740 COSMOS. 



once explored, the number of known heavenly bodies was 

 increased, and attempts 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 afforded by the importance of the 

 acquisition of this celestial knowledge, and of the unity of the 

 efforts called forth by the use of the telescope. If we com- 

 pare 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 ingeni- 

 ous 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 con- 

 nection between the various departments of modern know- 

 ledge that imparts such difficulty to the description and limi- 

 tation of its separate branches. We have very recently 

 seen that electro-magnetism, acting on the direction of the 

 polarised ray of light, produces modifications like chemical 

 mixtures. Where, by the intellectual labours 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 recently departed. 

 In the historical considerations I have almost everywhere 

 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- 



