THE 



POPULAR SCIENCE 



MONTHLY 



AUGUST, 1915 



THE CONSTITUTION OF MATTER AND THE EVOLUTION 



OF THE ELEMENTS 1 



By Professor Sir ERNEST RUTHERFORD, P.R.S. 



UNIVERSITY OF MANCHESTER 



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 

 put forward long ago by the Greek philosophers, and was advanced 

 again with varying degrees of confidence by philosophic men at the 

 dawn of the scientific age. For example, Newton suggested that mat- 

 ter was composed of atoms which were likened to "hard massy balls/' 

 while Robert Boyle regarded a gas to consist of atoms which were in 

 brisk motion. The first definite formulation of the atomic theory as a 

 scientific hypothesis was given by Dalton of Manchester in 1803 in 

 order to explain the combination of atoms in multiple proportion. The 

 necessity of distinguishing between the chemical atom and the chemical 

 molecule was soon recognized, while the famous hypothesis of Avogadro 

 that equal volumes of all gases at the same temperature and pressure 

 contain equal numbers of molecules still further extended the useful- 

 ness 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 

 eighty distinct types of elements, each of which has a characteristic 

 atomic weight, and in most cases sufficiently distinct physical and 

 chemical properties to allow of its separation from any other element by 

 the application 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 were supposed 

 to be permanent and indestructible. The close study of the variation 

 of chemical properties of the elements with atomic weight led Frank- 

 land and Mendelief to put forward the famous " periodic law," in which 

 it was shown that there was a periodic variation in the chemical proper- 



i First course of lectures on the William Ellery Hale Foundation, National 

 Academy of Sciences, delivered at the Washington Meeting, April, 1914. 



vol lxxxvii.— 8. 



