiment is to be made, so much mercury is placed in the tube that it will rise to some portion of the slit, within the camera; and the membrane is laid on the heart or the artery the pulsations of which are to be recorded. Every pulsation disturbs the level of the mercury in the upper part of the tube; and as light can pass to the sensitive plate only through the tube, a picture having an undulating lower margin is formed. The sensitized plate moves at the rate of one centimetre per second; but the effect is magnified so that the curve representing it has an extent of fifteen centimetres. The rate and energy of the pulsations of the heart or of any artery is in this way accurately and satisfactorily recorded.

LITERARY NOTICES.

THE THEORIES OF COPERNICUS AND PTOLEMY. By a Wrangler. Longmans. No proposition, however well established, ought to escape a frequent re-examination, as the development of the human mind is not promoted by the reception of any doctrine, however true, merely upon authority, but rather by a constant search after truth, through the collection of facts, and the operations of reason thereupon. Whatever is taught upon authority only, should be held as a matter for provisional acceptance only, and not advanced higher, until the inquirer has been able to discover or follow the train of reasoning

by which it is established. In the absence of any sufficient original investigation into the grounds upon which any proposition that receives the sanction of authority rests, the authority, if supposed trustworthy, affords a convenient resting place, and establishes in the mind of every one who thinks it more likely to be right than wrong, a certain balance of evidence in favour of the proposition it affirms. The evidence is, however, of this character-Smith is an intelligent man-he has studied the subject, he says so, and he is likely to be right. True, but he is also likely in a greater or less degree to be wrong. A high degree of probability is all that we can expect to attain to; but after the probableness of a statement reaches a certain point, it becomes reasonable to act upon it, and to regard it as true, but faith in the most probable statement should never hinder the perception of the improbability, however small it may be, that remains attached to it, and which cannot be regarded as a constant and ascertained quantity, but must be esteemed as a quantity which further discovery may at any time change the value of, either in the direction of its augmentation or its diminution.

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The "Wrangler" who puts forth the pamphlet on the "Theories of Copernicus and Ptolemy," deserves the thanks of those who recognize the truth of the propositions we have thus sketched out. is no doubt common to assume that the Copernican theory rests upon a more thoroughly complete mass of evidence than can be claimed for it; but its defenders are only bound to show that, as compared with the Ptolemaic theory it is sustained not only by a balance of probability, but by enough probability to be a legitimate basis for thought and action. That the conception of gravitation as an universal force, resident in, or essential to, all matter, and causing all particles to attract each other proportionably to their mass, and in an inverse proportion to their distance, could not be maintained by anything like proof. Astronomers have to recognise repulsive forces as well as attractive ones, and we know of no argument in favour of the supposition that the attraction of gravitation is not correlative with any other mode of force, but always existing without change as an absolute property of each particle of matter, and in eternal antagonism to all repellant forces. Views of this kind have been several times put forward in our pages.

The " Wrangler" contends, not for the truth of Ptolemaic astronomy, but that its major requirements are not improbable, and it is here that most philosophers will disagree with him, and we are not sure that he sufficiently recognises the evidence of improbability that attaches to the best proved systems, or sufficiently admits that some amount of improbability is no ground for disbelief. It is important, however, to bear in mind the doubts and objections of the "Wrangler," which are well put, though not, it strikes us, at all new. Our solar system may be but a portion of a greater system, and the centre of gravity of the whole may be nearer or further than astronomers fancy. This will be generally admitted, so will the analogy between the particles of a small body, and that of sun and the planets regarded as particles of the giant whole. The constitution of nebula, the appearance of a repulsive