Developments in the Practical Use of Photocells for Measuring Faint Light.

Infrared-sensitive emission photocells do not operate with high efficiency in an electronic tube amplifier unless a grid resistor of at least 2.5 X 1O' ohms is used or unless the gas-multiplying factor of the cell can be made large without sacrificing stability. A method for practicable use of grid resistors at least as high as 5.0 X 1013 ohms is given. In addition, a method is given for making photocells operate stably with high gas multiplication. The material in this paper may be used as the basis for design of an astronomical photoelectric photometer for use in spectral regions, including the near infrared. The photometer will have satisfactory linearity over large brightness ratios, and it will perform on faint light as efficiently and as usefully for astronomical purposes, as an equivalent system using a multiplier phototube.