354 COSMOS. 



made to determine their forms and orbits. Mankind now 

 first attained to the possession of the " celestial sphere" of the 

 Cosmos. Sufficient foundation for a seventh section of the 

 history of the contemplation of the universe seemed to be af- 

 forded by the importance of the acquisition of this celestial 

 knowledge, and of the unity of the efibrts called forth by the 

 use of the telescope. If we compare another great invention, 

 and one of recent date, the voltaic pile, with the discovery of 

 this optical instrument, and reflect on the influence which it 

 has exercised on the ingenious electro-chemical theory ; on 

 the production of the metals ; of the earths and alkalies ; and 

 on the long-desired discovery of electro-magnetism, we are 

 brought to the consideration of a series of phenomena called 

 forth at will, and which, by many different paths, lead to a 

 profound knowledge of the rule of natural forces, but which 

 constitute rather a section in the history of physical science 

 than a direct portion of the history of cosmical contemplation. 

 It is this multiplied connection between the various depart- 

 ments of modern knowledge that imparts such difficulty to the 

 description and limitation of its separate branches. We have 

 very recently seen that electro-magnetism, acting on the di- 

 rection of the polarized ray. of light, produces modifications 

 like chemical mixtures. Where, by the intellectual labors 

 of the age, all knowledge appears to be progressing, it is as 

 dangerous to attempt to describe the intellectual process, and 

 to depict that which is constantly advancing as already at the 

 goal of its efforts, as it is difficult, with the consciousness of 

 one's own deficiencies, to decide on the relative importance 

 of the meritorious efforts of the living and of the recentlv de- 

 parted. 



In the historical considerations T have almost every where, 

 in describing the early germs of natural knowledge, designated 

 the degree of development to which it has attained in recent 

 times. The third and last portion of my work will, for the 

 better elucidation of the general picture of nature, set forth 

 those results of observation on which the present condition of 

 scientific opinions is principally based. Much that, accord- 

 ing to other views than mine, regarding the composition of a 

 book of nature, may have appeared wanting, will there find 

 its place. Excited by the brilliant manifestation of new dis- 

 coveries, and nourishing hopes, the fallacy of which often con- 

 tinues long undetected, each age dreams that it has approxi- 

 mated closely to the culminating point of the recognition and 

 comprehension of nature. I doubt whether, on serious reflec* 



