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( 15 ) and not sticking fast in the operation. Through this clearance the powder gases will rush, and will rapidly erode the surface of the bore. Something must be provided to prevent this. Something was provided, called a gas-check. This consisted of a disc of copper attached to the base of the projectile, and of such diameter that it could be passed down the bore from the muzzle, but so constructed, that on firing, the pressure of the powder gases should swell it out, and cause it to fill up the bore and the rifle grooves themselves.

This may be the right time to give you an instance of the power of powder gases in eroding steel.

I have here a steel cylinder 5½ inches long, and having through its axis a cylindrical hole of a little over a fifth of an inch in diameter. This cylinder is to be screwed into a vessel containing 13 lbs. of powder, and the hole forms the only outlet from the vessel. On the powder being fired, the whole 13 lbs. of gases rush out through this hole, with the result shown by a corresponding cylinder, which has been used in an experiment. This result is, that the hole which was, before the firing, so small as only to admit a pen-holder, is now by the one passage of the gases of 13 lbs. of powder increased to such a diameter as to admit my forefinger.

When tested by weighing, it will be found that with the quality of steel of which this sample was composed, nearly ¾ lb. of steel has been removed.

This instance will give some idea of the effect in the bore of a gun, of a rush of gas past the projectile.

A further objection to muzzle-loading was this, that although the gas-check might thoroughly fit the bore when it was expanded, it did not steady the projectile as a driving band does, and thus the extreme accuracy of the shooting was impaired.

The remedy for all this is no doubt breech loading. With breech-loading guns the length of barrel may be indefinitely increased without adding to the difficulty of inserting the charge; the cartridge not having to pass down the bore may