that this complication of the pendulum would be rather inconvenient. At all events, the variations of the barometer were not very great, especially if the compensation of the pendulum be made as great as possible. He submitted these hints to those celebrated artists, whose admired works had very greatly contributed to the promotion of astronomical purposes, and the determination of the longitude.

A discussion took place, in which Sir Thomas Brisbane, Mr. Dent, Mr. P. Clare, and Professor Stevelly took part, and which, having departed from the points of Professor Bessel's paper, was properly checked by Sir John Herschell, who said, the question was, whether the arc of vibration was or was not completely nullified. By Professor Bessel's plan of compensation, that was brought within a short period of fifteen or twenty minutes, which, according to the ancient modes of determination, would have taken a whole day.

[The Chairman, in proposing the thanks of the section to Professor Bessel, spoke of him as an illustrious astronomer, whose whole life had been devoted to the advancement of astronomical science, and who possessed in a remarkable degree the most profound knowlege of the principles on which every instrument submitted to his care was constructed, combined with the highest application of physical astronomy.-Sir Wm. Hamilton would repeat what he had said, in a former year, of Professor Bessel, who, for the consummate union of theory and practice, must be placed in the very foremost rank, and might be placed perhaps at the very head of the astronomers now living.]

MAGNETS.

The Rev. Dr. Scoresby made a communication "On improved permanent magnets, and the mode of determining their powers, with certain undescribed phenomena in permanent magnets." In the cases of powerful compound magnets, where large masses of steel were required, the absolute conditions were, that these masses should be of the best possible quality of [Swedish] steel, of the denomination of cast steel (and not shear or blister); and that they should be hardened to the greatest possible degree of hardness. For want of attention to these conditions, he frequently found magnets of bundles of eight or ten steel bars, when even two bars would have a stronger power. The Rev. doctor illustrated these matters by copious explanations, diagrams, and experiments with a powerful compound magnet, consisting of two bundles of steel bars or plates in a wooden frame, which took up about 11,000 nails (tin-tacks); which, when in suspension,

were capable of being moulded in the most curious manner. Holding a key (weighing 3,000 grains) at four inches from the ends of the magnets, this key became temporarily so powerful a magnet as to take up and suspend another key, weighing between 2 and 3,000 gr. Dr. Scorseby showed, that, by drawing a piece of steel down the back of his hand in one direction, the palm of his hand being pressed against his powerful magnet, he could give the steel a considerable magnetic power through his hand, and by reversing the direction of the steel, he could as easily demagnetize it. Of nine sea compasses, sent to him from her majesty's stores, the material of one was not better than the steel for coach springs; hence it would only lift 600 grains, while his own, of the same weight, would raise 3,309 grains. He had ascertained the means of testing magnets with such accuracy, that it would be as absurd to have a bad compass in future as a bad sovereign.

ACTION OF AIR AND WATER UPON IRON.

Mr. Mallet read a paper on the action of air and water on iron. This is the third report for which the Association is indebted to Mr. Mallet. The object of former tabulated results was to determine the actual loss by corrosion in a given time, and the comparative durabilities of rust of the principal kinds of cast-iron of Great Britain, and to discover on what durability depended. The tables of experiments now presented show, that the rate of corrosion is a decreasing one in most cases; and that the rapidity of the corrosion in cast-iron is not so much dependent upon the chemical constitution of the metal as upon its state of crystalline arrangement, and the condition of its constituent carbon. The present report, too, extends the inquiry to wrought-iron and steel, of which between thirty and forty varieties have been submitted to experiment. The results show, that the rate of corrosion of wrought-iron is in general much more rapid than that of cast-iron or of steel. The finer the wrought-iron is, and the more perfectly uniform in texture, the slower and more uniform is its corrosion. Steel corrodes in general more slowly, and much more uniformly, than wrought or cast-iron. The results of the action of air and water in the several classes of iron have been examined and chemically determined. The substance spoken of as plumbago was next described. It is produced by the action of air and water on cast-steel, especially that in the raw ingot, in the same way as it is in the case of cast. iron. A quantity of plumbago, found in the wreck of the Royal George, absorbed oxygen on exposure to the air with such rapidity,

