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the Society that have been made by the Council in their recent revision of them; by one of which, the meetings of the Society will commence, in future, for each Session, on the first of the two Thursdays preceding the Anniversary, and terminate on the third Thursday in June.

The Society then adjourned accordingly, to Thursday the 20th of November next.

A paper on the Compressibility of Water, Air, and other Fluids; and on the Crystallization of Liquids, and the Liquefaction of Aëriform Fluids, by simple pressure, was prepared by Mr. Perkins, for the purpose of submitting it to the Royal Society; but it was accidentally misplaced, previously to the last meeting, and therefore could not be announced to the Society with the other papers. It contained, we are informed, a minute description, accompanied with figures, of his compressing, apparatus ; a diagram, showing the ratio of the compressibility of water, beginning at the pressure of 10 atmospheres, and proceeding regularly to that of 2000; and some experiments on the compression of atmospheric air, which appears by them to follow a law varying from that generally assigned to it by philosophers. Mr. Perkins intended to announce, also, in this paper, that he had effected the liquefaction of atmospheric air, and other gaseous substances, by a pressure equal to that of about 1100 atmospheres; and that he had succeeded in crystallizing several liquids, by simple pres



May 9.–At this meeting, a paper on the Mercurial Compensation Pendulum, by Francis Baily, Esq. FRS. was read, but owing to its length, it could not be completed.

June 13.-The reading of Mr. Baily's paper on the Mercurial Compensation Pendulum was resumed and concluded. It contains an account of many experiments made to determine the rates of expansion of the various substances used in the construction of such pendulums, the results of which are given in a tabular form. The expansions of mercury, as given by different authors, are collected, and it is shown that none of them can be safely applied to the purposes of the pendulum without certain modifications which are pointed out in this paper. The principles of the Compensation Pendulum are then investigated, and a formula deduced for determining the height of the quicksilver in the cylinder, the result of which is different from those given by preceding writers on this subject. Mr. Baily then points out some improvements in the usual mode of constructing and regulating pendulums, which appear very simple and efficacious ; and concludes his paper by the description of a compensation pendulum, of great cheapness, being formed of wood and lead alone, but which, he states, may be made available for many useful purposes.

The Society then adjourned to Friday the 14th of November next.

We have heard with pleasure that the Council has awarded several gold and silver medals to be presented by the Society at one of its future meetings to some of the continental astronomers, for their discoveries ; and a gold medal to Mr. Babbage, as a token of their high estimation of his invaluable invention of applying machinery to the computation of astronomical and mathematical tables. As soon as we receive correct information, we shall lay the particulars of these honorary tokens before our readers.

MEDICO-BOTANICAL SOCIETY OF LONDON. April 25.-A paper, on the Essential Oil of Bitter Almonds, was read, by Mr. Frost, and Experiments were made (before the Society) on Animals with the Oil.

At this meeting a paper was also read, on Atropa Belladonna.

May 9.-Mr. Frost delivered a lecture on Stalagmitis Cambogioides, and Acorus Calamus.

A paper was also read from P. J. Brown, Esq. Corresponding Member of the Society, on several Medicinal Plants used by Swiss Practitioners.




1. Letter from Mr. Faraday, respecting the Historical Sketch of Elec

tromagnetism published in the Annals.

(To the Editor of the Annals of Philosophy.) DEAR SIR, You did me the favour to insert in the second and third volume of the Annals of Philosophy, a paper which I had written, entitled, “A Historical Sketch of Electromagnetism.”. To that paper, the initial of my Christian name only was affixed. Wishing now, for reasons which will shortly be made public, to acknowledge myself as the author of it, I will thank you to insert this letter in the Annals as an assent on your part to the correctness of the statement which it contains. I remain, dear Sir, yours, very truly,


II. Diurnal Variation of the Magnetic Needle. We understand that Mr. Christie has continued to pursue his inquiries on this subject, as noticed in our report of Mr. Barlow's paper, and that he has been led to conclude from them, that it is the calorific and not the colorific rays that produce the change in question. He has found that a change of temperature in his opposing magnets, to the amount of one degree only, will produce a change of nearly a degree in the direction of the needle. He showed by the most satisfactory experiments, before Professors Oersted and Barlow, that the mere change of beat produced by applying his hand to the magnet, when the needle was thus nicely adjusted, caused a deviation to the amount of between two and three degrees.

Mr. Christie has communicated the first part of his experiments to the Royal Society, as announced in our report of the final proceedings of that body for the present Session.

III. Frauds and Imperfections in Paper-making. In order to increase the weight of printing papers, some manufacturers are in the habit of mixing sulphate of lime or gypsum with the rags to a great extent. I have been informed by authority, upon which I place great reliance, that some paper contains more than one-fourth of its weight of gypsum ; and I lately examined a sample which had the appearance of a good paper that contained about 12 per cent.

The mode of detecting this fraud is extremely simple: Burn 100 grains, or any given weight of the paper in a platina, or earthern crucible, and continue the heat until the residuum becomes white, which it will readily do if the paper is mixed with gypsum. It is certainly true that all paper contains a small quantity of incombustible matter derived from accidental impurities, but it does not amount to more than about one per cent.; the weight then will indicate the extent of the fraud.

With respect to the imperfection of paper, I allude to the slovenly mode in which the bleaching by means of chlorine or oxymuriatic acid is effected. This, after its operation, is frequently left in such quantity in the

that it

may be readily detected by the smell. Sometime since, a button-maker in Birmingham, who had manufactured the buttons in the usual way, was surprised to find that after being a short time kept, they were so tarnished as to beunsaleable; on searching for the cause, he found that it was derived from the action of the chlorine which had been left in the paper to such an extent as to act upon the metallic buttons.--Edit.

