suggested the transference of power to a distance, by the rarefaction of air in pipes, by means of suitable machinery. His experiments, however, were unsuccessful.

In the year 1810 Mr. Medhurst, engineer, of Denmark-street, Soho, published an account of "A new method of conveying goods and letters by air," followed in 1812 by "some calculations and remarks tending to prove the practicability of the scheme." "These publications," says Mr. Medhurst, "met with that indifference and contempt, which usually attend all attempts to deviate so widely from established customs." Nothing daunted, however, in 1827 Mr. Medhurst published a tract of 34 pages, entitled "A new system of inland conveyance for goods and passengers." In this work Mr. Medhurst sets forth two plans, the one consisting of a canal 6 feet high and 5 feet wide, within which suitable carriages were proposed to be propelled upon stone or iron railways, by alternately injecting or exhausting air, A second plan consisted in employing a small tube, within which a piston was made to traverse, communicating in an air-tight manner through the tube, with the carriages placed externally upon a pair of rails, between which the air-tube was laid. A third ⚫ modification consisted in employing the large canal for the transmission of goods, and also communicating the moving power to carriages for the conveyance of passengers placed externally above.

In 1824 a patent was taken out by Mr. Vallance for a mode of employing atmospheric pressure for locomotion. Like Mr. Medhurst, he proposed to form an air-tight tunnel the whole length of the railway, and large enough for the train of carriages to travel inside it. The tunnel being provided with an air-pump, and exhausted on one side, the pressure of the atmosphere acting upon a piston attached to the foremost carriage, was expected to propel the train forward. The impracticability of this plan must be appa rent to all, as, independently of the immense expense of forming an air-tight tunnel of these dimensions for the whole length of the line, the inconvenience of travelling in it, for any long distance, would altogether preclude its use. In 1834 a Mr. Pinkus attempted to obviate these de

87

fects, by adopting Mr. Medhurst's second plan of a smaller tunnel. He proposed to employ pipes like common gutter pipes, 40 inches in diameter; and he took out a patent for covering the lateral opening in these pipes with a rope. The covering of rope, he expected, would make the pipes air-tight enough, to allow a sufficient vacuum being obtained in the tunnel to draw a train of carriages on the outside. A second patent was taken out by Mr. Pinkus, in 1836, altering his system to a vacuum locomotive engine, and varying the covering of the lateral openings; but neither of these plans have been carried into execution, from its being found impossible to cover the lateral opening sufficiently air-tight. These difficulties have been at length surmounted by Mr. Clegg, who has succeeded in rendering the power of the atmosphere available for locomotion, with a degree of economy and perfection, even beyond his most sanguine expectations. We attended at Wormholt Scrubbs, on Monday last, to witness some trials, on an experimental line, half a mile long, which has been laid down by Messrs. Clegg and Samuda. The gradient is a rise of 1 in 120 about half way, and 1 in 115 for the remainder. A continuous line of cast-iron pipes, 9 inches in diameter, put together with deep socket joints, is laid between the rails; the inside of this pipe is not bored, but is lined with a coat of pressed tallow, of an inch thick, which lubricates and lessens the friction of the piston which traverses within the tube. There is an opening all along the upper surface of the pipe about 1 inch wide. This opening is closed by a valve extending the whole length of the line, formed of leather, riveted between two pieces of iron, the lower piece exactly filling the aperture, and making up the circle of the pipe, while the upper piece is wider than the opening, serving to prevent the external air from forcing the leather into the pipe, when a vacuum is formed within it. As the mode of constructing and closing this continuous valve, constitutes the chief peculiarity and most striking feature of Mr. Clegg's invention, we extract the following description of it from his specification:—

"My improvements consist in a method of constructing and working valves in com bination with machinery. These valves work on a hinge of leather, or other flexible ma

