Apparatus for Measuring Photographic Densities

Abstract

IN NATURE of March 8, Dr. Slater, Price refers to two new types of photometric density measurers. Therein he strongly advocates the use of a selenium cell for such purposes, rather than the photo-electric cell containing one of the alkali metals. Recently Dr. Toy and Mr. Rawling kindly allowed me to see their density measurer, referred to by Dr. Price, in which a selenium cell is used. After being accustomed to use a density measurer containing a photoelectric cell, which has perfect steadiness, and entire absence of lag, it was at once evident that the lag of the selenium cell is a most serious drawback, and makes accurate measurement both slower and more difficult.