"Then Professor Lowell announced his great conception, which has given rise to so much controversy, and has also been much misunderstood and misrepresented. "Briefly, his conclusions were as follows:--'Science teaches that a small planet will become cool and develop life much sooner than a large one. Similarly a small iron casting will become cool in a few days, whilst a large one will be many weeks or even months in cooling. A small planet will also develop more rapidly, and reach its final stage when it will be incapable of supporting life, very long before a larger planet like our earth will have reached that stage. Applying this to Mars, a much smaller planet than our earth, it is scientifically reasoned that Mars has passed through nearly all its stages and is approaching its last. It has lost much of its atmosphere, all its large bodies of water, such as oceans or seas, and, as regards the land, that has become levelled by erosion, and about five-eighths of the whole area has become desert. "'Science also shows that in such circumstances rain would cease to fall over the larger part of the planet, but the water vapour in the air would be carried by natural circulatory currents of air to the polar regions, and there deposited in the form of snow or hoarfrost, thus forming a large snow-cap at the north pole in one season of the year, and a still larger snow-cap at the south pole in the opposite portion of the year. "'These snow-caps would begin to melt in the spring as soon as the tilt of the planet brought the pole to the position where the sun would take effect, and would continue during the early summer. As there is no permanent glaciation on a planet which has lost its water, the snow-cap would melt to a very large extent, and the resultant water must go somewhere. "'The inhabitants of the planet could not exist without water, and their land would become entirely desert unless supplied with moisture. It will, therefore, be seen that the only thing possible, as a means of self-preservation, would be for them to make channels to carry the water in the most economical way from the poles to the parts where it was needed. Unless they found a means of doing this death stared them in the face. What greater incentive could there be!' "This is what Professor Lowell is convinced has actually been accomplished upon Mars, with the result that there is a network of canals all over the planet by which water is conveyed from each pole and carried across from one hemisphere into the other. The lines seen show where the canals are, but not the canals themselves, because they are too narrow to be seen. The lines really are broad bands of vegetation irrigated by the canals which run through them, hence the seasonal changes which have been noted in their colour.