y the means above described, can be set at, say, 18,000 lb., in
which event the pointer is reduced to the minimum movement of only 2,000
lb. to register 20,000 lb.

It will be evident that much greater accuracy of measurement of maximum
pressures can be obtained by the minimum movement of the pointer, as both
the inertia and the momentum are reduced to the minimum quantity. The
subsidence of pressure resulting from explosives being about as sudden as
the creation of pressure, causes the pointer to move too rapidly for
correct ocular observation, on which account a static electric current is
employed, causing a stream of electric sparks to shoot off from the end
of the pointer, B, to the brass outer ring, M. The gauge is insulated for
that purpose by glass plate, S, which is secured concentrically to the
gauge proper and the ring, M. Binding posts for the electric wires are
provided 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