similar to the "clinkers," or small, hardburned bricks, so generally used for roadmaking in Holland.

The second specimen was formed with broken stones; but the materials, owing chiefly, no doubt, to the high rate of wages, are not broken sufficiently small to entitle it to the name of a Macadamised road." It is, however, a wonderful improvement on the ordinary pitched pavement of the country; and the only objections to its general introduction, as already noticed, are the prejudicial effects produced on it by the very intense frost with which the country is visited, and the expense of keeping it in re. pair.

The third specimen is rather of an original description. It consists of a species of tessellated pavement, formed of hexagonal billets of pine wood, measuring 6 inches on each side, and 12 inches in depth. From the manner in which the timber is arranged, the pressure falls on it parallel to the direction in which its fibres lie; so that the tendency to wear is very small. The blocks are coated with pitch or tar, and are set in sand, forming a smooth surface for carriages, which pass easily and noiselessly over it. There can be no doubt of the suitableness of wood for forming a roadway; and such an improvement is certainly much wanted in all American towns, and in none of them more than in New York. Some, however, have expressed a fear that great difficulty would be experienced in keeping pavements constructed in this manner in a clean state, and that, during damp weather, a vapour might arise from the timber, which, if it were brought into general use, would prove hurtful to the salubrity of large towns.

In the northern parts of Germany, and also in Russia, wooden pavements are a good deal used. My friend, Dr. D. B. Reid, informs me that at St. Petersburg, a wooden causeway has been tried with considerablə success. The billets of wood are hexagonal, and are arranged in the manner of the American pavement. At first, they were simply embedded in the ground; but a great improvement has been introduced, by placing them on a flooring of planks laid horizontally, so as to prevent them from sinking unequally. This has not, so far as I know, been done in America.-Stevenson's Engineering of America.

AMERICAN STEAM-BOILER EXPLOSIONS.AN ACT FOR INSTITUTING EXPERIMENTS UPON SAFETY APPARATUS.

An Act authorising the appointment of persons to test the usefulness of invention to improve and render safe the boilers of steam-engines against explosions.

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Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That the President of the United States be, and he hereby is, authorised to appoint three persons, one of whom at least shall be a man of experience and practical knowledge in the construction and use of the steam-engine, and the others, by reason of their attainments and science, shall be competent judges of the usefulness of any invention designed to detect the causes of explosion in the boilers; which said persons shall jointly examine any inventions made for the purpose of detecting the cause and preventing the explosion of boilers, that shall be presented for their consideration; and if any one or more of such inventions or discoveries justify, in their judgment, the experiment, and the inventor desires that his invention shall be subjected to the test, then the said persons may proceed and order such preparations to be made, and such experiments to be tried as in their judgments may be necessary to determine the character and usefulness of any such invention.

Sec. 2. The said Board shall give notice of the time and place of their meeting to examine such inventions, and shall direct the preparations to be tried, at such place as they shall deem most suitable and convenient for the purpose; and shall make full report of their doings to Congress at their next session.

Sec.3. To carry into effect the foregoing objects,there be, and hereby is, appropriated out of any money in the Treasury not otherwise appropriated, the sum of six thousand dollars; and so much thereof as shall be necessary for the above purposes shall be subject to the order of the said board, and to defray such expenses as shall be incurred by their direction, including three hundred dollars to each, for his personal services and expenses: Provided however, And their accounts shall be settled at the Treasury, in the same manner as those of other public agents.

THE CANAL LIFTS ON THE GRAND WESTERN CANAL: BY JAMES GREEN, M. INST. C. E. [From the Proceedings of the Inst. of Civ. Eng.]

The lift which is the subject of the following paper was erected by Mr. Green in the year 1835, on the Grand Western Canal, and has been in operation ever since. Lifts are not intended to supersede the use of canals in all cases, but in those in which a considerable ascent is to be overcome in a short distance, and in which the water is inade

quate to the consumption of a common lock, or in which the funds are inadequate to the execution of the work on a scale adapted to such locks.