that it became nearly red-hot. Mr. Mallet next described a method of protecting iron by a modification of the zink process. It was found impossible to cover the surface of iron with zink, to which it had no affinity. The first process was to clean the surface of the iron, taking off the coat of oxide, and then immersing it in double chloride of zink and ammonium, which covered it with a thin film of hydrogen, by which its affinity for the zink is much increased. The iron was then covered with a triple alloy of zink, sodium, and mercury. Mr. Mallet produced several specimens of his alloy, one of a bolt to be driven into a ship's side, and another a cannon shot covered with his preparation, and exposed to the weather on the roof of a building, and which was perfectly preserved. Cannon balls were so much oxidised by exposure to atmospheric influences, that in five or six years they become useless. The French Institute had been engaged in experiments to protect these, and had tried zink, but had been compelled to abandon it. Mr. Mallet also brought under the notice of the section a method of preventing the fouling which takes place on the bottoms of iron ships, especially in tropical climates, by means of which new invention he had ascertained plants and animals were prevented from adhering to the ship's bottom. Another series of experiments related to the rate of corrosion of cast-iron, wrought-iron, and steel, exposed to atmospheric influencesa matter of great importance to the engineer. The characteristic form of corrosion in air, as contra-distinguished from that of water, was also pointed out. This series of inquiries was now complete. The next matter which had engaged his attention was the rate of corrosion of rails on railways. The general opinion was, that the rails travelled over were not corroded at all. He had been enabled to lay down three sets of rails on the Dublin and Kingstown Railway; one not travelled over, the second in use, and not exposed to corrosion, and the third also in use, but made impervious to moisture. The loss of the first was 2555, of the second 5344, and of the third 2650-results which seemed to indicate, that the rail travelled over does corrode more slowly than that out of use.

COMBUSTION OF COAL AND PREVENTION OF SMOKE.

Mr. Fairbairn read the report of a committee appointed at the meeting held at Glasgow, in 1840, (in consequence of a paper read by Mr. C. W. Williams,) to make experiments upon the combustion of coal and other fuels, with a view of obtaining the greatest calorific effect, and avoiding the generation of smoke. The report stated, that very

great ignorance existed on the subject of combustion, and a most extravagant waste of fuel was committed in most of the districts in which steam power is extensively used. In Cornwall, where necessity had compelled the introduction of great economy in the management of steam-engines, a system of slow and complete combustion was practised which unfortunately, could not be generally adopted in Lancashire, where most of the proprietors of steam-engines had subjected themselves to serious evils by a want of capacity in their boilers, and a system of overworking, in every way opposed to perfect combustion, and attended with consequences equally objectionable, whether as regarded the public nuisance of smoke, or the increased expenditure of fuel. In many establishments, engines were loaded to almost double their nominal power; requiring steam far beyond the just capability of their boilers, and to be obtained only by forcing their fires, and too frequently dispersing through the atmosphere a quantity of valuable fuel, which, under other circumstances, might be usefully and beneficially employed. These were evils which could be abated only by the zealous concurrence of proprietors of steamengines themselves; but it was to be hoped that a few striking examples of great economy and perfect combustion would have considerable effect in directing the attention of these parties to a due consideration of their own interest and of the public welfare. The report then went into a minute description of the relative proportions of furnaces, boilers, flues, and chimneys, in this and other districts, from which we select the following points. In Manchester, the usual proportion of the area of the fire-bars to the heating surface of the boiler is about one to eleven, or 100 square inches to eight square feet of flue per horse-power. In a well proportioned boiler on the plan usually adopted in this district, a pound of moderately good coal will evaporate about 7.46lb. of water, being nearly the maximum duty effected here. A number of experiments had been made upon engines in this town, the results of which were given in a table exhibited to the meeting, specifying the nominal power of each engine, the power at which it is worked, the proportion of heating surface to the grate. bars, the height of the chimney, the consumption of fuel per horse-power, &c. The greatest consumption of coal (13lbs. per horse-power per hour,) was in an engine of 45 horse nominal power, worked up to 76 horse, and having the grate-bars in the proportion of 10.87 of the heating surface of the boilers. The smallest consumption (8.8lbs. per hour) was in an 80 horse-engine worked to 110 horse, and having its grate-bars

