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twice as often as that of the latter It may be mentioned as a diminution of the advantages of large wheels, that in order to preserve the requisite strength, they are necessarily cumbersome, and too heavy for use. But could this objection be obviated, a limit must be assigned for the size of carriage wheels, which is that the axle should not be above the level of the draught, or breast of the horse. Indeed, in practice, is found expedient to place the point of draught somewhat lower than the middle of the horse's breast. According to Dr. Gregory, a power which moves a sliding body along a horizontal plane, acts with the greatest advantage, as far as friction is concerned, when the line of direction makes an angle of about 18 degrees with the plane. M. Deparcieux states from experiments with carriages, that the angle made by the trace with a horizontal line, should be one of 14 or 15 degrees.

Broad Wheels. Much has been written on the comparative utility of wheels, which have a broad, or a narrow rim. The advocates for the former kind of wheels, urge, that they pass more easily over ruts and holes, and sink to a smaller depth in soft and sandy roads. Hence, while narrow rimmed wheels render a road uneven, by causing deep and narrow ruts, the broad constantly act as rollers upon the surface. The principal objections to broad wheels are, their greater weight, greater expense, and the greater number of obstacles which they meet in their

passage.

Form of Wheels. Were roads in all cases level and smooth, the proper form of wheels would obviously be an exact cylinder, with their spokes set precisely parallel to the same plane. But experience has proved the advantage of wheels which are somewhat conical or dishing. In this case, when, by reason of an inequality in the road, the weight of the carriage is chiefly thrown on one wheel, the spokes on the under side of that wheel becoming more nearly vertical, are better able to sustain the increased pressure. A further advantage presented by this form of wheels is, that the circumference being farther from the body of the carriage, less mud is thrown upon it, and the passengers are less annoyed. The chief objection to this form of the wheel, is presented in an increase of friction, it being found that the degree of lateral motion and friction increases in proportion, as the wheel is conical or dishing.

MODE OF ATTACHING A HORSE. In cities, it is the general custom, growing probably out of the circumscribed limits of wharves, which draymen much frequent, and the narrowness of the alleys through which they pass, to harness draught horses before each other, in a single line. This, is however, a bad mode of attaching horses, since only the shaft horse has an advantageous line of draft. The other horses draw nearly in a horizontal line, and of course to a disadvantage. Besides, the foremost horses, drawing at the ends of the shaft, do not act directly upon the load, but expend a part of their force in a vertical pressure upon the back of the shaft horse. A better mode of attaching horses, is to make them work abreast-since they are then in the same line of traction, and are equally near to the load.

RAIL ROADS. By the term rail road, is understood a road formed by laying distinct tracks of timber, iron, or stone, for wheel carriages to run upon. They are of modern invention. The earliest rail roads were con

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structed of wood only. Stone is sometimes employed, but iron only should be used where durability is expected.

Iron rail roads are of three kinds-the Edge rail-the Tram road-and the Single rail.

In the edge rail way, the rails, as indicated by the term, are laid with the edge upwards, and the carriage is retained upon them by a flange, or projecting edge, attached to the wheels instead of the rail. Tram roads are flat rails, usually made of cast iron, with an elevated edge or flange on one side, to guide the wheels of carriages in their path. Tram rails are weaker than edge rails, and it is sometimes necessary to strengthen them with ribs underneath. In the single rail way, the carriage consists of two boxes suspended on each side of the rail by an iron frame, and having two wheels placed one before the other.

Where the amount of travel is very great, the rail road is double, one set of tracks being designed for carriages moving in each direction. A single road, however, is generally sufficient, if it be provided with double places, called sidelings, for carriages to pass each other at convenient distances.

Horses are commonly employed for drawing loads upon rail ways, and it is estimated that a horse will draw eight times as much upon a rail way, as upon a common road. Within a few years, steam engines have been employed for propelling carriages, especially in England, by means of which, the most surprising velocity is with perfect security attained.

Rail Roads in the United States have not been attempted to any considerable extent: yet several are in contemplation, and it can scarcely be doubted, but that in a few years this mode of conveyance will be extensively adopted, and in preference to canals.

In England, rude tram roads, constructed of wood, were in use nearly two centuries ago; but the present improved mode of constructing and laying the rails with iron is of very recent date. The first rail road established by act of parliament was the Stockton and Darlington, a distance of twenty-five miles. The act was obtained in 1823, and the road was opened in September, 1825. It consists of a single line of rails, with sidelings every quarter of a mile, for carriages to pass each other. It is principally used for the conveyance of coals and travellers.

Still more recently, the important and stupendous undertaking of constructing a rail road from Liverpool to Manchester, a distance of something more than thirty miles has been completed. The interest excited in this rail way has arisen chiefly from the excavation of a tunnel, some account of which must be interesting to our readers.

