BOOK I. 



TERRESTRIAL ADAPTATIONS. 



WE proceed in this Book to point out relations 

 which subsist between the laws of the inorganic 

 world, that is, the general facts of astronomy and 

 meteorology ; and the laws which prevail in 

 the organic world, the properties of plants and 

 animals. 



With regard to the first kind of laws, they 

 are in the highest degree various and unlike each 

 other. The intensity and activity of natural in- 

 fluences follow in different cases the most different 

 rules. In some instances they are periodical, in- 

 creasing and diminishing alternately, in a per- 

 petual succession of equal intervals of time. This 

 is the case with the heat at the earth's surface, 

 which has a period of a year; with the light, 

 which has a period of a day. Other qualities are 

 constant, thus the force of gravity at the same 

 place is always the same. In some cases, a very 

 simple cause produces very complicated effects ; 

 thus the globular form of the earth, and the incli- 

 nation of its axis during its annual motion, give 

 rise to all the variety of climates. In other cases 

 a very complex and variable system of causes 

 produces effects comparatively steady and uni- 



