Page:Popular Science Monthly Volume 40.djvu/829

Rh them as we approach the nineteenth century, but we have a right to assume that that is because the records are fuller near our times, not necessarily because extremes are growing more frequent or marked. None of the instances, ancient or modern, betoken greater severity than the frosts of 1234—sixteen years before the "Great Summer" year—when "the Po and Rhône were frozen, and loaded wagons crossed the Adriatic on the ice opposite Venice"; 1236, when "the Danube was frozen to the bottom for a considerable time"; or 1305, fifty-five years after it, when "the Rhône and all the rivers of France were frozen." With all the greater completeness and systematic organization of modern observations, the records of the nineteenth century contain no mention of such seasons as those of 1323, 1333, 1349, 1402, and 1407, when the southern part of the Baltic was frozen so hard that men could ride on horseback from Copenhagen to Lubeck and Dantsic.

These occasional winters of exceptional severity can not be taken as typical of the general character of the seasons, any more than we can characterize a winter by an extreme day in January, or a summer by an unusually sultry July day winding up in a thunder-shower. A surer guide to the habitual climate would be afforded by regarding the development of plant growth and the maturing of crops. Of these the vine has been taken as a type. It is said that, cultivated in the time of Julius Cæsar only in the southern parts of Gaul, or France, it was gradually carried northward to the fullest expansion in the thirteenth century, when there were vineyards and wine was made as far north as Flanders and England. Since then it has retired from the most northern points it had reached, where the grape is now ripened under glass. So the cultivation of the olive is said to be falling back toward the south; the sugar-cane has disappeared from Provence, where it once grew; less tender plants are taking the place of the orange in some quarters; and a depression of the zone of forest vegetation is mentioned as taking place in the Alps and the Carpathians.

There are many other causes than climate, as the present operations of agriculture and horticulture amply demonstrate, by which the cultivation of a crop in any place is determined. It may be found after some years of experiment to be unprofitable or of poor quality there; or may be supplanted by new and better varieties growing in more favored localities, or superseded by the introduction of new and more profitable products, which the cultivator is always ready to take up. Such causes have more force now than they ever had before, because of the great increase in the facilities for exchange under which it is no longer necessary to cultivate anything except in the places where it will do best. M. Angot has, moreover, found, by consulting the