METEOROLOGY. 



541 



mers. Each of the fifteen Junes of these years, 

 except that of 1873, which was 0-2 above it, 

 and the means of the months from April to 

 December, were below the average, while the 

 means for January, February, and March had 

 been above the average. Thirty-eight hard 

 winters had occurred, lasting from two to six 

 months each, of which eighteen had been fol- 

 lowed by "good" summers and twenty by 

 "bad " summers. 



The committee of the British Association to 

 investigate the depth of permanently frozen 

 soil in the polar regions, etc., has collected a 

 large number of observations from various quar- 

 ters in the Eastern and Western Continents, 

 without obtaining such results as might enable 

 them to formulate a general law. At the 

 American stations ground-ice has been found 

 at depths ranging from six or eight feet to 

 about fifty feet. At the circumpolar station 

 of Fort Rae, on the Great Slave Lake, latitude 

 64 20' north, longitude 124 15' west, the soil 

 is frozen at a depth of four feet from Novem- 

 ber to June, inclusive, and is at the lowest tem- 

 perature at that depth in March. The mean 

 temperature of the soil reaches its minimum 

 at about the time of the vernal equinox. A 

 rise was observed in the earth-temperature of 

 February above that of January or March. It 

 did not appear that temperatures below 32 

 F. extend lower than eleven or twelve feet. 

 Capt. Dawson believes that the earth-tempera- 

 tures recorded here are above what is proba- 

 bly the average in that latitude, because of 

 the southwesterly slope of the ground and 

 its consequent direct exposure to the sun; 

 whereas in most places the ground is either 

 covered with thick moss or shaded with brush- 

 wood. Relative to other American stations 

 the committee reports that " there is want of 

 proof of the existence of permanent ground- 

 ice beyond the district of Mackenzie river in 

 the northwest; but frozen soil hasbeenknown 

 to exist at a depth of seventeen feet at Fort 

 Simpson, at Prince Albert, and at Yorkton, 

 and it may be questioned whether the wave 

 of summer heat has time to descend to such a 

 depth befere it is overtaken by the refrigerat- 

 ing influence of the early winter. It certainly 

 exists also in the neighborhood of Hudson 

 Bay, on the eastern side, and it is evident that 

 under favorable conditions frost, without be- 

 ing permanent, may, in some cases, last in the 

 soil all the year round over a wide area, and 

 in other years disappear. At whatever level 

 we locate the maximum of absorbed heat, it 

 must be remembered that when the winter 

 sets in and freezes the surface, which it does 

 rapidly to the depth of a foot or two, the heat 

 will then be abstracted in both directions, and 

 its rate of descent checked." 



Dr. Woeikof observes, in a paper on the 

 climate of Eastern Siberia, pertinently to the 

 great depth (from about 300 to 600 feet) to 

 which the soil is permanently frozen near 

 Yakutsk, in the Lena valley, that the farther 



north, the longer is the duration of cold in 

 valleys in comparison with that on higher 

 ground. The effect extends to a part of au- 

 tumn and spring, and is observable in the 

 mean temperature of the year. At the heights 

 on the left bank of the Lena in the vicinity of 

 Yakutsk, the earth-temperature is from 8'1 to 

 8'6 F. higher than it is in the town and val- 

 ley at the same depth, and it is even lower at 

 300 feet in the former than at fifty feet in the 

 latter locality. The total depth of frozen soil 

 is, according to Mittendorf, more than twice as 

 great in the valley as it is on the heights ; and 

 these lesser heights are in winter relatively 

 colder than higher isolated mountains. Kup- 

 pfer asserts that in Bergivier Nerchinsk, in 

 the Trech Swjatitilei mine, frozen soil was 

 found at a depth of 174 feet, but that in 

 Wossdwishenst mine, which lies 230 feet 

 higher, the frozen soil ceased at fifty feet. 

 Even in Altai it is acknowledged that many 

 valleys are colder than the neighboring heights. . 

 Dr. Woeikof sums up a number of observa- 

 tions in the following sentences, which ap- 

 ply to the greater part of East Siberia, but 

 more particularly to the northeast portion : 



1. As the greater cold coincides with calms 

 and light winds, the valleys and lower grounds 

 are colder than the heights. 



2. The temperature of isolated mountains is 

 relatively higher than that of lesser elevations. 



3. The lowering of temperature in the val- 

 leys is so lasting and considerable that the 

 mean of the year is also lowered, as is proven 

 by the observations of earth-temperature. 



4. The depth of the frozen soil is greater in 

 valleys, and is so lasting and considerable that 

 the mean of the year is also lowered. 



5. In the tundras of the far north (answer- 

 ing to the barren grounds and muskegs of the 

 Northwest Territory of Canada) the winter is 

 warmer than in the valleys of the forest-zone, 

 probably because the stronger currents of air 

 do not permit the cold stratum to remain so 

 long stagnant. 



Dew t Mr. Aitken has promulgated a theory 

 that dew is a condensation, not of moisture in 

 the atmosphere, as is supposed by the usually 

 accepted theory, but of moisture that exudes 

 from the ground. His attention was called to 

 the subject by observing at night that the 

 ground, at a short distance below the surface, 

 was always hotter than the air over it, the 

 contrary of the conditions required by the ac- 

 cepted theory. The author inverted shallow 

 painted trays of metal over the grass. These, 

 known to be dry when set down at night, were 

 coated with dew in the morning, while the 

 grass under them was wetter than that outside 

 of them. The rise of vapor from the ground 

 was thus demonstrated. Other experiments 

 showed that ground on which dew was formed, 

 whether sod or bare soil, lost weight in the 

 process, whereas it should have gained if the 

 dew had been deposited from the atmosphere. 

 In times of frost, clods and stones were more 



