472 POPULAR SCIENCE MONTHLY 



irregularity of the lens structure and thus to supply illusive satellites 

 to planets or fictitious companions to double stars. 



Chromatic Kings 



The illusive chromatic rings which follow do not bear so much on 

 questions of Martian topography as the preceding halo and rays. Yet 

 they are interesting of themselves and have an influence on color 

 estimations. The first is the broad prismatic ring which extends from 



about 31/2 ° to 5° from the 

 source of light with red on 

 the outside and green or blue 

 on the inside. This shows well 

 on any brilliant light such as 

 the full moon or a bright elec- 

 tric light. 



The second is a narrow 

 blue ring, of interest on ac- 

 count of its beauty. It is best 

 seen on an electric arc light of 

 intense blue color — and the less 

 continuous spectrum the light 

 shows, the better. Standing at 



fig. 10. rays and detached spots. a distance of one hundred and 



fifty or two hundred feet, one 

 may see a beautiful narrow blue line forming a circle fully two feet 

 in diameter about the light. As the color of the light changes to 

 yellow, which it frequently does, the ring rapidly disappears into the 

 center of. the light. 



This ring may be seen in the laboratory by passing the blue light 

 of the spectrum through a pin hole. In mid-blue its radius is about 

 12'. Various experiments show that this illusion is produced at the 

 margin of the pupil by the bending of the blue rays too sharply toward 

 the optical axis of the eye. These rays therefore focus in front of 

 the retina and on reaching it form a blue ring outside of the true 

 image. 



Badiating Lines from Near the Center of a Blank Disk 



The only remaining illusion to which I call attention is one of 

 much importance in planetary work, but one for which I shall not 

 attempt an explanation. Frequently in observing a blank white disk, 

 lines have appeared to me to radiate from some point near the center. 

 When first I observed lines of that character, not knowing whether 

 they were really there or not, I considered them genuine and for a 

 long time represented them in the form of a star with four or eight 



