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Journal of Experimental Biology 53,753-762 (1970)
Published by Company of Biologists 1970

The Study of Evaporation from Small Surfaces by the Direct Measurement of Water Vapour Pressure Gradients

JOHN MACHIN ¹

¹ Department of Zoology, University of Toronto Toronto 5, Canada

1. The construction, maintenance and calibration of a sensitive instrument capable of making numerous vapour-pressure measurements within humidity gradients by the dew-point method is described.

2. Coefficients of diffusion of water vapour in air, calculated from observed vapour-pressure gradients and measured rates of evaporation agree with theoretical and other experimental values in still air.

3. Apparent coefficients in wind speeds between 10 and 100 cm/s were significantly lower than those in still air.

4. This finding, together with the performance of the dew-point probe, is discussed in relation to its possible use in the study of evaporation from animals and plants.