could be of great importance. Still, it was useful to know from what the first vegetables derived the nitrogen they required.

"On the Electric Origin of the Heat of Combustion," by J. P. Joule. The author is of opinion that he has succeeded in rendering evident the fact that the heat of combustion is an electrical phenomenon, and that the method of its developement is by resistance to electric conduction. He has entered upon other cases of chemical heat, but finds them more difficult than he expected, and intends to examine the heat of combustion again, being satisfied that, when its electrical character is completely established, the theory of all chemical heat will find its proof at the same time.

Dr. Daubeny read a paper "On the Causes of the Irregularities of Surface which are observable in certain parts of the Magnesian Limestone Formations of this Country."-The magnesian limestone rock in some of the quarries in Derbyshire, presents a remarkable appearance. They do not possess an undulating surface, as the limestones generally do, but the surface is covered with irregular elevations and depressions of a very marked character. Prof. Sedgwick had cursorily noticed the configurations which these magnesian limestones possess, and ascribed it to an arrangement of the particles of the rock which took place in the act of its consolidation. Dr. Daubeny, however, was inclined to ascribe them to the action of atmospheric influences, and to that of water impregnated with carbonic acid.

"On the Composition of the Blood and Bones of Domestic Animals," by Prof. Nasse, of Marburg. The author of this paper had made an elaborate series of proximate analyses of the blood of man, the dog, cat, horse, ox, calf, goat, sheep, pig, goose, and fowl, ascertaining the relative proportions in each of water, serum, albumen, fibrine, and fat, together also with the usual saline constituents. The results of his analyses he exhibited in a series of tables, which are too extended for insertion. He drew some conclusions with respect to the relation of each constituent part to the rest. Thus, from purely chemical evidence, he arrives at the conclusion, that the less iron and more alkaline carbonates and fibrine which are contained in the blood, the weaker will the constitution of the animal be, and the more liable to disease. Thus the blood of the English horse contains much more iron and less alkaline matter or fibre than the German horse; and it is well known that the blood is far less liable to disease in the former than in the latter. Prof. Nasse then examines the variation in the composition of wounded and of healthy bones. The conclusion deduced from his analysis is, that the bones of injured limbs are deficient in organic constituents, such as in their gelatine, as well as in the carbonate of lime. The proportion of phosphate of lime remains unchanged, but that of carbonate of lime is much diminished. The Professor accounted for this phenomenon from the circumstance of carbonate of lime being soluble in carbonic acid. When a limb is injured, blood thickens

in the substance of the bone, and in this state contains more carbonic acid than that which freely circulates, and would, therefore, favour its solution. The liquid taken from the injured part contains more than its normal quantity of albumen, which, under certain circumstances, favours the solubility of carbonate of lime.-The thanks of the Section were given to Prof. Nasse for his communication.

Dr. Playfair drew attention to some points connected with Professor Nasse's tables of the composition of the blood of the various animals. He (Dr. Playfair) had shown, by some analyses published in "Liebig's Physiology," that the ultimate composition of blood and flesh were nearly identical. Hence the professor's results might be considered as tables of the economic value of the flesh of animals, and the results agreed closely with actual facts. Thus, according to the author of the paper, the blood of man contained 74.194 of albumen; the blood of the ox, which formed, after being transformed into flesh, the most nutritious food for man, contained 74.45 of the same body; the pig, the flesh of which was equally nutritious, contained also exactly the same as that of man-viz. 74.80. Then in those animals, the flesh of which is less nutritious, we find the proportion of albumen considerably less than in man; thus in the blood of the goat it is only 62.905; in the goose 48,695; in the fowl 48.52.

