74G 



Mr. H. E. Ives on the 



be considered " correct/' The previous work of the writer 

 cast doubt on this belief, since the equality of brightness 

 luminosity curves were found to change their shape and 

 position after intervals of time sufficient to destroy one's 

























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EQUALiry OF BRIGHTNESS 



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SURROUA 



IBlNG FIELD 







memory of previous settings. The present work seems to be 

 conclusively against the belief that a " correct " criterion of 

 equal brightness may be attained by mere practice. While 

 with any given comparison source quite definite and con- 

 sistent spectral luminosity curves may be obtained, these 

 experiments show that after working with several different 

 comparison sources, a return to the first one does not mean a 

 return to the original criterion. It appears therefore that 

 the differences introduced by changing the standard of com- 

 parison must be looked upon as psychological. One's judg- 

 ment is disturbed, and the part played by judgment in the 

 case where different colours are matched for brightness may 

 be very large. The results plotted in fig. 1 are for high 

 illuminations and small field ; similar results were obtained 

 for the other conditions of illumination and field size. 



These remarks apply only to the equality of brightness 

 method. The curves obtained by the flicker method showed 

 no deviation from each other which could with certainty be 

 considered greater than the errors of measurement. In fig. 1 

 therefore is plotted a single flicker curve. The equality of 



