been reached by any other means. To this extent it may be said to have invented or originated new duties not overlapping those of the older Arms. It is equally true that, so far, it has not seriously encroached by its employment on the duties of the other Arms—it has not replaced cavalry in any measurable degree, neither has aeroplane bombardment been found effective as a .substitute for gun-fire. There is, however, one important consideration that should prevent us from drawing too hasty a conclusion from these facts. The number of aeroplanes at present in service (as already pointed out) is small in comparison with the size of the armies in the field, so much so that we can only afford to employ our aeroplanes for work for which they are pre-eminently suited; that is to say, to perform mainly those duties which cannot be done by other means.
The position is perhaps most easily illustrated by means of an analogy. Some years ago, when the milling-machine was first introduced into our general engineering shops, it was not an uncommon thing to see one such machine installed (more or less experimentally) in a large machine-shop alongside some hundred or so lathes and other machine-tools; such a machine usually had allotted to it a number of odd jobs that could not be done conveniently or cheaply on any other machine. Any superficial observer asked to report on the innovation might have been tempted to say, "By means of this new machine work may be undertaken which could not, commercially speaking, be done previously; it does not, however, show any promise of replacing to any extent the older forms of machine-tool, and can only be regarded as useful for doing the special work for which it has shown itself of unique value." Such a view would, we know, have been utterly wrong. The milling-machine to-day is doing a multitude of jobs formerly looked upon
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