specific gravity is still further increased, the action on the magnetic needle is prodigiously augmented, and the mass acquires some polarity. This formation is the last which Mr. Watt's experiment presented. The remainder of this valuable memoir is occupied by deductions from the above facts, in which the production of amorphous, globular, and prismatic basalt, is most beautifully illustrated, and the impression of difficultly fusible crystals by those of easy fusibility, is shown to be no longer impossible, even on the volcanic theory. But these, and the explanation of many other geological difficulties, it is impossible to convey to the reader, without occupying a much larger space than we can afford; and this is the less necessary, as the whole paper is pregnant with the most interesting remarks, and will be the object of profound study to all those for whom the science of geology possesses any attractions. 12. An Analysis of the Magnetical Pyrites, with Remarks on some of the other Sulphurets of Iron. By CHARLES HATCHETT, Esq. F. R. S. THE magnetical pyrites, which had been procured only from Norway, and some parts of Germany, was discovered by the Hon. Rob. Greville, in 1798, near the base of the mountain Moel Elia, in Caernarvonshire. This Welsh pyrites is the subject of Mr. Hatchett's experiments. From two very careful analyses, it appears to consist of 36.5 sulphur, and 63.5 of iron; this latter being very nearly, if not quite, in the metallic state. By way of comparison, five varieties of the common, or unmagnetic sulphuret were then decomposed, and found to consist of 52.15-51.34 sulphur, and 47.8545.66 iron. This result leads Mr. Hatchett to a very interesting inquiry concerning the effect of sulphur on the magnetical property of iron. He began, by preparing an artificial sulphuret, by adding sulphur to fine iron wire in a moderate heat; the substance resulting from this union bore a considerable resemblance to the magnetical pyrites, and by being placed between magnetical bars, acquired a large and permanent quan tity of magnetic polarity. By distilling some of this artificial pyrites with sulphur, it combined with an additional quantity, so as to contain thirty-five per cent. of sulphur, yet still retained its ca pability of magnetism. By a further distillation with sulphur, it was made to contain 45 or 46 per cent. of this substance: it had now acquired the greenish yellow colour of common pyrites; but was still completely attractable by the magnet. Now, since metallic iron with forty-six per cent. of sulphur is perfectly obedient to the magnet, and entirely ceases to be so when combined with fifty-two per cent. of the same, it is certain that the limit of saturation is between these two extremes, unless some unsuspected change in the iron or sulphur tras taken place. Hence there appears to be a strong analogy between carbon and sul phur in their effects on iron, a certain quantity of either enabling this metal to acquire and retain magnetic polarity, and a larger portion entirely destroying this capability; and, in this respect, phosphorus exactly coincides with the two former inflammable bodies. 13. Account of the voluntary Expansion of the Skin in the Neck of the Cobra de Capel lo, or hooded Snake of the East Indies. By PATRICK RUSSEL, M. D. F. R. S. with a Description of the Structure of the Parts that perform that Office. By EVERARD HOME, Esq. F. R. S. THE curious apparatus of the hood of the cobra here described, is formed by an elevation of the ribs nearest the head, and a corresponding extension of the skin of the back. We cannot be well understood without the plate. No conjec ture is given as to the use of this singular piece of natural mechanism. 14. Continuation of an Account of the Changes that have happened in the relative Situation of double Stars. By W. HERSCHEL, LL. D. F. R. S. THE first part of this paper contains the arguments of this able astronomer on the motion of the double star a, of the twins, and the remainder the account of changes in various stars. From the list it appears, that of fifty changeable double stars, " twenty-eight have undergone only moderate alterations, such as do not amount to an angle of ten degrees. Thirteen of the stars have altered their situation above ten degrees, but less than twenty. Three stars have undergone a change in the angle of position, of more than twenty, and as far as thirty de grees." The other six have undergone a greater change, from forty to a hun dred and thirty degrees. From the changes in a Herculis, it is inferred, that there is a mutual revolution of the two stars round each other. From the extraordinary change of position of , ursæ, we may expect in a few years to obtain considerable information on the cause of its motion; w leonis is supposed to have a real motion, as is also arietis H. 4, aquarii 144, has a real motion, whose nature cannot remain many years unknown, its velocity hitherto having been at the rate of nearly two degrees a year of angular change. The observations on the other stars are all curious, and deservihg attention: but we may justly doubt, whether we have by