as much sensibility as possible. With this intention, our author undertook the experiments of which he now gave an account, and from which he draws the following inferences: "1. That the best material for compass needles is clock-spring; but care must be taken in forming the needle, to expose it as seldom as possible to heat, otherwise its capability of receiving magnetism will be much diminished. 2. That the best form for a compass needle is the pierced rhombus, in the proportion of about five inches in length to two inches in width; this form being susceptible of the greatest directive force. 3. That the best mode of tempering a compass needle, is first to harden it at a red heat, and then to soften it from the middle to about an inch from each extremity, by exposing it to a heat sufficient to cause the blue colour which arises again to disappear. 4. That in the same plate of steel, of the size of a few square inches only, portions are found varying considerably in their capability of receiving magnetism, though not apparently differing in any other respect. 5. That polishing the needle has no effect on its magnetism. 6. That the best mode of communicating magnetism to a needle appears to be placing it in the magnetic meridian, joining the opposite poles of a pair of bar magnets, (the magnets being in the same line,) and laying the magnets so joined flat upon the needle, with their poles upon its centre; then, having elevated the distant extremities of the magnets, so that they may form an angle of about two or three degrees with the needle, they are to be drawn from the centre of the needle to the extremities, carefully preserving the same inclination; and having joined the poles of the magnets at a distance from the needle, the operation is to be repeated ten or twelve times on each surface. 7. That in needles from five to eight inches in length, their height being

equal, the directive forces are nearly as the lengths. 8. That the directive force does not depend upon extent of surface, but, in needles of nearly the same length and form, is as the mass. And, 9. That the deviation of a compass needle, occasioned by the attraction of soft iron, depends, as Mr Barlow has advanced, on extent of surface, and is wholly independent of the mass, except a certain thickness of the iron, amounting to about two-tenths of an inch, which is requisite for the complete developement of its attractive energy.'

"

On the 22d, the reading of Dr Henry's paper on the Aeriform compounds of Charcoal and Hydrogen, (which had commenced at a previous meeting,) was concluded. The first object proposed by the author, was to ascertain whether there be a compound answering in its characters to light carbureted hydrogen gas. The result of his inquiries was, that such a chemical compound does exist, having uniformly the same composition and chemical properties, and the same specific gravity, (0.556,) and constituted of 100 parts, by weight, of charcoal, united with 34.40 of hydrogen, while olefiant gas consists of 100 of charcoal, combined with 16.70 of hydrogen. His next experiments relate to the best method of analyzing mixtures of olefiant gas with hydrogen, carbureted hydrogen, and carbonic oxide; and of olefiant gas with all those three gases. Chlorine, he shews, may be employed with perfect accuracy, provided certain precautions, which he points out, are observed. The chief of these is complete exclusion of the light. By these analytical processes, he proceeds to examine the composition of oil gas and coal gas; and the general result is, that oil gas (as he had formerly shewn with respect to coal gas) is very far from being uniform in composition, but differs greatly in specific gravity and combustibility, when prepared at dif

ferent times, even from the same kind of oil, owing to variations of temperature, and other circumstances. Essentially, the gases derived from oil and coal are composed of the same ingredients, though in different proportions, viz. simple hydrogen, light carbureted hydrogen, and carbonic oxide gases, with the addition of variable proportions of an elastic fluid, which agrees with olefiant gas in being condensible by chlorine, but combines more oxygen, gives more carbonic acid by combustion, and has a higher specific gravity than olefiant gas, or even than common atmospheric air. Whether this ingredient be strictly a gas, permanent at all temperatures, or a mixture of olefiant gas with some new gas, constituted of hydrogen and charcoal, in different proportions from what are found in the known compounds of those elements, or merely the vapour of a volatile oil, the author leaves to be determined by a future course of experiments.

The only paper of any interest read to the Society in the course of March, was one by the President, Sir H. Davy, on the Papyri of Herculaneum. In this paper Sir H. gives an account, 1. Of his first experiments, performed in England in 1818, upon several fragments of papyri, which induced him to hope that chemistry might afford some assistance towards unrolling these interesting relics. 2. Of the state of the MSS. found at Herculaneum. 3. Of the chemical processes employed on the MSS. in the Museum at Naples, and of the reasons which ultimately compelled him to abandon the attempt; together with some general observations on the MSS. of the ancients. The papyri in question appear to consist of leaves reduced to the state of cinder, cemented by a matter soluble in certain liquids, but especially in muriatic and nitric ether. Now, as chlorine, while it has a strong

