the power spent on them is expended to no purpose. So it is with paddle wheels. A boat never progresses in the ratio of their revolutions, because of the yielding medium in which, and against which, they act. They slip always-a result inevitable when massive solids wade through fluids. The distance between the Atlantic steamers' docks, in Liverpool and New York, has been calculated at 3,023 miles, but their paddles, in each trip, pass over a space varying from 5,000 to 8,000 miles. In steamers unaided by sails, the disproportion is often greater. Now can this be modified, by giving the paddles a better hold on the fluid they sweep through? The experiments, figs. 5, 6, 7, 8, 9, 11, 12, 14, 16, and 17, furnish replies to the interrogatory.

The moral of the foregoing experiments is this:-As the propelling power of a paddle is greatest at its lower or outer extremity, and diminishes to nothing at the surface, so its face should enlarge with the dip, and be nothing, or next to nothing, above.Let d, fig. 18, represent the end of an ordinary blade, or paddle. Its upper part barely touches the water, and only for the moment it is in the position shown. But suppose it were immersed to the line c, c,-say four or five inches-it would even then be no sooner under, than above the surface again, so brief would be its immersion. The lower edge, in the meanwhile, would sweep along the extended curve there delineated.

C

Fig. 18.

Of what use, then, to make the upper part of a blade of equal extent with the lower? Why accumulate surface where it is of little avail, and withhold it from where it is most wanted?-expending materials and power without any adequate return, if not at an absolute loss. The quantity of water carried over a wheel, is certainly greater by ordinary, than it would be by triangular, paddles. The popular form and position of paddles are unphilosophical, if viewed simply as propellers. Embrace the same area in any other outline-in a circle, ellipse, square, pentagon, hexagon, octagon, or other polygonous figure, and the propelling properties would be increased, and the jar arising from their striking the water also diminished.

If the long paralellogram be preferred, because of the ready application of wooden planks, then is the principal sacrificed to an accessory-the greater to the less. If triangular, or other improved blades, require the adoption of plates of metal, would it be wise to reject them on that account?-But of this by-and-bye. We shall see that thick wooden blades ought to be condemned on account of defects inherent in them.

But what is this expansion of the lower part of a paddle, and contraction above, but Nature's own plan? In the tails and fins of fishes, in wings of birds and insects, and especially in the palmipeds, she has nowhere sanctioned a rectangular propeller. All are inclined to equilateral, scalenous, or isosceletic triangles, or are made up of them. Nor does she ever unite the levers that work them to their sides. The junction is invariably at an angle, and the reason is apparent-that the largest surface may have the longest sweep.

With this view, the bodies of fishes taper down to meet the blades; retaining only sufficient muscle to work them. The other day, I had an opportunity of sketching the following. I am ashamed to acknowledge that, till then, I was ignorant of the exact forms of these natural propellers, although most of them had passed under my observation on a thousand occasions. Too many of us spend no more thought on the infinitely curious and instructive mechanisms submitted by the Creator to our inspection daily, than does the ox on the vegetable glories he feeds on. The sentiment applies not more to religious than to physical truths"Light shineth in darkness, and the darkness comprehendeth it not." We grope, as if blind, for that which is patent before

us.

The general outlines and proportions are given in the annexed

I confess I had no idea of meeting with figures so closely allied to the artificial ones which I had found most effectual as propellers. With the exception of the first two, the whole approach to equilateral triangles.

In the absence of a more extended acquaintance with the minuter aqueous and sub-aqueous organisms, the nearest of natural analogues to steam-vessels seem to be the principal swimming-birds. These glide through two elements at once. Their long and heavy bodies, adapted to float gracefully on water, are provided with organs of propulsion, placed far behind their common centres of gravity-the cause that makes them such awkward travellers on land. When a gale blows in the direction they wish to pursue, like human navigators they take advantage of it; they spread their wings to catch it, and are driven onward then, as steamers are, by both wind and paddles.

