Microscope Illumination and Fatigue

Abstract

THE further letter from Mr. H. J. Denham in NATURE of December 15, p. 496, does not in any way alter my opinion that the method of varying the intensity of illumination in the microscope described by him is not the best or the most convenient at present available. The use of a monochromatic lightfilter does not affect the question, as such an accessory is used or not as may appear desirable in any given circumstances. At this institute several sources of light are installed, the one that is regarded as the most useful in high-power work being the mercury vapour lamp. It is obvious, therefore, that if light-absorbings screens of known opacity are available, nothing further is needed whether the light is monochromatic or otherwise. As I have already stated, such screens as we use here alter the intensity, and not the character, of any visible light which they transmit. If Mr. Denham regards the change of quality of his light as an advantage, I do not think that many microscopists will agree with him or adopt his methods while more efficient ones are at hand.