Vision in the Ultra-Violet

Abstract

ALTHOUGH normal visible light is generally considered to extend from 7500 A. to 4000 A., most spectroscopists are familiar with the fact that the 3650 line of the mercury spectrum is oluite visible. Saidman and Dufestel reported¹ that this latter line is visible after a period of accommodation, and that its colour sensation is identical with that of the 4047 A. line. They report that no lines farther in the ultra-violet are visible. I have recently found with the new Müller-Hilger universal double monochromator normal vision down to 3125 A. This instrument gives monochromatic light of a high intensity and of a very high degree of purity. The purity was confirmed by means of calibrated filters. The object for these tests was the slit of the monochromator, across which were placed two wires in apart. Most of the observations listed below have been confirmed by eight observers. There were no failures to confirm.