One great beauty of this device, when used for exhibition purpose, was the fact that if it failed to work, the aviator retained his seat as comfortably as if nothing had happened. As a life-saver, of course, this peculiarity had little or no value, inasmuch as a flyer in distress would be lost if the parachute failed to pull him out of his seat.

Before each of his experiments, Irving had tested the "sky-umbrella" with a dummy heavier than himself in order to be certain that there was no danger of ripping the silken cloth. A slight tear produced by the strain on the parachute while he was being dragged from his seat might become larger during the descent and cause him to fall with sufficient shock to seriously injure or kill him. This was really the only considerable danger in the whole performance, but it was one that needed to be guarded against very carefully.

Up flew the aeroplane with graceful sweep and joined the flock of two score other "night birds" that were starting out on a raid. The flight to the front lines was quickly made and without incident of note. In fact, not an enemy plane arose in the air to oppose the attacking squadron until the leading flyers were directly over No Man's Land, brilliantly illuminated with the fireworks of battle, and then something happened that must have thrilled every aviator who witnessed it, accustomed though he was almost daily to thrills that make the life of a soldier on land or a Jackie of the navy seem like a tame existence in comparison.

Suddenly there was an upheaval of earth almost directly below him, followed by another and another in quick succession; then a regular concert of upheavals in almost a straight line, and a very long line at that, evidently, even to a pair of eyes looking down from a great height in the air. There was a magnitude in the scene that could not be mistaken, although the ridge of land that was visible only a few moments before looked like little more than an elongated anthill.

"My goodness!" Irving exclaimed, though the noise of the motor and the propeller and the rush of air about him made it impossible for him to hear himself. "My goodness! they've actually blown up Vimy Ridge."

The machine swept on with the flock of mechanical war-birds, on over No Man's Land and past the enemy front lines. Meanwhile Irving gazed down, fascinated by the scene far, far below. It was a scene of the most diminutive dwarfs now. The trenches looked like little more than pen scratches on a dim-colored sheet, certainly not more than chalk marks, of no particular color, on a "faded blackboard." And the people--the soldiers! Yes, he could see them now, in large numbers. They looked like ants--no, let's not understate it,--they looked like mice, small mice, however; and they arose--on the Canadian side--out of the "chalk marks" and dashed forward, a very short distance, it seemed, only a few inches or feet at the most, but they chopped off their steps so short that they appeared just to creep along. Irving was astonished at the clearness of the night scene under the battle's illumination.

But they made it finally, up the side of the hill, if indeed any hill remained, and into the crater--Irving could see an altered condition following the trinitrotoluol explosions, and concluded that there must be a long, a very long, crater--miles of it--in the place of Vimy Ridge. They were cheering like mad--Irving knew it, though he could not hear a voice. Yes, into the crater they went, a myriad of insects, or wee animals,--they had possession of it--the enemy seemed not to offer any resistance. They were whipped, thoroughly--they knew it. Tons and tons of high explosive planted under that ridge had blown it to the sky.

"No, it didn't, either," Irving mused with a smile of "altitude amusement." "It was only a flash in the pan. Not a pebble came half as high as we are, and the sky is hundreds of miles--umph! How much higher is it? My! if the world could only get up here and look at itself, I wonder if things wouldn't go a little differently. No, I'm afraid not! There'd always be somebody then trying to grab a bigger slice of the moon than he's entitled to.

"But what am I thinking about? My head must be getting giddy. That won't do a bit. I'm on very serious business. The bombing planes are hovering over the rear line trenches and dropping their flower-pots on 'em. The anti-aircraft guns are getting busy, too. There went one right ahead of us. They're getting our range. And here comes a fleet of German planes to meet us. Well, it won't be safe to wait very long, and it won't be fair to my pilot. Just as soon as we get well beyond that third trench there, I'll take my plunge."

Irving set himself fixedly as if about to make a mighty leap or a pistol-shot start in a foot race. As a matter of fact, he was going to do nothing of the kind. Only a sort of passive effort was required of him, and yet, his nerves had never been more tense. He put his right hand on the release lever and leaned forward, his left hand almost touching the pilot, and looked down over the side of the car, then off toward the approaching enemy squadron, then at the camouflaged positions of the belching anti-aircraft guns, then here and there at the exploding shells in the midst of the invading fleet, then back again at the ground scene directly below.