xii PEEFACE. 



tliat in all cases where I do draw upon it I shall be careful 

 to state the source to which I am indebted. 



[The above was written when I sent this work to the 

 publishers several months ago, and I have thought it 

 best to leave the concluding paragraph as it originally 

 stood. But in making this explanation, I cannot allude 

 to the calamity which has since occurred without paying 

 my tribute, not alone to the memory of the greatest 

 genius of our age, but still more, and much more, to the 

 memory of a friend so inexpressibly noble, kind, and 

 generous, that even my immense admiration of the 

 naturalist was surpassed by my loving veneration for the 

 man.] 



