It was a lovely night from his point of view; clear, cool and almost cloudless. The young moon was just rising to the eastward, and as he looked up at that portion of the south-western sky from which the Celestial Invader was approaching he could almost persuade himself that he saw a dim ghostly shape of the Spectre from Space. But when he got to the telescope the Spectre was no longer there. The field of the great reflector was blank, save for the few far-away star-mists, and here and there a dimly-distant star, already familiar to him through many nights of watching. What had happened? Had some catastrophe occurred in the outer realms of Space in which some other world had been involved in fiery ruin, or had the comet been dragged away from its orbit by the attraction of one of those dead suns, those derelicts of Creation which, dark and silent, drift for age after age through the trackless ocean of Immensity? There was no cooler-headed man alive than Gilbert Lennard when it came to a matter of his own profession and yet the world did not hold a more frightened man than he was when he went to re-adjust the machinery which regulated the movement of the great telescope, and so began his search for the lost comet all over again. One thing only was certain--that the slightest swerve from its course might make the comet harmless and send it flying through Space millions of miles away from the earth, or bring the threatening catastrophe nearer by an unknown number of days and hours. And that was the problem, here, alone, and in the silence of the night, he had to solve. The great gun at Bolton and the other at Pittsburg might by this time be useless, or, worse still, they might not be ready in time. It was curious that, even face to face with such a terrific crisis, he had enough human vanity left to shape a half regret that his calculations would almost certainly be falsified. That, however, was only the sensation of a moment. He ran rapidly over his previous calculations, did about fifteen minutes very hard thinking, and in thirty more he had found the comet. There it was: a few degrees more to the northward, and more inclined to the plane of the earth's orbit; brighter, and therefore nearer; and now the question was, by how much? Confronted with this problem, the man and the lover disappeared, and only the mathematician and the calculating machine remained. He made his notes and went to his desk. The next three hours passed without any consciousness of existence save the slow ticking of the astronomical clock which governed the mechanism of the telescope. The rest was merely figures and formulae, which might amount to the death-sentence of the human race or to an indefinite reprieve.