u8 THE POPULAR SCIENCE MONTHLY. 



sorted 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 south- 

 erly 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 south- 

 erly 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 temper- 

 ature 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 



