To seek a cab, to be whirled away at a gallop to the university, to burst into Marston in his citadel, required but little time. The professor was walking up and down excitedly. "It has come! All the world knows it!" he shouted as Corbett entered, and he grasped him by the hand and wrung it hardly. "What has come?" gasped the visitor. "What has come, man! All we had hoped for or dreamed of--and more! Why, look! Look for yourself!" He dragged Corbett to the eye-piece of the great telescope and made him look. What the man saw made him stagger back, overcome with an emotion which for the moment did not allow him speech. What he saw upon the surface of the planet Mars was a duplication of the glittering figures on the pampas of the South American Republic. They were in lines of glorious light, between what appeared bands of a darker hue, provided, apparently, to make them more distinct, and even at such vast distance, their effect was beautiful. And there was something more, a figure he could not comprehend at first, one not in the line of the others, but above. "What is it--that added outline?" he cried. "What is it! Look again. You'll determine quickly enough! Study it!" roared out Marston, and Corbett did as he was commanded. Its meaning flashed upon him. There, just above the representation of the right-angled triangle, shone out, clearly and distinctly, this striking figure: [Illustration: diagram] What could it mean? Ah, it required no profound mathematician, no veteran astronomer, to answer such a question! A schoolboy would be equal to the task. The man of Mars might have no physical resemblance to the man of Earth, the people of Mars might resemble our elephants or have wings, but the eternal laws of mathematics and of logic must be the same throughout all space. Two and two make four, and a straight line is the shortest distance between two points throughout the universe. And by adding this figure to the others represented, the Martians had said to the people of Earth as plainly as could have been done in written words of one of our own languages: Yes, we understand. We know that you are trying to communicate with us, or with those upon some other world. We reply to you, and we show to you that we can reason by indicating that the square of the hypothenuse of a right-angled triangle is equivalent to the sum of the squares of the other two sides. Hope to hear from you further. There was the right-angled triangle, its lines reproduced in unbroken brilliancy, and there were the added lines used in the familiar demonstration, broken at intervals to indicate their use. The famous _pons asinorum_ had become the bridge between two worlds.