Physiological and Ecological Studies in the Analysis of Plant Environment

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Abstract
The design is based on the principle that changes in the current passing through a vacuum emission cell, induced by variations in the light quanta received, control the rate of charge of a condenser. When the striking voltage of a discharge tube is reached the resultant flow of current energizes an electromagnetic relay which, in turn, is connected with a Post Office counter. In order to eliminate possible errors due to changes in temperature, the compartment containing the discharge tube is kept at a constant high temperature (100° F.), while a stabilized mains source of electricity is used. A ground-glass diffusing dome is used and a filter to exclude infra-red and ultra-violet radiation. With a photometric cell of relatively uniform sensitivity in the visible spectrum the recorder gave a linear response up to the maximum intensity investigated. No change in the calibration factor occurred in two summers' continuous use in the open. The electrical components, including the photo-electric cell, cost c. £25, while the construction only demands normal workshop facilities.

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