8 SCIENCE AND THE HUMAN MIND 



retain their jurisdiction. When, based on fact and 

 supported by experiment, it passes over dry-shod to 

 science, the philosopher's work is done ; and, if he 

 be wise, he turns to other problems. The realm of 

 metaphysics is always contracting ; but each suc- 

 cessive concentration gives more power of intensive 

 attack on the deeper and better defined problems 

 which remain behind. The philosopher is continu- 

 ally losing to science ground which he has surveyed 

 for himself, and is always gaining by his loss, 

 i The debt which science owes to philosophy is two- 

 fold. From philosophy it learns its limitations and 

 its interrelations ; from philosophy it takes over one 

 problem after another, often in an advanced state of 

 preparation for mathematical or experimental treat- 

 ment. Philosophy may recognize the existence of 

 the problem and formulate the possible solutions. 

 Science alone can decide between them. Greek 

 thinkers could point out that matter must be either 

 continuous or atomic, and follow some way along the 

 path of logical deduction from each hypothesis. But 

 each philosopher was at liberty to take either alterna- 

 tive, and was powerless to convince his neighbour of 

 the justness of his cause. It needed the slow accumula- 

 tion of the definite experimental knowledge of chemical 

 combination, available at the opening of the nineteenth 

 century, to enable Dalton and Avogadro to bring 

 forward overwhelming evidence in favour of the 

 atomic theory, and to establish it in the name 

 of science. It needed the marvellous advance of 

 another hundred years to demonstrate directly to 

 human eyes the existence and movement of the 

 ; individual atom. 



