ment; but to such objections I reply, that this accuracy costs nothing additional in the execution, and may therefore, at all events, be as well attended to as not."

The proportions to be observed in the construction of parrallel rails, must depend, of course, on the magnitude of the weights which they are likely to be required to sustain. The rules which Mr. Barlow gives for calculating the bearing capacity of rails of this description are, as he states, of a "very simple character,” and illustrated by some examples worked out at length, and in so plain a manner, that any person, with a knowledge of common arithmetic, may understand them. Of these examples, that numbered 4 seems to be the one which approaches nearest to Mr. Barlow's beau ideal of a good rail. Its proportions are as follows:-depth throughout, 4 inches; thickness of rib, 7th of an inch, and of bottom web, 1.39; weight, 50lbs. per yard. The strength, or absolute elastic power of a rail of this form, is equal to eight tons; the degree of deflection with that weight, being only 55 (less by 11 than a fish-bellied rail of the same weight). Now supposing the extreme weight of a locomotive carriage to be 12 tons, the greatest weight likely to be thrown on one rail would be 6, being two tons less than the weight which such a rail is capable of bearing. Mr. Barlow recommends, however (page 93), that in such a case the strength should be raised to 9 tons, so as to leave a surplus of 50 per cent.; and he thinks it possible, by the following slight modification of the above form of rail, to obtain that strength, without any increase of weight :

"I have allowed rather more metal for the head, I believe, than is generally employed, which, if transferred to the lower web, would give all the additional strength required; or, perhaps, the centre rib might bear a slight reduction. At all events, leaving every thing as it is, except adding 2lbs. per yard to the bottom web, the rail would come up to the whole strength of 9 tons, as required. And here, I would observe, is the great advantage of working by rule rather than by opinion, for if we had only the latter to guide us, we should be hard to believe that an increase of th in the weight could be made to add about 4th to the strength and stiffness of the bar; yet such is unquestionably the case."

Practical men may possibly hesitate to follow rules so much at variance with the

notions hitherto prevalent among them; and some may even continue, as hereto fore, to believe in the infallibility of "the Pope of Railway Engineers,"* and to regard all dissentients from his authority as theorists and visionaries: but they will, one and all, do well to observe, that there is nothing recommended in this publication of Mr. Barlow's which has not for its basis actual experiments, of a far more varied and comprehensive description than can have fallen within the experience of any other individual whatever. "I have not," says Mr. Barlow, ami e d the question on theoretical, but on mechanical principles, with a view to one specific object, and have purposely avoided testing any point on mere hypothesis. Every thing is made to depend on experimental results; and from the uniformity and agreement of these, I have every confidence the rules founded on them will enable practical men to compute such cases as may occur with all the precision that can be desired."

NOTES AND NOTICES.

ex

Grand Irish Railway.-The English Government is said to have taken the bold resolution of transferring the foreign packet station from Falmouth to Valentia, a harbour situated in that part of Ireland which extends the furthest into the Atlantic ocean, and about 200 English miles from Dublin. In order to connect Valentia with the Irish capital and its new harbour of Kingstown, an iron railroad will be made, the execution of which will be entrusted to Messrs. Vignoles and Cubitt. The Government gives a large sum to this undertaking, in order that the railroad may be laid down, as nearly as possible, in a straight line, without regard to the towns lying between, which, of course, will not fail to obtain, by means of branch railroads, a participation in the immense advantages of so speedy an intercourse with the capital. It is calculated that, by means of the steam-packets (and railways ?), the mails and passengers will be conveyed in thirty-one hours, by way of Liverpool and Dublin, from London to Valentia; from which place the packets, without being exposed to the dangers of the channel, may immediately put to sea, and thus reach Canada, the West Indies, the Mediterranean, &c., in a far shorter time than they can now calculate with certainty on doing. This plan will be of infinite advantage, not only to England and Ireland, but to the communication of all Europe with the other quarters of the globe.Hanoverian Journal.