in the proportion to the flues of 1 to 12.70. The second in point of economy, however (9.1lbs. per hour,) had the smallest proportion of heating surface of the whole number experimented upon. The general average of the consumption of coal was 10-53lbs. per horsepower per hour. That this was far beyond what it ought to be, was exhibited by the fact, that the average consumption in the best Cornish engines was only 2 per hour -something less than one fourth of the amount in this neighbourhood. The report proceeded to detail the results of some experiments on the comparative consumption of coals in a furnace to which Mr. Williams's apparatus for the consumption of smoke had been applied, when that apparatus was at work, and when it was thrown out of use. Some of these experiments appeared to be vitiated by the want of a perfect closing of the air passages when that apparatus was not used. Further experiments were consequently tried with the air passages open at one time, and at another closed by a brick wall. result was, that the average consumption with the apparatus at work was 276 lbs. per hour, and with the air passages effectually closed, 308 lbs. per hour, showing a difference of 32 lbs. per hour in favour of Williams's plan, or a saving of rather more than 10 per cent. The report stated, in conclusion, that there could not be the slightest doubt about the practicability of abating the nuisance of smoke so much complained of in many districts.

The

Mr. Henry Houldsworth said, that for six months past, he had had practical experience of the working of Mr. Williams's patent, which he had applied to six different furnaces; and he could now say confidently, from the results of that experience, that without any particular trouble or care of management, it would prevent, at the very least, three-fourths of the smoke which was now made. He did not doubt that other inventions might be equally effectual when they were carefully managed; but he preferred Mr. Williams's, because of its extreme simplicity, depending as it did solely on the admission of air in a proper manner, without any of those mechanical contrivances, worked by some moving power, which many other plans contained. There was one fact connected with Mr. Williams's patent, which he considered of some importance, which he would communicate to the section. He had that morning fitted up a contrivance for ascertaining the comparative temperature of flues under different circumstances, which had not previously been very satisfactorily ascertained. Mr. Williams had used a thermometer, inserted in a bar of iron, which was placed in a flue; but he (Mr. Houldsworth)

was not satisfied with that plan, and had passed a copper wire through the flue from one end to the other. This was kept in a state of tension by a weight, and by its expansion or contraction, acted upon an index, which would give a very correct measure of the relative temperature. He had tried some experiments with it that morning, and had obtained very striking and important results. It had generally been supposed, that, when there was a perfected red fire in the furnace, and when no smoke was generated, the admission of cold air at the bridge would do harm instead of good, by reducing the temperature in the flues. He had, however, tried the experiment that morning. After having the air passages closed for some time, he had opened them when the coals on the fire were perfectly charred, and found an immediate and decided increase of temperature in the flue. The increase of temperature was certainly most striking, if the air passages were opened shortly after a large quantity of fresh fuel had been put on ; but at all times he found there was an increase when the air was admitted, and a decrease when it was excluded.-In answer to a question from Mr. E. Corbett, Mr. Houldsworth stated, that in one experiment, about three cwt. of coals were thrown upon the fire at once, so as to produce a thick black smoke; when the air passages were closed, that smoke was immediately dissipated by opening them, and the temperature rose rapidly. On closing them again, the smoke returned, and the temperature as rapidly declined.—Mr. Taylor (the treasurer of the Association) said, the subject before the section was undoubtedly of great importance to the manufacturers of this district; for they had already heard from Mr. Fairbairn, that, whilst the average consumption of ten engines in Manchester was 10 lb. of coal per horse-power per hour, the average consumption in the Cornish engines was only 24 lbs., so that they did as much work with one pound of coal as a Manchester manufacturer did with four pounds; and, at the same time, they made very little smoke. In the parish of Gwennap, with which he was connected, there were twenty-five engines, all of very large power, from the chimneys of which very little smoke indeed would be seen. He did not know that they adopted any contrivance for the prevention of smoke, beyond that of admitting air at the bridge; but they gave plenty of furnace room and plenty of boiler room, and made a rule of keeping bright their fires, and of coking all their coal in the front of the furnace. The great source of their superiority was, however, in his opinion, to be found in the fact, that as the engines were all employed in pumping water,

