[Illustration:  Sketch 19.]

Here is a diagram showing how necessarily true this is.  The howitzer, lobbing its shell with a comparatively small charge, has the advantage of being able to hide behind a steep bit of ground, but on such a trajectory the range is short.  The gun in the fortress does not lob its shell, but throws it.  The course of the gun shell is much more straight.  It therefore can only hit the howitzer and its crew indirectly by exploding its shell just above them.  Until recently, the gun was master of the howitzer for three reasons:—­

First, because the largest howitzers capable of movement and of being brought up against any fortress and shifted from one place of concealment to another were so small that their range was insignificant.  Therefore the circumference on which they could be used was also a small one; their opportunities for hiding were consequently reduced; the chances of their emplacement being immediately spotted from the fortress were correspondingly high, and the big gun in the fortress was pretty certain to overwhelm the majority of them at least.  It is evident that the circumference {~GREEK SMALL LETTER ALPHA~}{~GREEK SMALL LETTER BETA~}{~GREEK SMALL LETTER GAMMA~} offers far more chances of hiding than the circumference ABC, but a still more powerful factor in favour of the new big howitzer is the practical one that at very great ranges in our climate the chances of spotting a particular place are extremely small.  Secondly, because the explosives used, even when they landed and during the short time that the howitzer remained undiscovered and unheard, were not sufficiently powerful nor, with the small howitzers then in existence, sufficiently large in amount in each shell to destroy permanent fortification.  Thirdly, because the effect of the aim is always doubtful.  You are firing at something well above yourself, and you could not tell very exactly where your howitzer shell had fallen.

[Illustration:  Sketch 20.]

What has modified all this in the last few years is—­

First, the successful bringing into the field of very large howitzers, which, though they do lob their shells, lob them over a very great distance.  The Austrians have produced howitzers of from 11 to 12 inches in calibre, which, huge as they are, can be moved about in the field and fired from any fairly steady ground; and the Germans have probably produced (though I cannot find actual proof that they have used them with effect) howitzers of more than 16 inches calibre, to be moved, presumably, only upon rails.  But 11-inch was quite enough to change all the old conditions.  It must be remembered that a gun varies as the cube of its calibre.  A 12-inch piece is not twice as powerful as a 6-inch.  It is eight times as powerful.  The howitzer could now fire from an immense distance.  The circumference on which it worked was very much larger; its opportunities for finding suitable steep cover far greater.  Its opportunities for moving, if it was endangered by being spotted, were also far greater; and the chances of the gun in the fortress knocking it out were enormously diminished.