The reciprocating action, and the expanding and collapsing features of their aqueous organs of progression, are supposed to be unsuited to the magnitude, materials, and velocity of artificial ones. Perhaps they are; but may not their contour be perfectly applicable: since, when open, and in action, the circumstances of the two bodies propelled the bird and the boat-are not essentially dissimilar? Now, there is a marked adhesion to the triangular form in the webbed feet of birds; showing that, in the judgment of the Creator, such an outline is the best for the purposes of their propulsion. Nor does it appear that this outline has, in any material way, been modified to meet other exigences. In the feet of water-fowl it is almost identical with the tail of the sea bass. The legs, or rods, that wield these ornithologic paddles, are invariably united to them at their points, or angles, and clearly for the reason already stated.

Fig. 20.

Fig. 20 represents the foot of a petrel. It is a type of all the swimming-birds' propellers. Few, except professional naturalists, could distinguish between it and the same organ in geese, ducks, gulls, swans, the albatross, cormorant, diver, flamingo, &c., &c. Although natural paddles are submerged when at work, and those of our wheels emerge into air to repeat their strokes, I doubt if a more efficient form could be given to the latter than the above. The cuspated extremity would ob

Account of Hydraulic and other Machines for Raising Water," by Thomas Ewbank, published in 1842, we there find, that "in some pumps both a solid and a hollow piston are made to work in the same cylinder. Such was the arrangement that constituted the single-chamber fire-engine of Mr. Perkins. A plunger worked through a stuffing-box; its capacity was about half that of the cylinder, consequently on descending it displaced only that portion of the contents of the latter. The apertures of discharge were at the upper part of the cylinder, and a single receiving one at the bottom. From the lower end of the plunger a short rod projected, to which a hollow piston or sucker was attached, fitted to work close to the cylinder, so that when the plunger was raised, this piston forced all the water above it through the discharging apertures."-And in the same page: "Such pumps are more compact than those with two cylinders, but they are more complex, less efficient, and more difficult to keep in order and repair. The friction of the plunger and sucker is much greater than that of the piston of an ordinary double-acting pump of the same dimensions; and the latter discharges double the quantity of water: for, although double-acting, the effect of these pumps is only equal to singleacting ones.

Some of the latter remarks are undoubtedly right, and we in some cases prefer the double-acting pump; and when two of the double-acting pumps are employed, fixed on each side of the main centre of the working beam of the steam-engine, we conceive it impossible to devise a more efficient arrangement for raising water from a few feet below the ground, to any reasonable height.

At the Waterworks at Trafalgar-square (erected by us in 1844), and also at Ramsgate, the water has to be raised from a considerable depth below the surface of the ground, by direct-acting engines, without balance-beams; consequently, had we not employed the plungers in the working barrels of the pumps, to counterbalance the weight of the pistons, pump-rods, &c., by displacing a quantity of water in their descent, the whole of the power required for lifting the pistons and pump-rods would have been We are, Sir,

wasted.

It may seem somewhat strange, that while canals of the greatest magnitude had been undertaken on the continent, England contented herself with scouring and deepening her rivers until the middle of the last century. The necessity, it must be owned, was not so stringent as in France. Yet the development of commerce in this country, long before the time we have mentioned, was sufficient to render almost necessary some better means of inland navigation than those afforded by our natural water-courses. It is true that the great southern towns, lying as they did either on large rivers or by the sea, did not require canals to the same extent as the cities of the northern and midland districts. As soon, therefore, as industry and enterprise had begun to assume importance in those parts of the island, the idea of forming canals to the various centres of manufacture followed as a matter of course; and in the year 1720 we find the first definite proposal for the execution of one of these important undertakings ever made in this kingdom. At that time the means of effecting a communication between the east and west seas, through the estuaries of the Aire and Ribble, had attracted the attention of the enterprising men of Yorkshire and Lancashire. Various schemes were set on foot for carrying this project into execution, which resulted in an act being obtained, in 1720, for the undertaking which has since ripened into the Leeds and Liverpool Canal.