it was exceedingly easy to ascertain the amount of work which each engine performed with a given quantity of coal. This was invariably recorded and published, and it produced great emulation amongst the engine-makers, the proprietors, and the workmen, each of whom was ashamed of being outdone by his neighbours; and from their joint care and exertions, and more especially from those of the workmen employed, resulted that extraordinary economy, of which the Section had just heard.—Mr. Richard Roberts said he quite agreed with Mr. Taylor, that with due care on the part of the fireman, a sufficient area of grate, and sufficient boiler room, smoke might be effectually prevented, without resorting to any particular contrivances.-After some further discussion, in which Mr. Edmund Ashworth, Mr. Webbe Hall, Mr. Joshua Milne, and other gentlemen took part, Mr. Jeremiah Garnett said, he could not permit the discussion to close without directing attention to one fact--viz., that, although they had had a variety of opinions about the best mode of preventing smoke, no one amongst the many scientific men and manufacturers present intimated the slightest doubt that smoke might be prevented, and that the nuisance if not entirely removed, might be exceedingly diminished. If, therefore, parties working steam-engines would neither consult their own interests, nor consider the public welfare, he trusted the legislature would interfere to compel them. There was one point adverted to by Mr. Taylor and Mr. Roberts, on which he would say a few words, as it might do harm out of doors. They had mentioned an abundance of grate and boiler room, as a means of preventing the nuisance of smoke; and no doubt it was So. But there was a danger that parties who were deficient in those respects might plead that deficiency as an excuse for continuing the nuisance. It was, therefore, necessary to remind the Section, that, though desirable, an abundance of grate and boiler room was not necessary to the prevention of smoke. He knew from Mr. Houldsworth, that the very successful experiments made by him were made upon engines which were limited in those repects. What had been done by Mr. Houldsworth could be done by any other parties; and, therefore, those who continued to poison their neighbours with smoke were without excuse.

At a subsequent meeting of the Association, Mr. Houldsworth said, that since the previous discussion on this subject, he had made some careful experiments with the pyrometer which he then described; and the results were, in his judgment, exceedingly satisfactory and conclusive. These experi

VOL. XXXVII.

ments were made upon a furnace fitted up according to Mr. Williams's patent, by putting three cwt. of coal upon the fire two different times, the fire being each time in the same state, and the temperature of the flue, as indicated by the pyrometer, being in each case about 700 degrees. On one occasion, the air-passages were left open, in the other they were closed; in each case the experiment was continued for 100 minutes. In the experiment in which the passages were left open, the average temperature of the flue was about 1,100 degrees; in that in which the passages were closed, and Mr. Williams's apparatus thrown out of use, the temperature averaged only about 900 degrees. During the whole time of the former experiment, there was an entire absence of smoke; during great part of the latter, the flues were filled with smoke. Mr. Houldsworth exhibited a diagram, showing, in a very striking manner, the results of his experiments.*-Mr. Fairbairn said, there could be no doubt whatever, that smoke might be most effectually prevented, and therefore the public ought no longer to be subjected to so grievous a nuisance.

THE ATMOSPHERIC RAILWAY.

Professor Vignoles introduced a long and elaborate communication on this subject by the following observations.

"The general interest of late attached to the generation of motion on railways by means of the pressure of the atmosphere, and the fact that, for the last two years, experiments of this sort have been publicly exhibited in the neighbourhood of London, must be the excuse for my presuming to present myself before the British Association, and attempting to be the humble expositor of the very ingenious and remarkable invention which is so characteristic of the present age. The allegations of the parties who have brought it forward, particularly of the inventor himself, to whom I shall presently take the liberty of calling your attention as a townsman of Manchester, are well worthy of consideration; more especially as the subject is exciting that degree of interest, that certain parties are about, and have recently begun, to adopt it on one of the railways of the United Kingdom, and the government have thought fit to depute some of the official parties to make a special report on the subject. Sir Mark Brunel has said, with very great propriety, that it was much easier to describe an operation when finished, than when in the course of preparation. I claim, therefore, your indulgence, if, in this respect, I have to describe an operation, which, if

This diagram we hope to be able to give in our next No.-ED. M. M.