attraction for hydrogen, exerts no action upon carbonaceous substances, and, as charcoal forms the basis of ancient writing-ink, it occurred to Sir H. that gas might be usefully employed to destroy the adhesion of the layers; he, therefore, made trial both of it and of other agents possessed of analogous properties, and his attempts were, to a certain extent, successful. The state of the Neapolitan specimens, and the undecomposed vegetable matter generally found in them, suggest some curious remarks respecting the causes of the changes they have undergone, and which, by the Svolgatori of Naples, have uniformly been ascribed to the action of fire, more or less intense. Sir H. has shewn that this opinion is entirely erroneous. The part of Herculaneum in which they were found had not been inundated by lava, but covered by a bed of tufa, composed of sand, volcanic ashes, stones, and dust, cemented by the action of water, probably at the moment of its ebullition. Nor is the action of fire necessary to produce the imperfect carbonization observed in the MSS.; for, at Pompeii, a town which had been buried by a shower of ashes, (which must have been cold, as they fell at the distance of seven or eight miles from the crater of Vesuvius,) the wood in the houses has been uniformly converted into charcoal; the colours on the walls, which heat would have either destroyed or altered, continue perfectly fresh ; and the papyri discovered have been in the form of white ashes, or burnt paper. Among the Neapolitan MSS. there are some covered with a glossy substance, resembling varnish, arising, Sir H. suggests, from the decomposition of the skin used to enfold them, and now converted into a brilliant animal charcoal, leaving porphate of lime when burned, but producing at the same time no inconsiderable quantity of ammonia. At Naples, one method only

has been adopted for unrolling the volumes of carbonized papyrus, and it is entirely mechanical. It is the invention of Piaggi, a native of the Roman States, and consists in applying a thin animal membrane, (gold-beaters' skin), by a solution of glue, to the back of the MS., and carefully elevating the lay ers when the glue is dry. Alcohol and ether were found useful auxiliaries in this delicate operation, and great advantage was also derived from throw ing heated air upon the surface of the leaves, precaution being taken that the temperature should not be too rapidly raised. The different MSS., however, required very different treat ment. During the two months Sir H. Davy was employed in these experiments at Naples, he succeeded, with the assistance of the persons attached to the Museum, in partially unrolling about 23 MSS., from which fragments of writing were obtained, and in examining about 120 others, which gave no hopes of success. "And I should gladly have gone on with the undertaking," he adds, "from the mere prospect of a possibility of discover ing some better results, had not the labour, in itself difficult and unplea sant, been made more so by the conduct of the persons at the head of this department in the Museum. At first every disposition was shewn to promote my researches; for the papyri remaining unrolled were considered by them as incapable of affording any thing legible by the former methods, or, to use their own words, disperati; and the efficacy and use of the new processes were fully allowed by the Svolgatori, or unrollers of the Museum; and I was for some time permitted to choose and operate upon the specimens at my own pleasure. When, how ever, the Rev. Peter Elmsley, whose zeal for the promotion of ancient literature brought him to Naples, for the purpose of assisting in the under

taking, began to examine the fragments unrolled, a jealousy, with regard to his assistance was immediately manifested, and obstacles, which the kind interference of Sir William A'Court was not always capable of removing, were soon opposed to the progress of our inquiries; and these obstacles were so multiplied, and made so vexatious, towards the end of February, that we conceived it would be both a waste of the public money, and a compromise of our own characters, to proceed."

The Roman MSS., existing in the Museum of Naples, consist, in general, of papyrus, of a texture considerably thicker than that of the Greek MSS.; the characters, though much less perfect in formation, are also larger, and the rolls more voluminous. From the intermixture of Greek characters in some fragments of Latin MSS., and from the state of decomposition in which they were found, Sir H. thinks it extremely probable that some of them were of very ancient date. The ink with which they were written was a mixture of charcoal and glue; while the silence of Pliny as to ink composed of galls and iron renders it improbable that such a composition was used up to this period, and leads to the concluclusion that parchment and our present writing ink were adopted together; " for a mixture of charcoal and solution of glue can scarcely be made to adhere to the skin, whereas the free acid of the chemical ink partly dissolves the gelatine of the MSS., and the whole substance adheres as a mordant."

The most ancient parchment MSS. are probably the Palimpsesta, or Codices Rescripti, lately discovered by M. Angelo Mai, in the libraries of Milan and of Rome. Sir H. examined these curious and valuable MSS., particularly that which contains several books of Cicero's treatise De Republicá, and which M. Mai refers to the second or third century. In these, time

has destroyed the vegetable of the ink, but the peroxide of iron remains, and M. Mai successfully employed solution of galls to revive its blackness. Sir H. made trial of different substances for restoring colour to the letters in ancient MSS. The triple prussiate of potash, used in the mannerrecommended by Sir Charles Blagden, with the alternation of acid, he found successful; but by making a weak solution of it with a small quantity of muriatic acid, and applying them to the letters, in their state of mixture, with a camel's hair pencil, the results were still better. After all, it is probable that we have sustained no great loss by the destruction of the Herculaneum MSS. It is remarkable that no fragments of Greek, and very few of Latin poetry, have been found in the whole collection. The sentences in which Mr Elmsley found a sufficient number of words to enable him to decypher their meaning, shew that the works of which these are the fragments, are of the same kind as those formerly examined, and belong to the schools of the Greek Epicurean philosophers and sophists. Sir H. concludes by remarking, that, should any new MSS. be discovered at Herculaneum, it would be desirable to have them immediately removed from the action of the air, by placing them in vases filled with carbonic acid. There can be no doubt, he thinks, that the more perfect specimens which have remained in the Museum, exposed, since the period of their discovery, about 60 years ago, to the action of the air, have undergone so great changes, as to render their entire unrollment nearly, if not altogether, impossible.