This lift is 46 feet in height, and consists of two chambers, similar to those of a common lock, with a pier of masonry between them; each chamber being of sufficient dimensions to admit of a wooded cradle, in which the boat to ascend or descend floats. The cradle being on a level with the pond of the canal, a water-tight gate, at the end of the cradle, and of the pond of the canal, is raised up, and leaves the communication betwixt the water in the canal and in the cradle free, and the boat swims into or out of the cradle.

The cradles are balanced over three castiron wheels of 16 feet in diameter, to the centre of one of which is fitted spur and bevil gear, so that the motion may be given by machinery worked by the hand, without any preponderating weight of water in the cradle, when scarcity of water renders this necessary. To this hand gear in also attached brake-wheels and a brake-lever for regulating the motion.

It is obvious that the weights of the additional length of the suspending chains on the side of the cradle which is the lowest, must be counterbalanced; for this purpose there is attached, to the under-side of each cradle, a chain of equal weight per foot with the suspending chain, and this elongates under the ascending, and is shortened under the descending cradle; thus the disparity in the weights due to the suspending chain is obviated.

It is so arranged that the water in the upper cradle is about two inches below the level of the water in the pond; the consequence of which is, that the upper cradle has a slight preponderance first, sufficient to set the machinery in motion; the weight of this water is generally about one ton; it may however be regulated at pleasure.

The strength of materials is the great desideratum in machinery of this nature, and though the lift here described is but 46 feet, and the boats about eight tons, the same method is applicable to much greater heights and larger tonnage. The advantages of these lifts over common locks are, great economy of construction, and a great saving of time and water.

The time occupied in passing one boat up and another down this lift of 46 feet is three minutes, whereas thirty minutes would be required to attain the rise of 46 feet by locks; thus the saving in time amounts to 9-10ths for boats of eight tons.

The quantity of water consumed is about two tons for eight tons of cargo, whereas in common locks it is about three tons of wa

ter per ton of cargo; the saving is, therefore, 22 parts out of 24, or very nearly 92 per cent. If the trade were all downward, there would, by the use of the lifts, be carried from the lowest to the highest level of the canal, a quantity of water equal to the loads passed down.

Mr. Green stated that in some parts of the canal it had been found impracticable to get a sufficient drain to empty the chamber-they were compelled, therefore, to use a half-lock of eighteen inches fall; that there were seven lifts and one inclined plane on the canal,effecting a rise of 262 feet in eleven miles. That he should not recommend them as applicable to boats of more than 20 or 30 tons. The width of larger boats was an obstacle. They were extremely advantageous for narrow canals; for boats of 50 or 60 feet in length, and about 30 tons.

Mr. Parkes remarked, that he considered the question of narrow canals as a most important one-the advantages to be derived from narrow canals was a subject to which sufficient attention had not been paid.

The President called attention to the remark in Mr. Green's paper respecting the quantity of water carried up from one level to another in a downward trade wherever these lifts are used; then a coal country on a high level may supply itself with as much water as it sends down coal. The subject of inclined planes being alluded to, especially those of the Morristown Canal of 200 feet each, where a rise of 1600 feet is effected by eight inclined planes, Mr. G. remarked, that more water and time must be expended, the friction and length being much greater. In the lifts there was only as much water consumed as was equal to the load, but that he should not consider them as practically applicable to more that 60 or 70 feet. vourable levels with ascents of more than 60 or 70 feet could seldom be found; could he have had the choice of the line in this particular instance, he should have effected by four lifts the rise for which seven are now employed.

Fa

RENDEL'S FLOATING BRIDGE ACROSS THE HAMOAZE FROM DEVONPORT TO TORPOINT.

[From the Minutes of Proceedings of the Institution of Civil Engineers.]

The floating bridge now described is used as a system of communication betwixt the opposite shores of the Tamer, a little to the north of Devonport. The width of the river at this site is 2550 feet, at high water, and its greatest depth at spring tides 96 feet. The ordinary velocity of the stream is 3 knots an hour, but under heavy land floods, it is increased to 5 knots. The line of pas

sage is directly at right angles to the current; this, combined with the exposure of the site, and the rapidity of the current, rendered an attempt to apply a twin boat, similar to those at Dundee, a total failure.

