an aperture three or four feet wide, the whole breadth of the window, by the mere inclination of the prism, which had the effect of producing a narrowing, facing the light. He had obtained 200 or 300 results, which he had not had any leisure to group; but he would mention some of the general results. When nitrate of lead was thrown into combustion, remarkably fine lines were produced in the spectrum. The luminous line D, of Fraunhofer, existed in almost every substance, especially in all into which soda entered, particularly in the flame of a common tallow candle; probably owing to the muriate of soda existing in the tallow. The hydrate of strontytes gave the lines very remarkably in yellow and green. The iodide of mercury did the same. Also in that remarkable substance, the lithoxanthemate of ammonia, first discovered and published by Mr. Fox Talbot, the fine lines were seen throughout the whole length of the spectrum; and there was a remarkable blue band, which he (Sir D. Brewster) had not distinctly recognized in any other flame. Indigo gave fine green and orange lines at equal distances from the D of Fraunhofer. Prussian blue did the same; calomel, nitrate of magnesia, litharge, also showed lines; the sulphocyanite of potash gave a violet and orange flame, with the lines extremely distinct. He hoped, at the next year's meeting of the association, to be able to embody these various results in a regular report.

Sir W. Hamilton said it was clear that these optical researches gave definite characters to things, which it would be necessary to include in any new history of chemical compounds.-Mr. Fox Talbot expressed his gratification, that Sir David Brewster had taken up this curious branch of inquiry. Nothing was more extraordinary than the first fact discovered by Fraunhofer, that the double yellow ray produced in most flames, especially when soda was in combustion, should answer exactly to the double black line in the solar spectrum. This was one of the most unintelligible things in natural philosophy.— Sir D. Brewster said that he might mention that the lines D were wanting in all spectra of the stars hitherto discovered. Fraunhofer, in his paper on the subject, stated that he had found, in all the spectra of the stars he had examined, black lines, but not the bright line D. He (Sir D. Brewster), in making experiments on the light of some of the coloured stars, particularly the blue and red stars, in many parts of the heavens, looking at them through a rocksalt prism at an angle of 79°, the largest angle that would transmit the light, and with Sir James South's telescope, he found those black bands existing in the star, and that those coloured rays were wanting which would account for the peculiar colour of the star; so that the peculiar colour of red, orange, or green stars was to be explained by the want of those rays necessary to make white light. Sir David mentioned one star in particular (we think a Herculis), as exhibiting this peculiarity.

Mr. Eaton Hodgkinson made a communication, "On the mode

of conducting Experiments on the Resistance of Air."—Mr. Hodgkinson said that, having been honoured by the Association with a request to pursue some experiments on the resistance of the air, he was desirous of exhibiting an instrument prepared for making the first series of these experiments. He proposed, in the first instance, to seek for the force of the wind moving at different velocities, upon plane surfaces of given dimensions, these surfaces being either perpendicular, or inclined at any angle, to its current; to determine this, he intended to place the apparatus upon the front of the first carriage of a railway train; the road along which the train passed having for a short distance poles stuck up, 100 or 200 yards asunder. He would try the experiment only on days when there was no perceptible wind; and then, if the time in seconds taken in passing between two poles be carefully observed, and the pressure indicated upon the discs (which were of two and of four feet area, both round and square), the resistance per square foot, with a given velocity, would be obtained. He hoped to determine these facts, with various velocities and at different angles of inclination in the discs, trying the same experiments with both discs at the same time, to ascertain whether the resistance to a square surface and a round one of equal area, was the same, and that the results might correct each other. The directors of the Manchester and Birmingham Railway had kindly consented, at Mr. Buck's request, to allow him to make these experiments; and he was indebted to Mr. Fairbairn for the apparatus. This was placed on the table. It consists of two discs of wood (which may be of any form), made inclinable at any angle, by means of screws, and having an attached quadrant to measure the angle. To ascertain the force of the wind, one of Salter's balance springs is placed behind each disc, attached to the cross piece which connects the two rods of the discs; and this indicated the force of the wind at any moment.

Professor Stevelly inquired whether a registering pencil was proposed, as, he conceived, if not, that the index would be in too constant motion to be observed with any accuracy. He also re

marked, that a conversation had taken place in the section at Plymouth on this subject, and Mr. Phillips proposed to avoid the necessity of waiting for calm days, by observing both when the train was going and on its return, and that thus, the effect of the air's own motion would disappear.-Mr. Hodgkinson did not think a registering pencil would be required; but if, during the progress of the experiments, he found that it was so, he would adopt it. He wished to avoid, if he could, introducing the element of the motion of the air itself at all, as, from the irregularity of those currents, he was not sure a perfect elimination of them could be obtained.