The American Boundary Commission.- Sir, I observe, in your 605th Number, page 447, a notice respecting the American boundary; and the claim advanced on the part of the United States (by Dr. Hassler, their surveyor) to apply the principle of geocentric latitude, in determining the line North of Vermont and New York, lat 45°, and from the Lake of the Woods to the Rocky mountains on the 49°, the rest of the line being determined by dif

* Vide Parliamentary Evid. Great Western Rail

Way Bill.

ferent and natural points. This claim was successfully combatted by the British Commissioners and their able and scientific surveyor, Dr. TIARKS, F. R. S., and not Dr. Watson, as erroneously stated in the article referred to. I am sure it will afford you pleasure to correct the error. Dr. Tiarks wrote several able papers on the subject, and is a gentleman well known to the scientific world. Having, for many years, enjoyed the pleasure of his personal acquaintance, I should be sorry the public were induced to bestow the merit that belongs to him on Dr. Watson, however deserving the latter may be in other respects. I am, Sir, your obedient servant-A CONSTANT READER.

Wonderful! if true.-" Manchester Police FireEstablishment.--This establishment, now undoubtedly the first in the kingdom, as regards efficiency, has just received the accession to its strength of another large, new, and powerful tire-engine, which, as we think very appropriately, has been named the Niagara. It is constructed generally upon the same principles as the other engines, and by the same builders; but the suction-pipe has a diameter of four inches, being an inch wider than any of the other engines, and the water ways gene. rally are of greater capacity. These advantages enable the engine to throw through the leather hose, the bore of which is about three inches in diameter, a ton weight of water in the short space of one minute, and with the metal jet screwed on, which is 24 inches in diameter, the same quantity of water can be thrown in a minute and a half. In one hour, then, forty tons weight of water may be thrown upon a building on fire, from this artificial type of the celebrated falls of Niagara. The last new engine, the Water Witch, on the occasion of a fire at Mr. Brignall's premises, notwithstanding the weather was unfavourable, threw water to the height of 126 feet; and it is expected, though in this way no trial of its powers has yet been made, that the Niagara will produce a still loftier jet d'eau. The number of engines at present in the establishment is only six,-the Aquarius, Vesta, Thetis, Neptune, Water Witch, and Niagara-but they are all of great power, and of more real use than would be thirty engines of inferior ca pacity and projectile force. In the mail-coach procession on the 1st of May, it is not unlikely that the Niagara will first exhibit its falls to the gaze of our fellow-townsmen."-Manchester Guardian, April 13, 1835.-The writer evidently lies under some unaccountable mistake. A jet of water 24 inches in diameter, thrown 126 feet high, supplied by forty tons of water per hour only, is preposterous. A jet ONE INCH in diameter will deliver that quantity in the time.-B.

Lambeth Wrought-Iron Suspension Bridge.A bill is now in progress through Parliament for the formation of an iron suspension-bridge over the Thames at Lambeth. It is to consist of a principal span in the centre of 450 feet, and two side spans of 225 feet, supported by two columnal piers, each composed of 16 iron cast pillars. The total length of the bridge, including the pillars, will be 940 feet; the height of the middle span 22 feet above the Trinity high-water mark, leaving a clear water-course, for the passage of large vessels, of 410 feet, and nearly the whole width of the river for boats and smaller vessels. Captain Brown, who constructed the Brighton Chain Pier, and other similar structures, is the projector.

The Bude Light is a name given by Mr. Gurney (of steam-carriage abortion celebrity) to a new light which he has discovered, and so named, after his new place of residence in Cornwall. It is obtained by directing a stream of oxy-hydrogen gas on a quantity of pounded egg-shells. The light is represented to be 140 times greater than any of those now employed in lighthouses-so intense, indeed, that Mr. G. lately stated to the House of Commons

Committee on Lighthonses, "his belief that it would be possible to make his light, by certain management, point out the precise situation of a coast beacon to a ship three or four miles at sea, under circumstances of a fog so dense that no other light-not even that of the sun-could penetrate it to any distance!"

Steam-Engines in Glasgow.-To such an extent is the business of steam-engine making now carried on here that there are thirteen firms engaged in it. Some of the works are more like national than private undertakings. Three houses alone employ upwards of a thousand persons. Dr. Cleland has ascertained that, in Glasgow and its suburbs, there are thirty-one different kinds of manufactures where steam-engines are used, and that in these, and in the collieries, quarries, and steamboats, there are 355 steam-engines = 7,366-horse power-average power of engines rather more than 20 horses each.-Ency. Britt., 7th edition.

