out saliently dark, a darkness due to contrast. The line of south temperate islands, with their separate identity, was then for the first time apparent.

Mean while the history of Hesperia continued to be instructive. From having been absent in June and conspicuous in August, it returned in October to a mid-position of visibility. Vacillating as these fluctuations in appearance may seem at first sight, they were really quite consistent; for they were probably due to progressive change in the one direction, a change that was manifested first in Hesperia itself, and then in the regions round about it. From June to August, Hesperia changed from a previous blue-green, indistinguishable from its surroundings, to yellow, the parts adjacent remaining much as before. As a consequence, the peninsula stood out in marked contrast to the still deep blue-green regions by its side. Later the surroundings themselves faded, and their bleaching had the effect of once more partially obliterating Hesperia.

While Hesperia was thus getting itself noticed, the rest of the south temperate zone, as we may call it for identification's sake, was unobtrusively pursuing the same course. Whereas in June all that part of the disk comprising the two Thyle, Argyre II., and like latitudes was chiefly blue-green, by October it had become chiefly yellow. Still further south, what had been first white, then blue, then brown, turned ochre.

Certain smaller details of the change that came over the face of the dark regions at the time were as curious as they were marked. For example, the Fastigium Aryn, the tip of the triangular cape which, by jutting out from the continent, forms the forked bay called the Sabaeus Sinus, and which, because of its easy identification, has been selected for the zero meridian of Martian longitudes, began in October to undergo strange metamorphosis. On October 15 it shot out a sort of tail southward.

On the 16th this tail could be followed all the way to Deucalionis Regio, to which it made a bridge across from the continent, thus cutting the Sabaeus Sinus completely in two. After it had thus appeared, it continued visible up to the close of the observations sufficiently detailed to show it.

Another curious causeway of the same sort made its appearance in November, connecting the promontory known as Hammonis Cornu with Hellas. Both of these necks of orange-ochre were of more or less uniform breadth throughout.

The long, dark streaks that in June had joined the Syrtis Major to the polar sea had by October nearly disappeared; in their southern parts they had vanished completely, and they had very much faded in their northern ones. The same process of fading uncovered certain curious rhomboidal bright areas in the midst of the Syrtis Major.

It will be seen that the extent of these changes was enormous. Their size, indeed, was only second in importance to their character; for it will also have been noticed that the changes were all in one direction. A wholesale transformation of the blue-green regions into orange-ochre ones was in progress upon that other world.

What can explain so general and so consecutive a change in hue? Water suggests itself; for a vast transference of water from the pole to the equator might account for it. But there are facts connected with the change which seem irreconcilable with the idea of water. In the first place, Professor W. H. Pickering found that the light from the great blue-green areas showed no trace of polarization. This tended to strengthen a theory put forth by him some years ago, that the greater part of the blue-green areas are not water, but something which at such a distance would also look blue-green, namely, vegetation. Observations at Flagstaff not only confirm this, but limit the water areas still further; in fact, practically do away with them entirely. Not only do the above polariscopic tests tend to this conclusion, but so does the following observation of mine in October.

Toward the end of October, a strange, and, for observational purposes, a distressing phenomenon took place. What remained of the more southern dark regions showed a desire to vanish, so completely did those regions proceed to fade in tint throughout. This was first noticeable in the Cimmerian Sea, then