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: