EXPLORING THE ATOM 



a series of lines in the spectrum. The chemical test 

 thus afforded is exquisitely delicate. There may be 

 but the smallest trace of a given substance present, 

 as in the case of our infinitesimal droplet of salt solu- 

 tion, but the tell-tale lines of the spectrum will 

 record the trace of this individual substance, even in 

 the midst of many other substances. 



If while examining our sodium flame through the 

 spectroscope we were to hold the flame between 

 the poles of a powerful electro-magnet, we should 

 observe that the sodium lines which before appeared 

 single are now split in two and separated. This 

 phenomenon is called the Zeeman effect in honor of 

 its discoverer, Professor Peter Zeeman of Amster- 

 dam. It is a phenomenon of vast importance from 

 the physicist's standpoint, inasmuch as it gives inter- 

 esting clues to the activities of the atomic forces, 

 and to the character of light. 



This phenomenon of the splitting up of spectral 

 lines has been observed by Professor George E. Hale, 

 Director of the Mt. Wilson Observatory, in connec- 

 tion with the light emanating from spots on the 

 surface of the sun. The observation shows that sun 

 spots are powerful magnetic fields. Thus the sun 

 spot gives a demonstration on a magnificent scale 

 of physical laws that may be tested, changed only in 

 degree and not in kind, in the laboratory. 



Incidentally, Professor Kale's observation serves 

 in a sense to explain the relation that had previously 

 been observed between outbursts of sun spots 

 which are in reality gigantic volcanoes of gaseous 

 matter and disturbances of terrestrial magnetism. 



8 105 



