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Excerpt from Papers From the Department of Engineering
The value Of the thermal diffusivity has been computed for suitable intervals of time covering the entire period now reported on. The results are tabulated below, and are also represented graphically on the aecom panying plate. These results Show that the value of lc/e is, for the lower strata, in general less than the average, but that for a short time in the spring or early summer, the contrary is true. The latter condition pro bably corresponds to a stage in which the moisture of the melting snow has penetrated to the lower depths, and the upper layers are relatively dryer.
When the ground is protected by snow and there is no percolation, the value of k/c is seen as in former years to be a minimum and very constant, the average value corresponding to 0015, which, as stated in former communications, may be taken as the value of diffusivity due to pure thermal conduction for the sandy soil in question in a dry condition. All values above this being due more or less to in¿uence from percolation. The normal value for the full depth, under average conditions of soil, during the summer months, may be put at '0075.
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