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Prediction of the weather. The daily predictions of the minimum temperature to be expected during the night, which have been published by the Royal Netherlands Meteorological Institute since 21st September, 1952, fulfil the statistical requirements, but on closer inspection it appears that the weak point in these predictions is the tolerance factor. The correlation coefficient of the expected and the observed tolerance during 86 observation days is only + 0.21. By replacing the tolerance factor in the prediction by its average value the Royal Netherland Meteorological Institute at De Bilt attains a correlation coefficient of + 0.884 between the observed and the expected minimum temperature, while the result of the persistency test (tomorrow the same weather as to‐day) is + 0.760. The investigation into variation (fig. 2) indicates the natural differences between the coastal areas and the inland areas; the variation decreases from the coast to the inland areas. The temperature differences between Den Helder and De Bilt (fig. 3, curve H) during the winter (average values for approximately 1000 observation days) increase according as the minimum temperature at De Bilt decreases. This effect is also observed in the summer (1950 and very high temperatures in 1947). The high correlation coefficient attained proves the reliability of the predictions.