[215]
It is evident that this decrease will be less rapid where the slope of
ascent is gradual, from such considerations as the angle at which the
sun's rays strike the slope, and the larger amount of surface which is
in contact with a stratum of atmosphere of any given thickness.
With these data, it is easy to arrive at some idea of the probable mean
temperature of the rock containing several of the glacieres I have
described. The elevation of some of them has not been determined with
sufficient accuracy to make the results of any calculation trustworthy;
but four cases may be taken where the elevation is known--namely, the
Glacieres of S. Georges, S. Livres, Monthezy, and the Schafloch. If we
take as a starting point the mean temperature of the town of Geneva,
which has been determined at 49 deg..55 F., the elevation of that town being
nearly 1,200 feet, we obtain the following approximate results for the
mean temperature of the surface at the points in question:--
S. Georges .... 40 deg..22 Fahr.
S. Livres (Lower) .... 38 deg.
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