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terial, which is practically air-tight, (similar to the valves commonly used in air pumps,) the extremity or edge of these valves is caused to fall into a trough containing a composition of bees-wax and tallow, or beeswax and oil, or any substance or composition, of substances which is solid at the temperature of the atmosphere, and becomes fluid when heated a few degrees above it. After the valve is closed, and its extremity is laying in the trough, the tallow is heated sufficiently to seal up or cement together the fracture round the edge or edges of the valve, which the previous opening of the valve had caused, and then the heat being removed, the tallow again becomes hard, and forms an air-tight joint or cement between the extremity of the valve and the trough; when it is requisite to open the valve, it is done by lifting it out of the tallow, with or without the application of heat, and the beforenamed process of sealing it, or rendering it air-tight, is repeated every time it is closed. This combination of valves, with machinery, is made in the application of these valves to railways, or other purposes by a line of partially exhausted pipes for the purposes of obtaining a direct tractive force to move weights, either on the railway or otherwise.

"This I effect by laying down a continuous length of pipe containing a lateral slit or opening its whole length; a piston is made to travel in this pipe, by exhausting or drawing out the air from the pipe on one side of the piston, and allowing free access to the atmosphere on the other side of it; an arm from this piston passes through the lateral opening to attach to the carriages on the railway, and draws them along with it. The whole of this lateral opening is covered

by the valve before described, and that part of it, through which the arm passes is lifted to allow it to pass, and also for the admission of air to the piston, by means of an apparatus connected to the arm; the carriage to which this arm is attached, we call the driving carriage; to the hinder part of this carriage a long heater is attached, which is drawn along by it upon the tallow contained in the trough, and reseals the valve ready for the next train, which repeats the operations above described. At certain distances which are regulated by the nature of the road, steam engines and air pumps, or other apparatus are fixed for exhausting the pipes and at a short distance beyond the connexion from the engine to the pipe, valves are placed closing the end of one length, or section of pipe, and the beginning of the next, between which, a space is left for stopping the trains if required; these valves also divide the pipe into suitable lengths to be exhausted by each apparatus,

or close to the end, where it is not required to be continued, as on acclivities where the carriages will run by their own gravity, thus every section of pipe is enclosed at the two ends, by these valves, and is exhausted by its own steam engine and apparatus ; these valves, which I call the separating valves, are opened by the driving carriage to allow the piston to pass, and are closed after the train has passed.

"If the trains are required to be started as frequently as possible, the engines are employed constantly exhausting the pipe, but if a longer period than is necessary to exhaust the pipe be required to elapse between starting the trains, the engines are employed in the interval to exhaust large vessels or receivers, which, when the train starts are opened to the pipe, to assist to obtain the vacuum therein, and to maintain it until the train has passed."

The construction of the valve will be rendered apparent, by reference to the accompanying engravings:-Figure 1. shows a section of the valve when closed, and figure 2, when opened. A A is a section of the cast-iron vacuum tube, B is the leather valve strengthened above and below with iron, and hermetically sealed by the composition C. D is a protecting cover, formed of thin plates of iron, in lengths of about 5 feet, hinged, with leather, for protecting the valve from rain, snow, &c. The end of each plate underlaps the end of the next, in the direction of the piston's motion, thus insuring the lifting of each in succession.

In the present instance the air-pump used to exhaust the pipe is 37 inches diameter, and 224 inches stroke, worked by a 16-horse power condensing steamengine. The vacuum was raised 18 inches of mercury, in 1 to 2 minutes; two gauges were fixed at the two ends of the line, and no difference was perceptible in the time at which they indicated the same degree of vacuum.

We have now before us tabular results of the experiments made on the Birmingham, Bristol, and Thames Junction Line, on the 11th, 15th, and 29th insts. In several of these instances, the airpump, making 42 strokes per minute, and the mercury standing at 18 inches, two carriages, with a gross load of 8 tons, was propelled at a speed of 22+ miles per hour. There were four experiments on the 29th instant; in two of them the velocity was 30 miles an hour-in one case 36, and in the other 40 miles per hour

the loads carried being 8 ton 2 cwt., and 5 ton 13 cwt.