This tunnel commences at Wapping, near the Queen's Dock, and extends under the town of Liverpool, a distance of yards, or rather more than a mile and a quarter. It was constructed in seven or eight separate lengths, each communicating with the surface by means of perpendicular shafts. The opening at Wapping is by cutting 22 feet deep, and 46 wide. The whole length of the tunnel is white-washed; and lighted by gas, and the effect produced is very singular and picturesque; but the atmosphere is cold and chill, and the vapor is at times so thick, that the mere spectator of this monument of human la

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bor and ingenuity will generally be satisfied with one visit, and not be tempted to repeat it. On the sides of the tunnel, at short distances are placed lettered boards, for the purpose of informing the visiter what part of the town he is then under. The distance from the roof to the surface of the ground above varies from 5 to 70 feet. The rails used on this road are made of forged iron, in lengths of five yards each, and weigh 35 lbs. per yard. Every three feet, the rails rest on blocks of stone, let into the ground, containing each nearly four cubic feet. Into each block, two holes six inches deep and one inch in diameter are drilled; into these are driven oak plugs, and the cast iron chairs or pedestals into which the rails are immediately fitted, are firmly spiked down to the plugs, forming a structure of great solidity and strength. On the embankments, where the road may be expected to subside a little, the rails are laid on oak sleepers. For eighteen miles of the road, the rails are placed on stone blocks, and for the other thirteen on sleepers. The double line of rails for the carriages are laid down with mathemati cal correctness, and consist of four equidistant rails, four feet eight inches apart, about two inches in breadth, and rising about an inch above the surface. In the formation of the railway there have been dug out of the different excavations, upwards of three millions of cubic yards of stone, clay, and soil, and the weight of the double lines of rail laid down is more than 4000 tons.

For the purpose of giving to our readers some conception of a steam carriage, designed to be used either on a rail road, or on the common high way, our engraver has copied the model of such a carriage, not long since exhibited at London.

A, Water Gestern-B, the Boiler-C, Steering Wheel, with the Conductor D, Steel Frame which carries the Boiler-E, the curved Steam Pipe, to supply the engines-F, Hand Pump and Pipe to fill the BoilerG, Safety Valve-H, Notice Cocks-I, Eduction Pipe to take the steam from the Engine to the Chimney-K, the Crank-L, the Pan for the Cylinders.

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The subject of Rail Roads is exciting much interest at the present time in the United States. Several short ones are already constructed; one of greater length, extending from Albany to Schenectady, is completed, and others still are in contemplation, and will, doubtless, in due time be completed.

STEAM ENGINE.-The steam engine, now extensively employed as an aid to locomotion on rail roads and in steam boats, as well as to assist in the mechanic arts, is generally attributed to the Marquis of Worces ter as the inventor; but the perfecting of it belongs to James Watt, a native of Greenock, in Scotland. The improvements made in the construction of the steam engine, within the last five and twenty years, are too numerous to be here described. We must content ourselves with giving our readers a brief description and a representation of a modern steam engine, which may of course be constructed of any required power, and applied to any purpose.

In the following representation, A represents a wrought iron boiler, about three parts filled with water; the bottom is considerably, and the sides a little concave, that it may receive more fully the force of the flame circulating around it. Boilers are usually of an oblong form, and are furnished with a part that takes off, in order that a person may get in to clean them when needful; they have also a valve called the safety valve, opening upwards, which is loaded so that the Steam escapes when it is stronger than the engine requires, and, if retained, would hazard the bursting of a boiler. It is not uncommon to have two boilers, one of which is a reserve, that the engine may not be stopped, when the other requires repair.

B, is an apparatus for regulating the fire, and giving action to a bell, which regulates the quantity of coals and time of firing.

C, the steam pipe from the boiler A, to the valve I.

D, the steam cylinder, generally called only "the cylinder;" it is connected at the top and bottom with the valve I.

E, the piston which, by its connecting rod e, gives motion to the beam F, the other end of which by another connecting rod, gives motion to the heavy fly wheel G, by means of a crank. Thus, after the engine has begun to work, its power is accumulated in the fly wheel, and may be disposed of at the pleasure of the machinist.

H, an eccentric circle on the axle of the fly wheel G; it gives motion by its levers, to the valve I.

I, a co slide valve, which requires no packing to make it steamtight, as there is always a vacuum under it; it answers the purpose of the four valves used in douce power engines, and from the simplicity of its construction, when well made auf, is not liable to get out of order. K, the steam admission valve and lever, connected with a governor, which regulates the speed of the engine.

L, the cylinder of the discharging pump, for extracting the water and uncondensed vapor from the condensor M.

N, a small cistern, filled with water. Into this cistern enters a pipe from the condensor M, the top of which pipe is covered with a valve, which is called the blow valve, sometimes the shifting valve. Through