Chap. I] CHARACTERS OF THE ARCTIC CLIMATE 665 



The difference in temperature between the air and objects under direct 

 insolation is accordingly much greater in polar countries than in those that 

 are free from ice and snow during summer. For the same reason, dry soil 

 is much more heated by the sun than is soil containing subterranean ice 

 near the surface. Sloping ground is also heated more than is flat ground 

 where water from melting ice and snow stagnates over the permanent ice in 

 the ground and is constantly frozen again and again from below *. Finally, 

 on sloping ground the gradient is extremely important, since when favour- 

 ably placed as regards the sun's rays the soil receives them at an angle 

 which is less oblique or may even be a right angle. 



The following data illustrate what has been said about the difference in 

 temperature between the air and directly insolated objects : — 



' According to Kane's observations with a blackened thermometer (in vacuo) at 

 Rensselaer Bay (78-5° N.) the temperature in the sun from the 16th of May to the 

 4th of September was always above freezing-point, and even reached 21° C. The 

 temperature of the air was above zero only from the middle of June to the middle of 

 August. In Assistance Bay (74 -5° N.) it was observed that even in March, with an 

 atmospheric temperature of - 3 1° to - 33 C, whenever the snow lay upon stones or 

 near the dark body of the ship, it melted in the sun 1 .' 



In the Vega expedition, the temperature of the air on the sandy shore near 

 Pittlekaj, on the 8th of July at 10 a.m. one meter above the ground, was 6-8° C, and 

 on the ground 14-5° ; at a depth of 10 cm. it was 23 , and at 15 cm. 17 C. 2 



Kihlman also directed his attention to this matter in Russian Lapland 4 : — 



'On the Tundra plateau, near Orlov, on the 10th of May at 1 p.m., when the 

 snow had melted only in places and the thermometer in the shade stood at 8° to 

 9° C, I observed the following local temperatures. In a horizontal lichen-heath 

 (the ground-ice at 5 cm. from the surface, and melted snow about 20 paces distant) the 

 temperature close to the ground was 14° ; at a height of 1 dm. from the surface, the 

 same height as the tips of the dwarf-birch twigs, the temperature was 12 ; at 5 dm. 

 from the surface, 9° C. A hillock of peat about 3 dm. higher and bearing Empetrum 

 and Cladina showed 24-5° C. on its steep southern side (ground-ice 5 cm. distant). 

 A second hillock, 4 dm. higher, but less steep, had a surface heated up to 30-2° C. 

 (ground-ice close under the soil). A dry depression in the ground, covered with Hypna 

 abounding with water, was 13-5° C. (ground-ice 4 cm. distant). In the preceding 

 night the minimum-thermometer sank to - 4-3°, and on the following night to 0-5° C 



The same investigator has also made some instructive observations regarding the 

 temperature of the soil under a snowy covering 5 : — 'A factor hitherto recognized 

 incompletely or not at all, but contributing to the diminution of the covering of snow, 

 I observed in the process of melting from below. On sunny spring days one actually 

 often sees along the edge of the snow-fields the lower surface of the snow separated 

 from the soil by a layer of air sometimes 10 cm. in height ; and not infrequently it 

 extends 2-3 feet inwards. . . . This is also true of objects projecting above the 

 ground, but still completely covered with snow. As soon as the contracting snow- 



1 Hann, op. cit. 2 Id., op. cit., Bd. Ill, p. 745. 3 Kjellman, op. cit. 



4 Kihlman, op. cit., p. 31. 5 Id., op. cit., p. 48. 



