AUTHOR'S PREFACE. 



tensive journeys in which I engaged,-r-I had still throughout 

 a higher aim in view; I ever desired to discern physical 

 phsenomena in their widest mutual connection, and to com- 

 prehend Nature as a whole, animated and moved by inward 

 forces. Intercourse with highly-gifted men had early led me 

 to the- conviction, that without earnest devotion to particular 

 studies such attempts could be but vain and illusory. The 

 separate branches of natural knowledge have a real and 

 intimate connection, which renders these special studies 

 capable of mutual assistance and fructification : descriptive 

 botany, no longer restricted to the narrow circle of the de- 

 termination of genera and of species, leads the observer, who 

 traverses distant countries and lofty mountains, to the study 

 of the geographical distribution of plants according to dis- 

 tance from the equator and elevation above the level of the 

 sea. Again, in order to elucidate the complicated causes 

 which determine this distribution, we must investigate the 

 laws which regulate the diversities of climate and the meteo- 

 rological processes of the atmosphere ; and thus the observer, 

 earnest in the pursuit of knowledge, is led onwards from one 

 class of phenomena to another, by their mutual connection. 

 I have enjoyed one advantage which few scientific tra- 

 vellers have shared to an equal degree, in having seen not 

 merely coasts, and districts little removed from the margin of 

 the ocean, as in voyages of circumnavigation, but in having, 



