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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-rnbber. 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 siit, 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 inagnified 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 or 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.

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. It 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 any. thing 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 nebule, the appearance of a repulsive

action in the sun on cometary matter, and other facts adduced by the “ Wrangler," all point to the conclusion that the laws we are acquainted with do not explain the whole system or cosmos. As the “ Wrangler's” paper is only a pamphlet of fifty-six pages, we abstain from extracts, merely recommending it to the notice of those who like to see inquiry stimulated, and the best established beliefs re-examined from time to time.

NOTES AND MEMORANDA.

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THE COLOUR OF WATER.-Father Secchi, in a paper on “Star Spectra,” in 'Comptes Rendus” (1867, No. 14), says: Having ascertained that the spectrum of sea-water is destitute of red at small depths, and of yellow and green—at least of their greater part—at successively greater depths, at which the water has a blue or violet colour, I wished to see if the same absorptions were exhibited in glaciers. Profiting by the incident of an artificial grotto having been dug in the glacier of Grindelwald, I made some experiments on this subject. The grotto in question is about 100 metres deep, its walls are transparent, and illuminated by sunshine passing through the ice. This light has a fine blue tint, in which the red is extremely weak, so that in the grotto human faces have a frightfully cadaverous aspect. Looking from a certain depth in this grotto back towards the entrance, the light there appears red, owing to the effect of contrast. A spectroscopic examination shows the light in the grotto to be almost deprived of red, and to have the yellow greatly diminished. The thickness of the ice is not suflicient to produce a more complete absorption. It is said to be about fifteen metres thick, but I should say less. The ice is perfectly compact and continuous in its texture. It is limpid as crystal, and contains here and there groups of air bubbles. Its hardness is not great; an iron point easily penetrates it. The result is thus identical with that which is obtained with sea-water at similar depths; and as in the Alpine ice we cannot suppose the presence of extraneous colouring matter that might be presumed to exist in the sea, it follows that the true colour of water is a blue mixed with violet, which grows darker as the thickness traversed by the light increases."

SULPHURIC ACID FORMED BY A MOLLUSK.-M. M. S. de Lucca and P. Panceri state, in “Comptes Rendus" (1867, No. 14), that the salivary organs of the Dolium galea secrete a fluid which contains more than three per cent. of sulphuric acid. They examined two specimens caught in the Gulf of Pozzuoles. When filled with liquid, the glands, two in number, are larger than ordinary fowls' eggs, and weigh about seventy grammes. They are formed of two distinct parts—one small and opaque, close to the excretory orifice of the gland; the other large and transparent, the membrane enveloping it being very thin and white. When incisions are made, so that the lower part of the gland comes in contact with the air, gaseous bubbles of pure carbonic acid are disengaged from the cul de sac tubes, of which almost all the gland is composed. A gland weighing seventyfive grammes discharged under water 200 cubic centimetres of carbonic acid. The liquid contained in the gland tastes like lemon juice, acts on marble, and changes the colour of litmus. A series of experiments show it to contain sulphuric acid. It was previously known that the Dolium galea ejected an acid liquid from its mouth which effervesced with carbonates, and when analysed by M. Bædeker, gave 2.7 per cent. of sulphuric acid. The authors of the paper state that they will continue their researches with a view to discover how the sulphuric acid is produced, and what function it performs in the economy of the animal. They say this Dolium " is the first animal which they knew of capable of making sulphuric acid by an unknown process.”

THE COLOUR QUESTION AND THE LUNAR ECLIPSE, SEPT. 13TH.-Referring to the accounts of this eclipse we published in our last number, we may say that

several observers besides Mr. Browning speak of absence of colour. M. Chacornac states the contrary. He says the greater part of the lunar disk plunged into the shade of the earth was of a red colour, the portion near the limit of the shadow slightly violet. Between these two extremes, yellow, orange, green, and blue exist, resulting from the decomposition of solar light by refraction of the terrestrial atmosphere. Mr. Huggins informs us that excess of light prevents a proper view of colour, and Mr. Knott has found too much light to interfere with a just appreciation of the tints of double stars. M. Chacornac's observations were made at Ville-Urbanne, but he does not say with what aperture. He has the large Foucault reflector there. The “Monthly Notices” contain Mr. Weston's observations made at Endsleigh Observatory, Bath. He describes the prevailing colour as "red-bluish and grey, and grey. The redness increased towards the darkened edge of the moon. He did not notice this colour at “the boundary line when the earth's shadow impinges on the moon ; but, on the contrary, it was confined to the opposite eclipsed region, darkening as it approached the northern parts, and attaining the greatest depth at the moon's periphery. ... That these effects did not result from any chromatic errors was proved by using different telescopes and powers. The colour and their relative positions differed entirely from those presented in the partial eclipse of Feb., 1858.”

Two NEW PLANETS, ( 13 and 9.-Mr. Watson, of Ann-Arbor, states in the “Astronomische Nachrichten,” that he discovered the first of these bodies on the 24th August, and the second on the 6th Sept. Both are of 11 mag.

Micro-CRYSTALS OF ALKALOIDS.-At the meeting of the Royal Microscopical Society, on the 9th Oct., Dr. Guy read a long paper on crystallizations and arborescent forms obtained by subliming minute quantities of strychnine and other alkaloids in the manner originally proposed by Helwig. Dr. Guy's process is to place the matter to be sublimed at the bottom of a small flat porcelain vessel, such as a crucible cover. Over it he puts a square of glass, about one-eighth of an inch thick, with a round hole in the middle. Over this hole he places a flat piece of glass. A moderate heat, carefully applied by a spirit lamp, sublimes the alkaloid, and it is condensed on the plate of flat glass, and ready for microscopic examination. Quantities such as the 10,000th part of a grain give satisfactory results. Many photographs of crystallizations, exbibited by Dr. Guy, were of great beauty. Evidence of this kind might be important in medico-legal inquiries, but it could scarcely be regarded as conclusive, though it might form part of a conclusive chain of proof.

THE COMING STAR SHOWERS.–Our readers should refer to the important paper by Mr. Proctor, in our last number, on this subject, before the arrival of the 14th. At a quarter past six on the morning of the 14th may be the maximum, but the meteors should be looked for some hours earlier to prevent disappointment.

A WAISTCOAT-POCKET MICROSCOPE. — The most elegant and convenient portable microscope is one devised by Mr. Highley, on the plan of the class microscopes introduced by Dr. Lionel Beale. Mr. Highley's instrument fits into a German silver case, rather less than four inches long and five-eights of an inch wide. It is furnished with a live-box, draw-tube, eye-piece, and dividing objective. Its power is sufficient to show the nature of urinary deposits and other morbid products; and as a field instrument for the collector of diatoms, desmids, minute alga, etc., it will be highly esteemed.

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