What knowledge we have of the size of the caps in degrees upon the surface of the planet at this their extreme equatorward extension has been given in the last chapter. Their aspect at the time together with what that aspect betokens was not there touched upon. With it, therefore, and the peculiarities it presents to view we shall begin our account of the caps’ annual history.
[Illustration: South Polar Cap in winter.]
When first the hemisphere, the pole of which has for half a Martian year been turned away from the sun, begins to emerge from its long hibernation, the snow-cap which covers it down even to temperate regions presents an undelimited expanse of white, the edges of which merge indistinguishably into the groundwork color of the regions round about. Of a dull opaque hue along its border, its contour is not sharp but fades off in a fleecy fringe without hard and fast line of demarcation. Such notably was the aspect of the north temperate zone in 1896 when, tilted as it then was away from us into a mere northern horizon of the planet’s limb, it showed prior to the definite recognition of the north polar cap in August of that year, and such too was the look of the disk’s southern edge both before and after the first certain detection of the southern cap in 1903 and 1905. Each was then in the depth of winter. For in Martian chronology the season corresponded in each at the time to what we know in our northern hemisphere as the latter part of February and the early part of March and the appearance of the planet’s surface in both was not unlike what we know at the same season in latitude 45°. Indeed, there is reason to suppose bad weather there then and the extreme fringe, from the pale tint it exhibited, to have been cloud rather than snow.
It is quite in keeping with what we know on earth or can conceive of elsewhere that such aspect should characterize the cap at or near the attainment of its greatest development. Whether it were not yet quite arrived at this turning-point of its career or had but slightly passed it a vagueness of outline would in either event proclaim the fact. For were the frost still depositing, the cap’s edge would show indefinite; and on the other hand had it just begun to melt, evaporation would give it an undefined edge before the melting water had gathered in sufficient quantities to be itself noticeable.