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