The floating bridge is a large flat-bottomed vessel, of a breadth or width nearly equal to its length, namely, 60 feet long, and 50 feet wide, divided in the direction of its length into three divisions, the middle being appropriated to the machinery, and each of the side divisions to carriages and traffic of all kinds. These side divisions have decks, raised from 2 feet to 2 feet 6 above the line of floatation, and carriages, horses, &c. pass on and off the deck by strong commodious platforms or draw-bridges, communicating with the landing-places, and over which carriages of all kinds drive on and off the bridge without difficulty or inconvenience.

The bridge is guided in its passage by two chains, which, passing through it, over castiron wheels, are laid across the river, and secured to the opposite shore; thus forming, as it were, a road, along which the bridge is made to travel forward and back from shore to shore. The peripheries of the wheels are cast with sockets, fitted to the links of the chain, so that when the wheels are stationary the bridge is moored by the chains; when the wheels revolve, the bridge moves in the opposite direction. Two steam engines, of 11 horse power each, are employed to turn these wheels. The author then describes the details of the wood-work, and the dimensions of the several parts; the draw-bridge, and the landing-places, or inclined planes, formed on each shore; the galleries; the enginehouse and machinery; the chains and balance weights; the accommodation, and regulations of the bridge.

The peculiar feature in these works are the balance weights. There would have been great difficulties in fixed moorings; the ends of the chains are attached to weights, suspended in shafts 16 feet square, and 20 feet deep, sunk in the landing-place above high water mark. The weights are cast-iron boxes, loaded with about five tons each. Thus the additional length requisite when the vessel is in the middle of the river, is obtained. Were the chains fixed to the shores, they would be too short, and consequently unnecessarily strained at this time, or so long as to allow the vessel to make lee way in her approach to the landing-place. This is altogether avoided by the balance weights; for as the vessel leaves the shore, the weights rise, and the chains lengthen, so as to adjust themselves to an easy curve; and as it approaches the other shore, the balance weights on that side fall, the chains are shortened,

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and the draw-bridges or platforms are brought straight and steadily to the landingplaces.

The economy, both as regards first cost and annual expenses of these floatingbridges, no less than their superior accommodation to every other mode of crossing estuaries. has already given Mr. Rendel the opportunity of establishing several: the latest was that at Southampton, across the Itchin ferry, over which there are 12 coaches daily, and great carriage traffic, although the public have the option of crossing a fixed bridge over the same river, and only a short distance farther round.

The Lords Commissioners of the Admiralty having sanctioned the establishment of a similar bridge across Portsmouth Harbour from Portsmouth Point to Gosport Beach, and a bill is nowbefore Parliament to incorporate a company for carrying the work into effect. The great national importance of this harbour, and the well-known jealousy of the Board of Admiralty in all matters connected with its economy, furnish the best proof that these bridges, though requiring chains to be laid across the river, do not occasion the slightest impediment to the navigation or tidal currents.

Mr. Rendel stated that the chains were kept bright by the rubbing which they received on the bed of the river. The bed, consisting of mud and not of gravel, the chains only scoured, and did not perceptibly wear. The chains, which have been in use four years, have not been sensibly diminished. They had tried chilled segments-these wore the chains; they consequently returned to good grey iron. Three sets of segments are worn out in the course of a year. In reply to a question respecting the deviation of the bridge under the action of the wind and current, Mr. R. stated, that he had never known it diverge more than by its breadth, or, 50 feet; owing to the particular form of the bridge, and the small draft of water, the current had but little effect.

The usual weight of the balance boxes is five tons; but in hard weather, it is usual to add a ton more. He conceived that no comparison could possibly be instituted betwixt the relative advantages of the floating bridge and the twin boat; the latter requiring very expensive wharfs-those at Dundee, for instance, having cost upwards of 25,0007., and still there is much attention and care required in bringing the boats to their piers. But the floating bridge requires no such expensive appendages; the chains on which it works, when the wheels are in motion, becoming the most secure fastening when the engines are stopped. The chains also act

as a pilot and crew, two persons only being required in a vessel of this kind, viz. an engine-man and one on the decks to attend to the drawbridges.

