HUMBOLDT'S LETTERS. 



HUMBOLDT TO VARNHAGEN. 



BERLIN, September 25th, 1827. 



MY HONORED FRIEND: 







ALLOW me to present you with the best copy of my 

 essay* left me. 



The end of it will, I hope, secure me your indulgence 

 for the whole. 



Tuesday. A. v. HUMBOLDT. 



* On the Principal Causes of the Variation of Temperature upon 

 the Earth. 



