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servation of the snow or ice of the preceding winter, but from the 
peculiar condition of the cavern during the hottest summer months. 
He states also that he particularly urged the authorities at Oren- 
burg as well as the directors of the Salines to keep accurate regis- 
ters of the temperature throughout the year, and to ascertain pre- 
cisely the changes which the cave undergoes between the extremes 
of summer and winter. ‘There is, he observes, a very marked dif- 
ference between the climate of the steppes south of Orenburg and 
that of Ekaterinburg, not merely due to the difference of six de- 
srees of latitude, but arising also from the altitude of the position 
of Ekaterinburg and the shortness of its varying summers as well 
as from the long droughty summers of the steppes, which are re- 
moved from all mountain chains, and possess comparatively no great 
altitude above the sea. In the southern region, he conceives, a sub- 
stratum of frozen matter cannot exist, there being a most extraor- 
dinary difference between the climate of Yakatsk (lat. 623° N. long. 
131° E.) and that of Orenburg (lat. 51° 46’ N.), the winter of the 
former lasting eight or nine months, with the thermometer during long 
_ periods constantly 30° and sometimes 40° of Reaumur below zero*. 
Respecting the explanation that the difference of temperature in 
the cave is due to the propagation through the gypsum hillock of 
the heat or cold of the preceding summer or winter season, Mr. 
Murchison conceives that the fissures which ramify from the .cave 
into the hill, present difficulties to such a solution. When he was 
on the spot, the existence of these fissures led him to speculate upon 
the possibility of the phenomena being due to currents of air 
passing over subterranean floors of moistened rock-salt, and on the 
effects which would be produced when such currents came in contact 
with a stream of dry heated air. 
2, Extracts from a letter addressed by Sir J. Herschel, Bart., 
F.G.S., to Mr. Murchison, explanatory of the phenomena of the 
freezing cave of Nletzkaya Zatchita. 
‘“‘ That the cold in ice-caves (several of which are alluded to ina 
part of this letter not published) does nor arise from evaporation, 
is, | think, too obvious to need insisting on. It is equally impos- 
sible that it can arise from condensation of vapour, which produces 
heat not cold. When the cold (by contrast with the external air, 
i.e. the difference of temperature) is greatest, the reverse process 
* Mr. Murchison ascertained during his journey in the North of Russia 
in 1840, that much remains to be done relative to the circumstances of the 
recorded frozen substratum at Yakatsk; and he states the following as points 
requiring attention. Ist. With the exception of about sixty feet of alluvial 
soil, the whole shaft to a depth of 350 feet was sunk through solid strata 
of limestone two to six feet thick, and shale with a little coal; 2ndly, That 
none of the sinkings took place in summer although renewed for several 
years, on account of the foul air generated in the shaft; Srdly, That when 
Admiral Wrangel descended the shaft during the summer, and the surface 
was burnt up, he found the thermometer to stand at 6° Reaum. below zero. 
