endurance of any gun is thus to be ascertained, the regular powder-charges, or any less quantity deemed desirable, may be used, the enlargements being recorded after each discharge.. A 9-pounder bore gun made of my metal but reduced 12 inches in diameter has been so tested, and has had 18 full charges of 14 lbs. fired from it. The expansion in the bore is now .1903 inches, and that of the outside diameter is .0485 inches. Van Nostrand's Eng. Mag.

VELOCITY OF CANNON BALLS.

At the late ordnance experiments at Fortress Monroe, the initial velocity of cannon balls was tested by a very delicate instrument, "the Schultz Chromoscope." The apparatus, which is operated by electricity, is thus described: two wire targets are placed, one about 20 yards from the gun, and the second about the same distance further on. These are connected by a fine insulated wire with the instrument, which is about 400 yards in the rear of the ordnance. The instrument is adjusted on a plan similar to an electro-balistic machine. When the shot is fired, it cuts the wire in the first target, and then that of the second, the instant each wire is severed being recorded by the instrument. The interval of time occupied by the ball in passing from one target to the other furnishes the data for obtaining the initial velocity of the shot.

SYSTEM OF MONCRIEFF.

It consists of three parts: 1st. The mechanical principle of the gun-carriages. 2d. The form, internal and external, of the batteries. 3d. The selection of ground for placing the batteries, and the arrangement for working to the greatest effect; or, in other words, the tactics of defence for positions where. the system is employed. The principle on which the carriage is constructed is the first and most important part of the new system, because on it depends the possibility of applying the other parts. This principle may be shortly stated as that of utilizing the force of the recoil in order to lower the whole gun below the level of the crest of the parapet, so that it can be loaded out of sight and out of exposure, while retaining enough of the force above referred to to bring the gun up again into the firing or fighting position. This principle belongs to all the carriages; but the forms of these carriages, as well as the method in which this principle is applied, vary in each case. For instance, in siege guns, where weight is an element of importance, the recoil is not met by counterpoise. With heavy garrison guns, on the other hand, which when once mounted remain permanent in their positions, there is no objection to weight. In that case, therefore, the force of gravity is used to stop the recoil, because it is a force always the same, easily managed, and not likely to go wrong; and as these carriages are employed for the most powerful guns, it is a great advantage to have the most simple means of working them. It has been already

mentioned that the principal difficulty arose from the enormous and hitherto destructive force of the recoil of powerful guns; and here I shall point out the manner in which that difficulty is overcome. That part of the carriage which is called the elevator may be spoken of and treated as a lever; this lever has the gun-carriage axle at the end of the power arm, and the centre of gravity of the counter-weight at the end of the weight-arm, there being between them a moving fulcrum. When the gun is in firing position, the fulcrum on which this lever rests is almost coincident with the centre of gravity of the counter-weight, and when the gun is fired the elevators roll on the platform, and consequently. the fulcrum, or point of support, travels away from the end of the weight-arm towards the end of the power-arm; or, in other words, it passes from the counter-weight towards the gun. Notice the important result of this arrangement. When the gun is fired, its axle passes backward on the upper or flat part of a cycloid. It is free to recoil, and no strain is put upon any part of the structure, because the counter-weight commences its motion at a very low velocity. As the recoil goes on, however, the case changes completely, for the moving fulcrum travels towards the gun, making the weight-arm longer and longer every inch it travels. Thus the resistance to the recoil, least at first, goes on in an increasing progression as the gun descends, and at the end of the recoil it is seized by a self-acting pawl or clutch. The recoil takes place without any jar, without any sudden strain, and its force is retained under the control of the detachment to bring up the gun to the firing position at any moment they may choose to release it. The recoil, moreover, however violent at first, does not put injurious horizontal strain on the platform. In my experiments at Edinburgh with a 32-pounder, I found that so slight was the vibration on the platform caused by firing, that the common rails on which the elevators rolled in that experiment, and which were only secured in the slightest manner, did not move from their position, nor even when heavy charges or double charges were used did sand and dust fall off their curved tops. Nostrand's Eclectic Engineering.

