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Show - 5 - the apparent microscopic temperature gradient, G is related to the actual microscopic gradient in the air spaces, G , as follows: ( a+ b) G- clG0 and thus G can be much larger than G. o By delicate cold laboratory experiments on a microscopic scale, this actual transfer between adjacent crystals was demonstrated, each individual I crystal showing growth opposite to the direction of heat flow. I Finally, Yosida showed strictly by theoretical reasoning that the heat transfer in snow due to water vapor must necessarily be as great as that due to air. Referring to the work of de Quervain and Mueller previously cited, this suggests that water vapor can account for 13% to 25$ of the heat transfer in snow with densities associated with a metamorphosed snow cover. Yosida goes on to demonstrate that this percentage is also related to the crystalline structure of snow, which may vary widely for a given density. He appeals to the " Formzahl" concept of Weiner ( 8) to characterize this structure, and shows the range of Formzahl which can be expected for a given density. For snow of density 0.1 g/ onr under optimum conditions, the water vapor contribution to heat flow is calculated to be 37% • Presumably it would be even greater for snow of lower density. Murcray and Echols ( 9) have recently suggested than an appreciable part of the heat transfer in snow at low temperature and high temperature gradient may be due to radiation exchange between the individual ice particles. This conclusion appears to be based on rather scanty observational evidence, and requires critical examination. An estimate of radiation transfer may be made by postulating a simplified theoretical model. Consider an idealized snow layer made up of equally-spaced thin ice laminae parallel to the surface and separated from one another |