36 Humboldt's Letters. 



granite rocks and to make this work instructive to the 

 mind, and at the same time attractive, by its vivid lan- 

 guage. Every great and sparkling idea must be noticed, 

 side by side with its attendant facts. The work shall 

 represent an epoch of the intellectual development of 

 mankind in their knowledge of nature. The prolego- 

 mena are, for the most part, ready. They are my 

 amended " discours d'ouverture " as they were delivered 

 from memory, although immediately afterwards care- 

 fully written down ; the picture of physical nature 

 incentives to the study of nature in the spirit of our age 

 these latter are threefold: 1. "Poesie descriptive" 

 and vivid description of natural scenery in modern 

 works of travels. 2. Landscape pictures, sensitive 

 description of an exotic nature when it originated, 

 when it became a necessity and a pleasure to the 

 mind ; the reason why antiquity (too passionate) could 

 not feel it. 3. Plants grouping of them, according to 

 the physiognomy of plants (no botanic gardens). His- 

 tory of the physical description of the world. How the 

 idea of the world of the connexion of all the pheno- 

 mena, became clear to the nations of the world in the 

 course of centuries. These prolegomena are the most 

 essential. They contain the general part of the work, 

 which is followed by the special part, the particulars 

 of which are arranged in systematic order. I send also 

 a part of the tabular register ; space of the universe; the 