any means a sufficient number of clear and decisive facts, on which the true theory of their motions can be grounded. Many years must elapse before this can be expected, but in the mean time every observation from this very accurate observer will be trea sured up for the instruction of future ages. 15. Observations on the Change of some of the proximate Principles of Vegetables into Bitumen; with analytical Experiments on a peculiar Substance, which is found with the Bovey Coal. By CHARLES HATCHETT, Esq. F. R. S. IN answer to the arguments which are generally adduced, to prove the vegetabie origin of coal, and the other bituminous mineral inflammables, it is commonly and fairly urged, that the ashes of vegetables afford potash, by lixiviation, which those of coal never do; and that the vegetable resins, and mineral bitumens, differ in many essential characters, and are never observed to graduate into each other. The paper before us is therefore of peculiar value, as furnishing a satisfactory reply to these objections, and as connecting the vegetable with the mineral world, and thus consolidating several important geological phenomena into a harmonious system. Among the specimens which sir Joseph Banks brought with him from Ireland, was a singular argillaceous, schistus, formed by thin alternate layers of earthy matter and alder leaves; these leaves are of a blackish brown colour, and are in part, though not entirely carbonized. When examined by the reagents, they appeared to contain a substance nearly resembling vegetable extract, and a small portion of resin; but the tannin had wholly disappeared, and the ashes, after combustion, gave not the smallest appearance of alkali. Here, therefore, was an acknowledged vegetable substance, forming an essential constituent part of a mineral stratum, and which, by some unknown agency, had been so far mineralized as to lose two of the substances which are obviously contained in the fresh leaves. Bovey coal is composed almost wholly of trunks of trees, which, like all extraneous substances that are found in argillaceous strata, are remarkably flattened and compressed; so that a horizontal section of the trunk, instead of being circular, is a very narrow ellipse. This fossil wood may be traced, by very easy gradations, froma perfectly ligneous and fibrous texture, to a compact glossy substance, nearly as heavy, and strikingly resembling common coal. A specimen, intermediate between these two extremes, was selected for analysis by Mr. Hatchett, which, upon examination, was found to have lost its vegetable extract and other matter soluble in water, but still retained a very small portion of resin. Its ashes, after combustion, afforded no alkali. Adhering to the coal are sometimes found moderate-sized masses of a yellowish brown inflammable substance, resembling resin; and this being examined by Mr. Hatchett, was found to be a singular compound, consisting of 55 resin, 41 asphaltum, 3 earthy residuum: France, were occupied upon it at the same time. The French chemists obtained from it a new metallic substance, characterized by the property of giving a deep red colour to the solutions of platina. Mr. Tennant discovered two metals, one of which was that which had been observed by Vauquelin. If the black powder is treated alternately with caustic alkali, and muriatic acid, it is divided into two portions; one soluble in the acid, and the other in the alkali. The acid solution is of a dark-blue colour; which afterwards changes to a dusky olive green; and, by further continuance of the heat, beconies of a dark red. From these variations of colour, Mr. Tennant has given it the name of iridium. The muriatic solution being evaporated to dryness, and afterwards dissolved in water, gave distinct octahedral crystals, which tinged water of a deep orange red colour. By simply exposing the crystals to heat, the acid and oxygen are expelled, and a white infusible metallic mass remains behind. Lead unites with this, and, by cupellation, the iridium is procured in the state of a coarse black powder. With silver it forms a malleable alloy, not decomposable by cupellation; with gold it also unites, so as to be inseparable by cupellation, or quartation; but, by solution of either alloy in acid, the iridium is left behind in form of a black powder. The other new metal is contained in the alkaline solution of the black pow. der mentioned above, and is procured in the following manner: put the solution into a retort, and add sulphuric acid, and distil by a very gentle heat; a clear liquor is collected in the receiver, of a sweetish_taste, and a peculiar pungent s.nell. It consists of water, holding in solution a very volatile metallic oxyd, which, from its odour, is called by Mr. Tennant-osmium. It may be obtained in a more concentrated state, by distilling the original black powder with nitre at a very low red heat. An oily fluid sublimes into the neck of the retort, which, on cooling, concretes into a solid colourless semitransparent mass, and this, when dissolved in water, forms a solution exactly similar to the first mentioned. This oxyd, in the