RECORDS OF MEETINGS OF 1907 357 



nosity if, on rapidly replacing one by the other before the eye, there is no 



sensation of flickering. The author has modified the flicker photometer 

 of Eood so as to use spectral colors. A white disk, rotating between the 

 telescope and the prism of a spectroscope, is cut away for half of its cir- 

 cumference, so as to admit the colored ray from the prism for half of the 

 time, while for the other half it reflects white light from a lamp the distance 

 of which is adjustable along a photometer bar. By moving the lamp along 

 the bar a point is found at which there is no flicker between the white and 

 the colored lights. In this way the luminosity of different parts of the 

 spectrum can be determined with reference to a given white. The relative 

 luminosity of different parts of the spectrum was not changed by fatiguing 

 the eye to one color. Though the eye be fatigued to green by several min- 

 utes' exposure to it, so that gray objects appear purple, yet the green of 

 the spectrum has the same luminosity relatively to the other parts of the 

 spectrum as when the eye is fresh. (An exception must be made to this 

 statement, in the case of prolonged exposure to red; if this exposure is not 

 simply long enough to give the complementary after-image, but is con- 

 tinued for a considerable number of minutes, the effect is to displace the 

 point of maximum luminosity towards the violet.) This seems good evi- 

 dence of the separateness of the luminosity and color senses. Another 

 fact bearing in the same direction is that the luminosity curve of red-green 

 blind eyes shows no constant deviation from the curve for normal eyes. 

 The color-blind eyes so far examined do indeed show luminosity curves 

 differing from that obtained from the majority of normal eyes, but the 

 deviations are in some cases in one direction, in others in the opposite; 

 and some eyes which are apparently normal in color vision have similar 

 deviations from the curve obtained from the majority. 



Professor Oattell said in abstract; The usual method of demonstrating 

 the fovea entoptically, by looking through a blue glass or a chrome alum 

 solution, fails with many individuals. But if the glass is removed after a 

 few seconds, an after-image effect shows the fovea clearer than the back- 

 ground ; and this is more readily seen than the effect while the blue screen 

 is before the eye. The explanation of the effect is probably that the yellow 

 spot abs rbs much of the blue light, so that that part of the retina is less 

 fatigued than the surrounding region. 



Dr. Wells communicated a study of the maximum rate of repeated vol- 

 untary movements during and at the limit of practise in one normal indi- 

 vidual, with comparative reference to the performance in other normal 

 and in pathological subjects. The maximum rate has little, if any, relation 

 to subjective feeling of efficiency. The practise curve shows less diurnal 

 variation in its earlier than in its later stages. The general effect of prac- 

 tise from day to day is to increase initial efficiency, while the general effect 



