FREEZING AND UUUNINCJ. 547 



witli luiltler intervals during tlie wiiitor, ami wiiere as a rule a warmer day succeeds 

 tlio cold iiiglit, whicli is tlie case wlierev'er tiie suu does not remain during the 

 winter below the horizon for weeks or perhaps months. All coverings which 

 protect from freezing in temperate zones are therefore entirely useless in Arctic 

 regions. The snow which, as stated, is in the north temperate zone one of the best 

 protective measures against severe tempenitures, cannot in the Arctic regions at all 

 hinder the penetration of the cold. Kane found the temperature in North-west 

 Greenland at 63 cm. under the snow to fall to — 213° and to — 16'3' at 126 cm. 

 below. The observations which were undertaken during the wintering of the 

 Swedish Polar Expedition in Mussel Bay on the north coast of Spitzbergen, showed 

 that on the 14th Febi'uary 1X73, when the temperature of the air was —35°, the 

 snow had fallen to — 26° at 26 cm. below the surface, and at a depth of 35 cm. to 

 — 20°. On the 23rd February the snow at a depth of 30 cm. showed a temperature 

 of —21°, while the temperature of the air was —32°. On the North Siberian coa.st 

 the snow at a depth of 30 cm. was found by the Vega Expedition on the 22d March 

 to be cooled down to - 161°,and the earth below it to — 151°, while the temperature 

 of the air was -182°. At the middle of March the sandy soil penetrated by the 

 roots of the Northern Bent Grass {Elymus mollis) exhibited at a dejith of 63 cm. a 

 temperature of —20°. 



It is quite different in the north temperate zone. When the sun shines on the 

 snow, if only for a few hours of the day, it becomes warmed and usually melted at 

 the surface. In the Alps, during the shortest days in December, when the temper- 

 ature of the air in the shade is —10° to —15°, melted drops may be seen in mid-day 

 trickling down from the sun-illumined roofs of the hay chalets situated high up on 

 the mountain slopes. Three Swiss, who had determined for the purpose of meteoro- 

 logical observations to pass the winter of 1865-66 in the hut situated at an altitude 

 of 3333 metres on the Matterhom, observed on the 18th December, 1865, and on 

 several other days, that in the sunshine the snow was melted. When the sun sets 

 behind the mountains the melted water, of course, again freezes, but the next day 

 the same process is repeated, while in Arctic regions, in the months of uninterrupted 

 winter night, the fallen snow remains powdery. On mountains of the temperate 

 zones, in consequence of melting under the influence of the sun's rays and the 

 succeeding hardening during the nights, the superficial I&jqv of snow forms a crust 

 of ice which in time becomes so thick that wide stretches of snow-field may be 

 traversed without breaking through it. 



This alternation of thawing and freezing in the upper layers of the winter coat 

 of snow has this important use, that in neighbourhoods where the sun shines in 

 the winter the deeper layers of snow, and the solid earth bearing the snow, are 

 never so much cooled as in the far north, where the cooling may continue for 

 months, and where, as the above figures show, it actually does so continue. 

 Minimum thermometers which were placed in the earth in the year 1869 on various 

 mountain heights in the Tyrol, and at the end of the winter were dug up, showed 

 the following temperatures: On the rocky summit of the Hafelekar, at Innsln-uck. 



