THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE 



-^ — 



[SIXTH SERIES.] 



SEPTEMBER 1901. 

 — 



XXIII. The Cause of the Structure of Spectra. 

 By William Sutherland *. 



THE following inquiry into the cause of the structure of 

 spectra brings out the result that the atoms of the 

 different elements are all equipped with the same, or nearly 

 the same, electrical apparatus, whereby the mechanical energy 

 of the atom is made communicable to the aether for radiation. 

 The atom with the kinetic energy assigned to it in the kinetic 

 theory of matter exercises no direct mechanical effect on the 

 aether, but is like a fly-wheel driving the dynamo to which we 

 may liken the electrical equipment of the atom. 



The atoms of the various elements are vastly different in mass 

 and size, as we know, but as they drive the same or nearly 

 the same electrical appliance (arrangement of electrons) 

 they have their spectra included in the comparatively limited 

 region of vibrations to which the human eye is sensitive, 

 comparatively limited, even when extended by bolometer and 

 photographic film. It is a very remarkable fact that the 

 most energetic part of the spectrum of so many diverse 

 elements lies within the one poor octave of human vision ; 

 and it must be on account of the great distinctness of our 

 colour sensations, that physicists have not realised that really 

 the biggest essential fact discovered by the spectroscope is 

 that the frequencies of the vibrations of the different atoms 

 are so nearly equal. For example, it will be shown that the 

 fundamental mechanical period of vibration of the caesium 

 atom is six times that of the lithium atom, and yet the ratio of 



* Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 2. No. 9. Sept. 1901. S 