The maximum velocity is not obtained on this line, in consequence of the shortness of the distance; the tables show a constant, though not an uniform, accumulation of speed. The want of uniformity is attributed, 1stly, to the variation in the gradient from 1 in 120, to 1 in 115; and, 2ndly, to irregularity in the speed of the air-pump, as the boiler does not generate sufficient steam to supply the engine, and its speed is, consequently, diminishing towards the close of each trip.

Some of the most striking advantages claimed for this construction of railway, are the following:

1st. In comparison with the locomotive-engine system, the entire absence of all unavailable weight.

2nd. In comparison with the stationary-engine system, the absence of the

weight and friction of the rope; in lieu of this there is merely the friction of the piston, &c., travelling through the pipes.

3rd. As the speed of a train, upon this system, depends entirely on the velocity with which the air is removed from before the piston, any velocity may be obtained by increasing the power of the stationary engines; and as two trains can never receive power in the same section of pipe at one time, no collision can ever take place.

4th. From the increased facility of ascending steep gradients, a large saving is effected in the first cost of a road; but a more material saving is effected annually in working on this system, as the expense of fixed engines (of the power required) is very considerably less than the expense of locomotive power, and nearly the whole cost of maintaining the way is avoided.

90

SIMPLE AND ECONOMICAL BARO

METER.

an article invented by me about two years and a half ago, which is, doubtless, less expensive and more compact than the present one. Wishing to furnish a model of a steam-engine with a barometer, and one of the usual form being too cumbersome, I endeavoured to find a substitute, and this was the result of my labours. I obtained a glass pipe from Bristol, the cost of which was eight-pence, the cock about one shilling more; so a good barometer may be had for the sum of thirty-pence, while Mr. Bedwell's, probably, costs as many shillings, and I dont think is quite so effective as mine, in consequence of the unequal rate of the fall of the mercury, owing to the form of the bulb which receives it, thereby rendering necessary the graduation of the tube. By experiment mine is so simple, as to require no explanation. The dotted line shows the level of the mercury when at rest. It may have any range. Four inches is sufficient for any engine that ought to be working. Perhaps the scale should have an additional range of an inch or two upwards (say to 36!), for Messrs. Peterson, Hall & Co. I remain, Sir,

Yours respectfully,
MOMUS.

Chacewater, June 6, 1840.

Sir,-Having seen in your journal for May an engraving of an article, termed Bedwell's patent barometer, I beg leave to submit, to the notice of your readers

DAMPIER'S PATENT GEOMETRIC BA

LANCE.

If the public are not supplied at the present time with a perfect balance-one which shall relieve all posterity from any further care about the matter-it will not be either from any paucity of designs for the purpose, or any doubt on the part of the respective inventors of most of them that they have happened on just the thing. The engravings on our next page represent one of the latest of this numerous tribe. It rests its claims to public preference on being self-adjusting, possessing great durability and simplicity, and denoting with instantaneous precision the weight applied to it, without calculation or adjustment. "In the ordinary scale," the proprietors remark, "amultiplicity of weights are used, whilst, in the Geometric Balance,' one weight only is required, which, having been stamped by the proper authorities, forms the basis on which the scale is founded."

The principle, they further remark, "upon which the 'Geometric Balance' is constructed being purely mathematical, renders it equally applicable to weigh ing the smallest particles, as well as the inost bulky packages; and, in all cases, with undeviating accuracy; it is also free from those objections to which instruments acting by a spring, or other internal machinery, are always liable by change of temperature and continual use."

Fig. 1 represents a balance of this description on a large scale, adapted to shipping and other commercial pur

poses. Fig. 2 the same on a small scale, suitable for letters.

The article is certainly very handsomely got up, and answers, for all common purposes, exceedingly well, though, we must confess, the geometry of the thingits "purely mathematical principle❞— rather eludes our search. Neither do we see that anything is gained, in point of accuracy, by the substitution of the circular plate for a straight lever and quadrant though doubtless, it may be thereby (especially when in or molu) rendered a much more ornamental article of furniture for the library or drawing-room table.