on the locomotive in every part of its course, and its distance from a stationary engine can never exceed half the distance between any two engines.*

In the atmospheric railway two methods only present themselves for modifying the speed, or stopping the train, namely, by the application of brakes, which must always involve some degree of inconvenience, if not of actual danger, when the motion is rapid, or by admitting air in front of the piston, which would often cause considerable

loss of power. In the pneumatic locomo

tive the speed may be modified, or the train stopped with the same ease as in common locomotives, simply by regulating or stopping the passage of air to the cylinders. The motion can also be reversed with equal fcaility,

The greatly diminished risk of collision gives a value to the atmospheric railway, which, by the proposed pneumatic system, cannot be obtained without modifying some of its peculiar advantages; still the risks of collision which it may involve are much less than with common locomotives. To take a case of the greatest danger: suppose two trains to be approaching each other on a single pneumatic line, it is evident that the stationary engines on each side will have a double quantity of air to exhaust from the pipe; consequently the rarefaction will be less complete, and the motion of both trains proportionately slower. This will neces sarily diminish the danger from collision, and the reduced speed of each train would indicate the probable vicinity of the other, and the consequent necessity for increased vigilance. A provision might be made to cause, either automatically or by hand, a free admission of air to the pipe in case of serious accident to a train; but as this would affect the entire line, it would be desirable to obviate all danger of collision at that particular part, while the remainder of the line should remain effective, This can be attained by having valves in the pipe near the stationary engines, which should be closed whenever the vacuum gauges indicated an unusual admission of air. The tube would thus be, for the time, divided into sections, but without the disadvantage of the atmospheric section valves, inasmuch as no piston has to pass them, and the accident to the train would affect only that one particular section; while the continued depression of the vacuum gauge would telegraph the accident at the neighbouring station,

In the atmospheric railway the propulsion

*Thus, if the stationary engines on the atmospheric railway are three miles apart, this distance may be doubled by the pneumatic locomotive system, and the engines may be placed six miles apart with equal effect.

How

does not depend on the adhesion of the wheels to the surface on which they roll, and the inclination of the road is limited only by the tractive power exerted by the piston. This is, perhaps, one of the most striking advantages of the system, but it is restricted to certain limits by mechanical and physical difficulties. To take advantage of the benefits which this construction of railway presents by diminishing the necessity for easy gradients, the surface of the line will, in most instances, present a series of undulations, regulated on the one hand by the surface level on which the railway is laid, and on the other by the tractive power which can be exerted by the piston. ever perfect the casting, and accurate the fitting of the joints, the interior of the pipe cannot be supposed to be truly cylindrical, or to present a very smooth surface, and the fitting of the piston cannot therefore be so accurate as to prevent much loss from leakage, without incurring, on the other hand, a considerable loss of power from excessive friction. The loss of effect from leakage will, of course, be inversely as the velocity of the piston; and as, in ascending a steep inclined plane, the piston must move at a comparatively slow rate to obtain a maximum effect of traction, the loss of power from leakage will be in proportion to the inclination. Moreover, with pipes of moderate diameter, the utmost power of the piston could not overcome more than a certain inclination with heavy trains, and steep descents would be inadmissible, although, in descending a steep inclination, the atmosphere might perhaps be excluded from the back of the piston to such an extent as to check the force of gravitation.

It has been stated that the pneumatic engine must work expansively to obtain a maximum economy of power, but on an ascent it would be advantageous to work at full pressure, thus increasing the tractive force at a temporary expense of power, which, however, would be compensated by the reduced admission of air to the cylinders during the corresponding descent or succeeding level. If requisite, the engines might easily be made to exhaust on a steep descent, and the force of gravitation would thus be partially counteracted, while, at the same time, it is made available as an equivalent source of power.

It has been stated in some descriptions of the atmospheric railway, that no delay takes place in performing any given journey, by making a moderate number of stops for a short time each, because, after the train has overcome its "vis inertiæ," it will move forward at whatever rate the air in the pipe is being withdrawn by the pump; and although the motion of the train must be

the required shape, and is placed in a wagon or frame of shelves, which frame travels along a railway. When the frame is filled, it is run into the close chamber and left there, subject to the artificial current and temperature, until the clay is sufficiently dry for burning. The time required for this process will vary according to the nature of the substance and form it is put into, and on the temperature and current to which it is subject. A temperature of about 80° Faht., and a current of about six feet per second, have been found most advantageous for that purpose; but these may be increased, taking care always that they be not too high, so as to crack the clay in drying. The close chamber may be heated by flues at the bottom and sides, or by hot water and steam pipes, or by the admission of heated air through small apertures, cold air being let into the chamber at other apertures, so as to mix with and regulate the temperature of the heated air. The warm atmosphere of the chamber may be set in motion by the draft of a chimney, or fanner, worked by steam, horse, or other power. Or the current may be created by injecting or withdrawing the air by pumps, the mechanical detail for that purpose being well understood.

