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The special thermal conditions of pits in the North have been studied in great detail [I-6]: these conditions need investigation in order to ensure good health conditions for underground workers and to preserve the high supporting capacity of the frozen rocks, which aUows the use of cheap and productive methods of working.However, lately little attention has been paid to the artificial control of thermal conditions in pits in the North. As a result, except for the Vorkuta pits, where operations go on below the frozen layer, the thermal conditions in these mines and pits have been the natural ones. Here the climatic conditions in underground workings are bleak during the cold part of the year: a chilled zone is formed, but the rocks thaw out slightly during the summer.The low temperature of the air and rocks in the pits has caused illnesses due to chilling [6, "/] and has been conducive to the presence of a great deal of dust (especially coal dust) in suspension in the air.In the central coalfields, climatic control consists only of heating the air to a positive temperature (above +2 ~ during the winter and the use of varlons methods of dust suppression and dust trapping. For mines in the permafrost, these measures may not be enough: ff the air is heated to +2", after passing through a long working it will be cooled down (especially at the face) to near the natural temperature of the rock; furthermore, heating of the air to a positive temperature leads to changes in the natural temperature field of the rock and the formation of thawing zones round the workings. All this affects mining operations, reduces output per man-shift and impairs safety, and leads to the necessity of additional expense on maintenance and support of the workings. Cases [6][7][8] are known where thawing of the rock has been the came of serious deformations in underground workings. At the "Kaierkan" pit (Notil'sk), the cost of supporting the workings rose after the heating equipment was repaired [9].To improve working conditions for the miners and avoid the harmful consequences of thawing, it is proposed that the air should be heated to about minus 8-12" during the cold season and cooled to 5-8" during the summer. However, these recommendations (set out in detail in publications of the Leningrad Mining Institute) require additional checking and practical evaluation in each particular case.In planning the ventilation of a pit and the methods of controlling the thermal conditions, it is necessary to predict the temperature variation in the air with time and along the length of the workings, as weil as to determine the temperature field around the workings. For mines outside the permafrost, methods of thermal calculation have been worked out in sufficient detail [10][11][12][13]. For mines in the North, this is very difficult, owing to the alternating temperature of the air fed to a pit and the occurrence of freezing and thawing in the rocks. It is especially difficult to calculate the parameters of the natural thermal conditions when the tempera...