C. Barus— Coronas with Mercury Light. 79 



As a rule s'" is less than twice s' '. The data for s' and s are 

 obtained alternately as the figure shows, the green color passing 

 from the disc of the first ring and returning again, in suc- 

 cession. 



Inferences. 



5. Interference and diffraction. — The tables and chart show 

 in the first place, that the disc and first ring of the coronas are 

 alternately of a vivid green, other colors being dull because the 

 remaining lines of the mercury spectrum are faint. At inter- 



