MODERN VIEWS ON MATTER. 293 



The final definite establishment of the fact that these flying par- 

 ticles are not atoms of matter, but are bits chipped off the atoms, frac- 

 tions of an atom as it were, the same identical kind of bits being 

 chipped off every kind of chemical atom, their mass always about one 

 thousandth of that of a hydrogen atom, and moving under favorable 

 circumstances with something not much less than the speed of light, is 

 due to the researches of Professor J. J. Thomson and his coadjutors 

 in the Cavendish Laboratory, Cambridge, and represents a, long series 

 of measurements devised and executed with consummate skill. 



I have no time to go into detail concerning these important and 

 elaborate and most interesting investigations. Suffice it to say that 

 portions of them are due to your own Wykeham professor of physics. 

 Professor Townsend, working in conjunction and collaboration with 

 others, under the leadership of Professor J. J. Thomson; and that 

 this whole series of Cavendish Laboratory researches may be said to 

 constitute the high- water mark of the world's experimental physics 

 during the beginning of this century. 



5. I must not dwell upon the properties and powers of electrons, 

 nor upon the experimental means by which these measurements were 

 made, for it is far too large a subject. I must exhibit a few diagrams, 

 and briefly summarize a few main facts. 



Electrons have been shown to be shot off from any negatively 

 charged body, especially from negatively electrified metals, when ex- 

 posed to ultra-violet light. 



When shot into a mass of air they ionize that air for a time, and 

 render it electrolytically conducting; also of course they can discharge 

 positively electrified bodies themselves, and can thus be most readily 

 detected in small numbers. 



Electrons in orbital motion have been shown to constitute the 

 mechanism by which atoms are able to radiate light; and a great 

 mass of semi-astronomical facts concerning these orbits and their 

 perturbations have been obtained by immersing the source of light 

 in a strong magnetic field, and observing the minute but very definite 

 changes of spectra thereby produced: a branch of science with which 

 the names of H. A. Lorentz, of Leyden, and Zeeman, of Amsterdam, 

 will be inseparably associated. 



In all these and other ways the electron has become a familiar 

 object. It constitutes the ionic charge of matter. Multiples of it, 

 but no fractions, are possible. Its mass, its charge and its speed 

 have been frequently measured by different processes, and always with 

 consistent results. It is the most definite and fundamental and simple 

 unit which we know of in nature. 



It has thus displaced the so-called atom of matter from its funda- 

 mental place of indivisibility. The atom of matter has been shown 



