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In the middle of the last century, Gensanne, director of the mines of Giromagny (Vosges), concluded that

M. Dauhuisson made, in 1802, a large series of experiments on the waters in the mines of Freyberg, where the mean surface temperature is 8 cent. The general results are contained in the following table.

The general result is an augmentation of 8° for 300 metres; or, all observations included, 1° for 40 metres: if the extremes alone be taken, 1° in 35 metres.

This conclusion was confirmed by new experiments, in 1805, under the direction of Mr. Trebra. The temperature of the rock was now tried, with great care, for two years, the observations being registered thrice in each day. The temperature never varied in this time.