True as the verses are of Earth, the poet could not have penned them otherwise had he meant to record the course of astronomic detection on Mars. For they sound like a presentiment of the facts. A surface thought at first to be part land, part water; the land next seen to be seamed with straits; and lastly the sea made out to be land. Such is the history of the subject, and words could not have summed it more succinctly. “Vidi ego, quod fuerat quondam solidissima tellus esse fretum” rings like Schiaparelli’s own announcement of the discovery of the ‘canals.’ Indeed, I venture to believe he would have made it had he chanced to recall the verse. So “vidi factas ex aequore terras” tells what has since been learned of the character of the seas. Of the three periods the first was that of the main or fundamental markings only. It came in with Beer and Maedler, the inaugurators of areography. That they planned and executed their survey with but a four-inch glass shows that there is always room for genius at the top of any profession and that instruments are not for everything in its instrumentality. Up to their day the reality of the planet’s features had been questioned by some people in spite of having been certainly seen and drawn by Huyghens and others. Beer and Maedler’s labors proved them permanent facts beyond the possibility of dispute. The second period was the period of the discovery of the now famous canals,—a new era in the study of Mars opened by Schiaparelli in 1877 (Map V). Unsuspicious of what he was to stumble on, he seized the then favorable opposition to make, as he put it, a geodetic survey of the planet’s surface. He hoped this undertaking feasible to the accuracy of micrometric measurement. His hopes did not belie him. He found that it was possible to measure his positions with sufficient exactness to make a skeleton map on which to embody the markings in detail—and thus to give his map vertebrate support. But in the course of his work he became aware of hitherto unrecognized ligaments connecting the seas with one another. Instead of displaying a broad unity of face the bright areas appeared to be but groundwork for streaks. The streaks traversed them in all directions, tesselating the continents into a tilework of islands. Such mosaic was not only new, but the fashion of the thing was of a new order or kind. Straits, however, Schiaparelli considered them and gave them the name _canali_, or channels. How unfamiliar and seemingly impossible the new detail was is best evidenced by the prompt and unanimous disbelief with which it was met. [Illustration: Map I. Beer and Maedler, 1840.] [Illustration: Map II. Kaiser, 1864. (From Flammarion’s _Mars_.)] [Illustration: Map III. Résumé by Flammarion, 1876. (From Flammarion’s _Mars_.)] [Illustration: Map IV. Green, 1877. (From Flammarion’s _Mars_.)]