LETTER FROM HUMBOLDT. 537 



comparison of the types belonging to our 

 planet, in its present condition, with those 

 now found only in a fossil state, so abundant 

 in the immense space lying between the shores 

 opposite to northern Europe and northern 

 Asia. The geographical distribution of or- 

 ganic forms in curves of equal density of 

 occupation represents in great degree the in- 

 flexions of the isothermal lines. ... I am 

 charged by the king, who knows the value of 

 your older works, and who still feels for you 

 the affectionate regard which he formerly ex- 

 pressed in person, to request that you will 

 place his name at the head of your long list 

 of subscribers. He wishes that an excursion 

 across the Atlantic valley may one day bring 

 you, who have so courageously braved Alpine 

 summits, to the historic hill of Sans Souci. . . . 



Something of Agassiz's astonishment and 

 pleasure at the encouragement given to his 

 projected work is told in his letters. To his 

 old friend Professor Valenciennes, in Paris, 

 he writes : " I have just had an evidence of 

 what one may do here in the interest of sci- 

 ence. Some six months ago I formed a plan 

 for the publication of my researches in Amer- 

 ica, and determined to carry it out with all 