GUNPOWDER HAMMER AND PILE-DRIVER.

At a late meeting of the Franklin Institute, there was exhibited a gunpowder hammer, invented and constructed by Mr. Thomas Shaw, of Philadelphia. In describing the apparatus, Mr. Shaw said: -

"A weight or hammer is suspended between vertical guides, and is provided on its under-side with a plunger that fits into the bore of a cylinder held between the same guides beneath the hammer. It is intended that the cylinder should rest upon the object to be pounded, and that the hammer should be held by a pawl, which catches into a rack secured parallel with the guides. The pawl is released from the rack by a cord connected with the same, whereupon the hammer is allowed to fall. A small amount of

powder is placed in the cylinder; the hammer, falling, forces its plunger into the cylinder, compressing and heating the air, which explodes the powder, forcing the hammer up again, and forcing the cylinder downward, with an effect fully 8 times as great as from the falling of the weight alone. At the top of the guideframe is suspended a plunger, which fits into a cylinder in the top of the hammer, thus making an air-chamber to receive the blow of the hammer, in case of an over-charge of powder, that no danger may result to the machine. The model which was exhibited on this occasion had a ram of about 3 pounds' weight, and a fall of 8 feet. The charge employed was half a grain of white gunpowder, made of chlorate of potash, ferrocyanide of potassium, and sugar. With a larger instrument, whose ram weighed 73 pounds, with a fall of 20 feet, the charge was 14 grains of the same powder. A pile placed under this, and driven one quarter inch at a stroke by the fall of the ram, without the use of powder, was driven two inches at each stroke when the powder was used, and after being driven, with a square end, into hard ground, to a depth of 4 feet, showed no splitting or injury to its head.". Journal of the Franklin Institute.

AMMONIA POWDER.

The following account of a new explosive material appears in the "Kolnische Zeitung," May 19, which gives the MilitörWochen-blatt as its authority: "It is now some time since the proprietors of the Nora-Gyttorn Powder Mills obtained a patent in Sweden for the discovery of the so-called 'ammonia powder,' a substance which has hitherto been only employed in a few miningdistricts, but which otherwise seems wholly unknown. We are, therefore, fully justified in calling attention to the particular properties of this new explosive material. During the short time that it has been employed, it has won the approval, not only of the proprietors of mines, but also of the working miners themselves. Its explosive force may be compared to that of nitro-glycerine, and, consequently, far surpasses that of dynamite. It cannot be exploded by a flame or by sparks, and the explosion is effected by a heavy blow from a hammer. Blast-holes loaded with this powder are exploded by means of a powerful cap, or, better, by means of a cartridge containing common powder, for this forms a more reliable exploder. Miners who have been obliged to give up the use of nitro-glycerine, on account of the danger connected with this powerful explosive agent, have a most satisfactory substitute in the ammonia powder, as the danger of using it is so small that it surpasses in safety every other blasting material. One of the useful and important properties of this new powder is, that it does not require heating in cold weather, whilst nitroglycerine and dynamite must first of all be warmed, and this has been the cause of many accidents. The price of ammonia powder is the same as that of dynamite." The same paper further adds: 66 'According to information we have received, ammonia

66

powder was discovered by the chemist Norrbin." The German Building News" contains extracts from a report of the Prussian architect, Steenke, who makes the following remarks upon the safety of ammonia powder: "Experiments were made by fastening a lamp to a pendulum, which was caused to oscillate; gunpowder, gun-cotton, nitro-glycerine, and dynamite all took fire as the flame passed over them, but the ammonia powder did not begin to burn till it had been touched by the flame 20 times. In making experiments upon the force of the blow required to explode it, it was found that, with the apparatus employed, where the fall of a weight from 4 feet to 5 feet would explode gunpowder, nitro-glycerine only required 13 feet to 2 feet, dynamite 24 feet to 3 feet fall, whilst a fall of from 12 feet to 15 feet was necessary to cause the explosion of the ammonia powder.

