452 THE CAUSES OF THE xi 



we shall have proved it as far as certainty is pos 

 sible for us ; for, after all, there is no one of our 

 surest convictions which may not be upset, or at 

 any rate modified by a further accession of know 

 ledge. It Avas because it satisfied these condi 

 tions that we accepted the hypothesis as to the 

 disappearance of the tea-pot and spoons in the 

 case I supposed in a previous lecture ; we found 

 that our hypothesis on that subject was tenable 

 and valid, because the supposed cause existed in 

 nature, because it was competent to account for 

 the phenomena, and because no other known cause 

 was competent to account for them ; and it is upon 

 similar grounds that any hypothesis you choose to 

 name is accepted in science as tenable and 

 valid. 



What is Mr. Darwin s hypothesis ? As I appre 

 hend it for I have put it into a shape more con 

 venient for common purposes than I could find 

 verbatim in his book as I apprehend it, I say, 

 it is, that all the phenomena of organic nature, 

 past and present, result from, or are caused by, 

 the inter-action of those properties of organic 

 matter, which we have called ATAVISM and VARIA 

 BILITY, with the CONDITIONS OF EXISTENCE, or, 

 in other words, given the existence of organic 

 matter, its tendency to transmit its properties, and 

 its tendency occasionally to vary ; and, lastly, given 

 the conditions of existence by which organic mat 

 ter is surrounded that these put together are the 



