viii A PREFATORY LETTER. 



by a late President of the Geological Society. If you find 

 its phraseology, in some places, to be more vigorous than seems 

 needful, recollect that it was written in the heat of our first 

 battles over the Novum Organon of Biology ; that we were all 

 ten years younger in those days ; and last, but not least, that 

 it was not published until it had been submitted to the revision 

 of a friend for whose judgment I had then, as I have now, the 

 greatest respect. 



Ever, my dear TYNDALL, 



Yours very faithfully, 



T. H. HUXLEY. 



LONDON, June, 1870. 



