MODERN THEORIES OF ELECTRICITY AXD MATTER.'^ 



By Madame Curie, ('Iianx' dc cotirs a hi ,Sorh<)ini<'.'> 



^Yhen one reviews the progress made in the department of physics 

 within the last ten years, he is struck by the change whicli has taken 

 place in the fundamental ideas concerning the nature of electricity 

 and matter. The change has been brought about in part by researches 

 on the electric conductivit}' of gas, and in part by the discovery and 

 study of the phenomena of radioactivity. It is. I believe, far from 

 being finished, and we may well be sanguine of future developments. 

 One point which appears to-day to be definitely settled is a view of 

 atomic structure of electricity, which goes to confirm and complete 

 the idea that we have long held regarding the atomic structure of 

 matter, which constitutes the basis of chemical theories. 



At the same time that the existence of electric atoms, indivisible by 

 cur present means of research, appears to be established with cer- 

 tainty, the important properties of these atoms are also shown. The 

 atoms of negative electricity Avhich we call electrons, are found to 

 exist in a free state, independent of all material atoms, and not hav- 

 ing any properties in common with them. In this state they possess 

 certain dimensions in space, and are endowed with a certain inertia, 

 which has suggested the idea of attributing to them a corresponding 

 mass. 



Experiments have shown that their dimensions are very small com- 

 pared with those of material molecules, and that their mass is only 

 a small fraction, not exceeding one one-thousandth of the mass of an 

 atom of hydrogen. They show also that if these atoms can exist 

 isolated, they may also exist in all ordinary matter, and may be in 

 certain cases emitted b}- a substance such as a metal without its 

 properties being changed in a manner appreciable by us. 



If, then, we consider the electrons as a form of matter, we are led 



a Translated, by permission, from Revue Seientifiqne, Paris, 5" Serie, Nos. 20, 

 21, vol. VI, November 17 and 24, lOOC. 



6 Opening lectvire of the course in general physics delivered at the Sorbonne, 

 November 5, 1906. 



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