"On the Improvement of the Telescope," by Mr. Fox Talbot.— Mr. Fox Talbot said, that this subject occurred to him about two years ago, when the Earl of Ross (then Lord Oxmantoun) was making much larger specula for reflecting telescopes than had ever been obtained before; and he thought, if once we had a very large and perfect speculum, it might be possible to multiply copies of it by galvanic means. He had observed, that if an electrotype cast were taken from a perfectly polished surface, the cast was also perfectly polished; so that no defect of form from this cause could have an injurious effect on the speculum. The great and obvious defect was, that electrotypes were in copper, which reflected but little light. He mentioned these ideas to Professor Wheatstone, who said the same had occurred to him; and he showed him a paper which he had drawn up some few months before, and in which he suggested the taking galvanoplastic casts of specula in platina, palladium, silver, or nickel, and for especial purposes gilding the copper; taking care that the two precipitations adhered well to each other. So that (said Mr. Talbot) the idea had suggested itself independently to both of them; but, on comparing notes, they found differences. Though it had occurred to him (Mr. Talbot) to precipitate white metals, yet he did not think that platina would have a sufficiently beautiful white metallic polish. Professor Wheatstone, had, however, made choice of platina; and varying the quantity till he found the required proportion, he obtained a mirror in platina, which appeared to him (Mr. Talbot) to have quite brilliant polish enough, and to be white enough to answer the purpose; and he considered, therefore, that

Professor Wheatstone had proved, that, at least in one form, the specula of telescopes might be made by voltaic precipitation. His own idea was, that it might be possible to whiten the surface of the copper without injuring the form; and, therefore, having obtained a speculum in very bright polished copper, he (Mr. Talbot) whitened it, and transformed it into sulphuret of copper; and, after having retained it about a year, he did not perceive the smallest alteration in any respect. This, therefore, appeared to him a mode by which important results for astronomers could be obtained. For the last year, perhaps, nothing further had been done, either by Professor Wheatstone or himself; but, the other day, being at Munich, he (Mr. Talbot) visited Professor Steinheil, who showed him his inventions, and told him he had discovered a method of making specula by the electrotype. It so happened, that both Professor Steinheil and himself had published their respective methods about a month or six weeks before; the professor having read a communication on the subject before the Academy of Sciences at Munich, and printed it, and he (Mr. Talbot) having published his in England. Their modes were, however, different, as Professor Steinheil precipitated gold upon the speculum of copper: and, having precipitated a certain thickness of gold, he then precipitated copper on the back of the gold, to give it sufficient thickness. He (Mr. Talbot) should have thought beforehand that gold would not reflect light enough to be available; but Professor Steinheil informed him he had found, by careful experiment, that it reflected more light than polished steel. He allowed Mr. Talbot to look through a Gregorian. reflecting telescope, of which the speculum was a common one, but gilded, and he found the image perfectly clear and well defined. A slight tinge of yellow was thrown over all the objects, but the image was perfectly clear and defined. Professor Steinheil said, that in the course of a year, he should have a very large telescope, furnished not only with a speculum, but also with other apparatus, voltaically formed, so that telescopes might be made all from a good model, so as to insure greater accuracy of proportions; and in this way even very large telescopes might be constructed at a comparatively trifling expense. With reference

to precipitating copper on the back of the gold, the professor had a simple expedient for securing adhesion. He first precipitated gold from the cyanide of gold, and he mixed with it cyanide of copper, and kept gradually increasing the quantity of the latter sort; so that an alloy was precipitated, which was continually increasing the copper with respect to the gold, till he had a speculum whose surface was gold, and which then became an alloy, the quality decreasing, till, at the bottom, it became pure copper. This was important: because, without such experiments, one would not have known that such results would have followed; for some philosophers supposed, that, if we attempt to precipitate the salts of two metals, only one was precipitated; but Professor Steinheil informed him that they

precipitated in union. He thus obtained a speculum with a face of gold and a back of copper. But, supposing the largest, cheapest, and best speculum were obtained, the framework of the telescope would be so gigantic, that few observers would be able to use the instrument. With a focal length of sixty to eighty feet, it would be quite unmanageable for any private individual. The idea occurred to him (Mr. Talbot), to have a tube fixed in an invariable position, and to have a perfectly true plane mirror, of a size somewhat larger than the concave speculum, placed in front of the tube, with an aperture in the centre. This plane reflector should be moveable about its centre in any direction; so that luminous bodies, falling first upon the plane reflector, were then reflected against the concave reflector, and passed through the aperture. The only motion requisite for its plane mirror would be one about its centre. The mechanical difficulties in the way of this plan would be far less than in the common method. Professor Steinheil's idea on this point was somewhat different. He (Mr. Talbot) did not think it important in what direction the tube of the telescope was directed. Professor Steinheil's idea was, that it should be pointed directly to the pole of the heavens, and kept as steady as possible, and that the plane mirror should have a 'simple motion of revolution, indeed two motions, but about a rectangular centre.

