VLll PEEFACE. 



man by an ignorant one. My ignorance would save 

 me from dwelling too strictly or too long on technical 

 details. With the exposition of your doctrine I would 

 mingle some fragments of your biography. I would 

 pass from a discovery to an anecdote, and so arrange 

 matters as to give the book not only the character 

 of a familiar scientific conversation, which would 

 hardly be more than. the echo of what I have learnt 

 while near you, but also to make it a reflex of your 

 life.' 



' You should postpone that until I am no longer 

 here.' 



' Why so ? Why, before assigning to them their 

 places, should we wait till those whose names will en- 

 dure have disappeared from the scene ? No ; it is you, 

 living, that I wish to paint you, in full work, in the 

 midst of your laboratory. And, in addition to all 

 other considerations, I would add, that your presence 

 in the flesh will be the guarantee of my exactitude.' 



July 188a 