The patentee declares that he does not claim the exclusive use of the constructions, arrangements, and adaptations hereinbefore described, except when the same are used in connection with, and for the purposes of his said invention of drying plastic substances in a close chamber at an artificial temperature, and under a current of air, as above described.

Pa

WILLIAM NORTH, OF STANGATE, SURREY, SLATER, for improvements in covering roofs and flats of buildings with slate. tent dated October 5, 1843; Specification enrolled April 5, 1844.

These improvements consist in using battens of slate, combined with slate covers for roofs and flats of buildings, whereby the slabs of slate used in covering roofs, &c., are not fixed to the rafter or joists, as is usual, and the joints of the slates are prevented from becoming defective. The battens of slate are dropped into notches or recesses formed in the rafters or joists, and the ends of the slabs of slate rest on the battens, and are imbedded in putty. The battens or fillets are connected by screws and nuts to the slabs, and these screws and nuts also combine the slabs and fillets to the slate battens. The whole covering of slate is thus bound and fixed together without being fixed to the rafters or joists.

The claim is, to combining the use of slate

battens with slate coverings for roofs and flats of buildings.

The Great Gun of the "Princeton" Steamer.-The following history of the large gun which, by its bursting, was the cause of the dreadful catastrophe on board the United States' steamer Princeton, is given in the report of the Naval Court of Inquiry appointed to investigate the causes of the accident:

In the year 1839 Captain Stockton, being in England, his attention was attracted to the extraordinary and important improvements which had recently been introduced into the manufacture of large masses of wrought iron, as a substitute for cast iron, for objects which required a combination of strength and adhesiveness, or toughness. Large shafts for steam-engines had been thus fabricated, which experience had demonstrated to be superior in those qualities which were desirable, to the same articles manufactured of cast-iron. These circumstances appear to have led Captain Stockton to consider the question how far the same material might be employed in the construction of cannon of large calibre. He appears to have been animated by motives the most patriotic, stimulated by the laudable desire of being himself instrumental in promoting the honour of his country, and of elevating that branch of the service with which he was personally connected. After much deliberation and several consultations, with calculations furnished from the same quarter, Captain Stockton determined upon the construction of a gun of the proposed dimension, for the purpose of testing the opinions of scientific men by the results of experi ence. A cannon was accordingly made at the Mersey works, of Yorkshire iron, which, being approved, was shipped to the United States. Having been properly prepared for the purpose, this gun was carried to Sandy Hook, and subjected to what was deemed the proper test. After the first firing, preparations were made to mount the gun. In doing this a crack was perceived opposite the chamber, which induced Captain Stockton to have the breech strengthened by putting bands around it. These bands are represented as being three and-a-half inches in thickness. With this additional strength given to the defective part of the gun, the experiments were renewed, and the result was a decided conviction upon the minds of all connected with them, that, in general, the anticipations of Captain Stockton were perfectly realized; and, secondly, that if a gun of this construction should yield to the force of the trial, it would be by a simple opening, and not, as in cast-iron, a violent disruption and scattering of the fragments. The success of these experiments was such as to decide Captain Stockton forthwith to direct the construction of another gun of a similar character, to be made of American iron, which is usually regarded as superior in strength and tenacity to the English iron. This second gun (the same which exploded on board the Princeton) was constructed with a chamber similar to that of the first gun, with an additional thickness of 12 inches at the breech-a difference, even if the metal were only of equal goodness, far more than sufficient to compensate for the bands by which the first had been fortified. Application was made to Colonel Bomford, of the Ordnance Department of the Army, who, it is well known, has been professionally occupied in experimenting upon guns of a large calibre, and his opinion requested as to the proper proof to which such a gun ought to be subjected. The new gun constructed by order of Captain Stockton exceeded in dimensions and weight, consequently, should also have surpassed in strength, that contemplated by Colonel Bomford, they being of the same calibre, and the proof to which this cannon was subjected was much more severe than what was proposed as sufficient by that experienced officer."