August 9, 1877] 



NA TURE 



295 



south-west there occurs at this season of the year in 

 Labrador, the Hudson's Bay territories and the Arctic 

 Archipelago, so great a fall of temperature, that the mean 

 temperature of January sinks from —20° to — 35° C. ; to 

 the east and south-east, on the contrary, the Gulf Stream, 

 even in mid-winter, maintains the temperature in the 

 Atlantic at from o^ to 5" C, so that the superincumbent air 

 can scarcely be supposed in general to be cooled under the 

 freezing-point. Lying between such opposite varieties of 

 temperature, the climate of Greenland must necessarily 

 be in a high degree dependent on the prevailing direction 

 of the wind at every particular period ; all winds from 

 south by west to north-east may bring comparative cold, 

 but east and south-east winds, on the contrary, heat, and 

 this ought specially to hold good of the south-east wind, 

 both because it comes from the warmest part of the 

 neighbouring Atlantic Ocean, and also because it has the 

 shortest way to travel over the ice-deserts of the interior 

 to reach the western coast. The character of the winter 

 in Greenland will therefore certainly depend on whether 

 the south or the east wind has prevailed during the course 

 of it." 



These explanations go a great way indeed, but still are 

 not altogetlaer sufficient. " Thus, when at Jacobshavn, 

 shortly before July, 9° C. of heat are recorded during a 

 south-east storm, while the normal temperature is — 12° C. ; 

 this high temperature cannot be derived alone from the 

 Atlantic nearest in the south-east to Greenland ; for it is 

 quite improbable that the air could have so high a tem- 

 perature at this season, and even if it may be supposed to 

 pass over Greenland in the short space of eight to ten 

 hours, it must by the way suffer a greater or less cooling 

 by contact with the cold ice masses. Indeed if we go 

 down to South Greenland we will there, in the month of 

 December, be able to observe over 14' C. of heat, a tem- 

 perature which we cannot simultaneously find in the 

 Atlantic much nearer than at the Azores, and it cannot 

 be supposed that the air has travelled from these islands 

 to Greenland with its temperature unchanged." 



" There are also other properties, besides its high tem- 

 perature, which specially characterise the south-east 

 wmd in Greenland. For it appears always to be very 

 dry ; the snow melts away from the low country without 

 any running water being visible. The storm begins first 

 on the mountain-tops, where the snow is seen whirling 

 high in the air, and then it afterwards works itself down 

 in the fiord valleys." 



These relations drew the writer's thoughts to other 

 regions of the earth. On the northern slopes of the Alps 

 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 

 towards the north, and throws the Alpine lakes into 

 frightful commotion. This wind, which is named FoeJtn, 

 has, although it comes from a snowy region, an unusual 

 warmth and dryness. Prof. Dufour has shown that 

 during a Fochn which raged during the 24th and 25th 

 September, 1866, the temperature was 6' to 9" C. over the 

 normal in northern Switzerland; indeed at the town of 

 Zug, although it lies 440 metres above the level of the 

 sea, the temperature was higher than it was at the same 

 time both north and south of the Alps. The unusual 

 heat and dryness of the Foehn is also shown by the cir- 

 cumstance that the boundary of the snow in the valleys is 

 seen to have receded very considerably when the storm 

 subsides ; it is therefore called, on that account, " the 

 great snow melter." 



At the same time that the southerly wind is found as a 

 warm and dry Foelin on the northern side of the Alps, 

 there blows, on the other hand, on the southern slopes of 

 the mountains a humid sirocco, generally accompanied 

 by an enormous fall of snow. 



Several years back Dr. Hann, of Vienna, solved this 

 enigma in a highly satisfactory way. 



We know that the pressure of the atmosphere decreases 

 upwards ; when, therefore, a mass of air is forced by any 

 cause to raise itself from the surface of the earth to a 

 certain height, it will be subjected to a constantly 

 diminishing pressure, and will accordingly expand, but as 

 every expansion is a work which is accompanied by a 

 consumption of heat, the air is cooled as it rises. As long 

 as the cooling is not greater than that the air can retain 

 its watery vapour, the heat will, according to calculations 

 which have been confirmed by observations, diminish 

 almost exactly 1° C. for every 100 metres the air rises. 

 On the other hand, if the dew-point is exceeded, so that 

 the watery vapour forms clouds, rain, or snow, the 

 moisture will pass from the form of vapour to the fluid or 

 solid state, whereby the combined heat is set free. The 

 cooling from this moment proceeds much more slowly, 

 and it may, within the limits of which we have experience, 

 be stated as about ^° C. for every loo metres. 



When a mass of air, on the contrary, sinks towards the 

 surface of the earth, it comes under higher pressure, is 

 compressed, and consequently heated. Its temperature 

 will rise more and more above the dew-point, and moisture 

 will, with continually increasing ease, be held dissolved in 

 the state of vapour. The heating during the whole 

 descent will be 1° C. for every 100 metres. 



These physical laws explain the properties of the Foehn. 

 The air comes from the Mediterranean saturated with 

 moisture, and passes over the summits of the Alps. 



" Leaving out of consideration the cooling which goes 

 on by the way, partly by radiation, partly by contact with 

 mountain masses, a simple calculation will give the result 

 th.at the temperature of a south wind will be about as many 

 half degrees Centigrade higher at the north foot of the 

 .'Vlps than at the south foot, as the height of the mountain 

 chain contains hectometres, for it is lowered half a degree 

 for every 100 metres ascent, but raised one degree for 

 every 100 metres descent." 



These phenomena repeat themselves on Greenland. 

 The writer sketches in detail a Fochn period which lasted 

 eighteen to twenty days in the end of November and 

 beginning of December, 1875. Jacobshavn was then for 

 quite eight days warmer than North Italy. Upernivik, 

 which lies about 10° to the south of the English North 

 Pole Expedition's wintering station, was during the dark- 

 ness of the Polar night warmer than the south of France. 

 Unfortunately all direct observations from the unin- 

 habited east coast of Greenland and the nearest parts of 

 the Atlantic are wanting ; but it may, however, be shown 

 that during the period referred to a strong south-east 

 wind blew from the sea over the land. For the so-called 

 Buys-Ballot law in its simplest form teaches that the 

 wind always blows so that it has the greater pressure of 

 the atmosphere on its right, and that the more unequally 

 the pressure is distributed the greater is the velocity of 

 the wind. Now just during the days in question the 

 barometer was much higher in Iceland than at Davis 

 Straits. Over the tract lymg between these places there 

 had thus prevailed a strong south-east wind. 



NOTES 



Out of above ninety candidates, Mr. James Edward Henry 

 Gordon, B.A., of Caius College, Cambridge, has been selected 

 by the Council of the British Association to be recommended 

 to the Association as Mr. Griffith's successor in the important 

 position of Assistant Secretary. 



The fiftieth Veisammluw; dadschcr Naturjorscher und Acrzte 

 takes place at Munich on September 18-22. The following is 

 the general programme :— Sept. 17, evening : Social gathering in 

 the large saloon of the Rathhaus. iS: General session in the 

 Odeon ; address of welcome from Dr. v. Pettenhofer, addresses 

 by Prof. Waldeyer, of Strassburg, on " C. v. Baer and his 



