iVTODERN VIEWS ON MATTER. 2l9 



stitutc the high-water mark of the world's experiincjital physics during- 

 the beginning- of this centurv. 



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 l)rieily summarize a few main facts. 



Electrons have been shown to be shot off from an}' negatively 

 charged body, especially from negatively electritied metals, when 

 exposed to ultra-violet light. 



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

 render it electroly tically conducting; also, of course, they can discharge 

 positively electritied bodies themselves, and can thus be most readily 

 detected in small numbers. 



Electrons in orlntal motion have been shown to constitute the mech- 

 anism bv which atoms are able to radiate light; and a great mass of 

 semiastronomical facts concerning these orbits and their perturl>ations 

 have been obtained by immersing the source of light in a strong mag- 

 netic held and observing the minute but ver}' detinite changes of 

 spectra thereby produced, a Vjranch 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 wa3'S 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 ])een 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 l)een shown 

 capable of losing an electron, of having at least one chipped off' it. 

 The^ electron has been shown to possess in kind, though not in degree, 

 the fundamental properties of the original atom of which it had 

 formed a part; and it liecomes a reasonable hypothesis to surmise that 

 the whole of the atom may be built up of positive and negative elec- 

 trons interleaved together, and of nothing else; an active or charged 

 ion having one electron in excess or defect, but the neutral atom 

 having an exact number of pairs. The oppositely charged electrons 

 are to bethought of on this hypothesis as flying about inside the atom, 

 as a few thousand specks like full stops might fly al)Out inside this 

 hall, forming a kind of cosmic system under their strong nmtual 

 forces, and occupying the otherwise empty region of space which we 

 call the atom — occupying it in the same sense that a few scattered l)ut 

 armed soldiers can occupy a territory — occupying it by forceful 

 activitv, not 1)V bodilv bulk. 



