128 



SCIENCE 



[N. S. Vol. XLIII. No. 1100 



retina to light of different wave-lengths 

 but of equal energy. This relation is 

 known for a great number of subjects to 

 a quite satisfactory precision. It estab- 

 lishes the ratio of the light unit to the 

 energy unit, hence, is of fundamental im- 

 portance in illuminating engineering. 

 Strictly speaking, we can neither define 

 nor measure light without it. 



"When it comes to measuring the light 

 sensation caused by a given light impres- 

 sion, an apparently insurmountable diffi- 

 culty is encountered, for a sensation can 

 not be directly measured. The sensation is, 

 however, the integral of the sensibility and 

 the sensibility is proportional to the recip- 

 rocal of the just noticeable difference in 

 intensity and this may readily be measured. 

 The necessary data are being accumulated 

 and before long we shall be able to formu- 

 late the general laws of the visual reaction 

 to light intensity in the case of white light. 

 Similar data relating intensity sensibility 

 to color, intensity and time must next be 

 obtained. 



On entering a dark room we become able 

 to distinguish objects after a shorter or 

 longer interval of time depending upon 

 various conditions not yet worked out. 

 Kate of adaptation curves must be deter- 

 mined for all initial conditions of adapta- 

 tion, not only for white light but more par- 

 ticularly for the reds, yellows and greens 

 used in the safe lights of dark rooms. 



Very little is yet known of the relation 

 between visual acuity and the brightness 

 of the object viewed. The ability to distin- 

 guish fine details is known to fall off rapidly 

 with decreasing illumination, but we have 

 not the data for the formulation of any 

 laws. 



Illuminating engineers require a mass of 

 such data on the properties of the retina, 

 for the eye is the sole means of judging 

 whether lighting is good or bad and the 



conditions for best seeing have been only 

 very roughly worked out thus far. We re- 

 quire to know what illumination levels and 

 what contrasts are best and what are the 

 effects of excessive contrasts and oblique 

 glare in depressing the sensibility of the 

 retina. 



The precise measurement of color is an 

 almost unworked but important field of 

 applied optics. The preliminary part of 

 the work only has been done. The under- 

 lying theory has been roughed out, methods 

 have been devised and precision colorim- 

 eters designed. But our fundamental color 

 scales have been but partly worked out and 

 the various laws of color combination are 

 practically unknown. The work urgently 

 requiring attention in this field amounts to 

 quite a number of man-years. 



Within the necessary limits of this dis- 

 cussion only the more urgent problems in 

 the more important fields of applied optics 

 could be reviewed. The special problems of 

 refractometry, photometry, radiometry, 

 interferometry, spectrophotometry, polari- 

 metric analysis and other fields can not even 

 be enumerated here. It is hoped, however, 

 that this brief outline may have impressed 

 upon us all the necessity for concerted 

 effort in solving the numerous problems 

 which confront us. We trust that the for- 

 mation of this society will, by promoting 

 team work and well directed research, prove 

 to be a powerful factor in the advancement 

 of applied optics. This city has long been 

 a leader in the production of optical mate- 

 rials, may it become the great source of 

 optical ideas and the recognized home of 

 optical learning. P. G. Nutting 



SCIENTIFIC NOTES AND NEWS 



Dr. William W. Keen has been reelected 

 president of the American Philosophical Soci- 

 ety for 1916. The vice-presidents, Professors 

 William B. Scott, Albert A. Michelson and 



