to which the Sun is setting, what he calls the heat-gradient (using a phrase suggested by terrestrial meteorology) appears to be steeper than on that part to which the Sun is rising. Generally, Very’s observations accord fairly with Lord Rosse’s. The Moon revolves round the Earth in 27 d. 7 h. 43 m. 11 s. at a mean distance of 237,300 miles, in an orbit which is somewhat, but not very, eccentric. Its angular diameter at mean distance is 31′ 5″, or, say, just over ½°. The real diameter may be called 2160 miles. A few words will probably be expected by the reader on the subject of lunar influences on the weather, and generally; this being a matter highly attractive to the popular mind. The truth appears to lie, as usual, between two extremes of thought. The Moon, of course, is the main cause of the tides of the Ocean, and it is not entirely inconceivable that tidal changes imparted to vast masses of water may be either synchronous with, or may in some way engender, analogous movements in the Earth’s atmosphere; though no distinct proofs of this, as a determinate fact, can be brought forward. There is no doubt whatever that at or near the time of full Moon, evening clouds tend to disperse as the Moon comes up to the meridian, and that by the time the Moon has reached the meridian a sky previously overcast will have become almost or quite clear. Sir John Herschel has alluded to this by speaking of a “tendency to disappearance of clouds under a full Moon”; and he considers this “fully entitled to rank as a meteorological fact.” He goes on, not unnaturally, to suggest the obvious thought that such dissipation of terrestrial clouds is due to the circumstance that, assuming heat really comes by radiation from the Moon (and we have seen on a previous page the probability of this) such radiant heat will be more potential if it falls on the Earth perpendicularly, as from a Meridian Moon, than if it comes to us at any one locality from a Moon low down in the observer’s horizon, and therefore has to pass through the denser strata of the Earth’s atmosphere and suffer material enfeeblement accordingly. I am aware that Mr. Ellis, late of the Royal Observatory, Greenwich, has sought to show by a seemingly powerful array of statistics that the idea now under consideration is unfounded, but I consider that we have here only one more illustration of the familiar statement that you can prove anything you like by statistics. I am firmly convinced, as the result of more than 30 years’ observation, that terrestrial clouds do disperse under the circumstances stated. Sir J. Herschel added that his statement proceeded from his own observation “made quite independently of any knowledge of such a tendency having been observed by others. Humboldt, however, in his _Personal Narrative_, speaks of it as well known to the pilots and seamen of Spanish America.” Sir John Herschel further remarked:—“Arago has shown from a comparison of rain, registered as