Before, however, any practical progress was made towards the completion of this scheme, the Duke of Bridgwater commenced the execution of his own magnificent canal, under the supervision of Mr. Brindley. All other projectors now appear to have held back until they could witness the result of this work; and, consequently, scarcely anything was done in the way of inland navigation between 1737 and 1761, during which 24 years the Bridgwater Canal was being carried through every obstacle and discouragement, by the indomitable genius of its engineer, to a triumphant completion. The history of that great work is too well known to

be repeated here; but the more than doubts expressed concerning it, and the prophetic warnings of inevitable failure which were uttered on all sides during its progress, prove how little was at that time understood in this country respecting that class of undertakings; and they prove, too, how extremely slow is the first growth amongst us of that very enterprise which we are afterwards destined to work out into such splendid development. The canal cost 220,000l.—an enormous sum at that time, and from the purse of a single individual. It is said that the Duke of Bridgwater had to live for many years upon 4001. a year, in order to pay for it. The recompense has been no less remarkable Long since the annual income netted by means of the canal was valued at 130,000l., and notwithstanding the completion of a whole network of railways through the district it traverses, that return, it is believed, is at present considerably exceeded.

One single canal was commenced during the interval above mentioned; and which, having been completed before the Duke's, has the honour of being the first work of the kind executed in England. This was the Sankey Canal, running from the mouth of the Sankey Brook, in the Mersey, to St. Helen's. It is, however, little more than an improved edition of the long-used river navigation, as the brook is all along a feeder to the canal, which was by the side of it. Its length is not more than 12 miles, the fall about 78 feet, with eight single locks and two double ones, so that this first of our canal enterprises was no great work. Mr. John Eyes, of Liverpool, was the engineer.

The opening of the Bridgwater Canal gave a new impetus to this branch of enterprise. The Louth Canal got its act in 1763, little more than a year after the opening of the Bridgwater. The greater part of this canal is on a continuous level, very little above the sea, running from the Humber, near Tetney Haven, to the River Ludd. The length is but 14 miles, and the original estimate 16,500/. It was so defectively constructed, notwithstanding the facilities of the county, that the whole affair, after 28,000l. above the estimate had been raised on loan, was assigned to a single man, Mr. Chaplin, to manage in his own way. This was the result of a too stringent economy in starting. It took a long time to get public companies to understand their own interest. The Louth Canal is now a useful work, as far as it goes, and very beneficial to the town of Louth and the neighbourhood.

The next canal attempted-in fact, the third opened in the country-was, like the Bridgwater Canal, the speculation of a single man. In 1764, Sir J. H. Duval cut a canal through the solid rock, for the purpose of connecting Hartlepool Harbour, in the county of Durham, with the sea. The canal is but 300 yards long. The next canal was likewise a private undertaking, projected and executed by a single man. Mr. J. Rymer made a canal from his coal and lime works to the tideway in Kidvelly Harbour. He obtained his act in 1766. Long after, in 1812, a company undertook to improve and extend the canal, construct tramroads in connection with it, &c., from which resulted the present Kidvelly Canal, with its branches and adjuncts.

Thus, out of the four canals first executed, three were strictly private. In 1766 the first really important public canal was commenced, the Staffordshire and Worcestershire. This work was engineered by Brindley himself, to proceed from the Severn, at Stourport, to the Trent and Mersey navigation, near Heywood, in Staffordshire. Its rise is considerable, as upon the top level it runs for 10 miles at a height of 294 feet above the Severn at Stourport, and of 352 feet above low-water mark at Runcorn. In length it is almost 47 miles, and it cost 112,000l., including a variety of accessary expenses in clearing away shoals from the bed of the Severn. The trade on this canal is immense.

