Then there is the question of hostilities between aircraft, to which several references have been made. Here, again, theory has to take the place of practice. It is perfectly certain that, as machines cross from their own lines to those of the enemy, engagements will take place between them and hostile craft—which will seek to check them in their aerial spying. [Illustration: TRAVELLING WORKSHOP. Photo, M. Branger. In the French manœuvres, a completely-equipped aeroplane repair shop, in the form of a motor-wagon, followed the military airmen as they moved from point to point. One of these invaluable "ateliers" is pictured above.] That special fighting machines will be built is practically certain, also; and it is probable that, in wars of the future, engagements between these aerial opponents will precede reconnoitring work. How such flights in the air will end it is, however, difficult to predict. If some form of light explosive shell is fired, one well-placed shot will probably wreck a machine, or render it unmanageable. An aerial duel promises to be over quickly. The skill will, no doubt, lie in getting in the first shot, and in making that an accurate one. Although, in some respects, the future is obscure, there is, upon one important point, most definite data to proceed upon. This is that the aeroplane is an instrument which will entirely change military reconnaissance. "We are in the presence of a new and formidable science that will revolutionise warfare." So spoke Colonel Seely, Parliamentary Under-Secretary of State for War, at a special gathering of the Aeronautical Society on 18th December, 1911. At the moment, all other problems are subservient to this: whatever its destructive powers may prove to be, and whatever may be the result of well-directed artillery-fire upon aerial scouts, no great nation can afford to neglect this new weapon. If any country dare to do so, and others go ahead, then the nation which lags behind will stand in imminent peril in war-time. It may have a fine army, or a great fleet, but if it does not possess aeroplanes, and its opponent has them, it will be at a very serious disadvantage. This point is no longer a matter of any supposition. It has been proved, beyond all question. It was, as a matter of fact, proved in 1910, and it was proved again in 1911. It needs no further proof. The aeroplane has shown what it can do, not in easy experiments, but under rigorous test conditions. If our War Office buys a few more foreign machines, and makes a small stir at our military school on Salisbury Plain, that cannot be regarded as any serious step towards making up our leeway. The whole problem needs taking in hand in a way that England has not yet done.