Abstract

A direct-reading, self-recording densitometer with single thermocouple and low-resistance D’Arsonval galvanometer has been constructed and used to measure the relative opacities of the photographic images of the lines in ordinary spectra and in X-ray powder photographs. By suitable gearing to an electric motor the photographic negative is given a slow motion at right angles to a beam of light passing through a horizontal lens system; and at the same time a drum carrying photographic paper, on which a spot of light from the galvanometer is focused, is caused by the same motor to rotate at such a rate that a certain distance on the drum corresponds to a certain distance on the negative. A permanent record of the true distribution of opacities is thus obtained, since the deflections of the galvanometer are inversely proportional to the opacities on the negative.

Preliminary experiments show that the apparatus is dead beat and quick in response; and that it is sensitive, stable, and accurate.

© 1928 Optical Society of America

Precision Densitometers for Photographic Photometry

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