PROCESS FOR THE PRESERVATION OF THE BOTTOM OF IRON

SHIPS.

A writer in the Comptes Rendus of July 26, 1869, says: "The iron actually employed in maritime construction is nearly always of an inferior quality, and presents a very great heterogeneity. From that cause foci of electric action exist which, provoking the decomposition of water or saline matter that it contains, lead to a prompt deterioration of the shell; the points attacked are then the parts left vacant by clusters of mollusks and weeds which clog the passage of the ship. The problem proposed to us, and which we believe to have solved, is to prevent this oxidation, the first cause of the clusters. In our system the ship is transformed to a kind of a vast pile of buckets; reservoirs in zinc are placed, under the form of tubes or boxes, on the interior sides. These tubes, in perfect communication with the iron of the ship, instead of bolts, rivets, or other instruments, are filled with seawater that is renewed every day. Plates of zinc between windows circulate in the interior of the ship, and hoop the different parts with the tubes or reservoirs. In the course of oxidation, the zinc charges itself with negative fluid, which it transmits by electricity to the iron; the shell becomes then like an immense electrode charged with this fluid. We thought at first that the iron, recovered, so to speak, with an envelope of negative fluid, ought to take, by this means, a certain electric polarity, and thus avoid the action of the electro-negative bodies contained in the air or the ocean; the negative fluid ought to flow out in a continuous manner into the water, and the positive fluid of the liquid to dissipate little by little into the humid air, and thus independently of the particular currents establish themselves in the interior of the boxes between the liquid and the iron bolts which fasten the reservoirs to the ship. Whether the electric communication was imperfect, whether the flow of the positive fluid into the air was insufficient, the carrier-boats of this kind of preparation have presented only a half success; thus the interior has been well

preserved, but the exterior was not slow in presenting traces of oxidation. We then continued the action of the reservoirs by a small plate of zinc, applied to the exterior of the shell, in electric communication with the reservoirs, and with its inferior part plunged into the sea.

"Some experiments made in this condition, for more than a year, have given us a complete success; some boats, plunged since the end of December, 1868, in a pond formed by some old salt-works, and where the water of the ocean is renewed at every tide, have been preserved until to-day, without presenting the least spot of oxidation. Every time that a part of the system was found to be altered, by wear or by accident, some sensible traces of rust appeared, and then disappeared after the preparation was renewed. Many boats placed in the same circumstances, but without preparation, have been perforated successively during this time. Some of these boats were scoured with acid before being submitted to this experiment; the others, immersed immediately after their departure from the work-shop, presented at the time of their putting in water numerous spots of rust, which all disappeared in the first 8 days of their immersion. To avoid the employment of the electrodes of zinc, we plunged one of the extremities of a copper wire, covered with gutta-percha, in the liquid of the reservoirs, and the other in the sea; but in this case, the results have been less satisfactory."-Comptes Rendus, July 26, 1869.

MAKING FOUNDATIONS IN MARSHES.

A new process of making foundations for bridges in marshy soils has been recently used on a branch line of the Charentes Railway Company, in France. This line crosses a peat valley to the junction of two small rivers. The thickness of peat was so great that any attempt to reach the solid ground would have been very expensive. In order to obtain cheaply a good support for the bridge two large masses of ballast accurately rammed were made on each bank of the river, and a third one on the peninsula between the two. The slopes of these heaps were pitched with dry stones, for preventing the sand from being washed away by the rains or by the floods in the rivers. Over the ballast a timber platform is laid; this platform carries the girders of the bridge, which has two spans of about 60 feet each. When some sinking down takes place, the girders are easily kept to the proper level by packing the ballast under the timber platform; this packing is made by the plate layers with their ordinary tools. This simple and cheap process has succeeded quite well. The same difficulty was overcome by a different plan on an ordinary road near Algiers. This road crosses a peaty plain nearly one mile broad; the floods and elasticity of the ground prevented the formation of an embankment. The road was to be carried over a viaduct across the valley, but the foundations of this viaduct presented serious difficulties, the thickness of peat or of compressible ground being nearly 80 feet. It was quite