Shortly after this paper had commenced, the distinguished astronomer, Professor Bessel, entered the Section. As soon as the President announced his name, which he accompanied with a few eloquently eulogistic sentences, the entire Section rose from their seats and applauded. M. Bessel expressed in warm terms his sense of the honour.-Mr. Isaac Holden observed that the late Earl Stanhope had actually constructed a reflecting telescope on the very principles now proposed, both with respect to the fixity of the concave speculum, and the use of a moveable plane mirror.-Sir D. Brewster mentioned a plan proposed by an American some years since, for generating a pro-tempore speculum, by causing quicksilver to revolve rapidly, when the centrifugal force would form it into a paraboloid, the very shape best adapted for the purpose.-The President inquired from Mr. Talbot whether some contrivance similar to the aërial telescope of Huygens and Hevelius might not be adapted so as to dispense with the plane mirror, the accurate construction of which was nearly, if not quite, as difficult a mechanical problem as the construction of the great speculum.—Mr. Talbot replied, that the principle of the aërial telescope was not, in his opinion, applicable to a reflector. The reflecting speculum being on the ground, it would be necessary, on that principle, that the observer should be elevated: an arrangement incompatible with his free change of place. In reply to a question from Sir T. Brisbane, Mr. Talbot said, that, with proper precautions, the original speculum would not run any risk of deterioration during the electrotype

process.

Sir D. Brewster then proceeded to make three communications : -1, "On Luminous Lines in certain flames corresponding to the defective lines in the Sun's light :" 2, "On the Structure of a part of the Solar Spectrum, hitherto unexamined;" and 3, "On the Luminous Bands in the Spectra of various flames." 1. After noticing Fraunhofer's beautiful discovery as to the phenomena of the line D in the prismatic spectrum, Sir David said, he had received from the establishment of that eminent man, at Munich, a splendid prism, made for the British Association, and one of the largest, perhaps, ever made; and, upon examining by it the spectrum of deflagrating nitre, he was surprised to find the red ray, discovered by Mr. Fox Talbot, accompanied by several other rays, and that this extreme red ray occupied the exact place of the line A in Fraunhofer's spectrum, and equally surprised to see a luminous line corresponding with the line B of Fraunhofer. In fact, all the black lines of Fraunhofer were depicted in the spectrum in brilliant red light. The lines A and B turned out in the spectrum of deflagrating nitre to be both double lines; and, upon examining a solar spectrum under favourable circumstances, he found bands corresponding to these double lines. He had looked with great anxiety to see if there was any thing analogous in other flames, and it would appear that this was a property which belonged to almost every flame. II. He had, by means of the prism from Munich, been enabled to extend the solar spectrum beyond the point where, according to Fraunhofer, it terminated immediately at the side of the line A, and he (Sir David) found one part to consist of about sixteen lines, placed so near to each other that it was difficult to recognise the separation; but the lines, as they approached to A, were much nearer to each other than as they receded from it; consequently, that portion of the spectrum appeared concave, resembling so much the scooped-out lines of a moulding on wood, that it was scarcely possible to suppose that the beholder was not looking at such a moulding. He was led to observe an analogous structure near the line B; and upon carrying on this comparison of structure of one part of the spectrum with that of another, it seemed to him, that, by and bye, something important would result; for there was a repetition of a group of lines, and similar lines, through different parts of the spectrum, as if the same cause which produced them in one part, produced them in another. III. He had endeavoured to procure all the minerals and artificial salts and other substances capable of combustion which could be had; and, in order to have a suitable combination, he used an oxygen light analogous to the Bude light. Every one conducting these experiments was aware that it was necessary to pass the light through a narrow aperture; but this would reduce the intensity of the light so much, as to make it difficult to observe the rays at the extremity of the spectrum; but he found that he could obtain the effect of a small aperture, by merely inclining the prism; so that, with a good rism, the great lines in the solar spectrum might be seen by using