The Trent and Mersey Canal was commenced in 1766. It was suggested by the Duke of Bridgwater, with whose water communication it is at one point connected, and was executed up to the time of his death by Mr. Brindley. The original estimate was 130,000l., but it cost 334,000l. Little wonder, for it comprises 127 aqueducts and culverts-one of the former over the River Dove being very extensive-91 locks, and 6 tunnels. The famous Harecastle Tunnel, 2,880 yards long, is situated on the summit level of this canal, whose total length is 93 miles.

The next undertaking in chronological order is one of the noblest works in the kingdom. The Forth and Clyde Canal was begun in 1768. This canal, commencing in the Forth at Grange.. mouth Harbour, passes within two miles of Glasgow, and thence into the Clyde, being the first realised attempt at connecting the two great seas of our island. Its length is 35 miles, and the greatest rise 155 feet. By the recent improvements it has undergone, sea-borne craft, drawing 10 feet water, are able to navigate through it, between the Irish Sea and the German Ocean. The

locks are 74 feet long by 20 wide; they are 39 in number. On its course are 33 drawbridges, 10 large aqueducts, and 33 smaller ones. Among its many reservoirs is one that covers 70 acres, with a depth of 22 feet at the sluice. The first idea of this undertaking dates as far back as the time of Charles II.-that monarch having taken preparatory measures for cutting a channel in the same direction for the passage of ships of war. The design was calculated to cost 500,000l., but was far too magnificent for the impoverished exchequer of the Stuarts. In 1723 a fresh survey and estimate was made by a good engineer, Mr. Gordon, but nothing more was done until 1764, when Lord Napier employed Mr. Maskell to make a report, the result of which was, that the celebrated Smeaton was engaged to undertake the work according to the present plan. Sundry difficulties, as usual, arose-the chief being the enormous enhancement of the cost. The estimates fixed this at 147,3377, but when this had been expended, and between 70,0007, and 80,000l. additional borrowed, the projectors found that only about half the length had been, though with much rapidity, completed. Disputes then occurred with the engineer, amidst which the works stood still, but being presently recommenced, the canal was brought to within 6 miles of the Clyde, when its further progress was again stayed by the want of funds. An act passed in 1784, alleviated this difficulty, by enabling the proprietors to borrow money from the Scotch Barons of Exchequer, out of the forfeited estates, and with this assistance the work was completed in 1790. The whole stock amounted at last to 519,840.-considerably beyond the sum estimated by Charles II. for his ship canal, and which, if mentioned at the beginning, would have stifled the project in its birth.

As a collateral assistance to the navigation of the Forth, the Borrowstoness Canal was commenced in the same year with the Forth and Clyde. It is a level canal, about 7 miles long, and cost 21,000, the original estimate having been 5,000l. In the same year Brindley commenced the Coventry Canal, running from the Trent and Mersey to Coventry. The project appeared a failure for some time, as the requisite capital was not forthcoming. But the Trent and Mersey Company took the matter up in 1782, and the works were begun in earnest; it was finished in 1790, and forms, with the Ashby-de-la-Zouch and Oxford Canals, which communicate with it, the longest canal line in England, being upwards of 70 miles, exclusive of branches. The length of the Coventry Canal is somewhat short of 38 miles, with very few locks, and a level at the highest of 81 feet. The expense was about 90,000l. Brindley's great object was to connect, by canal navigation, the ports of London, Liverpool, and Hull. The last link in this great chain was that grand undertaking, for the time, the Oxford Canal. This work was commenced in 1769, beginning from the Coventry Canal at Longford, and extending to the Thames at Oxford. The whole capital authorised to be raised for this purpose was upwards of 300,000.-the original estimate being 178,6487. The length is 80 miles, carried at the summit level at the height of 3871 feet above the level of the sea. It has three aqueducts, the one at Brinklow nearly 300 feet long, and two tunnels, the longest, at Fenny Compton, being 3,564 feet. The level, at its commencement at the Coventry Canal, is no less than 74 feet above the surface water of that channel, and rises from thence to the summit level about 75 feet. On the whole, this is one of the most important canals in the kingdom, as forming the connecting link between the inland navigation of the northern and southern districts.

