It is therefore definitely established that the intensity discrimination of the retina in the "deteriorated" image is far from being a limiting factor in the resolving power of the eye for a grating. 180 VISUAL ACUITY AND ILLUMINATION The small, almost insignificant, lowering of the maximum visual acuity by means of the 1/8 grating led me to investigate further the basis of Hartridge's minimum value of a 10 per cent intensity differ- ence in the image of a just resolvable single line.
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