TERRESTRIAL ADAPTATIONS. 19 



construction, certain periodical functions, which 

 have a reference to alternations of heat and cold ; 

 the length of the period which belongs to these 

 functions by their construction, appears to be 

 that of the period which belongs to the actual 

 alternations of heat and cold, namely, a year. 

 Plants and animals have again in their construc- 

 tion certain other periodical functions, which 

 have a reference to alternations of light and 

 darkness ; the length of the period of such func- 

 tions appears to coincide with the natural day. 

 In like manner the other arbitrary magnitudes 

 which enter into the laws of gravity, of the effects 

 of air and moisture, and of other causes of per- 

 manence, and of change, by which the influences 

 of the elements operate, are the same arbitrary 

 magnitudes to which the members of the organic 

 world are adapted by the various peculiarities 

 of their construction . 



The illustration of this view will be pursued in 

 the succeeding chapters ; and when the coinci- 

 dence here spoken of is distinctly brought before 

 the reader, it will, we trust, be found to convey 

 the conviction of a wise and benevolent design, 

 which has been exercised in producing such an 

 agreement between the internal constitution and 

 the external circumstances of organized beings. 

 We shall adduce cases where there is an apparent 

 relation between the course of operation of the 

 elements and the course of vital functions ; be- 