Caoutchouc Whips.-" When H. F., Jun., asserts, that two years since he made whips of a similar construction as those proposed by me, I am bound to believe his assertions; but I must affirm, that it was with me purely an original invention, having never received the slightest hint from any one on the subject. If there is, however, any merit in the invention, be it his or mine, I think I am entitled to the merit of being the first to make it known to the world."-E. B.

J. T. Riches. Yes.

J. N. has been anticipated by Lord Dundonald. See Mech. Mag., No. 583.

We do not think it would be of any use to republish Mr. Lunt, of Chester's letter, on the Thames Tunnel, inserted in our Journal of the 28th February, 1829 (No. 290)). Mr. Brunel and his friends have now got too fast a hold of the loan from the public purse, to be accessible to argument or remonstrance.

Colonel Macerone's letters are left for him, as requested, with our publisher.

Communications received from J. L.-Mr. Woodhouse A Florist-J.-Mechanicus-Mr. Andrews -A Sheffield Manufacturer-F. H.-Mr. Henderson-J. W.

The Supplement to our last Volume, containing Titles, Index, &c., with a Portrait, on Steel, of Samuel Clegg, Esq., C. E., is now published, Price 6d.; also the Volume complete, in boards, Price 8s. 6d.

Our Publisher will give double price for copies of Nos. 236, 237, 238, 239, 256, 258, and One Shilling and Sixpence each for copies of the Supplement to Vol. X.

Patents taken out with economy and despatch; Specifications prepared or revised; Caveats entered; and generally every Branch of Patent Business, promptly transacted. Drawings of Machinery also executed by skilful assistants, on the shortest notice.

LONDON: Published by J. CUNNINGHAM, at the Mechanics' Magazine Office, No. 6, Peterborough court, between 135 and 136, Fleet-street. Agent for the American Edition, Mr. O. RICH, 12, Red Lion-square. Sold by G. G. BENNIS, 55, Rue Neuve, Saint Augustin, Paris. CUNNINGHAM and SALMON, Printers, Fleet-street.

DESCRIPTION OF THE PROCESS OF USING

HEATED AIR, AS
ADOPTED AT THE
CLYDE IRON-WORKS, BY MESSRS. NEIL-
SON AND CO., THE PATENTEES.

(From Report by M. Dufrenoy, Engineer of Mines to the Directors of Public Roads and Bridges of France, 1834.*)

Some experiments by Mr. Neilson, Director of the Glasgow Gas-Works, led him to think that advantage would be gained by previously heating the air to supply the smelting-furnace. He communicated his ideas to Mr. Mackintosh, long known for his inventive genius, and they united in undertaking at the Clyde Iron-Works, in concert with Mr. Wilson, one of the proprietors of the establishment, a series of experiments to determine this important question.

In the first experiment, the air from the blowing-machine was passed through a rectangular trunk of sheet-iron, 10 feet long, 4 feet high, and 3 feet wide, where it was heated previous to its entrance into the furnace.

Notwithstanding the imperfection of this method, by which the temperature of the air could not be raised above 200° Fahr., it was evident from the experiment that the plan of Mr. Neilson was destined to produce a revolution in the manufacture of iron.

This first apparatus was soon destroyed by the action of the heat, and its renewal being very costly, they sustituted a castiron pipe, having in the middle an enlargement like the bulb of a thermometer.

This second apparatus produced beneficial effects; it lasted much longer, and the temperature of the air was raised by it to In 1829. The combustion being maintained

280° Fahr. This increase, though small, produced a visible economy in fuel. Messrs. Neilson, Mackintosh, and Wilson, then understood the advantages which would result from raising the temperature many hundred degrees. They abandoned this heating tube, and constructed a new apparatus, presenting a great number of tubes, heated in many points of their length. By this means the temperature of the air was raised to 612° Fahr., a temperature above that of melted lead.

Though this temperature was much below that required for smelting iron (estimated at about 1500°), it produced a considerable saving in the consumption of fuel. Another advantage was obtained, of great importance -that of being enabled to substitute crude coal for coke, without injury to the walling of the furnace. The quality of the iron was, on the contrary, improved, and the furnace which produced but little more than half its quantity of No. 1 and half of No. 2, when fed with coke, gave a proportion much greater of No. 1 iron, after the substitution of crude coal. Besides, the consumption of fuel was considerably diminished. This last circumstance was owing, probably, to the fact that the temperature of the furnace becoming higher, it was not necessary to add so great a quantity of flux to ensure the vitrification of the gangue which accompanied the mineral. It is probably owing to this elevation of temperature that coal may be substituted for coke.

