measures more complex and multiform. It ought therefore to be avoided, unless some necessity can be shown in its favour. Hence it would seem to be expedient to abolish from these calculations all primes except 2, 3, and 5; and here an important question arises, viz. should these be retained, or shall we be satisfied with 2 and 5, omitting 3?

We are thus brought to one of the great discussions of the present day, the expediency of decimalizing our measures, weights and coins.

The consequence of the simple fact, 2x5=10, is, that all decimal systems are also binary and quinary, the principal quantities expressed by tens, hundreds, thousands, &c. being divisible by 2 and by 5 without remainder, so that their doubles and their halves can be introduced and reckoned without the least difficulty or inconvenience. But such systems do not readily admit the number 3, because in the majority of cases the quantity cannot be divided by 3 without a remainder, and in many cases the division by 3 produces a repeating decimal. This is the ground on which many persons have insisted on 12 as a multiplier for measures, weights, and coins, rather than 10. But it is to be observed, that if 10 cannot be divided by 3, on the other hand 12 cannot be divided by 5 without remainder. Hence it seems to follow, that the choice must be made between decimal and duodecimal modes of computation, according as a preference is given to 3 or to 5 as a divisor. If it is more necessary or convenient to divide by 3 than by 5, duodecimal methods are entitled to the preference, so far as this circumstance is concerned. I cannot, however, discover any reason for making this assumption. I think it probable, that division by 5 is required as frequently as by 3, whilst every other consideration is decidedly in favour of the decimal scale.

The investigation which we have been pursuing is, therefore, first, in favour of decimal measures, weights, and coins; and secondly, supports the views of those who think that the subordinate multiples and divisions should be made by 2 and 5 only, and not by 3.

In this conclusion I have the satisfaction to observe that I am countenanced by the authority of the late Mr. Drinkwater Bethune, one of the Commissioners appointed by the present Lord Monteagle, when Chancellor of the Exchequer, to consider the steps to be taken for restoring the standards of weight and measure. In his letter to the Chancellor of the Exchequer, dated 21st of September, 1841, he maintains the following positions :

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1st. That "the Tables of Weights and Measures now in use are complex and inconvenient, and that it is very desirable to get rid of inconvenient multiples such as the factor 7, which connects the pound avoirdupois with the stone, and thereby with its multiples, the hundredweight and ton; and the factor 11, which connects the yard with the chain, and thereby with the mile and acre."

2nd. That "it is desirable, that no numbers, which are not multiples either of 2 or of 5, should anywhere appear in the Tables."

MECHANICAL SCIENCE.

Address by LORD ROSSE, the PRESIDENT of the Section.

LORD ROSSE Commenced by apologizing for any oversight he might commit, as he had never at any previous Meeting of the British Association presided over the Mechanical Section. He was happy, however, that there could be no danger of serious errors on his part, as there were able men on both sides of him who had made Civil Engineering their special study. He proceeded to say that the question had sometimes been asked why a Mechanical Section was necessary; might not all mechanical questions be conveniently discussed in the Mathematical and Physical Section? To that question, on some occasions, an answer has been returned. It may at once be said, that it has been found eminently useful to have separate Sections for each distinct department. It is only under such an arrangement that discussion can be really effective in bringing out new truths. If a considerable portion of the Section is not intimately acquainted with the subject in all its details, what prospect can there be of

new and sound views being elicited; and indeed if the whole Section has not some general knowledge of the branch of science which has been committed to its care, what hope can there be that discussions will be heard with interest, and will have real efficiency in awakening and strengthening a taste for science? This has been felt, indeed strongly felt, at the Royal Society, where there are no Sections, and the subjects are of a very varied nature, comprehending the whole range of the Mathematical and Physical Sciences, and all the Natural Sciences. A paper perhaps is read on Pure Mathematics: very possibly there may not be in the room at the time more than two or three persons who are intimately acquainted with that branch of science: a discussion of course is out of the question. A paper follows on one of the Natural Sciences: if there are a few who are working in that direction a discussion takes place; but it is of little interest even to those engaged in other branches of Natural Science; and almost, if not altogether without interest to the Mathematician, the Chemist, the Astronomer, the Geologist, and the Physicist. So it rarely happens that there is a discussion at the Meetings of the Royal Society, of general interest or of real value; and for that there is no remedy. Here, by the happy expedient of breaking up the Association into separate Sections, the way has been prepared for discussing subjects in that effective manner which, originating with the Geological Society, has already so much advanced geological science.

