It was a fine clear night. The sky was cloudless and of a deep dark blue, which revealed the highest heavens and the silvery lustre of the Milky Way. The great belt of Orion shone conspicuously in the east, and Sirius blazed a living gem more to the south. I looked for Mars, and soon found him farther to the north, a large red star, amongst the white of the encircling constellations. Professor Gazen was quite alone in his observatory when I arrived, and busily engaged in writing or computing at his desk. "I hope I'm not disturbing you," said I, as we shook hands; "I know that you astronomers must work when the fine night cometh." "Don't mention it," he replied cordially; "I'm observing one of the nebulas just now, but it won't be in sight for a long time yet." "What about this mysterious light on Mars. Have you seen anything of it?" Gazen laughed. "I have not," said he, "though I did look the other night." "You believe that something of the kind has been seen?" "Oh, certainly. The Nice Observatory, of which Monsieur Perrotin is director, has one of the finest telescopes in existence, and Monsieur Javelle is well-known for his careful work." "How do you account for it?" "The light is not outside the disc," responded Gazen, "else I should ascribe it to a small comet. It may be due to an aurora in Mars as a writer in _Nature_ has suggested, or to a range of snowy Alps, or even to a bright cloud, reflecting the sunrise. Possibly the Martians have seen the forest fires in America, and started a rival illumination." "What strikes you as the likeliest of these notions?" "Mountain peaks catching the sunshine." "Might it not be the glare of a city, or a powerful search-light--in short, a signal?" "Oh dear, no," exclaimed the astronomer, smiling incredulously. "The idea of signalling has got into people's heads through the outcry raised about it some time ago, when Mars was in 'opposition' and near the earth. I suppose you are thinking of the plan for raising and lowering the lights of London to attract the notice of the Martians?" "No; I believe I told you of the singular experience I had some five or six years ago with an old astronomer, who thought he had established an optical telegraph to Mars?" "Oh, yes, I remember now. Ah, that poor old chap was insane. Like the astronomer in _Rasselas_, he had brooded so long in solitude over his visionary idea that he had come to imagine it a reality." "Might there not be some truth in his notion? Perhaps he was only a little before his time." Gazen shook his head. "You see," he replied, "Mars is a much older planet than ours. In winter the Arctic snows extend to within forty degrees of the equator, and the climate must be very cold. If human beings ever existed on it they must have died out long ago, or sunk to the condition of the Eskimo."