Mr. Vignoles remarked, that the plan now proposed would obviate many difficulties which occurred in the case of railroads; there were many situations in which the floating bridge might be adopted with great service, and he could not refrain from expressing his admiration of the great forethought, skill, and design, which were here exhibited; at the minuteness with which the details had been studied; and, not the least, the adaptation of the balance weights for the chains; the chains not having elongated, proves of itself how completely they answered their intended purpose.

On a subsequent occasion Mr. Rendel remarked, that as the same velocity could not be acquired in the manner proposed as by a paddle-boat, the question to be considered was, as to the advantage of employing the floating bridge in preference, in particular cases. They had to consider to what width of ferry the floating bridge is applicable; what the maximum velocity; what the expense of piers for paddle-boats. The great disadvantage of paddle-boats results from the difficulty of making fast, and of getting the cargo on and off. If we take as the measure of advantage the facility afforded by the floating bridge, then its superiority is very great. But the question is one of time, as well as of accommodation. He was of opinion, that a velocity of more than eight miles could not be attained by these boats. Now if a paddle-boat could be impelled ten miles an hour, the time of landing, which would amount to ten minutes, would compensate for the increased speed. He conceived that the chain might be applied to a distance of three miles; the time of crossing and the expense of the chain were the only limits. Mr. Parkes remarked, that Mr. Rendel undervalued the advantages of his plan. In crossing the Mersey, for instance, excepting at high and low water, they had to run up or down, whereas the floating bridge would go straight across. There was great loss of time and uncertainty with the paddle-boats. They were frequently only a quarter of an hour in crossing the Mersey, but he had himself been three

quarters of an hour in crossing from Liverpool to Birkenhead. A simple beach being sufficient for landing was a great gain, whereas to get paddle-boats alongside, extensive and expensive piers are required.

NOTES AND NOTICES.

Steam Navigation to India.-Captain Sir John Ross passed through this town the other day on his return from Greenock, whither he had gone to inspect a splendid steamer, built for the company by Messrs. Scotland and Sinclair, of that town. This beautiful ship will be launched in about a month from the present date, and will be ready to sail for Calcutta direct or shortly after Christmas next, calling only at Hout's Bay, Cape of Good Hope. In extreme length the said vessel is 201 ft., in breadth 40, in depth 25, measuring 1,200, and will carry 1,500 tons, with accommodation for 150 passengers. Her name, we believe, has not yet been fixed; but, be this as it may, she will be the first of a most superior line of steamers direct to Calcutta-itself a very high achievement, which the uncertainty of the Red Sea route is daily rendering of increased moment.-Dumfries Courier.

Discovery of a New Continent.-M. Doubonzel, an officer on board the Zelle (the expedition to the South Pole), has written a letter, dated Valparaiso, March 30, confirming the details given by M. D. D'Urville. A new circumstance mentioned by him is the discovery of a great continent to the south of South Shetland. "We carefully explored and dedetermined," says that officer, "forty leagues of coast, notwithstanding the surrounding ice. This discovery is a real service to nautical and geograprical science."-Le Constitutionnel, Sept. 30.

The Royal William, which left Liverpool on her second voyage for New York on the 21st ultimo, had on board 67 cabin passengers. The amount of fares for passengers, freight, cargo, parcels and letters, considerably exceeded 3,000. She carries also with her 40 tons of the new scientific and useful invention, for which Mr. C. W. Williams, the able and enterprising manager of the City of Dublin Steam Packet Company, has lately obtained a patent. From the circumstance of each ton of this discovery being able to do the work of three of the common coal, the proprietors of the vessel have been enabled this voyage to take 50 tons of cargo, with the full complement of passengers. Description of Fuel.

Coal

Peat stone fuel

Total........

Tons. Cwt. 310 ..

Qr. ib.

14.. 1 .. 0

52..

1.. 0.. 7

Draught of water at starting. Feet. Lighter than on previous voyage.. 0 Forward

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The Railway Map of England and Wales continues on sale, in a neat wrapper, price 6d.; and on fine paper, coloured, price is.