Page:Popular Science Monthly Volume 32.djvu/500

482 which we receive most of our storms; so that the apparition of the old moon in the arms of the new, virtually means that there are vast cloud-banks over the North Atlantic Ocean which, in all probability, are drifting up to us, and will, before long, bring us "dirty" weather. I am not disposed to go so far as Mr. John Aitken, who, in a paper recently read before the Royal Society of Edinburgh, suggested the use of the moon's dark limb as an "outlying signal station," but it is satisfactory to know that this venerable prognostic has a sound physical basis, and is as worthy of respect as ever it was. The other explanation to which I referred is the greater "visibility" of the air which generally precedes rough or unsettled weather, this clearness allowing the ghostly disk of the old moon to loom forth in a way it could not do through a misty atmosphere. Though, doubtless, a part explanation of the phenomenon, it is not a whole one, and must be taken along with the other.

The halo is an old sign of bad weather;

 When round the moon there is a brugh, The weather will be cold and rough."

Of sixty-one lunar halos observed in the neighborhood of London, thirty-four were followed by rain within twenty-four hours, nineteen by rain within four days, and only eight by no rain at all. The cause of halos is the formation of an extremely attenuated form of cloud which floats in the van of all cyclonic disturbances, Messrs. Abercromby and Marriott, who made a detailed comparison between a number of popular weather prognostics and the actual distribution of weather as disclosed by synoptic charts, found the lunar halo to be a true sign of the approach of a "cyclone" or area of depression, just aa a clear moon indicates the presence of an anti-cyclone, or area of high pressure, with the likelihood of cold or frost. Similarly, a pale or watery moon marks the advent of a disturbance, while the blunting of the cusps is due to the same cause, and has the same significance. The variation of this last prognostic, which makes a sullied lower horn the sign of foul weather before the full, and a sullied upper horn the sign of foul weather about the wane, is purely fanciful.

Just one word about that enticing object of research—as fascinating in its way as perpetual motion or the exact value of π—the lunar circle.

Dr. E. B. Tylor, says: "The notion that the weather changes with the moon's quarterings is still held with great vigor in England. That educated people to whom exact weather records are accessible should still find satisfaction in the fanciful lunar rule, is an interesting case of intellectual survival." I am willing to be with the foremost in combating such absurdities as "Herschel's Weather Table," and all theories which would assign to the lunar phases an immediate control of our weather; but it so happens that the notion Dr. Tylor condemns is one for which there may be some foundation. A moon's quarter is roughly equivalent to a week, and Mr. Carpmael, the