Page:Physical Geography of the Sea and its Meteorology.djvu/199

Rh leading across the calm places. That celebrated microscopist reports that he found South American infusoria in the blood-rains and sea-dust of the Cape Verd Islands, Lyons, Genoa, and other places (§ 325); thus confirming, as far as such evidence can, the indications of our observations, and increasing the probability that the general course of atmospherical circulation is in conformity with the suggestions of the facts gathered from the sea as I had interpreted them, viz., that the trade-winds of the southern hemisphere, after arriving at the belt of equatorial calms, ascend and continue in their course towards the calms of Cancer as an upper current from the south-west, and that after passing this zone of calms, they are felt on the surface as the prevailing south-west winds of the extra-tropical parts of our hemisphere; and that for the most part, they bring their moisture with them from the trade-wind regions of the opposite hemisphere. I have marked on Plate VII. the supposed track of the "Passat-Staub," showing where it was taken up in South America, as at P P, and where it was found, as at S S; the part of the line in dots denoting where it was in the upper current, and the unbroken line where it was wafted by a surface current; also on the same plate is designated the part of the South Pacific in which the vapour-springs for the Mississippi rains are supposed to be. The handspoint out the direction of the wind. Where the shading is light the vapour is supposed to be carried by an upper current. Such is the character of the circumstantial evidence which induced me to suspect that some agent, whose office in the grand system of atmospherical circulation is neither understood nor recognized, was at work in these calm belts and other places. It may be electrical, or it may be magnetic, or both conjoined.

359. Quetelet's observations.—The more we study the workings of the atmospherical machinery of our planet, the more are we impressed with the conviction that we as yet know very little concerning its secret springs, and the little "governors" here and there which regulate its movements. My excellent friend M. Quetelet, the astronomer royal at Brussels, has instituted a most excellent series of observations upon atmospherical electricity. He has shown that there is in the upper regions of the air a great reservoir of positive electricity, which increases as the temperature diminishes. So, too, with the magnetism of the oxygen in the upper regions.