After, several nights of unusual cloud, the evening of August 15th displayed a clear blue vault of sky, and the full moon starting from behind the purple summits of Grand Canary, commenced to establish almost a second day. The cloud referred to as unusual, was of course composed of the S.W. cirrocumuli, floating high in the air; for the lower N.E. cumuloni were never disturbed, from month's end to month's end, from their sluggish position below.

That there is a preponderance of clear weather on the night of full moon, and that such clearness is due to a dissolving of vaporous clouds, by heat reflected from the lunar orb, are ideas started by Sir John Herschel. While if he and other experimenters, have been unable with their most sensitive instruments, to detect any symptom of that heat, the want of success, he has suggested, may be due to the caloric being expended in upper parts of the atmosphere, in this very dissolution of vapour. And owing to its original low temperature, such lunar heat would have great difficulty in passing through, even a transparent medium.

Some confirmation of these views was at once found on this occasion; for the upper clouds had vanished before our eyes, under the presence of a full moon; and if the lower ones had not also disappeared, that might be considered only as a consequence of the higher strata, having exhausted the full potential energy of heat thrown upon them.