When the planet’s differences of color were first observed, the reddish-yellow portion was supposed to be land, and the areas of varying bluish-green and gray were thought to be the waters of the ever-changing seas. A little after the middle of the last century some keen eyes saw a few streaks or markings of some sort across the land areas, and in 1877 a close study of the planet by an eminent Italian astronomer, Schiaparelli, brought to his view many greenish streaks, all directed toward the so-called seas, and sometimes seeming to intersect there. In publishing this discovery Schiaparelli called these streaks _canalli_, which is properly translated “channels,” but appeared in English as “canals.” Since “canal” with us means artificially constructed waterways, the discovery became at once one of universal interest; for artificial waterways mean human beings to construct them, and it was an intensely interesting thing to know that Mars was probably inhabited with beings at least somewhat after our own kind. It was a new world. The little planet became a topic of absorbing interest to all of us. And thus began the controversy over the habitability of Mars, and the meaning of its surface features, in which astronomers, seeking only for the truth, have taken a much more dignified part than they have sometimes been more or less sensationally represented as doing. The discoverer of the so-called canals himself believed them to be natural waterways cutting through the land after the manner of our straits and channels, and had very little to say in explanation of them. But his work gave a new impetus to the study of this little brother world of ours. In our own country the observatory at Flagstaff is the one the best known among those doing research work on Mars; but it is not the only one. The observatory there is finely situated in the thin, clear atmosphere of Arizona, the mechanical facilities for such work are good, and there seems no doubt that there are there some observers who have eyes that were made for seeing. All that the sharp vision of Schiaparelli saw has been seen there, and much more. Several hundred canals have been discovered, and at certain seasons many of them have appeared to become double. Their courses have been followed, and their appearances and disappearances have been watched. Somewhere near six hundred of them have been mapped. According to these maps, the canals seem to be laid out with a geometrical precision such as nature is not likely to follow; they run across some regions that were formerly supposed to be water, and they have points of convergence every here and there, forming at such points large dark areas.