Abstract
IT is interesting to note from Mr. J. E. Barnard's letter in NATURE of December 8, p. 468, that other workers have taken up the problem of variable illumination for the microscope. But in criticising the method outlined in these columns on November 17 Mr. Barnard seems to have overlooked the important fact that a monochromatic light-filter is used, so that the question created by the shift of the dominant radiation does not arise. This shift—which in its simplest expression amounts to a reddening of the light as the temperature of the source is decreased—was fully recognised when the method of regulation was originated, and in practice is a distinct advantage, since the apparent decrease of illumination of the field, when a filter is used which passes only a small band of the spectrum, is greater than that of the light source alone, where the full spectrum is present. Hence any increase of the resistance of the circuit doubly decreases the light in the field.
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DENHAM, H. Microscope Illumination and Fatigue. Nature 108, 496 (1921). https://doi.org/10.1038/108496b0
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DOI: https://doi.org/10.1038/108496b0
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