62 THE POPULAR SCIENCE MONTHLY. 



temperature generally remains below the point of congelation till the 

 middle of June that is, till a time when these latitudes receive daily 

 a much more considerable quantity of solar heat than is received at 

 the equator ; and that frosts last there for a month or six weeks dur- 

 ing which the sun never sets. Besides this, the solar rays are seldom 

 intercepted by clouds, for the month of May is usually very clear in 

 the northern regions. At Polaris Bay, latitude 81 86', in Northern 

 Greenland, the sun does not set after the 11th of April, and yet, in 

 1872, on the 1st of June, the temperature of the air had not risen be- 

 yond the freezing-point except for ten hours on the 21st of May, while 

 after the 2d of June the temperature was constantly above 32 ; and 

 the days during April and May were generally clear. The United 

 States Expedition under Captain Hall passed the winter at Polaris 

 House, latitude 78 23', where the sun did not set after the 20th of 

 April. Here, again, there was no general thaw before the 31st of May, 

 but only partial thaws on the 16th, 22d, and 2?th, although the days 

 were quite clear. On the 8th of May the sky was wholly clear for 

 several hours, before and after noon, and the temperature was 14 - 4 

 C. at noon, and 15*1 at three o'clock in the afternoon. It was also 

 perfectly clear on the 31st, at six o'clock in the morning and six o'clock 

 in the evening, and the temperature did not rise above 8'8. The 

 observations of the Vega at Pitlekaj, near Behring Strait, in a much 

 lower latitude, gave analogous results. We therefore see that in high 

 northern latitudes the heat of the rays of the sun at the end of spring 

 and the beginning of summer can not raise the temperature above the 

 freezing-point. To what, then, shall we attribute the thaw ? Proba- 

 bly to the winds that have passed over warmer countries, over conti- 

 nents, or open seas. According to the observations of the Vega, the 

 winds came from the north till the 12th of June, and then, on the 

 13th, passed around to the south-southeast. These warm winds melt 

 the upper layer of the snow ; when it freezes again, it changes into 

 neve, or takes on a condition less diathermanous to solar heat, in which 

 it less readily sends back the warmth which it receives. 



The melting of the snow may be speeded by the dust which the 

 wind brings from the continental spaces whence it has already disap- 

 peared. If the warm winds do not last long enough and are not strong 

 enough, they will not produce durable results ; but a new fall of 

 snow will give a new layer, which is only slightly diathermanous, and 

 possesses great radiating power. As a large quantity of caloric is 

 expended in the melting of snow, the warm winds lose much of their 

 heat, and may thereby produce a considerable refrigerant effect. But 

 along the frontiers of the region covered by snow, the surface of the 

 ground, after that is nearly melted, may be warmed by the sun, and 

 thus become a source of heat to countries farther north. The move- 

 ment begins along seas that never freeze and continental spaces in 

 which the snow never, even in winter, forms a permanent bed ; it then 



