VARIATIONS IX CLIMATU. 807 



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 fre- 

 quent 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 Rhone 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 

 Rhone and all the rivers of France were frozen." With all the 

 greater completeness and systematic organization of modern ob- 

 servations, the records of the nineteenth century contain no men- 

 tion 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 

 thuuder-shower. A surer guide to the habitual climate would be 

 afi'orded by regarding the development of jjlant 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 CaBsar only in the 

 southern parts of Gaul, or France, it was gradually carried north- 

 ward 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 Car- 

 pathians. 



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 bet- 

 ter varieties growing in more favored localities, or superseded hj 

 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 in- 

 crease 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 offi- 



