PENETRATION OF EARTH AND MASONRY. 
505 
As regards the craters made, a well-placed shell of about the size I Craters, 
have mentioned as being economical in use, viz., 200 lbs., may be 
expected to remove from 600 to 1000 cubic feet (or from 22 to 37 cubic 
yards) of soil of an average nature. 
It is necessary that I should state that the size of shell, viz., 200 lbs., Estimate of 
which I have mentioned as about the smallest economical size for work, slZ0of she11, 
taking mobility, accuracy, and effect combined, is arrived at merely as 
the result of my own observation of facts, and differs from that laid 
down (somewhat hastily, as I believe) by others who mention a much 
lighter shell. This is not a question of the mere weight of ordnance to be Weight of 
transported to the front in siege warfare (which has most to do with the account. ° 
effect of projectiles on earth and masonry). Whatever be the gun, its 
weight is but small compared with the weight of ammunition which it 
will be required to fire and which must also be brought up to the 
fighting line. Further experiment, or better still, the experience of 
actual war is needed to settle how the attack of both earth and masonry 
can be accomplished with an expenditure of the smallest weight of am¬ 
munition, with the more modern and larger howitzers and shell. 
To further economise the number of rounds required for any given information 
task it is necessary to learn something of the nature of defences Defences 
attacked, or there will not be a reasonable chance of placing the mines ™ luable * 
contained in shell in the most favourable position for effect, and a fur¬ 
ther knowledge of what effect shell are really producing is of immense 
advantage. Ordinarily the attacker has to pick up this information 
how he can from the means of observation he has at his disposal. The 
effect of projectiles in both earth and masonry, studied from a distance, 
give him a good deal to go upon. It is frequently possible for a prac¬ 
tised eye to tell the nature of the target work from the debris blown 
into the air. Earth can readily be distinguished from masonry, for 
instance, loam from clay or shingle, and concrete from brickwork, 
and that at ranges of some 3000 yards and more. If a plan of the 
defences attacked is available, it is frequently possible to estimate with 
considerable accuracy the part of the target work into which shell have 
fallen, a section of the work attacked will also aid. 
If a shell bursts low in a hollow the cloud of smoke takes an appre¬ 
ciable time to rise, while the debris, instead of being in the form of a 
Fbusteum. 
Indicating Burst in Hollow. 
Cone. 
Indicating Burst on Plane. 
cone, as it would be if the shell burst actually in sight, appears more 
in the shape of a frustrum. When the shell strikes on level unmoved 
ground the flash is almost instantly seen. Frequently objects from 
which conclusions may be drawn are blown into the air, and are very 
distinguishable against the sky. 
