138 BARUS— ELLIPTIC INTERFERENCE. [April 21. 



a corona were produced by a sufficient number of fog particles dis- 

 tributed throughout a plane normal to the undeviated rays. Now 

 let the alternate particles be moved in the same way slightly to the 

 rear of their original position and let the distance between the two 

 planes be small relatively to the wave length of light. In such a 

 case there should be two identical coronas, superimposed in all their 

 parts and they should therefore interfere. Inasmuch, however, as 

 even small fog particles are of the order of size of .0001 cm. and 

 their mean distance apart fifty times larger, i. e., .005 cm., it remains 

 to be proved whether such an effect can be looked to as an explana- 

 tion of the disc colors of coronas. 



Brown University, 

 Providence, R. I. 



