ON LIGHT. 339 



burning stick is whirled round, forming a ring of light), 

 and in the circle so formed spaces highly coloured 

 red, blue, or green, as well as dark and bright will 

 be seen, corresponding to the state of the image at the 

 instant it occupied those spaces, forming an easy, pleas- 

 ing, and very interesting experiment. 



(i 18.) An effect, the precise parallel to the scintillation 

 of the stars, might be produced, affecting the ear instead 

 of the eye, by sounding together two strings, at first ex- 

 actly in unison, and then very slightly increasing and 

 diminishing alternately the tension of one of them, thus 

 producing a succession of beats, not regular as in the 

 case of two strings permanently differing by a minute 

 interval of pitch, but capricious in their succession. 



