* INTRODUCTION. 



spoken of, first in the contemplation of the universe as a 

 natural whole, and next in an endeavour to show how in 

 the course of centuries, at different periods in the history 

 of the human race, and in the most different regions of the 

 earth, mankind had progressively advanced towards a recog- 

 nition of the concurrent action of the forces of nature. 

 Although the arrangement in a significant order of the 

 descriptions of phsenomena is in itself adapted to lead us to 

 recognise their causal connection, yet it could not be hoped 

 that a general representation should appear fresh, animated, 

 and life-like, unless restricted within such limits as should 

 not permit the general effect to be lost, under the excessive 

 and too crowded accumulation of separate facts. 



As in collections of geographical or geological maps, 

 representing graphically the configuration of land and sea, 

 or the characters and arrangement of the rocks at the earth's 

 surface, general maps are made to precede special ones ; so 

 it has appeared to me most fitting that in the Physical De- 

 scription of the Universe, its representation as a whole, 

 contemplated from more general and higher points of view, 

 should be followed by the separate presentation, in the two 

 last volumes, of those special results of observation on which 

 the present state of our knowledge is more particularly based. 

 These two last volumes, therefore (as I have already remarked, 

 Bd. iii. S. 4 9 ; Engl. p. 49), are to be regarded simply 

 as an extension and more careful elaboration of the general 

 representation of Nature, which constituted my first volume ; 

 and as the third was devoted exclusively to the uranological 

 or sidereal domain of the Cosmos, so the present and last 

 volume is designed to treat of the telluric sphere, or of the 

 phsenomena belonging to the globe which we inhabit. We 