Where one of the great objects of these meetings is to elicit truth by discussion, it is evident how unwise it would be to group together in one Section a variety of subjects, each requiring special studies, a special line of thinking, and special experiences. In Section A, human ingenuity and human knowledge are employed in the solution of mathematical and physical problems; while in Section G, human ingenuity and human knowledge, but of a different kind, are employed in the solution of questions of practical engineering. This may so far perhaps be considered, in one sense at least, a sufficient answer to the question, why is a Mechanical Section necessary? The question, however, may be put in another sense. Where the investigations are not abstract, but practical, and where the results generally are of immediate interest, is it necessary that the British Association should interfere at all? Will not private individuals, from motives of self-interest, devote themselves to the pursuit of Civil Engineering in its higher branches, without any adventitious stimulus? Will not public men, seeing that the interests of the State, both in peace and war, are bound up with the full development of the resources of engineering, make it their business to acquire such a general knowledge of the subject as will enable them to ascertain when and where to apply for aid in time of difficulty? The reverse unfortunately is the case; experience has shown that men, whether in their private or public capacity, do not act in these matters exactly as we should expect; they do require both to be aided and urged forward.

In this eminently practical country, private individuals, very often relying on experience, neglect the means necessary to render calculation effective. Experience, however, is not always at hand, and is often very costly. How often do we see the ingenious mechanic working on false principles, vainly perhaps attempting to accomplish something which a little elementary knowledge would have shown to be impossible! There are perhaps few gentlemen present who could not point out instances where individuals had sustained heavy losses from the want of adequate theoretical knowledge. In his limited experience he had known several. This perhaps is a striking one. Some years ago he was invited by a physician of eminence in London to visit the works of an ingenious mechanic, who was endeavouring to employ air heated by gas as a prime mover. The physician had embarked £12,000 in the project; a lady of wealth had speculated in it to the extent of £30,000; and various individuals had advanced sums altogether to a large amount. At the entrance of the premises there was the wreck of a gigantic machine of unknown construction: other machines in a dilapidated state were lying about in all directions. It appeared from the explanation of the mechanic, that these huge masses of ruined machinery had been constructed partly for the purpose of ascertaining facts to be found in every elementary treatise, and partly for the accomplishment of objects manifestly impossible. In the construction of the engine itself there was a striking display of great ingenuity constantly engaged in a struggle with the laws of nature. It was perfectly evident that the whole was fated to end in disappointment; still the mechanic and his patrons,

undismayed by repeated failures, and heedless of warnings, which, where there was no science, were without force, struggled on till the project came to an end from exhaustion. Some of the parties were ruined, while all lost the capital they had embarked in the speculation.

One of the objects of the Mechanical Section is to prevent such disasters, and no doubt to a certain extent this has been effected. Another object has been effected also the importance of engineering science in the service of the State has been brought more prominently forward. There seems, however, something still wanting. Science may yet do more for the navy and army, if more called upon.

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A few years ago, in sailing through the harbour of Portsmouth, as the boat proceeded along, the sailors gave a little history of each ship laid up there; they said, That ship has been but once at sea, and it rolled so it was almost impossible to keep masts in her; she is not likely to go to sea again. There is another ship which sails so badly that she can neither chase nor run away. There is a ship which can scarcely beat to windward, and if it was blowing hard upon a lee-shore, she would have but little chance. Other ships had other defects. Strange uncertainty who could avoid asking the question, is naval architecture really guided by science? About that time a little book came out which solved the mystery. It is called Lectures on the results of the Great Exhibition: the lectures are by first-rate men. In it there is a lecture by Captain Washington, "On the Progress of Naval Architecture," an officer of high scientific attainments, now Hydrographer to the Admiralty. After mentioning the well-known historic fact, that during the late great war our best ships were copies, and not always very successful ones, of foreign models, he proceeds to say, that all who served in the blockading fleets were painfully alive to the fact that our ships were inferior to those of France and Spain in speed, stability, and readiness in manœuvring. That much loss of life might have been spared if our ships had been in form more on a par with those of our opponents. He attributes their inferiority to the fact, that while in France and Spain, and other continental countries, the aid of science had been called in, and the greatest northern nations had turned their attention to ship-building, the only English treatise at all of a scientific character was published by Mungo Murray, who died a working shipwright. That England has not to this day one original scientific treatise on Naval Architecture. He further states, that of the forty-two men who were educated in the School of Naval Architecture which had been established in 1811, and after a few years suppressed, but five had to this day risen to stations of responsibility, and that the sight might have been seen of men familiar with the differential calculus, chipping timber in the dockyards in company with common mechanics. Cruze, in his article on Naval Architecture in the Encyclopædia Britannica,' makes similar statements.

