PENETRATION OP EARTH AND MASONRY. 
503 
by the first shell, so that one shell falling in the right place and power¬ 
ful enough to make the size of crater required does a given task more 
economically than two shell, the craters of which are collectively equal 
in area to that of the large shell. 
There is, of course, a practical limit to the size of shell, leaving Poetical 
mobility out of account. Whether large or small shell are dealt with, ofsheii. 3120 
before an effective hit can be obtained, howitzers have to be ranged 
for each task they are called on to perform by a process which must 
waste a certain number of shell, and probably about the same number 
of rounds would be required for each for this purpose. A small 
howitzer begins to become effective at a comparatively early economical 
period. 
Practically a shell weighing about 200 lbs. has so far been found to 200 -ib. shell, 
give the most economical results, and to be capable of being used with 
tolerable ease iu siege work. If this is really the economical size no 
smaller shell should be employed for attack. 
The quality of the earth has a very considerable influence on the Nature of 
effect of projectiles. The more closely the molecules of soil stick earth * 
together the greater the effect obtained by shell. Damp earth, for 
instance, is easier to breach than dry. Clay, and especially moist 
tenacious clay, gives a maximum of effect. Enormous craters are for¬ 
med by shell which explode at the right spot, and the soil is thrown 
in large lumps to a considerable distance, leaving a clean breach. 
Sand and shingle are the forms of earth most fatal to artillery effect. 
The former, however, does not offer nearly so effective a resistance to 
breaching when it is wet as when it is dry, the grains having then a 
tendency to adhere. Shingle is always difficult to blow away and wet 
does not seem to make much difference to it. The detached molecules 
of dry sand and shingle offer so little combined resistance that a burst¬ 
ing charge cannot blow them away far enough to make a good crater. 
Iron rails, and similar loose iron protection and gabions, used in Loose iron 
conjunction with earth, often turn a shell aside and waste it, and may gablons > &c * 
even break it up, but they have not been found of much advantage on 
the whole, for when a shell chances to get under or through them they 
tend to greatly enhance the effect of a bursting charge, which blows 
them and all over them high in the air. Large rails and pieces of iron 
become then almost as dangerous to defenders as the shell itself. 
When masonry is the target high explosive shell should be most 
effective, their great rending power shaking and destroying the struc¬ 
ture more than similar shell filled with gunpowder. Masonry is 
generally presented in the form of a vertical target, and the object of 
the attacker is to form a breach with a ramp to it. There is then no 
need for the greater distributive effect obtained by a slow explosive 
like gunpowder. All that is wanted is to tumble down the masonry, 
with what it supports, to form the ramp. 
Masonry escarps are generally protected by ditches with covering Covering 
mounds of some sort; and their destruction is attempted either by I " naa " a 
high angle fire, with the intention of clearing the obstruction in front; 
by blowing away the covering mass and so obtaining a clear line of 
fire ; or by a combination of the two. 
