PHYSICAL CONTEMPLATION OF THE UNIVERSE. 107 



«olav" light be radiated from a sclid mass or from a gaseous 

 envelope. The eaumeration of the experiments which, since 

 Huygens's time, have gradually led to Arago's discovery ol 

 colored polarization, must be reserved for the history of optics. 

 The consideration of the development of the principles, in ac- 

 cordance with v/hich variously-formed plants admit of being 

 classified in famihes, falls, in like manner, within the domain 

 of the history of phytognosy, or botany ; while the geography 

 of plants, or a study of the local and climatic distribution of 

 vegetation over the whole earth — alike over the solid portions 

 and in the basins of the sea — constitutes an important section 

 in the history of the physical contemplation of the universe. 



The intellectual consideration of that which has led man 

 to an insight into the unity of nature is, as we have already 

 observed, as little entitled to the appellation of the complete 

 history of the cultivation of mankind as to that of a history 

 of the natural sciences. An insight into the connection of 

 the vital forces of the universe must certainly be regarded aa 

 the noblest fruit of human civilization, and as the tendency to 

 arrive at the highest point to which the most perfect develop- 

 ment of the intellect can attain ; but the subject at present 

 under consideration must still constitute only a part of the 

 history of human civilization, embracing all that has been 

 attained by the advance of different nations in the pursuit of 

 every branch of mental and moral culture. By assuming a 

 more limited physical point of view, we necessarily become 

 restricted to one section of the history of human knowledge, 

 and our attention is specially directed to the relation existing 

 between the knowledge that has been gradually acquired and 

 the whole extent of the domain of nature ; and we dwell less 

 on the extension of separate branches of science than on the 

 results capable of generalization, and the material aids con- 

 tributed by different ages toward a more accurate observation 

 of nature. 



We must, above all, distinguish carefully between an early 

 presentiment of knowledge and knowledge itself With the 

 increasing cultivation of the human race, much has passed 

 from the former to the latter, and by this transition the his- 

 tory of discovery has been rendered indistinct. An intellect- 

 ual and ideal combination of the facts already established often 

 guides almost imperceptibly the course of presage, elevating it 

 as by a power of inspiration. How much has been enounced 

 among the Indians and Greeks, and during the Middle Ages, 

 regarding the connection of natural phenomena, which, at first 



