This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1895 edition. Excerpt: ... WATER I. THE POLAR CAP After air, water. If Mars be capable of supporting life, there must be water upon his surface; for, to all forms of life, water is as vital a matter as air. On the question of habitability, therefore, it becomes all-important to know whether there be water on Mars. To the solution of this inquiry, also, the planet's polar cap turns out to hold the key. For just as the fact of change in the cap proves the presence of air, so the manner of that change implies the presence of water. It not only does this; it turns out to do a deal more. For to the whole water question it appears to play the part not only of occasion but of cause. In more senses than one, it is in that great glistening white patch that our water problem takes its rise. On the 3d of June, 1894, the south polar cap stretched, almost one unbroken waste of white, over about 55 degrees of latitude. A degree on Mars measures 37 miles; consequently the cap was 2,035 miles across. Inasmuch as the inclination of the Martian equator to the plane of the Martian orbit is, according to Schiaparelli, 24 52', it must have then covered more than the whole south frigid zone of the planet. Now, to take in the full meaning of the condition of the cap at this time and of the changes that ensued, we must begin by determining the Martian time of year. This is done by fixing the dates at which the Martian pole reached its maximum tilt toward or from the Sun, and the dates at which it was not tilted either to or from, but sideways to, the Sun; the former gives us the Martian solstices, and the latter the Martian equinoxes. It thus appears that on April 7, 1894, occurred the vernal equinox of the Martian southern hemisphere, on August 31, its summer solstice, and on...