THE CONSTITUTION OF MATTER AND THE EVOLUTION 

 OF THE ELEMENTS.^ 



By Prof. Sir Ernest Kuthekford, F. R. S. 



[With 5 plates.] 



Speculations as to the constitution of matter have occupied an 

 important place in the development of scientific knowledge. The 

 idea that all matter was composed of minute particles called atoms 

 was j)ut forward long- ago by the Greek philosophers and w^as ad- 

 vanced again with varying degrees of confidence by philosophic 

 men at the dawn of the scientific age. For example, Newton sug- 

 gested that matter was composed of atoms which w^ere likened to 

 " hard massy balls," while Robert Boyle regarded a gas to consist 

 of atoms which were in brisk motion. The first definite formula- 

 tion of the atomic theory as a scientific hypothesis was given by Dal- 

 ton, of Manchester, in 1803 in order to explain the combination of 

 atoms in multiple proportion. The necessity of distinguishing be- 

 tween the chemical atom and the chemical molecule was soon recog- 

 nized, while the famous hypothesis of Avogadro that equal volumes 

 of all gases at the same temperature and pressure contain equal num- 

 bers of molecules still further extended the usefulness of the theory. 

 The whole superstructure of modern chemistry has been largely 

 reared on the foundations of the atomic theory. The labors of the 

 chemist have revealed to us the presence of more than 80 distinct 

 types of elements, each of which has a characteristic atomic weight, 

 and in most cases sufficiently distinct physical and chemical proper- 

 ties to allow of its separation from any other element by the applica- 

 tion of suitable methods. 



It has been generally assumed that all the atoms of one element 

 are identical in shape and weight, and until a few years ago w^ere 

 supposed to be permanent and indestructible. The close study of 

 the variation of chemical properties of the elements with atomic 

 weight led Frankland and Mendelief to put forward the famous 

 " periodic law," in which it was shown that there was a periodic 



^ The William Ellery Hale Lecture, delivered at the annual meeting of the National 

 Academy of Sciences, Washington, D. C, 1914. Reprinted by permission. 



167 