On the 5th of April, a paper was read on the Separation of Iron from other Metals, by J. F. W. Herschell, Esq. The proposed basis of a rigorous separation of iron from the metals (manganese, cerium, nickel, cobalt,) pot precipitated by sulphuriated hy,

drogen, is a peculiarity in the peroxide of iron, in virtue of which it is incapable of subsisting in a neutral solution at the boiling temperature. If a solution of this peroxide be neutralized when cold, and then heated, a portion is deposited in the state of a subsalt, and the liquid becomes acid; if allowed to cool, and again neutralized, a fresh portion of the metallic contents separates on re-applying the heat, and so on till the quantity held in solution is no longer sensible to the most delicate re-agents. If, on the other hand, the neutralization be performed while actually boiling, we attain this limit at one operation. Hence, Mr Herschell recommends the following process:Having peroxidized, by means of nitric acid, a solution containing iron, and any of the abovementioned metals, drop into it, while boiling, carbonate of ammonia, till the acid reaction is entirely destroyed, even going a little beyond the point of exact neutralization. The whole of the iron, to the last atom, is separated, while the liquid retains in solution the other metallic oxides, as well as the minute portion of their carbonates due to a trifling excess of the alkaline precipitant. In the cases of cobalt and cerium, the alkaline carbonate may be added in considerable excess, without separating any of the metals, and their solution, so freed from iron, is then a most delicate test of the presence of the latter metal.

On the 31st of May, the reading of Mr Herapath's paper on Absolute Zero, (which had been commenced at a previous meeting,) was concluded. The object of Mr Herapath was to determine the law of temperature, and the point of absolute cold, or zero. For this purpose, he contrived an apparatus for obviating the effects of radiation; and having mixed equal weights of mercury at a very high and low temperature, he carefully ascertained the temperature of the mixture. In

seven experiments of his own, thus made, and two of M. De Luc's, he found that the results followed a law, from which they differed, at a medium, not more than 1-10th of a degree. This law is, that the square of the temperature of a given portion of gas, varies as the elasticity and volume conjointly; and, therefore, when either continues the same, the temperature is as the square root of the other. Hence Mr H. found, that the heat of boiling water is to that of melting ice, as the 11 to the 8, or as 1.1726 to 1 nearly; and the point of absolute cold he also determines in a manner inde. pendent of any theory of heat, from the principle of an air thermometer.

In June nothing of any particular interest was communicated to the Society; and in July, the only paper we shall notice, was communicated on the 12th, and entitled, " On a New Compound of Chlorine and Carbon," by Messrs Phillips and Faraday. This compound was brought to England, and given to these gentlemen by M. Julin, of Abo, in Finland. It was formed during the distillation of green vitriol and nitre, for the production of nitric acid; is of a solid crystalline body, fusible and volatile by heat,

without decomposition; is insoluble in water, but soluble in alcohol, ether, and essential oils; sinks in water; burns with a red flame, giving off much smoke, and fumes of muriatic acid gas; is not acted upon by acids; and gives out chlorine, and deposits charcoal, when its vapour is heated in a tube till decomposition takes place. Potassium burnt with it, forms chloride of potassium, and liberates charcoal; its vapour, detonated with oxygen over mercury, forms carbonic acid, and chloride of mercury; passed over hot oxide of copper, it constitutes a chloride of copper and carbonic acid; and over hot lime, it occasions ignition, and produces chloride of calcium, and carbonic acid. It is composed of chlorine and carbon, and, from the experiments detailed, two parts appear to be formed of

1 portion of chlorine.. 44.1..33.5 2 portions of carbon.. 15.0..11.4 Hence it is a sub-chloride of carbon. All attempts to form it by other means have hitherto failed.

After hearing another paper, by C. Bell, Esq., on the Structure and Functions of the Nerves, read, the Society adjourned till the usual period.

AFTER the usual adjournment, this Society resumed its sittings on the 15th of November, 1819, when a paper, by Dr Brewster, was read, on the subject of Circular Polarization, a name by which he proposed to distinguish the phenomena first discovered by M. Arago, along the axis of rock crystal, afterwards analyzed by M. Biot, and

subsequently discovered by MM. Biot and Seebeck in several fluids. M. Biot had shewn, that, in some specimens of rock crystal, a certain succession of tints was produced, by turning the analyzing prism direct from right to left, while, in other specimens, the same succession was developed by turning the prism in a retrograde di