It has been objected, however, that the powers of engineering science have been overrated; that they had been brought to the test during the late war and had but little strengthened our hands. People seemed to think that scientific invention should have carried all before it. Inventions, however, do not come forth at our bidding; and are we sure there has been much to attract highly cultivated inventive powers to the science of war? Have we never heard a whisper of official prejudices and official discouragement? Moreover, if you invent, the invention soon falls into the hands of a vigilant enemy and you have achieved nothing.

It was not by little inventions that the engineering powers of England could have been brought to bear effectually in the late war. If, when war was imminent, civil engineers had been consulted in conjunction with military engineers and naval men, means perhaps would have been found by which the gigantic engineering resources of this country would have been rendered available. It was going a little too far when it was said that Cronstadt could have been taken by contract. Of this, however, there could have been no doubt, that a certain thickness of wrought iron would have resisted the heaviest ordnance then in use; that the sea could have carried the weight; and that no stone walls could have long resisted the close fire of large guns. Moreover, there were actually French experiments made a few years before, which, in the absence of new experiments, would have afforded tolerably accurate data for the necessary calculations.

Let it not be said that engineering science was almost powerless in the late war, till it can be shown that it had a fair trial,—that its aid had been called for at a proper time and in a proper manner.

1857.

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It is scarcely necessary further to insist upon the importance of the Mechanical Section. It is obviously the interest of public men, no less than of private individuals, to pay increased attention to Mechanical Science. If this Section can contribute ever so little to bring out new facts, or to direct attention to facts already known, it will have rendered good service.

A detailed Model of the Boyne Viaduct which carries the Belfast Junction Railway over the River Boyne at Drogheda, with a description of it, and the Principles of its Construction. By JAMES BARTON, Č.E.

The dimensions of this work are,-height above high water, 90 feet to soffit of bridge; open of centre span, 264 feet; of side spans, 140; besides fifteen stone arches of 61 feet span each. The three centre spans are crossed by wrought-iron lattice beams designed by the author; and the chief feature of interest connected with this work is the mode in which the results of careful investigation of the strains on every bar and plate have been practically applied. Having ascertained the maxima strains, whether tensile or compressive, that each bar could be subjected to by the weight of the structure, combined with the passing load entire or in part, the areas of iron and the form of the parts were then designed and made proportionate to their maxima strains; the limit assumed being that no part should ever be subjected to more than 4 tons per inch of iron of compressive, and 5 tons per inch of tensile strain, and that the parts under compressive strain should be so arranged and braced that they should not yield by flexure.

The three spans are crossed by a continuous beam; and the author explained how this arrangement, whilst it was economical and decreased deflection, involved much more complicated calculation. He showed when the points near the top and bottom of the beams, called the points of inflection, were under different states of the load, and how these points travelled along as the load passed over, these points being points at which there is no strain of either tension or compression, the top and bottom on either side of these points being under opposite kinds of strain.

The iron used for this structure was much less than ever the same spans had been crossed with before by any Girder Bridge, and was at the same time as strong as any. The total iron used was 740 tons, and the cost complete was about £24 10s. per ton as it stands, exclusive of scaffolding below the ironwork. The iron was from Staffordshire; that subject to a tensile strain, of the quality known as "best best;" that only subject to compression, of the quality termed "best iron." The correctness of the calculations, had been proved in some remarkable ways: the points where theoretically there should be no strain in the top under a uniform load having been determined for the large span of 264 feet, the author, after the bridge was relieved of its supports, severed the top of the main beam in these places, and the strict maintenance of equilibrium in the structure proved that no strain was then passing through the open joints of the ironwork. Again, it was calculated that when a load of 2 tons per foot forward would be put upon the centre span, in addition to its own weight, the points of inflection of the side spans would pass the ends of the beams, the result of which would be that the side spans ought not to rest any longer on the abutments of masonry, but stand out as overhanging beams from the piers between them and the centre span. This actually took place; and when the centre span was thus loaded, the ends of the side spans were found to have lifted 1 inch off their bed plates and rollers; nor did they descend until a locomotive from the centre span travelling along the side span from the centre came within about 40 feet of the end. The bridge had been tested with 1100 tons and in a variety of ways, and the results were most satisfactory.