The better to judge of the progressive increase of economy obtained at the Clyde Works, in the experiments to be noticed, we give for each of them the different consumptions of coal and flux: by cold air

At this last epoch the employment of heated air had augmented the yield of the furnace more than one-third, and consequently had effected a great saving in labour. In fine, the quantity of air required to maintain combustion in the furnace, was also found to be sensibly diminished. The blast-engine of 70-horse power, which was sufficient in 1829 for only three furnaces, was found of ample power for the blast of four.

By comparing the results which will be indicated, it will be perceived that the economy in combustible is in proportion to the increase of temperature. As to the absolute saving, it varies in each furnace according to the nature of the coal, and the care used in carrying on the operation.

*

*

The vicinity of Glasgow is one vast coal region, the first in Great Britain, both in the extent and the thickness of the veins. This coal basin is also very remarkable for the abundance of its iron ore, both imbedded in the argillaceous schist of the region, and in regular veins, often of considerable extent.

The layers of coal in the vicinity of Glasgow, which belong to the lower strata of the coal formation, alternate with beds of mountain limestone, so that, in the same locality, are often united the coal, the ore, and flux, and the fire-clay used in the construction of the furnaces.

These invaluable advantages are in part compensated by the enormous loss incident to the carbonisation of the coal in this locality, as well as by the lightness of the coke produced. From these circumstances, a ton of iron requires at the Glasgow Works, for its production, a much larger quantity of fuel than in any district of England.

The employment of the heated air has produced a revolution in the Scotch Works, and enabled them to sustain a competition with those of Wales.

The Clyde Iron-Works were, as before stated, the first in which the heated air was tried.

The apparatus now in use (figs. 1 and 2) is composed of a double row of horizontal pipes, a a a a, 150 feet long. These pipes are nineteen inches in diameter, and one inch and a half thick. The exterior row passes behind the furnace, and enters the other row, dividing the air into two parts; so that the blast is carried equally to each tuyere.

The valves placed at E regulate the distribution of air, and stop either branch when repairs are required.

In the length of 150 feet, the tubes pass through five furnaces, or heaters, F F F F F, of which two are placed near the tuyeres; so that the air has no time to cool before enter

ing the surface. Figs. 1 and 2 give an exact idea of the form and disposition of the five heating fires; they are connected by a con: duit of brick, ggg, which envelopes the pipes; by this means the flame which escapes from the fire-place circulates about the pipes, and heats their whole length. To preserve the parts of the pipe immediately in contact with the flame, they are encased in fire-brick the whole length of the furnace. In the first apparatus of this kind which was constructed, the ends of the pipes were inserted one in the other, having some play, to prevent any rupture by expansion; the result was a great loss of air, and the plan was abandoned. Besides, it was remarked that a great waste always took place at the joints of the pipes; so that it was not sufficient to fasten them with bolts and nuts; the joints were therefore covered with a ring of iron cast on after they were finished. By means of this precaution, the pipes lasted a long time; and at the time of my visit they had been five months in use without repairs.

On the exit pipes are made small holes, V V, by means of which any change of temperature in the air might be ascertained. This precaution is indispensable, because one of the essential conditions in the use of heated air is, that its temperature be kept uniform -with this apparatus they raised the air to 6120 Fahr., which is higher than the melting point of lead. In the Clyde Works, two of the four furnaces have each an apparatus like the one described, but in the other two there was no room for the extent of pipes, and they are contracted into smaller space, by being doubled upon themselves.

The working of a furnace with heated air, requires no particular precaution; the operas tion is the same as before its introduction, the only difference consisting in the substi tution of raw coal for coke. This substitution did not immediately follow the adoption of the new plan; it was some time after, and only when the temperature of the air was raised above the melting point of lead, that the immense benefit of the change was discovered, giving a consequent diminution in the expense of manufacture.

The general idea adopted in Scotland is, that certain qualities of coal cannot be employed crude, except when the air is highly heated. We have already said that at the Monkland Works, where the air is heated to 460° and 490° Fahr., coke is still used.

The descent of the furnace is very regularthe distances between the charges are nearly equal, the charging being regulated by the space left empty in the throat. The richness of the ore not roasted, varies from 22 to 34 per cent., and the composition of the charges follows this variation, At the time of my