THE ROYAL ARTILLERY INSTITUTION. 
73 
producing a practicable breach. The most unfavourable case, as re¬ 
garded the smallness of the charges, happened at Breach No.. 10. Only 
O’25 metre of the height of the escarp could be seen from the battery. 
Short rifled 24-prs. were used. The distance was 760 metres, and 
there were fired— 
120 shot with a charge of 0-675 k.g. and 10° elevation 
211 . « 0-835 „ . 8° „ 
8 „ „ 2-5 . . 2^° „ 
Of the 339 shots fired 258 struck the parapet or scarp, and a 
practicable breach, 4 metres wide, with a slope of 34°, was formed. 
The line of fire met the scarp at an angle of 86°. The latter had a 
thickness of 2*4 metres, and was built of brick. The fort was con¬ 
structed between the years 1810 and 1836. 
The angles of descent may be taken to have been somewhat over 1° 
greater than the angles of elevation.' We have no information as to the 
initial and final velocities, but the latter were probably about 145 metres 
with 0*675 k.g., and about 160 metres with 0*835. With a charge of 
•0*675 the hollow shot, 24 k.g. in weight, penetrated to a depth of 
from 0*35 to 0*40 metres in the brickwork. 
The first of the two methods of breaching mentioned above—viz., by 
battering the scarp from the top downwards—seems in every sense the 
more rational; because the masses of masonry which first fall become 
covered with the earth that subsequently rolls down, and the formation 
of a practicable breach is thereby materially assisted. If the height, 
of the upper half of the scarp to be breached were inconsiderable, the 
employment of different charges would appear to be impracticable. 
The resulting vertical dispersion would, moreover, render unnecessary 
any change of the point of impact in a vertical direction. 
Further experiments must first be undertaken as to how far (with 
different calibres) the final -velocity may be reduced and the angle of 
descent increased, in order to demolish masonry of various capabilities 
of resistance sufficiently to produce a practicable breach without dis¬ 
proportionate expenditure of ammunition. In this respect the experi¬ 
ments carried on at Grraudenz in 1873 were not sufficiently decisive. 
Instead of firing with the short 15 c.m. gun, as was intended, and 
with an oblique line of fire (60°) at 2500 metres, and with a charge of 
1*5 k.g., by which an angle of descent of 15° and a final velocity of 
208 metres would have been attained, the breaching had, owing to local 
circumstances, to be effected at 1050 metres, with 1*2 k.g. (final velocity 
204 metres), whence resulted an angle of descent of 6° 45', while an 
oblique line of fire of 57° 42' was adopted. 
Although, by this means, the normal component of the striking velo¬ 
city remained the same as would have been the case with the originally 
intended distance of 2500 metres, the other conditions were materially 
altered, especially as regarded the probability of striking. - * 
* With, the Austrian short 15c.ru. B.L. gun, and a charge of 1*6 k.g., the 50 per cent, vertical 
and lateral spread at 2500 metres amounts to 9 and 3'1 metres respectively, and with 1*2 k.g. 
at 1056 metres to only 2 metres and 1 metre, 
