SUPERPOSED STROBOSCOPIC VELOCITIES 515 



is drawn, may include the zero value, or stationary condition. Also, 

 with reference to the f and N curves, with B constant, the same pos- 

 sibility is again obvious, from the intersections of the line N=con- 

 stant, with the velocity curves. The actual production, through a 

 proper choice of the necessary quantities in a suitable apparatus, 

 of such a visual complex eiTect, confined to a single row of dots on 

 the stroboscopic screen, and due to but one illumination frcciuency, 

 is an undertaking that would appear to be worth while. 



In conclusion, the several mathematical situations described sug- 

 gest a definite line of experimental study, of possible interest in 

 psychology. 



Washington, D. C. 

 September, 1919. 



