No abstract

AMONGthe first applications of the modern photoelectric cell was its use to replace the human eye in photometric measurements. Many circuits and cell arrangements for specialized types of photoelectric photometry have been proposed in the literature (4, 8, IS, 17). The earlier photometers were of the direct-reading type and employed a single photoelectric cell. In 1919, Gibson (8) of the Bureau of Standards described the null method for photometric measurements, using it for the routine photometry of lamps. The null method with two photoelectric cells eliminates many of the inaccuracies entering through direct reading.More recently the photoelectric cell has received attention as a means of minimizing the human element as a factor in colorimetry. Müller (11) in 1928 described a photoelectric colorimeter of the direct-reading type and discussed its ap-

No abstract

No abstract

No abstract