THE 80-TON GUN, 
469 
As was expected, the increase of the space in which the charge was 
ignited at once caused both the velocities and pressures to drop, and 
the question was which would rise first as the charge was successively 
added to. Comparing round 10 with round 9, we see that the increase 
of space caused a loss of 10 ft. in the velocity, while the mean pressure 
dropped 4J tons. It is true that 10 lb. more powder were used, but 
this is of little consequence: as has been previously stated, the real 
criterion is the ratio of velocity (or penetration) to pressure. Increasing 
the charges of 1'5-in. powder to 2601b., and using the heavy shot, we 
see that 22,000 tons of energy are obtained, at a cost of barely 21 tons 
mean pressure. This is obviously a great improvement on round 3, 
fired with 1'7-in. cubes. At this point the brand of 1'5-in. cubes 
hitherto used in this experiment was exhausted, and another brand 
was taken. Comparing rounds 21 and 23, fired with the new brand, 
with rounds 13 and 14 with the old one, but little difference in quality 
is perceptible, -and practically the powders may be considered equal. 
The experiment was continued, and the charges were increased to 
300 lb., the space of 30 cub. ins. to the pound being preserved. With 
300 lb. the fine result of 24,100 tons energy at a cost of 22'6 tons 
mean pressure behind the shot was obtained; but a slight wave action 
was perceptible, and it became apparent that the cartridge—which 
now attained the length of 52'8 ins.—could not be much farther elon¬ 
gated without risk of setting up that inconvenient vibratory motion of 
the gas which is the hete noire of the gunner. 
Round 26 deserves special notice. It had been intended to fire 
280 lb., but by mistake an extra weighing of 23'3 lb. was placed in 
the cartridge, which was then compressed into the space allotted to the 
280-lb. charge. The powder, therefore, had barely 28 cub. ins. per 
pound in which to expand, and the remarkable energy of 24,517 ft. tons 
was realised. The mean pressure, as might be expected, was high; 
but no trace of wave action was perceptible, and the limits laid down 
by the Committee were not exceeded. Had circumstances permitted, 
it would probably have been thought advisable to have pursued the 
experiment into the complicated question of varying air spaces with 
each charge; but time pressed, and the expense of trials of this mag¬ 
nitude is too great to permit the entire elucidation of all the knotty 
points which present themselves to the enquirer during a lengthened 
experiment of so novel a character. 
Proceeding pari passu with the 1'5-in. cubes, the 1'7-in. and 2'0-in. 
powders had been fired in successively increasing charges; but a study 
of the table given above will show that they had not proved equally 
successful, and it is not necessary for me to dilate on the peculiarities 
of the series fired with them. 
At this point we appear to have reached the limit of power to be 
realised in the 15-in. calibre, even when increased by the contrivance 
of an air space of 30 cub. ins. per pound of charge. We have now to 
consider another device containing still more novelty, and destined in 
all probability to play a part of great importance in the history of 
artillery of all sizes. If we turn back to Table A, we see that round 4 
was fired with 250 lb. of 2-in. powder, rammed up, and that the 
