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CHAPTER XVIII.

RETROSPECT. FURTHER NOTES ON THE N-SQUARE LAW. PARTIAL CONCENTRATION. AIR RAIDS: VALUE OF NUMBERS. STRATEGIC EMPLOYMENT OF AIR POWER.

§ 114. Scope and Limitations of the Present Work. In the present work it has been the author's endeavour to give an account of the existing position and the future possibilities of aircraft in its Military and Naval usage; in so far at least as present day knowledge permits of a reasoned forecast. There remains considerable ground however, to cover which no attempt has been made; thus we have the whole subject of aeronautical photography in its present relation on which much might have been said; also many quasi-technical questions connected with aeronautical signalling, by wireless and otherwise, might legitimately have been introduced. Beyond this the whole subject of aeroplane design, as affected by the various kinds of usage in warfare, is itself one of vast and intricate interest,—this has been barely touched upon. In these matters considerations of secrecy have necessitated reticence; the author had obviously to steer clear of much that was known to him on the subject of our aeronautical equipment, and to confine himself for his facts to such material as was common property before the date of hostilities, or had become so since. As an indication that the position has not been without difficulty, it may perhaps be mentioned that (contrary to what might be expected) it is not always permissible to reproduce matter which has

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