concentrated ART. II. The Tran actions of the Royal THE most valuable articles in the present volume are the mathematical ones, state, gives a permanent dark stain to the skin, and, with an infusion of galls, produces a purple colour, which soon be comes of a vivid blue. If the aqueous solution of oxyd of osmium is shaken with mercury, an amalgam is produced, and, by distilling off the mercury, a darkgrey or blue powder remains, which is pure osmium; when heated with access of air, it oxydizes, and evaporates with its characteristic smell; but, when in closed in a charcoal crucible, and exposed to a strong white heat, it fuses into a button. In this state it is not acted on by nitro-muriatic acid, but, when fused with caustic alkali, it combines with it, forming the same compound as is produced by treating the original black powder in the same manner. 17. On a new Metal found in crude Platina. By WILLIAM HYDE WOLLASTON, M. D. F. R. S. THIS is an obscure and unsatisfactory paper: the quantities operated upon were very small; and, as appears to us, this new metal, to which Dr. Wollaston gives the name of rhodium, is no other than Mr. Tennant's iridium. It is procured from the nitro-muriatic solution of platina, after this latter metal has been separated by sal ammoniac. But, according to M. Descotils, a small portion of iridium is always taken up during the action of nitro-muriatic acid on platina; therefore the solution from which Dr. Wollaston procured his new metal ought to contain iridium also; but, in the analysis which he gives of it, there appears only platina, copper, lead, iron, palladium, and rho dium; either, therefore, Dr. Wollaston's analysis of the nitro-muriatic solution is incorrect, or his rhodium is iridium. The palladium of Mr. Chenevix, which was supposed by that gentleman to be an artificial amalgam of platina and mercury, appears to be contained in the crude platina, and is probably a simple substance. This discovery Dr. Wollas ton had made before Mr. Chenevix undertook his experiments; since, if we are not misinformed, all the palladium which was announced in so mysterious a manner, and sold at a much higher rate than even Hahnemann's pneum, was prepared by Dr. Wollaston himself. Irish Academy. Vol. 9. 4to. pp. 680. which bear strong testimony to the pro found knowledge of the astronomical THE great patron of science in England, Baron Maseres, has, it is well known, employed much of his time, and been at great expence, in collecting every paper of importance on the subject of logarithms; and in the sixth volume of the Scriptores Logarithmici, on which he is now engaged, the original work of Neper will be inserted, together with an investigation of various methods of calculating logarithms, particularly this which makes the subject of the paper before us. The generality of students, and of those who use the tables of logarithms, are content with the vulgar definition that they are a set of numbers in arithmetical corresponding to another set in geometrical progression, or if numbers are represented by the powers of a given number, then their logarithms correspond to the indexes of those numbers. The definition corresponding to the meaning of the term that they are measures of ratios, contains something too subtle, and is too frequently neglected. This was however the idea of the inventor, and the principal difference between him and Dr. Halley consists in the manner of extracting the root. The subject is here concisely explained. By ratiuncula is meant a ratio of inequality very near to equality, thus the ratio of 1+r, or 1-r to unity is when r is exceedingly small a ratiuncula. Let there be placed between unity and ten 999999999 mean proportionals, then will the ratio of unity to ten be compounded of 1000000000 ratiuncule, each equal to the ratio of unity to the first or least of those means. Now if the ratio of unity to two is compounded of 301029995 ratiunculæ of this kind, then will 1000000000 and 301029995 be the logarithms of the ratios of unity to ten, and of unity to two. But unity may be 2. Account of the Whynn Dykes, in the Neighbourhood of the Giant's Causeway, Bally Castle and Belfast, in aLetter to the Lord Bishop of Dromore, from WILLIAM RICHARDSON, D. D. late Fellow of Trinity College, Dublin. A CONSIDERABLE part of the counties of Derry and Antrim is basaltic. The tract occupied by this species of rock is from twenty to thirty miles from east to west, and more than thirty-five in its greatest length from north to south; it comprehends the precipices of Fairhead, and the celebrated columnar rocks at Portrush and the Giant's Causeway. The basalt is divided into sixteen or more prodigiously thick strata, accumulated on each other, to the height, in some places, of 1200 feet. This enormous mass appears to rest on a bed of white limestone, about 200 feet in thickness. Below the limestone stratum, ånd beyond the visible limits both of this and of the basalt, there extends on the west a tract of argillaceous schistus, and on the east of sandstone and clay, alternating with coal. Dr. Richardson resides in the neighbourhood of the Giant's