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Mr. P. G. Nutting on the 



representing it, and the related Purkinje effect, and made a 

 rough determination of its principal constant, the maximum 

 ratio of the candle to the watt. 



Recently Ives * has applied the flicker photometer to the 

 determination of visibility with excellent results, and has 

 published data for eighteen different subjects in the region 

 from '48 to -6*4//,. I have here to present a similar set of 

 data for twenty-one subjects with extensions of the visibility 



Fig. 1. — Diagram of Visibility Apparatus. 



Q 



-< 



I/O 



curves farther into the red and violet, and the results of a 

 number of direct determinations of the maximum ratio of 

 the candle to the watt. 



* H. E. Ives. Phil. Mag. Dec. 1912. See also Thurmel, Aim. Ph. 

 xxxiii. p. 1154 (1910). 



