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perfect precision, to near and remote objects; Mr. W. observes, that he has seen many instances of persons of very advaneed age, and who had been a long time accustomed to the use of convex glasses of considerable power, having ceased to require their assistance, their eyes having undergone some change which enabled them to see perfectly without them. It is, perhaps, not easy to determine the nature of the change which produces this alteration. It has been attributed by some to the absorption of adipose substance, which is found in tbe orbit. Mr. W. supposes it to happen from a partial absorption of the vitreous humour, by which the axis of the eye becomes leugthened. · He remarks, also, that from bis own experience, near-sighted persons have not so extensive a range of vision as others have; and that, contrary to general belief, the defect of pear-sightedness does not diminish with the approach of age. Several instances of a change of vision from long to short-sightedness, be informs us, have come under his notice, which were relieved by the use of leeches and evacuant remedies. This change was not connected with age; for though several of the individuals in whom it occurred, were rather advanced in life, others had scarcely arrived at the age of puberty. V. The Bakerian Lecture. On the elementary Particles : of certain Crystals. By William Hyde Wollaston, M.D. Sec. R: S.
Our knowledge of the figure of the ultimate particles of bodies, can be derived only from theoretical considerations; but their truth or fallacy, as applied to the formation of crystallized bodies, may, in general, be subjected to the test of pretty rigorous demonstration.
There are some forms of crystal, of very frequent occurrence, with respect to which, there is considerable difficulty in determining its primitive form, and, consequently, the figure of its ultimate or elementary particles. This is especially the case with the regular octoedron, a form which is common to a great variety of bodies, in which it is extremely difficult to decide whether the octoedron, or the tetraedron, is entitled to a preference, since they are so easily convertible into each other. And, in either case, the elementary particles assigned to them by Hauy, are but ill adapted to form the basis of any permanent crystal
The object of Dr. Wollaston, on this occasion, is, to shew with what admirable simplicity the supposition of the elementary particles being perfect spheres, which, by their mutual attraction, have assumed that arrangement which brings them most intimately into a state of mutual contact, will remove every difficulty relative to bodies which assume these forms of crystallization. The idea is at once simple and ingenious ; and might have maintained the claim of originality, if the same theory had not been employed by Dr. Hook, to explain the structure of the crystals of quartz, and to which the attention of Dr. W was directed by a friend. This, however, can hardly be considered as detracting from the originality of Dr. W.'s first suggestions, since he had engaged to make bis theory the subject of the Bakerian Lecture, before his attention was directed to the micrographia, and, consequently, before he was acquainted with the fact of its having been anticipated in any degree by Hooke.
Dr W. shews in how perfect a manner the octoedron, the tetraedon, and the acute rhomboid, may be deduced from elementary particles of this form; and he remarks, with truth, that the simplest arrangement of the most simple solid, affords a complete solution of one of the most difficult questions in crystallography In the subsequent part of the lecture, he proceeds to shew, that particles having the form of oblate spheroids, will form the obtuse rhomboid, and that the hexagonal prism will result from oblong spheroids, arranged according to the law of their mutual attraction. This theory, however, does not apply, with equal advantage, to the cube ; for though spherical particles, placed four and four above each other, would form a crystal of that figure, yet that is not an arrangement which they would naturally assume; and there are objections to the supposition of its being formed of oblate spheriods. If, however, a cubical crystal be supposed to consist of spherical particles of two different kinds, but all of the same magnitude, then, Dr. W. observes,
• If it be required that, in their perfect intermixture, every black ball shall be equaliy distant from all surrounding white balls, (this mode of distinguishing the particles is used in reference to the plate by which the subject is illustrated, and that all adjacent balls of the same denomination shall also be equidistant from each other, these conditions will be fulfilled, if the arrangement be cubical, and that the particles will be in equilibrio.'
This view of the subject recommends itself by its simplicity, and by its correspondence to the present theory of chemical combination, where the crystallized body is a compound. VI. On a Substance from the Elm Tree, called Ulmin. By
James Smithson, Esq. F. R. S.
The properties of Ulmin were first examined by the celebrated Klaproth; and that which Mr. Smithson had the opportunity of analizing, was derived from the same source, both specimens having been supplied from Palermo, by the same indi. vidual. When in masses, it is almost of a black colour ; in thin slices, it is transparent, of a deep red, which is the colour also of its concentrated solution ; but if much diluted, the solution becomes yellow. It slowly restores the colour of tungsole paper, which has been reddened by an acid.
Most of the acids decompose the solution, and occasion : copious precipitation, the liquid affording, on evaporation, a salt of which the base is potash. From several experiments made with that particular view, Mr. S. estimates the proportion of potash in ulmin at 20 per cent.; which would appear to be in the caustic state, since no mention is made of the extrication of carbonic acid when an acid is added to its aqueous solution. The precipitate, when dried, has a glossy, resinous appearance, and is very sparingly soluble either in alcohol or water; dor does the addition of immonia or carbonate of soda to the water, increase its solubility; but on the addition of potash, it becomes abundantly soluble, the solution having all its original proper ties. Ulmin would appear, therefore, to be more nearly allied to extraction matter than to the resins. M. S. submitted some Ulmin, obtained from an elm tree growing in Kensington Gardens, to similar experiments. It appeared to differ principally in containing a higher proportion of alcali.
