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Show - k - Starting with the general diffusion equation for water vapor, 2P 2 2. = n / i! L , 22P + 2f£_) where p = partial pressure of water vapor D0 = diffusion coefficient of water vapor in air Yosida was able to show that a transport of mass ( and hence heat) in the snow cover takes place by sublimation, and that the mass divergence at any point should be proportional to the second derivative of temperature with respect to height when the above expression is reduced to 2P. , nil 2T " P- 22^^ " 7 the single- dimensional case found in a normal winter snow cover. He was able to demonstrate experimentally the general nature of this transport by measurement of mass changes in snow samples inserted in the snow cover. Turning next to laboratory experiment, Yosida precisely measured mass transport in a column of snow subjected to a fixed and known temperature gradient, and concluded, that the coefficient of diffusion of water vapor in snow, D, was 1) almost independent of density 2) apparently was unaffected by direction ( i. e., by gravity) and 3) was four to five times larger than DQ This latter conclusion is expecially important, for it is a key to the character of vapor transfer in snow. Instead of acting as obstacles to diffusion of water vapor through intercrystalline spaces, the snow crystals contribute to it by a process of " handling on" vapor molecules across the small intercrystalline distances. Yosida pointed out that if lengths of air spaces and ice particles are given respectively by a and b |