Mr. Hodgkinson then read a notice of his "Experimental Inquiries on the strength of stones and other materials."-After noticing the present state of knowledge (we might say of comparative ignorance) on this subject, and the experiments of Barlow,

Rennie, and of experimentalists on the continent, Mr. Hodgkinson said, he had long felt anxious to ascertain how the three forces, the crushing, the tensile, and the transverse strength, and the position of the neutral line (that separating the extended and compressed fibres in a bent body), were connected in bodies generally and his experiments had for several years been directed to discovering facts upon each of these matters, in order to determine the question. His experiments some years ago, made for the British Association, with respect to the values of hot and cold blast iron, had shown that the ratio of the forces of ultimate tension and compression was nearly constant in all the species of cast iron; and a few experiments made at that time on sandstone and marble, had led him to suspect that nearly the same would be the case in these and other hard bodies. Through the liberality of his friend Mr. Fairbairn (who had, as usual, given him every assistance his establishment afforded), he (Mr. Hodgkinson) had made a great many experiments upon wood, sandstones, marbles, glass, slate, ivory, bone, &c., to ascertain the tensile, crushing, and transverse strength of each: also, as far as possible, the situation of the neutral line. He had sought for these in thirteen kinds of timber, including oaks, pines, teak, &c.; all the different sorts of experiments were made, as far as possible, out of the same specimen in each case. The wood was of good quality, and perfectly dry, having been chosen for this purpose, and laid in a warm dry place for four years or more. After describing the mode and character of his experiments on the various substances named above (specimens of which he produced), Mr. Hodgkinson gave the following summary of their comparative results on marble stones of various degrees of hardness:

--

or calling the mean crushing strength per square inch, in the different articles experimented upon, 1,000, we have,—

1

8.9, taking the hardest only.

The ratio of the crushing force to the transverse force is nearly the same in glass, stone, and marble, including the hardest and the softest kinds. Hence, if we know the transverse strength, in any of these bodies, we may predict the other; and, as glass and the hardest stones resist crushing with from seven to nine times the energy that they do being torn asunder, we may get an approximate value of the tensile force from the crushing force, or vice versa. These results render it probable, that the hardest bodies, whether castiron, glass, stone, or marble, admit of certain atomic displacements, either in tearing asunder or crushing; these displacements being in a given ratio to each other, or nearly so. In future calculations as to the strength of bodies, the crushing strength ought to be made the fundamental datum, for the reasons shown in this notice. The ratio of the transverse strength to the crushing strength is greater in cast-iron than in glass, marble, and sandstones, arising from the ductility of that metal. The necessity of enlarged inquiries in these matters will be seen, when it is reflected that calculations of the tensile strength of cast-iron, or marble, or stones in general, made from the transverse strength by the modes used by Tredgold, Navier, and others, give the tensile strength twice or three times as great as it ought to be.

The President observed, that Mr. Hodgkinson was too well known to the members of the Section to make it requisite to point out his peculiar accuracy and success as an experimental investigator; the fact, however, that he had been last year awarded the Royal Medal showed the value which the Royal Society attached to his researches. The field upon which he had now ventured was of the utmost importance, even in a national point of view; since, without a knowledge of the strength of materials, we could not hope to raise durable structures without waste: we could not unite stability and economy.-Mr. Hodgkinson thanked the President for the kind terms in which he had adverted to his feeble exertions in the cause of practical science. The building in which they were assembled was, indeed, an exemplification of the importance of the researches which he had been bringing under their notice; as he had proved to the Committee of the House of Commons, that the cast-iron pillars on which it stood were, by one-half at least, too strong for the weight they were called on to support.

66

Mr. John Davies, of Manchester, then read a paper On the Manufacture and Purification of Coal Gas."-Besides the illuminating gases obtained by the distillation of coal, other gases are at the same time evolved, which are not adapted for the intended purpose. These gases are carbonic acid and sulphuretted hydrogen. The latter is particularly objectionable both from its offensive odour, and from other noxious properties. A volatile hydrocarbon usually accompanies the coal gas, and adds materially to the illuminating powers. It is well known that its two former constituents are removed from coal gas, by means of lime; but if the purification be carried too far, the hydrocarbon is also removed. Dr. Ure had shown this in the case of olefiant gas, and Mr. Davies was able to testify to the accuracy of His experiments, and to extend the remark to other hydrocarbons, which are occasionally evolved. The best means of avoiding this loss of illuminating properties is, to employ a coal containing a smaller proportion of sulphur than usual. Mr. Davies then adverted to Mr. Phillips's patent for removing ammonia from coal gas, by passing it through a purifier containing a solution of alum. He had found it, on several occasions, perfectly successful. He then adverted to the origin of the ammonia obtained in the distillation of coal. He did not think that the quantity of nitrogen contained in coal could sufficiently account for its formation. The analyses of Regnault and Richardson have, however, shown that nitrogen is contained in notable quantity in all kinds of coal.

In the course of a conversation which followed this paper, Mr. Leigh, of Manchester Gas Works, stated, that as much as two ounces of muriate of ammonia exist in one gallon of gas water.-Mr. West had examined many specimens of coal, and had never met one specimen free from sulphur. This sulphur was not always in combination with iron.—Mr. Blyth mentioned the curious fact, that in the water of a coal mine, which he had lately examined, a large amount of silicate of soda existed.

Dr. Schunk then read the paper "On the Formation of Cyanuret of Potassium in a Blast Furnace," by Dr. C. Bromeis, of Cassell.M. Zincken discovered at the bottom of the blast furnace at Mägdesprung, in the Hartz Mountains, a mass which Dr. Bromeis. found to contain ferro-cyanuret of potassium. The furnace, from which it was obtained, had been fed with charcoal. The other ingredients of the saline mass were, caustic potash, carbonate, silicate, and manganate of potash, together with a large portion of cyanate of potash, and cyanuret of potassium. It is probable that the ferrocyanuret of potassium did not exist ready-formed in the mass, but was produced after dissolving the cyanuret of potassium in water. The cyanite, of potash, by its decomposition, gives rise to carbonate of potash and ammonia. Dr. Bromeis supposes that the formation of the cyanogen must have been occasioned in the following manner : -the nitrogen of the atmosphere, being exposed to a great pressure and high temperature, combined directly with the carbon of the