VII. On a Method of Freezing at a Distance. By William
Hyde Wollaston, M. D. Sec. Ř.S.
The principle on which this process is founded, is precisely the same with that of Professor Leslie, the object in both being to condense the vapour formed by the spont neous evaporation in vacuo, by which means the temperature of the liquid is rapidly reduced so low, as to occasion it to freeze. Dr. Wollaston's contrivance, however, has the merit of being extremely simple and unexpensive, while Professor Leslie's requires the aid of an air-pump. It consists of a glass tube, having its internal diameier about 1-8th of an inch, and terininated at each end by a ball about an inch in diameter, but being bent to a right angle at each extremity, at the distance of half an inch from each ball. One of the balls is to be about half full of water, and the remaining part of the cavity, as perfect a vacuum as can be obtained by the method employed in the formation of these sort of instruments. When the instrument is used, the empty buil is to be immersed in a freezing mixture of salt and snow, and if the vacuum is tolerably perfect, the water in the other ball is converted into a mass of ice in a few minutes. The theory of its action will be sufficiently obvious to those who are at all familiar with chemical science.
IX. A Description of the solvent Glands and Gizzards of
the Ardea Argula, the Casuarius Emu, and the longlegged Casorary, from Nero South Wales. By Sir Everard Home, Bart. F.R.S.
The principal difference in the structure of these organs, as described in this paper, is in their magnitude, in the number of cells of which each gland is composed, and in the situation which they occupy, in the cardiac cavity, eircumstances which may probably have some relation to the quality of their food, and the ease with which it may be digested. The glands of the Casuarius Emu, which is a native of the fertile island of Java, are of small size; and it is an instance of design deserving of particular notice, that the gizzard in this bird is so pluced, that the food may pass along the canal without being subjected to its grinding operation, and it appears, therefore, to be called only into occasional employment, while the Struthio Camelus, which inhabits the deserts of Africa, has glands of a more complex structure, and the gizzard is so situated, that the whole of the fuod must be submitted to its action.
There is also a most remarkable difference in the length of the intestinal tube in each, which Sir Everard Home conjectures to be connected with their circumstances as to food, the former being only six feet in length, while in the latter they are seventytwo feet. These are the two extremes, and the whole seem to form a series in which the structure of the digestive organs becomes the more fitted to economize the food, when the country, which each species inhabits, becomes less fertile, and the supply of food consequently more precarious, because less abundant. X. Additional Remarks on the state in which Alcohol existe
in fermented Liquors. By William Thomas Brande, Esq. F.RS.
In a former communication, inserted in the Transactions for the year 1811, Mr. Brande adduced pretty strong evidence in support of the opinion, that the alcohol obtained from wine, by distillation, was merely separated by that process; but still the proof could not be considered as demonstrative, until it could be shewn that the alcohol might be procured in a separate state by means purely chemical, such as were known to be capable of effecting the separation of alcohol from water. This Mr. Brande bas at length accomplished, and the details are given in the paper now before us." In order to effect the separation of alcohol from wines, it is requisite that the colouring and extractive matter be previously separated, which Mr. Brande has found may be readily effected by the acetate, or subacetate of lead, or the subnitrate of tin. The addition of either of these substances to wine, occasions a dense precipitate to be thrown down, but the subacetate of lead is the most powerful in its action, and occasions the most impediate and perfect separation of these matters, as well as of the acid which wine usually contains. After this precipitation of the colouring and extractive matter, a colourless liquid is obtained, from which the alcohol is speedily separated by the addition of dry subcarbonate of potash. The proportion of the subacetate of lead, enployed by Mr. B. was about oneeighth of a concentrated solution, but a little excess is of no importance, since it does not interfere with the result. The proportion of alcohol obtained from wine by this means, corresponds very nearly to the proportion afforded by distillation, except when the proportion contained in any wine is below 12 per cent.
Mr B. considers the action of the subcarbonate of potash not an accurate test, for this agent produced no separation in a dilute solution of alcohol in water containing 4 per cent; and in a so. lution, containing 8 per cent, it effected the separation of only seven parts; but in stronger solutions, containing sixteen or twenty parts, it always separated the whole within 0-5 per cent. The proportion of alcohol obtained, therefore, from the different kinds of wine by this method, corresponded very nearly to that obtained by distillation, as stated in the table given with Mr. Brande's former communication. From an examination of a number of specimens of what were considered good port wines, Mr. Brande' has determined their average strength to be about 22 per cent. of alcohol, by measure.
There can be no doubt, now that these facts are ascertained, that the colouring and extraction matter contained in wines, have a very important influence in modifying the effect of the large proportion of alcohol which they contain; for the different effects produced by the potation of wine, and of spirit and water of the same degree of strength, is a matter of general experience. To what change the improvement of wine, by age, is to be attributed, we have yet to learn.
XI. On a new Variety in the Breeds of Sheep By Colonel
David Humphreys, F.R.S. In a Letter to the Right Hon. Sir Joseph Banks, Bart. K.B. P.R.S.
Colonel Humphreys has here presented us with a curious history of a new variety of sheep, which originated in the flock of an American farmer, residing in the state of Massachusetts. It appeared, in the first instance, in a single male individual, the peculiarity, or, rather, deformity of whose structure, was afterwards propagated in the flock, in the expectation that it would be advantageous to the farmer, from its being less capa