IN ITS RELATION TO THE EYE. 477 



servers, with the exception of two meridians for one observer, the 

 point of maximal sensitivity to discomfort was out of the center of 

 the retina; the nasal half of the retina was more sensitive than the 

 temporal half and the upper half more sensitive than the lower. 

 In passing from the center to the periphery of the retina, the sensi- 

 tivity is found first to increase and then to decrease, becoming ex- 

 tremely little at the limits of the field of vision. In the horizontal 

 meridians both on the temporal and nasal sides, maximal sensitivity 

 is found around and in the region included between 15 "-45° ; in the 

 vertical meridians, around and in the region included between 15° 

 and 30°. 



V. The Effect of Different Illuminants on the Power of the 

 Eye to Sustain Clear and Comfortable Seeing. 



In the work as conducted up to the present time a study has been 

 made of the effect on the eye of differences in the way in which the 

 light is delivered to it from a given type of illuminant. In work now 

 in progress, a series of similar studies is being made of the illuminant 

 itself. Different illuminants are being used with the same conditions 

 of installation, shading, etc., and a correlation is being made between 

 the lighting effects obtained and the power to sustain clear and com- 

 fortable seeing. As the tests are being conducted, color value is the 

 only variable present of any magnitude from illuminant to illuminant. 

 The tests so far as completed show that color value, while not exer- 

 cising so important an influence as improper and inadequate shading 

 on the power of the eye to sustain clear and comfortable seeing in 

 lighting conditions as we have them in current practice, is a factor 

 that should not be ignored in the work that is being done in the in- 

 terests of the conservation of vision. 



Bibliography. 



Ferree, C. E. Tests for the Efficiency of the Eye Under Different Systems 

 of Illumination and a Preliminary Study of the Causes of Discomfort. 

 Trans. Ilium. Eng. Soc, 1913, VIII., pp. 40-60. 



. Untersuchungsmethoden fur die Leistungsfahigkeit des Auges bei ver- 



schiedenen Beleuchtungssystemen, und eine vorlaufige Unt'ersuchung iiber 

 die Ursachen unangenehmer optischer Empfindungen. Zeit. f. Sinnes- 

 physiol., 1915, LI., pp. 59-78. 



