MR. IRWIN G. PRIEST has been good enough to send me a copy of the above letter concerning the description, in my recent book “Photometry”, of the instrument developed by him for heterochromatic ...

I WISH to clarify a somewhat confused account of some work of mine given in Walsh's “Photometry”, pp. 244–245 (London: Constable, 1926). Since the same mistake has also boon made by others heretofore ...

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