It may be worth while to revert for a moment to the distinction drawn in a preceding paragraph between the pusher propeller and the tractor which revolved in front of the aviator and of his machine gun. It would seem almost incredible that two heavy blades of hard wood revolving at a speed not less that twelve hundred times a minute, a speed so rapid that their passage in front of the eyes of the aviator interfered in no way with his vision, should not have blocked a stream of bullets falling from a gun at the rate of more than six hundred a minute. Nevertheless it was claimed during the earlier days of the war that these bullets were not appreciably diverted by the whirling propellers nor were the latter apparently injured by the missiles. The latter assertion, however, must have been to some extent disproved because it came about that the propellers of the later machines were rimmed with a thin coating of steel lest the blades be cut by the bullets. But the amazing ability of modern science to cope with what seemed to be an insoluble problem was demonstrated by the invention of a device light and compact enough to be carried in an airplane, which applied to the machine gun and timed in accordance with the revolutions of the propeller so synchronized the shots with those revolutions that the stream of lead passed between the whirling blades never once striking. The machine was entirely automatic, requiring no attention on the part of the operator after the gun was once started on its discharge. This device was originally used by the Germans who applied it to their Fokker machines. It was claimed for it that by doing away with the wastage caused by the diversion of the course of bullets, which struck the revolving propellers, it actually saved for effective use about thirty per cent. of the ammunition employed. As the amount of ammunition which can be carried by an airplane is rigidly limited this gave to the appliance a positive value.
[Illustration: The Terror that Flieth by Night.
Painting by William J. Wilson.]
Reference has been made to the extraordinary immunity of flying airplanes to the attacks of anti-aircraft guns. The number of wounds they could sustain without being brought to earth was amazing. Grahame-White tells of a comparison made in one of the airdromes of the wounds sustained by the machines after a day's hard scouting and fighting. One was found to have been hit no less than thirty-seven times. Curiously enough the man who navigated it escaped unscathed. Wounds in the wings are harmless. But the puncture of the fuel tank almost certainly means an explosion and the death of the aviator in the flame thousands of feet in the air. During an air battle before Arras, a British aviator encountered this fate. When his tank was struck and the fusillage, or body, of his machine burst into flames, he knew that he was lost. By no possibility could he reach the ground before he should be burned to death. A neighbouring aviator flying not far from him told the story afterwards:
Jack was not in the thick of this fight [said he]. He was rather on the outskirts striving to get in when I suddenly saw his whole machine enveloped in a sheet of flame. Instantly he turned towards the nearest German and made at him with the obvious intention of running him down and carrying him to earth in the same cloud of fire. The man thus threatened, twisted and turned in a vain effort to escape the red terror bearing down upon him. But suffering acutely as he must have been, Jack followed his every move until the two machines crashed, and whirling over and over each other like two birds in an aërial combat fell to earth and to destruction. They landed inside the German lines so we heard no more about them. But we could see the smoke from the burning débris for some time.
