Showing papers by "John L. Monteith published in 1954"

A sensitive recording dew‐balance

Abstract: The instrument described gives a continuous record on photographic paper of the change in weight of a naturally exposed grass surface, 330 cm2 in area. The sensitivity is 2 mg cm−1 per cm of record and the time scale is 0.5 hr/cm. Observations suggest that on very calm nights the condensation of vapour reaching the surface by diffusion from the atmosphere is only a small fraction of the total ‘dew.’ The maximum rate of deposition that has been observed on short grass is 0.03 mm hr−1.

Error and Accuracy in Thermocouple Psychrometry

Abstract: The paper discusses the main sources of error in the determination of vapour pressure with a thermocouple psychrometer. The predictions of theory and the results of experiment lead to no general agreement on the value of the constant in the classical psychrometer equation. A new derivation of the equation suggests a reduction of the commonly accepted value by a power of the ratio of diffusion coefficients for heat and water vapour. An expression is derived for the radiation error due to the difference of temperature between the wet bulb and its surroundings. Conduction of heat along the thermocouple wires and extraneous radiation produce errors for which an expression is derived for a particular thermocouple model. Finally, wet-bulb temperature errors are related to the corresponding vapour pressure errors.