532 F. L. Tufts — Photometric Measurements. 



these readings. From the numbers thus obtained the percent- 

 age of light from the incandescent lamp transmitted by each 

 of the three glasses respectively was calculated for the differ- 

 ent observers. These results are given in the first three rows 

 of the second table. 



Table II. 



Percentage of light from lamp A 

 transmitted by — 

 Observer Eed glass Green glass Violet-blue glass 



W. S. Dennett 13-0 9'62 1 -30 



F. L. Tufts 12 9-62 1*20 



J. T. 2*04 13-8 4-75 



J. T., using ordinary 



wedge photometer __ 2-2 14*4 4*6 



Standard eye 13*7 9-62 1'39 



As a standard of color vision, the one already used by Pro- 

 fessor Rood was chosen. This he defined in substance as fol- 

 lows : The standard was the mean color vision of eleven per- 

 sons possessing, according to ordinary tests, normal vision. 

 This standard was indicated by 100 in the case of red, green 

 and violet-blue. One hundred was also taken as the maximum 

 attainable by any person in each case, as the experiments did 

 not deal with the general sensitiveness of the eye to light, but 

 with its relative sensitiveness to light of different colors. That 

 is to say, in the case of the color curve of each person, the 

 highest ordinate, whatever it may be, is set equal to 100, the 

 others following where the observations indicate on this 

 assumption. 



Both Dr. Dennett and the writer had had their color vision 

 expressed in terms of this standard, and the results, taken from 

 Professor Pood's article,* are given in the first two rows of 

 Table III. From these figures the percentage of the light 



Table III. 







Eed 



Green 



Violet -blue 



93-8 



100 



91'5 



89-9 



100 



87-8 



W. S. Dennett.,.. 



F. L. Tufts ._.".. 



J. T. 4-84 45-2 100* 



from an incandescent lamp which the standard eye would see 

 transmitted by the three glasses respectively, was computed 

 both from Dr. Dennett's readings and from the readings of the 

 writer. The averages are given in the last row of Table II. 



* This Journal, vol. viii, p. 258, Oct., 1899. 



