mi AUTHOR S PREFACE. 



ural science are, moreover, capable of being reciprocally fruc- 

 tified by means of the appropriative forces by which they are 

 endowed. Descriptive botany, no longer confined to the nar- 

 row circle of the determination of genera and species, leads 

 the observer who traverses distant lands and lofty mountains 

 to the study of the geographical distribution of plants over the 

 earth's surface, according to distance from the equator and ver- 

 tical elevation above the sea. It is further necessary to in- 

 vestigate the laws which regulate the differences of tempera- 

 ture and climate, and the meteorological processes of the at- 

 mosphere, before we can hope to explain the involved causes 

 of vegetable distribution ; and it is thus tffat the observer who 

 earnestly pursues the path of knowledge is led from one class 

 of phenomena to another, by means of the mutual dependence 

 and connection existing between them. 



I have enjoyed an advantage which few scientific travelers 

 have shared to an equal extent, viz., that of having seen not 

 only littoral districts, such as are alone visited by the majority 

 of those who take part in voyages of circumnavigation, but 

 also those portions of the interior of two vast continents which 

 present the most striking contrasts manifested in the Alpine 

 tropical landscapes of South America, and the dreary wastes 

 of the steppes in Northern Asia. Travels, undertaken in dis- 

 tricts such as these, could not fail to encourage the natural 

 tendency of my mind toward a generalization of views, and to 

 encourage me to attempt, in a special work, to treat of the 

 knowledge which we at present possess, regarding the sidereal 

 and terrestrial phenomena of the Cosmos in their empirical 

 relations. The hitherto undefined idea of a physical geog- 

 raphy has thus, by an extended and perhaps too boldly imag- 

 ined a plan, been comprehended under the idea of a physical 

 description of the universe, embracing all created things in the 

 regions of space and in the earth. 



The very abundance of the materials which are presented 

 to the mind for arrangement and definition, necessarily impart 

 no inconsiderable difiiculties in the choice of the form under 



