Although the Tsar had made trips with John Castellan in the Flying Fish, he had never had quite such an aËrial experience as his trip to Greenwich. The Auriole rose vertically in the air, soared upward in a splendid spiral curve, and vanished through the thin cloud layer to the north-eastward. Twenty minutes of wonder passed like so many seconds, and Admiral Hingeston, beside whom he was standing in the conning-tower, said quietly:

"We're about there, your Majesty."

"Greenwich already," exclaimed the Tsar, pulling out his watch. "It is forty miles, and we have not been quite twenty minutes yet."

"That's about it," said the Admiral, "this craft can do her two miles a minute, and still have a good bit in hand if it came to chasing anything."

He pulled back a couple of levers as he spoke and gave a quarter turn to the wheel. The great airship took a downward slide, swung round to the right, and in a few moments she had dropped quietly to the turf of Greenwich Park alongside the Observatory.

Lennard's calculations had already reached the Astronomer Royal, and he and his chief assistant had had time to make a rapid run through them, and they had found that his figures, and especially the inexplicable change in the orbit, tallied almost exactly with observations of a possibly new comet for the last two months or so.

They were not quite prepared for the coming of an Imperial—and hostile—visitor in an airship, accompanied by the discoverer of the comet, the millionaire who owned the great telescope, and an American gentleman in the uniform of a British admiral; but those were extraordinary times, and so extraordinary happenings might be expected. The astronomer and his staff, being sober men of science, whose business was with other worlds rather than this one, accepted the situation calmly, gave their visitors lunch, talked about everything but the war, and then they all spent a pleasant and instructive afternoon in a journey through Space in search of the still invisible Celestial Invader.

When they had finished, the two sets of calculations balanced exactly—to the millionth of a degree and the thousandth of a second. At ten seconds to twelve, midnight, May the first, the comet, if not prevented by some tremendously powerful agency, would pierce the earth's atmosphere, as Lennard had predicted.

"It is a marvellous piece of work, Mr Lennard, however good an instrument you had. As an astronomer I congratulate you heartily, but as citizens of the world I hope we shall be able to congratulate you still more heartily on the results which you expect that big gun of yours to bring about."

"I'm sure I hope so," said Lennard, toying rather absently with his pencil.

"And if the cannon is not fired, and the Pittsburg one does not happen to be exactly laid, for there is a very great difference in longitude, what will be the probable results, Mr Astronomer?" asked the Tsar, upon whom the lesson of the afternoon had by no means been lost.

"If the comet is what Mr Lennard expects it to be, your Majesty," was the measured reply, "then, if this Invader is not destroyed, his predictions will be fulfilled to the letter. In other words, on the second of May there will not be a living thing left on earth."

At three minutes past ten that evening the Tsar looked into the eye-piece of the Greenwich Equatorial, and saw a double-winged yellow shape floating in the centre of the field of vision. He watched it for long minutes, listening to the soft clicking of the clockwork, which was the only sound that broke the silence. During the afternoon he had seen photographs of the comet taken every night that the weather made a clear observation possible. The series tallied exactly with what he now saw. The gradual enlargement and brightening; the ever-increasing exactness of definition, and the separation of the nucleus from the two wings. All that he had seen was as pitilessly inexorable as the figures which contained the prophecy of the world's approaching doom. He rose from his seat and said quietly, yet with a strange impressiveness:

"Gentlemen, I, for one, am satisfied and converted. What the inscrutable decrees of Providence may or may not be, we have no right to inquire; but whether this is a judgment from the Most High brought upon us by our sins, or whether it is merely an ordinary cataclysm of Nature against which we may be able to protect ourselves, does not come into the question which is in dispute amongst us. Humanity has an unquestioned right to preserve its existence as far as it is possible to do so. If it is possible to arrange for another conference at Aldershot to-morrow, I think I may say that there will be a possibility of arriving at a reasonable basis of negotiations. And now, if it is convenient, Lord Kitchener, I should like to get back to camp. Much has been given to me to think about to-night, and you know we Russians have a very sound proverb: 'Take thy thoughts to bed with thee, for the morning is wiser than the evening.'"

"That, your Majesty, has been my favourite saying ever since I knew that men had to think about work before they were able to do it properly." So spoke the man who had worked for fourteen years to win one battle, and crush a whole people at a single stroke—after which he made the best of friends with them, and loyal subjects of his Sovereign.

They took their leave of the astronomer and his staff, and a few minutes later the Auriole, still flying the flag of truce, cleared the tree-tops and rose into the serene starlit atmosphere above them.

