at O and P, which wires are shown in Fig. 2.  A spring clamp, N, Fig. 2, enables the insertion of chemically prepared or other paper, which lies against the inner side of brass rim, M, and held in place by the clamp, N. The electric sparks above spoken of pierce the strip of paper with small holes and colored marks.  These holes, etc, show the exact limits to which the pointer has traveled under pressure, and thus an indelible record is kept by the electrical indications shown upon the strip of paper.  The paper can have the pressures corresponding to gauge printed upon the same, when the holes are made prominent by holding the paper to the light, exposing an exact indication of the pressures or explosives operated with.

The gases resulting from the explosives are injurious to the gauge packings, etc., on which account the bore in gun, W, and the connecting steel plug, B, are filled with fluid.  A screw plug, U, enables the insertion of the fluid, after first pushing an elastic wad of rubber, B, or cork, in the bore near the inner wall of the gun, which wad will prevent the escape of the fluid to the interior, and be sufficiently free to prevent any interference with the pressures.  The patentee and manufacturer of this gauge is prepared to fill orders up to 50,000 lb. per square inch.  This gauge is made of the best steel, and is very compact, the weight being inside of twenty-five pounds.

The inventor has heretofore made mercury column gauges for gunpowder pressures, which were too large for direct attachment to guns, but were connected with special powder chambers to test the pressure, etc., of confined explosives.  The experience thus gained enabled the construction of the instrument here shown, which is adapted to direct attachment to the gun, making it as easy now to measure gunpowder pressures as it had been, heretofore, to measure steam pressures.  The effect of this movement is to reduce the exaggerated statement of high pressures, obtained from ordinary sporting powders; these have been accredited with pressures up to 40,000 lb. per square inch, but they only really gave 22,000 lb. by actual gauge measurement.  Artillerists and ordnance officers have, in this instrument, a true pulse of the internal pressures of the gun, of inestimable value when determining the quantity of powder and the proper weight of shot.  These are important matters in ordnance practice.

This gauge is a compact machine, designed to measure and indicate the quick pressures resulting from gunpowder explosives and the slow pressures of hydraulic force; the same mechanism used in both cases permits the ready testing and examination of gauge under hydraulic pressure, to determine its accuracy, for the more sudden pressure occasioned by the use of gunpowder.

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IMPROVED PLAITING MACHINE.