WIDMARK has made a series of experiments with a grating spectroscope in order to determine the sensibility of the retina for ultraviolet rays. He finds the following. The normal human eye perceives only a small portion of the ultraviolet rays. The limit of the visible spectrum varies with different individuals, but usually lies within L-M. The rays are perceived directly, and not through fluorescence. Older persons recognize fewer of the ultraviolet rays than younger. This is especially noticeable in persons over sixty-five. The lens is the chief factor in preventing the visibility of the extreme rays, and after its removal the violet end of the visible spectrum is considerably elongated.
A look at the past . . .. Arch Ophthalmol. 1999;117(9):1191. doi:10.1001/archopht.117.9.1191