D

not quite in its infancy, at all events has not met that degree of public attention which it so eminently deserves. I consider that the time has now arrived when it is quite proper that this principle of producing motion should be put before the public in a familiar manner; and I am happy and proud in having been selected as the instrument to bring it thus before the public, for the first time, in an official manner. The object of this discourse is to invite discussion,-to court inquiry,-to elucidate truth. When we consider the enormous expense which we have incurred in the construction of the principal lines of railway, and the still greater proportionate expense in working them out, it is not singular that all the efforts of ingenious men should be directed to the ascertaining, amid the numerous secrets which nature still holds, some means of producing motion upon more economical principles. I will take the liberty of making a quotation from one of the most eminent railway individuals in this country-from one who has done more towards advancing the improvements of railway conveyances than any other man, Mr. Henry Booth, the talented manager of the Liverpool and Manchester Railway. He says, that in all countries, and under all circumstances, it is an object worthy of the statesman and the philosopher to give a right direction to public expenditure, and to prevent the reckless waste of the national resources."

The learned Professor proceeded to give an historical sketch of the various plans which had at different times been proposed for obtaining mechanical power from the pressure of the atmosphere-by Papin, Lewis, Medhurst, Vallance, Pinkus, and lastly, Mr. Clegg, the inventor of the system which has, during the last two years, been exhibited in successful operation at Wormwood Scrubbs. Mr. Vignoles then described Mr. Clegg's plan very fully and minutely, and with great ability and clearness, but as we have already given a sufficiently ample account of it in our pages (see Mech. Mag. vol. xxxiii. p. 86) we shall pass on to the general conclusion at which the Professor arrived. Having alluded to the discussions that had taken place respecting the relative advantages of locomotive and stationary power, when the Liverpool and Manchester Railway was constructed, Mr. Vignoles pointed out the waste of power arising from friction, atmospheric resistance, and other causes, and then drew attention to a table giving a comparative analysis of the power of Mr. Clegg's air-pipe under various circumstances. The result was, that, with a pipe six inches in diameter, and an airpump 21 inches in diameter, he could,

having deducted all resistances, drive a carriage laden with 45 tons, with a uniform velocity of 30 miles an hour. Mr. Vignoles also exhibited and explained to the meeting a diagram representing the vaious degrees of pressure in various inclinations, and remarked, that the general adoption of the atmospheric railway would be a great public convenience, there being no necessity for stopping from one end of the line to the other, and the saving that would be effected being very considerable. He also observed that railways already constructed might, with a very trifling expense, be adapted to the pneumatic principle. A commission had been appointed for the purpose of investigating the proposed plan; and, although they had not reported in a very decided manner, still they pronounced opinions respecting the system which were quite conclusive as to its practicability. The directors of the Dublin and Kingstown Railway had obtained a government grant for the purpose of extending their line two miles further. The extension of this line was to be constructed by Mr. V., and the locomotive power was to be on the atmospheric principle.

LOCOMOTIVE AXLES.

Professor Vignoles [made a communication on Straight Axles for Locomotives. He stated that an unfounded prejudice existed in favour of cranked axles, which, in his opinion, were inferior to straight ones in almost every point of view. With straight axles, the cranks were thrown outside the wheels, which gave more room for the arrangement of the working parts; and another great advantage was gained by lowering the boiler nearly fifteen inches, and thereby increasing the safety of the engine, by placing the centre of gravity nearer the rail. The original expense of the engine and of the repairs was also much lessened. These advantages might be shown by a reference to the Dublin and Kingstown Railway. By introducing straight axles and outside cranks the expenses had been greatly decreased; no accident had ever occurred from breakage; and such increase of room had been obtained, that they had placed the tender underneath the engine, thus fixing the centre of gravity as low as possible, and dispensing with the separate tender. By this arrangement they could run fifteen miles without stopping for water. Many accidents had taken place in consequence of the breaking of cranked axles and Mr. François and Col. Aubert, in their report to the French government, had remarked that the fractures of broken axles, instead of the fibrous appearance of wrought iron, presented the crystallized appearance of cast iron, which they attributed to magnetic