20 INTRODUCTORY [ch. 



with the facts of embryology or the phenomena of inheritance, the 

 common language of the, books seems to deal too much with the 

 material elements concerned, as the causes of development, of 

 variation or of hereditary transmission. Matter as such produces 

 nothing, changes nothing, does nothing; and however convenient 

 it may afterwards be to abbreviate our nomenclature and our 

 descriptions, we must most carefully realise in the outset that the 

 spermatozoon, the nucleus, the chromosomes or the germ-plasma 

 can never act as matter alone, but only as seats of energy and as 

 centres of force. And this is but an adaptation (in the light, or 

 rather in the conventional symboHsm, of modern science) of the old 

 saying of the philosopher : apx^ yo.p r) <j>voLs fxdXXov rrjs vXrjg. 



Since this book was written, some five and twenty years ago, 

 certain great physico-mathematical concepts have greatly changed. 

 Newtonian mechanics and Newtonian concepts of space and time 

 are found unsuitable, even untenable or invahd, for the all but 

 infinitely great and the all but infinitely small. The very idea of 

 physical causation is said to be illusory, and the physics of the 

 atom and the electron, and of the quantum theory, are to be 

 elucidated by the laws of probability rather than by the concept 

 of causation and its effects. But the orders of magnitude, whether 

 of space or time, within which these new concepts become useful, 

 or hold true, lie far away. We distinguish, and can never help 

 distinguishing, between the things which are of our own scale and 

 order, to which our minds are accustomed and our senses attuned, 

 and those remote phenomena which ordinary standards fail to 

 measure, in regions where (as Robert Louis Stevenson said) there 

 is no habitable city for the mind of man. 



It is no wonder if new methods, new laws, new words, new modes 

 of thought are needed when we make bold to contemplate a Universe 

 within which all Newton's is but a speck. But the world of the 

 Hving, wide as it may be, is bounded by a famihar horizon within 

 which our thoughts and senses are at home, our scales of time and 

 magnitude suffice, and the Natural Philosophy of Newton and 

 Gahleo rests secure. 



We start, like Aristotle, with our own stock-in-trade of know- 

 ledge: dpKTeov OLTTO Tcov rjfjuv yvajpLjjLojv. And only when we are 