In the 20 years that followed, up to 1790, the number of canals executed in the country was 17-few of them of equal importance with the preceding. Brindley projected the Chesterfield Canal in 1769; it was carried on under his direction and that of his brotherin-law, Mr. Henshall, till its completion in 1776, at a cost of 150,900. Its length is 46 miles, with 65 locks, and one very extensive tunnel, 2,850 yards long, near Harthill. Mr. Grundy had proposed another plan, which would have saved 5 miles, and between 20,0001. and 30,000l., but Brindley's experience was preferred. The undertaking was a very successful one; but the most important of Brindley's later suggestions was the Ellesmere and Chester Canal. The famous aqueduct over the Dee is on this canal carried at a height of 125 feet above its bed, on 19 pairs of stone pillars, 52 feet apart. Several others of the great specimens of canal works in the kingdom were of his undertaking. It runs from Ellesmere Port to the Montgomery Canal, a distance of 61 miles, with numberless collateral branches. During the progress of this canal the greatest possible difficulty was experienced in raising the money. The shares at one time were sold at 1 per cent. of their original value. The whole cost was nearly 400,000l.

The Thames and Severn Canal, another of Brindley's projects,

was commenced in 1783. The longest of the tunnels-the Tarleton Tunnel-is on this canal; it is 23-miles long. It runs from Stroud to Cirencester, with a length somewhat above 30 miles. The original estimate for this work was 190,000l., the actual cost above 500,000l.; one of the largest excesses in canal history-and the more strange, as there are no branches. It has 42 locks. A union between the Thames and Severn, by means of the Avon, was another of Charles II.'s projects.

The other canals executed during the period alluded to were the Basingstoke, about 40 miles long, cost about 186,000.; the Erewash, running from the Trent to Langley-bridge, about 12 miles, cost 23,000l.; the Cromford, from the Erewash to Cromford, 18 miles, on which are one or two of our finest aqueducts, cost 86,000l.; the Bradford, 3 miles long, cost 9,000l.; the Dudley, of which the original plan was a length of 13 miles, at a cost of 12,000l., but the expense of cuts and connecting branches amounted to somewhere about 150,000l. additional; the Market Weighton, 11 miles long; the Andover, 224 miles long, cost 65,000l.; the St. Columb, 6 miles long; the Shropshire, a canal of 7 miles from the furnaces at Coalbrook Dale to the Severn; the Stourbridge, and three private canals-one executed by Sir J. Ramsden, near Huddersfield, another by Sir N. Gresley, near Newcastle-under-Lyne, and the third by Lord Thanet, a short affair, near Skipton Castle.

After 1790 a violent impetus was given to canal speculations. Between that date and 1795 no less than 43 canals were planned, and acts relative to 15 new undertakings were passed in 1793-the largest number of any year in history. The dates of the first acts, relative to two of the most important undertakings in the kingdom, the Grand Junction and the Kennet and Avon, belong to this period, being passed, the one in 1793, and the other in 1794. The first of these, one of the most spirited enterprises of the kind, begins at the Oxford Canal, near Braunston, to the Thames, at Brentford-a course of 90 miles. The undertaking was the last step in Brindley's grand plan of inland communication throughout the country. We had attained already a complete water connection between Liverpool, Hull, and London; but the old river communication, with its tortuous course and manifold disadvantages, still existed in a most important part, that between Oxford and London; and it was to make the canal communication complete that Lord Rockingham, in 1792, employed Mr. Baines to make the survey for the present canal. The first estimate was 600,0007.; but, as usual, cuts and extensions required the raising of a further sum of 550,000l., making this one of the most expensive undertakings in the kingdom. The length is above 90 miles. There are 98 locks and two tunnels, with several deep cuttings; one near Bulbourne 3 miles long and 30 feet deep for the greater part of the way. There are, besides, several embankments-in fact, this, on the whole, came nearer to modern railway enterprise than any work previous to the commencement of the iron age. From the summit level at Tring to Harefield-park, a distance of about 21 miles, there is a fall of 300 feet-the height of the summit part being 380 feet above the Thames at Limehouse. The Paddington branch, which is a continuation of the Grand Junction, is for 34 miles quite level; the water-course for 20 miles, from Paddingto Uxbridge, requiring but a single lock. The greater part of this canal was completed in about 10 years.

