Page:Popular Science Monthly Volume 39.djvu/128

118 to imaginary volcanoes in action, or to the hypothesis of a comparatively mild climate in the interior—which it would be impossible to sustain on meteorological grounds; for the interior of every continent must necessarily be colder, by the effect of radiation, than the coast, where the sea is an ameliorating factor. Another attempted explanation depended on the Gulf Stream, whence the southeast winds were supposed to blow warm; but this, though reasonable, was insufficient.

When Hoffmeyer's attention was directed to these facts, his thoughts turned to other regions of the earth, and finally to the Foehn of the northern slopes of the Alps, where "a stormy southerly wind sometimes begins to blow very suddenly, which, from the snow-covered summits, hurls itself with irresistible force through the valleys which lead toward the north, and throws the Alpine lakes into frightful commotion. This wind, which is named Foehn, has, although it comes from a snowy region, an unusual warmth and dryness." At the same time that the southerly wind is found as an unusually warm and dry Foehn on the northern side of the Alps, a humid sirocco, generally accompanied by an enormous fall of snow, is blowing on the southern slopes of the mountains. This phenomenon had been accounted for by Dr. Hann, of Vienna, as the effect of the condensation, coming down from the tops of the mountains, of the air which had been cooled and deprived of its moisture by precipitation, in ascending the opposite slopes. Dr. Hann's calculations showed that the temperature of a south wind, lowered half a degree for every hundred metres of ascent, was raised one degree for every hundred metres of descent. These phenomena repeat themselves in Greenland. The author sketched in detail a Foehn period which lasted from eighteen to twenty days in the end of November and beginning of December, 1875, when Jakobshavn was for eight days warmer than north Italy. Unfortunately, direct observations from the uninhabited east coast of Greenland and the nearest parts of the Atlantic were wanting; but it was possible to show that during the same period a strong southeast wind blew from the sea over the land; for, according to the Buys Ballot law, the wind always blows so that it has the greater pressure of the atmosphere on its right, and, the more unequally the pressure is distributed, the greater is the velocity of the wind. Just during the eight days of heat at Jakobshavn, the barometer was much higher in Iceland than at Davis Strait. Over the tract lying between these places there had thus prevailed a strong southeast wind.

In the other paper, which is declared to be "an original and highly important contribution to science, whether regard be had to the method of investigation or to the results" Hoffmeyer showed that Greenland and Iceland exert a powerful influence