Meteorological ConstUuiion of the Earth. 313 



sions from them about climate. If we find them speak of 

 plants and animals, which now only occur in colder climates, 

 the conclusion that the climate had been changed would not 

 be directly warranted. Thus it is certainly not a higher tem- 

 perature which has driven the beaver from the greater part of 

 Europe, and which in North America compels it more and 

 more to retire into the interior ; but it was the increasing popu* 

 lation and the cultivation of the soil which did not allow the ani- 

 mal to remain in that undisturbed state which is required for its 

 existence. And it may be owing more to a bad management 

 of the wood than to any change in the climate, that in some 

 places of Switzerland no wood is now growing although stems 

 and roots of trees are found on the very plains. With respect 

 to cultivated plants it is not enough to know that a plant was 

 not cultivated by the ancients; but we must ascertain whether 

 they knew it, and whether they, without success, attempted its 

 cultivation. The conclusion, too, that the climate has be- 

 come colder, because plants formerly cultivated there are not 

 so now, is not directly to be justified, for want of industry or 

 other changes in the state of man may have occasioned it. 



Only such plants or animals can be of great use in the in- 

 quiry into the supposed changes of climate, which have either 

 their polar or their equatorial limits in the country of which 

 the climate is doubtful. Thus it proves nothing, if it is as- 

 certained that wheat in former times, as well as now, was culti- 

 vated in upper Italy under 45° of latitude ; because that species 

 of corn has its northernmost limit at about 60° of latitude, and 

 its southermost at about 20°. If, on the contrary, it could be 

 ascertained that a plant, which now has its polar limit in the 

 said country, also was found there in former times, it is proved 

 thereby that the climate has not become warmer; and the 

 former existence of a plant which now h^s its equatorial limit 

 in the same place would prove that the climate has not become 

 colder. If, in the same country, two plants were found, of 

 which the one had its polar, the other its equatorial limit there, 

 the proof of the unchanged state of the atmosphere would be 

 complete ; and knowing the mean temperature for this limit, 

 we should be able to ascertain almost with certainty the mean 

 temperature which that region had about 2000 years ago. By 

 such inquiries the geography of plants and animals which as- 