The Kennet and Avon Canal.-The most important water link between the west and east of the southern counties in England, was commenced in 1794. It runs from the Avon, at Bath, to the Kennet, at Newburn; and, as the former river runs on to Bristol, and the latter to the Thames, a communication is effected between Bristol and London; in fact, between the Irish Channel and German Ocean. It completes moreover the water circuit from the northern districts round the island, and passes through or near several of the most important towns in the south. The original estimate 570,000l.: but a further sum of 702,000l. was required to be raised under four successive acts, to complete the undertaking. The engineering difficulties were in some parts very great. In Somerset and Wiltshire, the country through which it passes is very rugged. At one place, near Devizes, a fall occurs of 239 feet in 2 miles, requiring 29 locks. The length is 57 miles, and the whole rise 210 feet, with 31 locks, and the fall 404 feet, with 48 locks. The expense per mile (22,3157.) makes this one of the most costly canals in the kingdom. As a property this undertaking has been most injured by the Great Western Railway. The company were only enabled to compete with the railroad for the carriage of heavy goods, by charging half their prices when they enjoyed the monopoly. The railway at first only professed to carry light goods, and thus disarmed the opposition of the canal, but it has ended, as might have been anticipated, in carrying everything. One or two of the aqueducts on the canal are of beautiful struc

ture, the Dundas aqueduct especially, which is situated about 4 miles from Bath.

The number of the works now undertaken prevented the commencement of new designs, and besides the continental disturbances began to be seriously felt. From 1795, to the end of the century, only four canals were commenced-the Grand Western, the Dorset and Somerset, the Newcastle Junction, and the Aberdeenshire. All these, though very useful works, were but of secondary importance. The first-named, running from the Exe to Taunton, cost about 330,000l.—the length is about 35 miles. The second was never executed; the third is a very trifling affair; and the fourth only goes to the length of 19 miles: 36 canals have been commenced in the present century, the principal of which are the Regent's and the Caledonian. The larger undertakings were often abandoned, at least in their chief points, which was the case with the Bridgwater and Taunton. The Caledonian, as will be seen, does not pay at all. The Grand Surrey, the original subscription for which was 45,0007., but which cost above 300,000l. additional, pays a very trifling per centage. The Edinburgh and Glasgow, the Macclesfield, and the Grand Union, are the three other of most importance. Enterprise was, however, busy about the old lines-most of which received important improvements in this period.

All the undertakings here enumerated have been completed by private persons, either singly or in association. The only work actually undertaken by the government has been the Caledonian Canal. Watt first surveyed this line, but it was carried into execution by Telford. It cuts completely through the Scotch islands, commencing at the foot of Ben Nevis, and running through three Scotch lakes to Inverness. The length of the whole is above 60 miles; but very little more than 23 of this is canal, the remainder being being lakes. The original intention was to facilitate the transport of Baltic timber, but the traffic has turned out far below the original expectation. The cost to the government has been above 1,000,0007.; and in 1842 the expenditure for wages and maintenance actually exceeded the receipts; the former being 2,0907., and the latter 2,0381. We must add, indeed, that 5761. of the charges are put down as extraordinary expenditure in building boat-houses, &c.; but, even so, the surplus would have been very little more than 500l. There are 28 locks on this canal, of which a chain of eight, called Neptune's Staircase, alone cost 5,000/. The works of the canal are of first-rate order, and the channel of enormous breadth and depth, as being intended for ship navigation. The width at top is 110 feet; at bottom, 50; depth, 20 feet; the locks 172 feet by 40. All this explains the cost, together with the nature of the country through which the canal passes; but it is an instance of the failure of government undertakings, as far as mere profit is concerned. Vessels of upwards of 160 tons often pass the canal.-Daily News,

THE CENTRE OF GRAVITY OF A LOCOMOTIVE ENGINE.

