F. L. Tufts — Photometric Measurements. 531 



Art. XL VII. — Photometric Measurements on a Person Pos- 

 sessing Monochromatic Vision ; by F. L. Tufts. 



In an article on " Color Vision and the Flicker Photome- 

 ter,"* the late Professor Ogden N. Pood reported some meas- 

 urements made by means of the flicker photometer on a num- 

 ber of persons possessing normal color vision and also on three 

 cases of red color-blindness. Through the kindness of Dr. W. 

 S. Dennett of New York City, the writer was enabled, some 

 three years ago, to extend these measurements to the case of a 

 person possessing monochromatic vision. Owing to the lim- 

 ited amount of time which the subject, referred to in this 

 article as J. T., could give to the work, the measurements were 

 not so complete as the writer would have liked to make them. 

 He has not previously published the results in hopes that cir- 

 cumstances might some time enable him to apply more exten- 

 sive tests. This now seems very improbable, and the results 

 of the work already done are given in the following pages. 



The flicker photometer used was of the same type as the one 

 already described by Professor Pood,f and the colored glasses 

 were the same as the three used by him in his work on color 

 vision.^ 



The candle powers of two incandescent lamps referred to as 

 A and B were compared by means of the flicker photometer, 

 first directly and then when each of the three glasses respect- 

 ively was placed between lamp A and the photometer wedge. 

 Each of these comparisons was made by Dr. Dennett, J. T. 

 and the writer, from ten to twenty readings being taken in 

 each case. The numbers expressing the relative candle powers, 

 given in the first three rows of Table I, were computed from 



Table I. 



, Candle power of — 



A A 



through through 



A red glass green glass 



in terms in terms in terms 



Observer of B of B of B 



W.S.Dennett 4-00 -520 -385 



F. L. Tufts 4-00 -480 -385 



J. T 4-94 -101 -683 



J. T., using ordinary 



wedge photometer 5*00 '11 '72 



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

 \ Ibid., vol. viii, p. 194, Sept., 

 % Ibid., p. 258, Oct., 1899. 



A through 



violet- 

 blue glass 

 in terms 

 of B 



•052 

 •048 

 •235 



•23 



