786 



SCIENCE. 



[N. S. Vol. VII. No. 180. 



In this manner Mr. T, known to be 

 somewhat color blind to red, was ex- 

 amined, and I found that putting the 

 amount of red light perceived by myself as 

 100 he perceived only 63.04 per cent. It 

 was also ascertained that his vision was 

 not only defective for red light, but to a 

 less extent for green, he perceiving only 

 85.5 per cent, of it. A set of control ex- 

 periments were then made on Mr. T. The 

 blue glass was replaced by the green glass 

 and the red glass was put next to the mov- 

 able lamp, and for the moment it was as- 

 sumed that the vision of Mr. T for green 

 light was the same as my own — in other 

 words, green instead of blue light was 

 made the standard, and it was temporarily 

 assumed that both of us were equally af- 

 fected by green light. The amounts of red 

 perceived by him in two experiments were 

 71.3 and 70 per cent., as compared with 

 100 by myself. But as he really perceived 

 only 85.5 per cent, of the green light, to ob- 

 tain the correct value of his perception of 

 red in these two experiments we must take 



^ of 70.6 = 60.4, which differs from the 



value for the red directly obtained by 2.6 

 per cent. It may be remarked, in passing, 

 that this case of color blindness was not 

 suspected till revealed by some flicker ex- 

 periments with colored discs made by my- 

 self in. Mr. T's presence. 



A second case which I examined was of 

 a more pronounced character, and had pre- 

 viously been known to exist. Out of 100 

 rays of red light perceived by myself, Mr. A. 

 was affected only by 19.44 per cent., violet- 

 blue, as befoi-e, being the standard. With 

 the same standard only 86.9 per cent, of the 

 green light was perceived. Taking green 

 as the standard, 22.9 and 23.3 per cent, of 

 red was perceived, and as before, |-|-| of 

 23.1 = 20, instead of 19.44, obtained in the 

 direct determination. 



The third case of Mr. B. was quite similar 

 to the last, a well-known and pronounced 

 instance of red color-blindness. Violet-blue 

 being taken as the standard, 20.4 per cent, 

 of red was perceived, and 83.8 of green light. 

 Green being made the standard, 25.5 per 

 cent, of red light was perceived, and as 

 before fl^'of 25.5 = 21.36, instead of 20.4, 

 as directly obtained when using violet-blue 

 light as the standard. 



In these determinations, as in all others 

 of a similar kind which I have superin- 

 tended, the persons experimented on moved 

 the lamp themselves, without assistance 

 from me, and, owing to the presence of 

 screens, were in complete ignorance of the 

 results they were obtaining. I have been 

 quite surprised to find how quickly persons 

 wholly unused to physical experiments of 

 any kind were able to obtain reliable re- 

 sults with the flicker photometer as now 

 arranged. They needed a little more time, 

 and their probable error was somewhat 

 larger than is the case with an experienced 

 person. Each result given above is ob- 

 tained ft-om the mean of from ten to fifteen 

 readings registered on the filet of paper con- 

 nected with the moving lamp. Finally, it 

 is to be remembered that in all of these de- 

 terminations I have for the time being as- 

 sumed my own color-vison to be strictly 

 normal, which, now that we have this ac- 

 curate photometric, method, is hardly quite 

 a safe proceeding for any man, or even 

 woman, as some of my unpublished results 



show. 



Ogden N. Eood. 

 Columbia Univeesity. 



THE OPENING OF THE NEW LABORATORY 

 FOR PHYSICAL CHEMISTRY IN LEIPSIC. 

 A short time ago an abstract of the ad- 

 dress delivered by Nernst at the opening of 

 the new laboratory for physical chemistry 

 at the University of Gottingen was given 

 in Science. The University in Leipsic has 