In all investigations as to the effects produced by the locomotive engine, it is absolutely necessary to determine accurately the position of its centre of gravity. As the ordinary method of ascertaining this point by calculation is both tedious and unsatisfactory, I am induced to give the outlines of a mode which has suggested itself to me, and which, with careful application, will, I find, give an accurate result. The annexed engraving represents a fourwheeled engine, whose axles are 7 feet from centre to centre. Having first carefully ascertained the total weight of the engine, the weight on each pair of wheels must be obtained by repeated trials on a good weighing machine. Suppose these weights are found to be respectively H-9 tons, and F-7 tons; the position of a vertical line ĈC'O, passing through the centre of gravity, can be fd found by the equation x=" where a distance of the line t CCO from hH; f= 7 tons, the weight on the front wheels; d= 7 feet, the distance between the axles; and t = 16 tons, or total weight of the engine.

Having thus found the line CC'O, it must be chalked upon the barrel of the boiler. Assume for a moment that C' is the position of the centre of gravity: draw the line Cf. If now the front wheels be placed on the weighing machine, and the hind part of the engine raised until the insistent weight indicated is equal to 16 tons, it is evident that the point C' will be in a vertical line passing through the points C and f. By suspending two plumb

Could the above method be practically applied, it would be the most simple way of arriving at a knowledge of the point; but as it would be dangerous both to the engine and machine thus to dispose a weight of (in some instances) thirty tons, it has only been mentioned that the following plan may be more readily understood:-On an inspection of the figure, it will be seen that the line EQ is equidistant between H and F, and in this line the centre of gravity would have been situated had the weights on H and F been respectively 8 tons. The front wheels having been again placed on the weighing machine, two plumb-lines must be suspended as before, but in a plane passing through the line EQ, which may be termed the line of equipoise. It is evident now that if we lift the engine behind, the plumb-lines will intersect the line CC', whenever the weight indicated by the machine is equal to 8 tons, and the centre of gravity will be situated in their intersection. In this operation, compensation must be made for that portion of the total weight which tends to move the front wheels forward. The amount of this force can be easily calculated, but it is better in practice to compensate it by passing the lifting rope round a pulley, so that its direction may be in a right line with the framing of the engine when lifted.

I have used a four-wheeled engine to exemplify my mode of proceeding, because it is the simplest; but a six-wheeled engine can be treated in the same way, when the lines CC'O and EQ have been found. If h, m, and ƒ represent the weights on the hind, middle, and front wheels, and d the distance between h and m,—a md point y must be found, by the equation y = where the h+ m2 weights h and m may supposed to be concentrated: if D be put for D the distance between y and f, will be the position of the line of 2

equipoise. Again, if t be put for the total weight of the engine, ƒD t

00= will be the position of CC'O, the vertical line passing through the centre of gravity.

R. M.

The High Level Bridge on the Tyne, at Newcastle, on the York and Berwick line of railway, will, it is expected, he opened on the 1st of August. The key of the last arch was driven home on the 7th ult., by the Mayor of Gateshead, Mr. Hawks, of Hawks, Crawshay, and Co., the contractors for the ironwork. The first pile was driven on the 24th of April, 1846, in presence of its designer, Mr. R. Stephenson, M.P.; and the first segment of the first arch was placed so lately as the 10th of July last. The ironwork rising to a height of 120 feet above the bed of the river, much caution was called for, and from the careful and expensive arrangements therefore made, there has been neither loss of life nor limb in the fixing of the six massive arches, many of the castings of which weighed from 10 to 12 tons each. The cost of the bridge when completed is estimated to be 243,0967; the viaduct through Gateshead and Newcastle, 113,057.; land, compensation, &c., 135,000 total, 491,153.