X AUTHOR S PREFACE. 



natural science are, moreover, capable of being reciprocally 

 fructified by means of the appropriative forces by which they 

 are endowed. Descriptive botany, no longer confined to the 

 narrow 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 vertical elevation above the sea. It is further 

 necessary to investigate the laws which regulate the differences 

 of temperature and climate, and the meteorological processes 

 of the atmosphere, before we can hope to explain the involved 

 causes of vegetable distribution; and it is thus that 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 travellers 

 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 towards a generalisation 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 geography 

 has thus, by an extended and perhaps too boldly imagined 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 



