174 FRAGMENTS OF SCIENCE. 



by the book itself which no exposition of it, however 

 luminous, can convey ; and that is the imprebsion of 

 the vast amount of labour, both of observation and of 

 thought, implied in its production. Let us glance at 

 its principles. 



It is conceded on all hands that what are called 

 * varieties ' are continually produced. The rule is pro- 

 bably without exception. No chick, or child, is in all 

 respects and particulars the counterpart of its brother 

 and sister; and in such differences we have 'variety' 

 incipient. No naturalist could tell how far this 

 variation could be carried ; but the great mass of them 

 held that never, by any amount of internal or external 

 change, nor by the mixture of both, could the offspring 

 of the same progenitor so far deviate from eacli other 

 as to constitute different species. The function of the 

 experimental philosopher is to combine the conditions 

 of Nature and to produce her results ; and this was the 

 method of Darwin. 1 He made himself acquainted with 

 what could, without any manner of doubt, be done in 

 the way of producing variation. He associated himself 

 with pigeon-fanciers bought, begged, kept, and ob- 

 served every breed that he could obtain. Though de- 

 rived from a common stock, the diversities of these 

 pigeons were such that ' a score of them might be 

 chosen which, if shown to an ornithologist, and he were 

 told that they were wild birds, would certainly be 

 ranked by him as well-defined species.' The simple 

 principle which guides the pigeon-fancier, as it does the 

 cattle-breeder, is the selection of some variety that 

 strikes his fancy, and the propagation of this variety 



1 The first step only towards experimental demonstration has 

 been taken. Experiments now begun might, a couple of centuries 

 hence, furnish data of incalculable value, which ought to be airp- 

 plied to the science of the future. 



