424 THE VOYAGE OF THE VEGA. [chap. 



July 



The figures in the maximum cohuiin, it will be seen, are by 

 no means very high. That the enormous covering of snow, 

 which the north winds had heaped on the beach, could disap- 

 pear so rapidly notwithstanding this low temperature probably 

 depends on this, that a large portion of the heat which the solar 

 rays bring with them acts directly in melting the snow without 

 sun-warmed air being used as an intermediate agent or heat- 

 carrier, partly also on the circumstance that the winds pre- 

 vailing in spring come from the sea to the southward, and before 

 they reach the north coast pass over considerable mountain 

 heights in the interior of the country. They have therefore the 

 nature oifohn winds, that is to say, the whole mass of air, which 

 the wind carries with it, is heated, and its relative humidity is 

 slight, because a large portion of the water which it originally 

 contained has been condensed in passing over the mountain 

 heights. Accordingly when the dry fohn winds prevail, a con- 

 siderable evaporation of the snow takes place. The slight 

 content of watery vapour in the atmosphere diminishes its 

 power of absorbing the solar heat, and instead increases that 

 portion of it which is found remaining when the sun's rays 

 penetrate to the snowdrifts, and there conduce, not to raise the 

 temperature, but to convert the snow into water.^ 



^ In Lapland, too, the melting of the snow in spring is brought about in 

 no inconsiderable degree by similar causes, i.e. by dry warm winds 

 which come from the fells. On this point the governor of Norbotten Ian, 

 H. A. Widmark, has sent me the following interesting letter : — 



"However warm easterly and southerly winds may be in the parts of 

 Swedish Lapland lying next the Kolen mountains, they are not able in any 

 noteworthy degree to melt the masses of snow which fall in those regions 

 during the winter months. On the other hand there comes every year, if 

 we may rely on the statements of the Lapps, in the end of April or begin- 

 ning of May, from the west (\.e. from the fells), a wind so strong and at the 

 same time so warm, that in quite a short time — six to ten hours — it breaks 

 up the snow-masses, makes them shrink together, forces the mountain sides 

 from their snow covering, and changes the snow which lies on the ice of the 

 great fell lakes to water. I have myself been out on the fells making measure- 

 ments on two occasions when this wind came. On one occasion I was on 

 the Great Lule water in the neighbourhood of the so-called Great Lake Fall. 

 The night had been cold but the day became warm. Up to 1 o'clock 

 P.M. it was calm, but immediately after the warm westerly wind began 

 to blow, and by 6 o'clock p.m. all the snow on the ice was changed to 



