Abstract
The most widely accepted model for the water vapor movement in soil under temperature gradients, proposed by Philip and deVries (1957), is critically examined. Many experiments made after their proposal have shown that the model is not necessarily satisfactory for explaining the results. However, no substitute for it has been proposed as yet. The present author asserts that the scale of soil pores is not larger enough compared to the mean free path of air molecules to be able to disregard the water vapor movement under the kinetic control in comparison with the diffusive transfer. It is shown that they can compare each other in soil pores of typical size; therefore, in reality, a cross between the two processes operates there. The driving force for the kinetic water movement is the deviation from equilibrium between gas and liquid (adsorption) phases caused by the gradient of temperature. Taking account of this mechanism, the basic features of the results of experiment on the present phenomenon can be consistently explained.
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