Page:Popular Science Monthly Volume 53.djvu/816

792 and mountainward tourists need their water boots in every glen; the gnat veil of ordinary years has thickened to heavy banks of gnat clouds, and the nights are made ghastly by the serenades of renegade tomcats that have exchanged the shelter of their native ranches for the freedom of the woods, but have to wait for the cloud-dispelling moon to celebrate their declaration of independence.

The supposed rain-attracting excess of heat has, however, nothing to do with the intervention of rainy summers. In the western provinces, where rain is often sorely needed, they are rare—much rarer, at least, than in the wood-covered southeast. Their recurrence seems somewhat to depend upon the above-mentioned cold-air waves from the woodlands of Central America, cool weather in June having a tendency to postpone the beginning of the rainy season and to increase the vehemence of the eventual downpour. In other words, the early showers of Yucatan and of the West Indian Islands are apt to occur in alternate years, but there are summers when cloud bursts break out without any other premonition but the steadily increasing sultriness of the weather during the latter half of July.

Hurricanes are still harder to predict. Experience has proved that they are generally more frequent in Santo Domingo and Porto Rico than in the western Antilles, but the occasional destructiveness of their rage in Cuba is attested by numerous cadenzas, or tracts of leveled forest lands, from Santiago to Pinar del Rio, and their genesis is still rather obscure. As a rule, the equalization of extreme contrasts of temperature is attended with violent gales, and in early spring northwest storms, traversing the mainland from Hudson Bay Territory to southern Texas, may approach the threshold of the tropics nearly a hundred degrees cooler than the atmosphere brooding over the coast plains of San Salvador, where pears begin to ripen in April. And the fortnight following the vernal equinox is really a season of shipwrecking gales, in east America as well as in western Europe and the Asiatic coast lands of the North Pacific. But the tornadoes proper, the wall-breaking and tree-uprooting whirl storms of the West Indies, are more frequent in August than in April, and may even assume their most portentous forms in September, when the summer sun at last prevails against the mists of the rainy season, and the vegas are some twenty or thirty degrees warmer than the Texas prairies—a mere trifle compared with the contrasts of early spring.

Moisture would seem to play almost as important a part as heat in the generation of cyclones, and Professor von Tschudi called attention to the fact that the dry if not wholly rainless coast regions of Peru enjoy a remarkable immunity from destructive storms.

Cold winds become afflictive only on the highest plateaus of the