472 
THE 80-TON OUN. 
enlargement of tlie chamber has caused a slight increase of work 
realised, accompanied by a small diminution of pressure. The increase 
of energy is probably due chiefly to the additional 6 ins. of travel of 
shot gained, while the diminution of pressure arises from the more 
compact and favourable shape of the cartridge. The 1‘5-in. cubes 
still preserve their superiority. 
Turning now to rounds 36, 37, and 38, fired with 270 lb. each, 
we see that the increase of 101b. in the constant length 40 ins. has 
reduced the air space to little more than 29 cub. ins. per pound. This 
has slightly raised the pressures, and these are now equal with those 
recorded in the comparative rounds 25, 19, and 20. The velocities are 
slightly in excess in the chambered bore. 
We next come to rounds 39, 40, and 41, fired with 2801b. each. 
Here the air space is reduced nearly down to 28 ins. per pound—which 
is about the density of a rammed-up charge of R.L.Gr. powder. The 
mean pressures at once ascend, and in each case surpass those obtained 
in the comparative rounds 27, 22, and 24. An increase of velocity— 
very marked with the 1‘5-in. cubes—was also' gained. It will be 
observed that in the comparative round 24 the charge had accidentally 
been compressed to a density of 29 cub. ins. per pound; so that the 
air spaces are about equal. Here the pressures also are practically 
about equal, and we simply gain the trifling increment of 6 ft., due to 
the lengthening of the travel of the shot by 7* 75 ins. 
The increase of the pressures offered a distinct warning that the true 
road to improvement did not lie in the direction of filling up the 
chamber; and accordingly the density of 30 cub. ins. per pound was 
returned to, and retained till the conclusion of the experiment. Since 
the cartridge now protruded considerably from the chamber into the 
bore, a portion of the beneficial action of the principle was sacrificed, 
but enough remained for the purposes of preliminary experiment. 
The 290-lb. charges were fired with a density of 30 cub. ins. to the 
pound, and it will be seen that in each instance the pressures dropped 
I ton, or nearly 5 per cent., on the square inch; while the energy 
extracted from the powder rose in two cases out of three, and in each 
round the ratio of work done to pressure was increased. 
The 300-lb., charges show a similar increase in this ratio; but the 
firing was postponed on account of excessive rain, and the cartridges 
probably absorbed an unusual amount of moisture, and therefore gave 
somewhat low results, both in velocity and pressure. 
The 3 LO-lb. charges, fired under ordinary atmospheric conditions, 
with the 1*5 and l*7-in. cubes, yielded very fine ballistic results. 
Round 48 was the best ever fired up to the date of the experiment. 
An energy of 24,493 ft. tons with a maximum pressure of 23‘3 tons 
and a mean pressure in the powder-chamber of 22‘5 tons per square 
inch was better than anything yet obtained from the 80-ton gun, and 
very far beyond any result realised elsewhere. It did not appear at 
this stage desirable to continue the experiment farther in the direction 
of increase of charge, and the gun, having keen examined and found 
none the worse for its efforts, was returned to the boring machine, that 
its calibre might be again enlarged—this time to a diameter of 16 ins. 
On completion of this alteration, the bore once more became cylindrical 
