had vanished, the western half being now actually the darker of the two. So fugitive an effect suggests cloud, forming presumably over high ground, and subsequently dissipating; it also suggests a deposition of frost, melting on the next day. It is specially noteworthy that the canals inclosing the region, the Galaxias, the Boreas, and the Eunostos, were not in any way obscured by the bright apparition. On the contrary, Mr. Douglass found them perceptibly darker than they had been, an effect attributable perhaps to contrast.
Although not storm-clouds, it is possible that these appearances may have been due to thin cloud, capping high land. There are objections to this view, but as there are graver ones to any other it may stand provisionally, the more so that there are appearances not easily reconcilable with other cause. For example, a most singular phenomenon was seen by Mr. Douglass on November 25, a bright detached projection, for which, from measurement, he deduced a height of thirty miles. This would seem to have been cloud, for the details of its changes in appearance seem quite incompatible with a mountainous character. With regard to its enormous height, it is not to be forgotten that a few years ago on the Earth phenomenal dust-clouds were observed as high as one hundred miles.