Causeway, and has been in the habit of attending to the curious geological appearances which present themselves on this bold and magnificent coast. The dykes which traverse both the basalt, and the adjoining sandstone strata, have especially attracted his notice, and, in the paper before us, are described the situation, structure, and other circumstances worthy of attention, of six dykes passing through basalt, and three intersecting the sandstone. These dykes are a few feet thick, and of un known length and depth, forming long compact walls, intersecting vertically all the strata in their way, and composed of basalt, either in horizontal columns, mixed sometimes with the globular variety, or amorphous. Of these, only one has been noticed before; and future mineralogists, when visiting this part of the country, will derive much advantage from a careful perusal of this interesting paper. 3. An Essay on Credulity. By WILLIAM PRESTON, Esq. THE main object of Mr. Preston in this essay is to establish the position, that credulity, or a disposition to believe without evidence, is an innate principle of the human mind: that it is rather an emotion of the human feeling, than an operation of intellect. To this circumstance he attributes the amazing success, which some of the most bungling impostures have experienced, and the readiness with which the most absurd rumours have been believed. He then notices the mischievous effects of this principle, and enquires into the means of counteracting it. He disapproves of the statutes, by which spreading false news, to make discord between the king and nobility, was made punishable by fine and imprisonment, and contends, that the only way of safely and effectually checking the growth of this evil, is by the diffusion of general knowledge, and facilitating the publicity of important facts, by means of a free press. 4. An Examination of various Solutions of Kepler's Problem, and a short Practical Solution of that Problem pointed out. By the Rev. J. BRINKLEY, A. M. Sc. UNLESS we were to transcribe the whole of this very valuable paper, we could not give to our readers a true idea of its contents. The problem is well known to be of the utmost importance, and to have exercised the talents of the most eminent mathematicians. The present times, from the discovery of the two new planets Olbers and Piazzi, and from the probability that the number will be considerably increased by a more attentive observation of the hea vens, call particularly for this investiga tion, and it could not have fallen into better hands, nor into any from whom greater advantage to science might be expected. Kepler's own solution, Boul liald's first hypothesis, and its simplifi cation by Seth Ward, commonly know by the name of the simple elliptic bypothesis, Boulliald's correction of Sch Ward's hypothesis, Mercator's hypothesis, Newton's two practical methods, Cassini's, Machin's, Dr. Matthew Stewart's methods, Simpson's practical rule, Lacaille's method, are each examined in the order mentioned, and to these is subjoined a convenient practical solution, exemplified on the planet Olbers. This solution takes its rise from Cassini's method; in examining which, it has been proved that the error of his first approximation depends only on the third and higher powers of the eccentricity. By considering the nature of this error, the writer is enabled to lay down the following practical rule for obtaining the true from the mean anomaly. "1. Subtract the Log. of the aphelion from the Log, of the perihelion distance, and call the remainder B. B+ the Log. tang. of the mean anomaly the Log, tang. of an arch, which being added to the uncan anomaly, the sum will be the approximate excentric anomaly. 2. Add together the constant Log: 5.3144251, the Log, of the excentricity and the Log. sine of the computed approximate excentric anomaly: the sum diminished te 10 will be the Log, of a number of secous to be added to the approximate excentric anomaly, to obtain the corresponding mean anomaly. "3. Find the logarithm C either by a table previously constructed, or by computation. viz. C=19.6959700-2 Log. cs. 4 *, - being an arch the Log, cosine of which excent + Log. cs of the approximated excentric anomaly. When the approximate. excentric anomaly is greater than 90° « is also greater than 90o. "4. Add the Log. of the error of the computed mean anomaly to C, and the sun wid be the logarithm of the error of the_first approximated excentric anomaly. This error has always the same sign as the error of the computed mean anomaly. 5. The sum of Band Log. tang. the correct excentric anomaly is the Log. tang of the true anomaly. "Note, when the mean anomaly is greater than 180°. Take its supplement to 360, and compute the corresponding true anomaly: its supplement to 300 will be the true anomaly required. By the above operations, the true anomaly will be had to less than a second, for all the planets. In orbits more excentric, it and fourth rules, using the corrected excenmay be necessary to repeat the second, third tric anomaly instead of that first computed. And then using the second corrected Excon |