14 Britain's Heritage of Science 



confining itself to that which it can see would have grown 

 very slowly indeed. We owe that much to the Greek 

 philosophers, that they took a wider view, and at any rate 

 tried to evolve a system which would satisfy our sense 

 of harmony in the perception and interpretation of Nature. 

 Their imagination frequently led them astray, but as often 

 prepared the way for the evolution of the correct view. The 

 idea that all matter is composed of separate small particles 

 which cannot further be subdivided appears very early 

 among the Greek philosophers. Anaxagoras, in the fifth 

 century before Christ, assumed the existence of indestructible 

 and immutable elements of which all bodies are composed, 

 and called them " seeds." Half a century later, Democritus 

 first used the word " atom," but differed from Anaxagoras 

 by ascribing the different properties of bodies not to a differ- 

 ence in kind, but merely to one in shape and arrangement. 

 Aristotle rejected this hypothesis completely, and his 

 unhappy doctrine, apparently borrowed from Indian sources, 

 which treats matter as an embodiment of mixtures in different 

 proportions of the imaginary elements, fire, earth, water, 

 and air, had a most paralysing influence on the history of 

 science. The atomic theory consequently remained through 

 centuries the subject of metaphysical speculations and the 

 plaything of philosophers; as the foundation of chemical 

 science, it takes its place only in modern times. But 

 one great obstacle had to be removed. The chemistry 

 of the eighteenth century was entirely under the influence 

 of an erroneous theory of combustion, according to which 

 inflammable bodies contained an invisible substance 

 " phlogiston " showing itself as a flame on being expelled, 

 and no progress was possible until the true nature of com- 

 bustion had been demonstrated by the eminent French 

 chemist Lavoisier. His explanations were so simple and 

 convincing that it is difficult to understand why the atti- 

 tude taken up by English chemists with regard to them 

 was entirely hostile. Cavendish, like Black and Priestley, 

 adhered to the phlogiston theory, even when the latter, by 

 his discovery of oxygen, had supplied the chief weapon by 

 which it ultimately fell. 



Robert Boyle (1627-1691) had clearly shown how a 



