TEMPERATURE. 9 



Before proceeding to the examination of the laws which 

 regulate the geographical distribution of any one species, 

 it is expedient that we previously make ourselves acquaint- 

 ed with the range of country it inhabits, the situations in 

 which it has been observed, and the peculiar characters it 

 exhibits in these different situations. But while this mi- 

 nute and varied information is requisite for the purpose of 

 investigating fully the physical history of any one species, 

 it is enough, for ordinary investigations, that we ascertain 

 those districts and situations where the individuals are most 

 healthy and most prolific, and those where they do not ex- 

 ist. By comparing the physical circumstances of the for- 

 mer with those of the latter, it will be no difficult matter 

 to discover those conditions which promote the vigour of 

 life in the one, and restrain or destroy its energies in the 

 other. What, then, are those conditions which limit the 

 geographical distribution of species ? They appear to be 

 limited to circumstances connected with Temperature, Food, 

 Situation, and Foes. 



I. TEMPERATURE. 



We have already stated, that the degree of heat at the 

 equatorial regions appears to be most favourable for the in- 

 crease of living beings, and that they diminish in numbers as 

 we approach the poles. There is no latitude, however, which 

 the perseverance of man has yet reached, where living be- 

 ings have not been observed. The icy shores of the arctic 

 regions are peopled as well as the arid plains or shaded fo- 

 rests of tropical climates. When, however, an inhabitant 

 of the colder regions is transported to a warmer district, 

 the increased temperature is painful, the functions be- 

 come deranged, and disease and death ensue. The inhabi- 

 tants of the wanner regions, when transported to the colder 

 districts, experience inconvenience from the change of tern- 



