Die Stereoskopie im Dienste der Photometrie und Pyrometrie

Abstract

THE physiological optical effect on which the photo-metrical method made use of in the instruments described in Prof. Pulfrich's book is based was described in NATURE of May 12, p. 648, and May 19, p. 691. In one of Prof. Pulfrich's instruments a pair of fixed and moving marks is employed, which is observed by both eyes simultaneously through a pair of telescopes provided with a suitable system of prisms; in others two pairs of marks are made use of, one of which is seen in the middle of the field of view of each of the two telescopes, so that the appearance is that of a single pair. The two moving marks are geared together, and driven either by hand or by a small hot-air motor. If the fields of view of the two telescopes are equally “bright,” the mark appears to move to and fro, horizontally, in a straight line, its point passing just above the point of the fixed mark; a difference of brightness makes it appear to revolve round the fixed mark. This is independent of the colour of the two lights which are being compared. It is also possible to adjust the two sides of the apparatus to equality of brightness with an accuracy of 2 to 3 per cent., however great the difference of colour may be, provided the observer has sufficient experience, and good spectroscopic vision. In the stereospectral photometer, two monochromators are employed,, one for each telescope, so that practically monochromatic light of different wave-lengths can be employed. A form of photometer, which enables one-half of the spectrum to be balanced against the other half, promises to be valuable in pyrometry.

Die Stereoskopie im Dienste der Photometrie und Pyrometrie.

Carl

Pulfrich

Von. Pp. iv + 94. (Berlin: Julius Springer, 1923.) 3s. 4d.