xiv AUTHOR'S PREFACE. 



It has frequently been regarded as a subject of discouraging 

 consideration, that whilst purely literary products of intellec- 

 tual activity are rooted in the depths of feeling, and inter- 

 woven with the creative force of imagination, all works treat- 

 ing of empirical knowledge, and of the connection of natural 

 phenomena and physical laws, are subject to the most marked 

 modifications of form in the lapse of short periods of time, 

 both by the improvement in the instruments used, and by the 

 consequent expansion of the field of view opened to rational 

 observation, and that those scientific works which have, to use 

 a common expression, become antiquated by the acquisition of 

 new funds of knowledge, are thus continually being consigned to 

 oblivion as unreadable. However discouraging such a prospect 

 must be, no one who is animated by a genuine love of nature, 

 and by a sense of the dignity attached to its study, can view 

 with regret anything which promises future additions and a 

 greater degree of perfection to general knowledge. Many im- 

 portant branches of knowledge have been based upon a solid 

 foundation which will not easily be shaken, both as regards 

 the phenomena in the regions of space and on the earth; 

 whilst there are other portions of science in which general 

 views will undoubtedly take the place of merely special; where 

 new forces will be discovered and new substances will be 

 made known, and where those which are now considered as 

 simple will be decomposed. I would therefore venture to hope 

 that an attempt to delineate nature in all its vivid animation 

 and exalted grandeur, and to trace the stable amid the vacil- 

 lating, ever- recurring alternation of physical metamorphoses, 

 will not be wholly disregarded even at a future age. 



Potedam, Nov. 1844. 



