and Nations on the extent and situation ^WltnttL 243 



The direction of the isothermal lines proves in detail, that 

 the influence of forests is universal, and that it affects the 

 climate of the continents as well as of the sea-coasts. By 

 carefully following out these comparisons, we arrive at 

 the conclusion, that on the influence of forests depends the 

 remarkable distinction between the Old and New World, 

 and that it produces the great contrast between the northern 

 and southern countries of Europe, between the north and south 

 of Germany, between the west and east of France, and be- 

 tween the northern and central provinces of Spain ; and that a 

 climate, subject to the influence of forests, is not only less hot, 

 but even much colder ; whence there arises a considerable and 

 material difference, plainly perceived by keeping in mind that 

 the entire vegetation depends on the distribution of heat dur- 

 ing the different seasons, and that the nearer the thermometer 

 approaches the freezing point, and the longer it continues in 

 that low state, the shorter will be the catalogue of indi- 

 genous and exotic plants, the more limited the number of 

 those useful to man. 



At the period when Asiatic tribes invaded Europe, its sur- 

 face was covered with wood. It appears from Arthur Young's 

 Travels, that the territory of Great Britain was densely 

 overspread with large forests ; for Ireland, at present entirely 

 clear of woods, is called the Woody Isle, and the descriptions 

 of Strabo and Ptolemy corroborate the existence of extensive 

 forests in Scotland, where, the Roman legions and auxiliaries 

 were, by the command of the Emperor Severus, employed in 

 rooting out and cutting down forests. According to the re- 

 port of Tacitus, the sky of England was constantly overcast 

 with clouds and rain ; the cold, however, was not very great, 

 and, according to Caesar's statement, the climate was much 

 milder, and the cold not so intense as in France.* At present 

 the contrast is more striking, for the removal of forests wrought 

 a considerable change in the physical condition of both coun- 

 tries, whence all their geographical relations became essen- 

 tially modified. We recommend a more careful investigation 



• Vita Agricolae, cap. 12, and Csesar de Bello Gallico, lib. v. cap. 10. 



