water would be converted into steam on Mars. So low a boiling-point would raise the relative amount of aqueous vapor held in suspension by the air at any temperature. At about 127° the air would be saturated, and even at lower temperatures much more of it would evaporate and load the surrounding air than happens at similar temperatures on Earth. Thus at the heels of similarity treads contrast.
We may now go on to some phenomena of the Martian atmosphere of a more specific character.
II. CLOUDS
Although no case of obscuration has been seen at Flagstaff this summer, certain parts of the planet’s disk have appeared unaccountably bright at certain times. That these are not storm-clouds, like those which, by a wave-like process of generation, travel across the American continent, for example, is shown by the fact that they do not travel, but are local fixtures. Commonly, the same places appear bright continuously day after day and recurrently year after year, different astronomers at successive oppositions having so observed them. To this category belong the regions known as Elysium, Ophir, Memnonia, Eridania, and Tempe, which at certain seasons of the Martian year are phenomenally brilliant. They stay so for some time, and then the brightness fades out
