HOW TO

FORETELL THE WEATHER.

IN commencing an account of some new subject, it is customary to quote its history; but that of the rainband, one of the most important features in the sky spectrum, and the first noticed, has been so frequently referred to that it would be a matter of supererogation on my part to adduce what is now so generally known. Suffice it to say that in 1872 Prof. Piazzi Smyth, the Astronomer-Royal for Scotland, was the earliest to draw correct conclusions from its appearance.

The subject of which we are about to treat depends mainly upon the amount of invisible

aqueous vapour contained in the atmosphere. Visible vapour influences the spectrum but slightly, and then only by reflected light. The records of hygrometry extend back for more than three hundred years. Mizaldus, in 1554, and Mersenne, in 1644, both noticed that the pitch of the strings of a violin varied according to the dryness of the air. The former says,' * 'Musicorum instrumentorum

subtensæ fidiculæ ruptim dissilientes, et hostia absque manifesta causa, aperiri claudique solito contumaciora, aerem pluvias nobis miscere. palam nuntiant;' literally meaning,

The

strained strings of musical instruments suddenly snapping, and sacrificed victims, without any apparent cause, opening and closing, and becoming more stiff than usual, plainly tell us that rains are disturbing the atmosphere.'

Even Pliny the elder, who lived a.d. 23 to A.D. 79, seems to have been a rough observer

* Mizaldus, A., ‘Ephemerides Aeris Perpetuæ.' Small 8vo. Lutetiæ, 1554.

of the dew-point, as instanced in the following quotation from the eighteenth book of his ' Historia Naturalis': 'Nec non in conviviis mensisque nostris vasa quibus esculentum additur sudorem repositoriis linquentia diras tempestates prænuntiant ;' which, translated, is: And also at banquets and at our tables, vessels in which there is any esculent moisture left on the trays foretell fearful storms.' Of all the numerous moisture-absorbers that man has applied his ingenuity to in adapting to the purposes of hygrometry, such as the beard of the wild oat; beard of musk grass, or geranium moschatum; internal membrane of the arundo phragmites; skin of the frog; Dutch weather house; schistose stone, a material so porous that when saturated it weighs nearly half as much again as when dry; and then the more modern and scientific instruments, viz., Daniell's, Regnault's, and Dines' hygrometers; and lastly, Mason's dry and wet bulb hygrometer, that is used more frequently than any