When the airship had gained a height of a thousand feet, and was heading south-west towards Aldershot at a speed of about a hundred miles an hour, the Admiral noticed a shape not unlike that of his own vessel, on his port quarter, making almost the same direction as he was. The Tsar and Lord Kitchener were sitting one on either side of him, as he stood at the steering-wheel, as the ominous shape came into view.

"I'm afraid that's one of your Flying Fishes, your Majesty, taking news from the Continent to Aldershot. Yes, there goes her searchlight. She's found us out by now. She knows we're not one of her crowd, and so I suppose we shall have to fight her. Yes, I thought so, she means fight. She's trying to get above us, which means dropping a few of those torpedoes on us, and sending us across the edge of eternity before we know we've got there."

"You will, of course, do your duty, Admiral," replied the Tsar very quietly, but with a quick tightening of the lips. "It is a most unfortunate occurrence, but we must all take the fortune of war as it comes. I hope you will not consider my presence here for a moment. Remember that I asked myself."

"There won't be any danger to us, your Majesty," replied the Admiral, with a marked emphasis on the "us." "Still, we have too many valuable lives on board to let him get the drop on us."

As he spoke he thrust one lever on the right hand forward, and pulled another back; then he took the telephone receiver down from the wall, and said:

"See that thing? She's trying to get the drop on us. Full speed ahead: I'm going to rise. Hold on, gentlemen."

They held on. The Tsar saw the jumping searchlights, which flashed up from the little grey shape to the southward, suddenly fall away and below them. The Admiral touched the wheel with his left hand, and the Auriole sprang forward. The other tried to do the same, but she seemed to droop and fall behind. Admiral Hingeston took down the receiver again and said:

"Ready—starboard guns—now: fire!"

Of course, there was no report; only a brilliant blaze of light to the southward, and an atmospheric shock which made the Auriole shudder as she passed on her way. The Tsar looked out to the spot where the blaze of flame had burst out. The other airship had vanished.

"She has gone. That is awful," he said, with a shake in his voice.

"As I said before, I'm sorry, your Majesty," replied the Admiral, "but it had to be done. If he'd got the top side of us we should have been in as little pieces as he is now. I only hope it's John Castellan's craft. If it is it will save a lot of trouble to both sides."

The Tsar did not reply. He was too busy thinking, and so was Lord Kitchener.

That night there were divided counsels in the headquarters of the Allies at Aldershot, and the Kaiser and his colleagues went to bed between two and three in the morning without having come to anything like a definite decision. As a matter of fact, within the last few hours things had become a little too complicated to be decided upon in anything like a hurry.

While the potentates of the Alliance were almost quarrelling as to what was to be done, the Auriole paid a literally flying visit to the British positions, and then the hospitals. At Caversham, Lennard found Norah Castellan taking her turn of night duty by the bedside of Lord Westerham, who had, after all, got through his desperate ride with a couple of bullets through his right ribs, and a broken left arm; but he had got his despatches in all the same, though nearly two hours late—for which he apologised before he fainted. In one of the wards at Windsor Camp he found Auriole, also on night duty, nursing with no less anxious care the handsome young Captain of Uhlans who had taken Lord Whittinghame's car in charge in Rochester. Mrs O'Connor had got a badly-wounded Russian Vice-Admiral all to herself, and, as she modestly put it, was doing very nicely with him.

Meanwhile the news of the truce was proclaimed, and the opposing millions laid themselves down to rest with the thankful certainty that it would not be broken for at least a night and a day by the whistle of the life-hunting bullet or the screaming roar and heart-shaking crash of the big shell which came from some invisible point five or six miles away. In view of this a pleasant little dinner-party was arranged for at the Parmenter Palace at eight the next evening. There would be no carriages. The coming and parting guests would do their coming and going in airships. Mr Parmenter expressed the opinion that, under the circumstances, this would be at once safer and more convenient.

But before that dinner-party broke up, the world had something very different from feasting and merrymaking, or even invasion and military conquest or defeat, to think of.

The result of Lennard's telegrams and cables had been that every powerful telescope in the civilised world had been turned upon that distant region of the fields of Space out of which the Celestial Invader was rushing at a speed of thousands of miles a minute to that awful trysting-place, at which it and the planet Terra were to meet and embrace in the fiery union of death.

From every observatory, from Greenwich to Arequipa, and from Pike's Peak to Melbourne, came practically identical messages, which, in their combined sense, came to this:

"Lennard's figures absolutely correct. Collision with comet apparently inevitable. Consequences incalculable."