latter shows, as in the case of the other variety, that we are here dealing chiefly with long and relatively low clouds formed after sunset or before sunrise; those so formed during daylight being few if any.
One more observation made at Flagstaff on the subject of cloud, is as peculiar as it is important. It was made by Mr. Douglass, and I shall give it in his own words. A more detailed account of it, together with his tables of figures, will appear in his paper upon it in the Observatory annals:—
"On November 25 and 26 a bright spot was seen in the unilluminated portion of Mars, to which, in my opinion, no other name than cloud can be applied. Its great height, size, and brilliancy, and, on the second evening, its singular fluctuations, render it of importance in the study of the Martian atmosphere.
"I first saw it at 16h. 35m., G. M. T., of November 25, and made an estimate of its height. It seemed to be rapidly increasing in length in a direction parallel to the terminator at that point. Subsequent estimates of its height gave a different and greater value than at first, until its sudden disappearance at 17h. 6m., or perhaps a minute later. After once attaining its size, it seemed to remain with little change, presenting the appearance of a line 115 miles long by 33 miles wide at the centre and lying parallel to