On Coal-burning Engines. By J. S. BEATTIE.

On Electro-Magnetic Engines. By J. S. BEATTIE.

On Improvements in Ordnance. By Captain BLAKELEY, R.A.

A 16-inch shot would present but 16 times the surface to the action of the air (to retard it, or make its flight inaccurate) as a 4-inch shot, and would weigh 64 times as much; it would therefore be retarded and blown out of its course but, or as much. A gun four times as accurate as a 9-pounder, and with the immense range due to the less resistance of the air, would be a powerful weapon on board fast steamers. A few 30-inch shell guns would be useful in war, and really conducive to peace if placed on the banks of the Thames, the Clyde or the Mersey. If any foreign power quarrels with us and suddenly appears with thirty or forty gun-boats armed with one monster gun each, he could destroy Portsmouth. None who know Mr. Armstrong's application of hydraulic power will doubt its adaptability to move guns of any size, and with little human labour. Large guns require more strength than small ones, as the powder occupying in each the same proportional space, the small shot moves in say o of a second a certain number of inches, the large shot in the same time moving fewer inches, so that at the end of that time the gas in the small gun would have much more proportionate room to expand in, and would therefore press less on the gun than in the large one. Added to this, the large shot would require more time to get its velocity, and the pressure must remain on the gun so much longer. May not the time a material can bear a tension be an element worthy of experiment; and may not cast iron bear a pressure during of a second, which if continued during half a second would destroy it? I believe the sudden and short strain caused by the explosion of gunpowder to be less, not more injurious, as is generally thought, than an equal strain applied gradually but left longer. However, a 32-pounder is the limit of cast-iron guns of the present shape, any larger than that being unsafe with full charges. Adding thickness to the metal would give little additional strength. Professor Barlow calculates that a cylinder one inch thick, and one inch in internal diameter when strained, stretches only as much in proportion outside as inside, the cross section remaining equal, so that the interior diameter being stretched to 1 X1, the exterior, instead of becoming 3× Tobo (as it would if the outside layer "put out" an equal strength to the inner, according to the law "ut tensio sic vis"), becomes only 3+ of Too or 3+3000. The cross section being (3+30‰o)2=9+3 minus (1+1000)2 =1+b; the difference, 8 round inches, being the same as when not strained, or (32-12).

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If with the present thickness the outside does but its duty, we can expect but little additional strength from adding to it; Professor Barlow arguing that the strength decreases as the squares of the distances from the centre. The same law puts a limit to the size of brass or cast steel guns, or of wrought iron if in one welded mass.

I would suggest for guns up to 10 inches a shape very like the present, but the outside at the breech strengthened with two layers of thin wrought-iron cylinders put on very hot, and hammered so that the outside shall be fully strained when the gun is fixed. One I made so stood 605 rounds, all with double charge, and the last 158 rounds loaded to the muzzle. This is evidently greater strength than is required for anything under 10-inch guns. Above that, I think, with a cast-iron cylindrical centre, that either rod-iron wound round at a great heat and welded, layer over layer, but each in cooling taking a permanent strain, or else iron wire wound round it, each layer having a greater initial strain than the one under it, would be the best way: we thus get all the fibre in one direction.

Mr. Armstrong of Newcastle made a gun of a solid steel centre, with bar iron coiled round it and welded. This gun has stood some thousands of rounds. I discovered early in 1855 that Mr. J. Longridge, C.E., agreed very nearly with me in opinion, having arrived quite independently at his conclusions, and since then we have been working together. I exhibit some brass cylinders strengthened with wire, which he experimented on; the strain cannot have been under 56 tons per inch on some of these, reckoning brass and wire, or at least 70 tons an inch on the wire, as there the strength lay. This would make very serviceable field howitzers; such howitzers need not weigh over 8 cwt.

If we do not possess the most efficacious weapons possible, we shall find ourselves overpowered some day. Any foreign power could secretly prepare a flotilla of gunboats, and manufacture the large guns to destroy our fleets and seaports immediately after a declaration of war.