16 



CORA D. REEVES 



distance and voltage, an area of the white stimulus plate 

 equal to that illuminated by the Nernst lamp with the 

 blue filter interposed and without a slit. These equal blue 

 and white areas were then similarly placed with refer- 

 ence to the flicker photometer, and were equated by vary- 

 ing the distance of the lamp. The tungsten lamp, at its 

 given voltage, was then calibrated by Dr. E. F. Barker 

 of the Physics Department of the University of Michigan. 



Fig 7 



Graph of light energy in terms of width of slit. The relative intensities of light 

 reaching the center and the margin P of the lens aperture is represented. Abscissae 

 give widths of slit, ordinates give relative light intensities. 



Measurements against Bureau of Standards Lamp No. 

 2435 gave 2.35 candle power for the lamp. As it was 1 

 meter from the plate when equated, the blue stimulus 

 patch had an intensity of 2.35 meter candles. It is to be 

 understood that the blue plate was kept as nearly as pos- 

 sible at this intensity throughout the experiments. 



In order to determine the relation between the light 

 energy reaching the lens aperture and the width of the 

 slit, and also to determine the relative light at the center 