IV. Boiling Spring of Milo. The 14th volume of the Annals, p. 27, contains an analysis of the water of the boiling springs of Milo; but this island is there incorrectly called Milto. For this correction I am indebted to the Rev. Mr. Holme, of Cambridge, by whom the water was supplied for analysis. -Edit.

V. Crystals

formed in Solution of Cyanogen. M. Vauquelin observed that a strong solution of cyanogen which he kept in his laboratory during the winter, became in about four months of a light amber colour, and deposited crystals of an orange-yellow colour, the quantity of which increased for some time. The solution in which they were formed was examined; it had a strong smell of hydrocyanic acid, and was alkaline; it gave a bluish-green precipitate with sulphate of iron, which a drop of sulphuric acid immediately rendered blue. From these effects, M. Vauquelin concludes, that the solution of cyanogen was converted into hydrocyanate of ammonia.

The crystals obtained were dendritical, and had no particular smell or taste; they were nearly insoluble in water ; solution of potash did not disengage any thing; it did not dissolve them; nor did the mixture give any blue precipitate with sulphate of iron. When heated in a tube into which a piece of paper was introduced moistened with sulphate of iron, the paper became blue, and there was a strong smell of hydrocyanate of ammonia. M. Vauquelin thinks it probable, that in this case, the carbon which is usually deposited from cyanogen during decomposition, had combined with a portion of the undecomposed cyanogen, and thus become insoluble, and precipitating slowly, it had time to combine with a small quantity of water, and assume the crystalline form. M. Vauquelin proposes to call this substance subcyanogen or protocyanogen. (Annales de Chimie et de Physique.)

VI. Preparation of Iodide of Potassium. M. Caillot suggests the following method of preparing this compound:-Hydriodate of iron is first formed, and then decomposed by carbonate of potash ; for this purpose he takes four parts of iodine, two of bright iron filings, and about twenty of water. These three substances are to be put in a glass or porcelain capsule. The mixture is to be stirred until the liquor which soon becomes of a deep-brown colour, is rendered colourless; the liquor is then made to boil, and a solution of subcarbonate of potash is to be added until precipitation ceases; or a small excess of the alkali may be used, and saturated with hydriodic acid after filtration. The residuum is to be washed till it ceases to afford a precipitate on the addition of permuriate of mercury: the filtered liquors being then mixed, the whole is to be evaporated till a pellicle appears.

The same process may be employed for preparing the iodides of sodium, magnesium, calcium, &c. The iodides of mercury may also be prepared by decomposing the protonitrate and permuriate of mercury by means of hydriodate of iron, which, as just shown, may be formed extemporaneously.-(Annales de Chimie et de Physique.)

VII. Butter. M. Chevreul has lately subjected the butter of cows' milk to examination. He finds that 100 parts of fresh butter consist of

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From numerous experiments, M. Chevreul concludes that there exist in the oil of butter at least two fluid substances, one of which is soluble in all proportions in cold alcohol, does not possess acid properties, and gives by saponification some sweet principle, butiric, caproic, capric, margaric, and oleic acids. M. Chevreul has given this oil the name of buterin, because it contains the butiric acid (or its elenients), to which butter owes its odour. The other fluid substance has the properties of olein.-(Ann. de Chimie et de Physique.) VIII. Carbonate of Magnesia in the Urinary Calculi of Herbivorous

Animals. M. Lassaigne remarks, that but few of those chemists who have examined the urinary calculi of herbivorous animals have mentioned carbonate of magnesia as one of their constituents; but MM. Wurser, John, and Stromeyer, have discovered its existence; the two first in the urinary calculus of the horse, and the last on a calculus taken from

a cow.



The results of M, Chevreul's analysis of the urine of the horse, which he found to contain carbonate of magnesia, induced M. Lassaigne to examine the urinary concretions of the same animal; in which he readily discovered it, as well as in those of the ox and the cow. By treating these calculi with sulphuric acid, sulphate of lime was principally formed, but by subsequent operations magnesia was procured. The quantity of carbonate of magnesia is small, forning only the 150th to the 200th of the weight of the calculus.-(Ann. de Chimie et de Phys.)

IX. Safety of Steam Engines. M. Dupin lately read to the Academy of Sciences, the conclusion of the report which he drew up in the name of a commission, to consider the employment of low and high pressure steam-engines, principally with regard to the safety of the public. The commissioners were MM. Laplace, Prony, Ampere, Girard, and Dupin. M. Gay-Lussac, whose opinions differed in many respects from those adopted in the Report, requested permission to withdraw from the commission.

The recommendations adopted by the majority of the Academy

1. To have two safety valves adapted to the boiler ; one of these valves being so placed as not to be altered by the workman who has the direction of the steam-engine. The other valve to be under his controul, since he may have occasion to diminish the pressure, whereas he would attempt in vain to increase it, because the valve which he could not alter would suffer the vapour to escape.

2. It is proposed to prove the strength of all the boilers by means of the hydraulic press, by causing them to withstand a pressure four or five times greater than they would be required for the usual working of the machine, as well as that this pressure should be limited to four atmospheres. And also that the proof pressure should as many times exceed that of the usual working pressure of the machine, as the latter does that of the atmosphere.

3. Every manufacturer of steam-engines should be compelled to declare his method of proof, and every circumstance which would tend to guarantee the solidity and safety of the machine, especially of the boiler and its appurtenances. The manufacturer ought also to acquaint those in authority as well as the public, with the pressure under which these machines ought to work.

4. The builers of those steam-engines which are near any house, to be surrounded with a wall, provided the engines are sufficiently power,

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