250 ANNUAL OF SCIENTIFIC DISCOVERY. 



vault! The cave is about 10 paces long, and 10 feet high. It has a 

 vaulted roof, in which great fissures open, which appear to communicate 

 with the body of the hillock. Saussure long ago gave the clue to the 

 real exposition of this paradoxical phenomenon ; and Professor Pictet, 

 following it out, has satisfactorily demonstrated that it is a beautiful 

 example of a practical illustration in nature of that first principle in 

 chemistry, evaporation produces cold. It is well known to the geolo- 

 gical student, that, in certain mines which have a horizontal gallery ter- 

 minating in a vertical shaft communicating with the atmosphere, a cur- 

 rent of air in summer descends the vertical shaft, and emerges from the 

 horizontal ; while in winter the current sets in at the horizontal, and 

 issues from the vertical shaft. The arrangement of this cave is very 

 similar. Thus the cave is the horizontal, and the vertical shaft lies in 

 the mass of the hill. Suppose, then, the mean temperature of the hill 

 to be about 48 or 50 degrees. The descending summer current passing 

 through the channels in the hill evaporates the water it meets with in 

 its progress, and so rapidly as to become colder in the descent ; until, 

 reaching the cave, it is even below 32 degrees, and there freezes the 

 water collected in it. The hotter the air outside, the greater the de- 

 struction of equilibrium between the interior and exterior columns, 

 which communicate at their base in the cave ; consequently, the more 

 rapid and intense the evaporation, the more severe the measure of cold 

 produced, " This view," says Sir R. I. Murchison, " is supported by 

 reference to the climate of the plains of Orenburg, in which there is a 

 great wetness of the spring caused by melting of the snow, succeeded 

 by an intense and dry Asiatic heat." 



THE SNOW-LINE IN THE HIMALAYA. 



LIEUT. STRACHEY, of the British army, has made some very exten- 

 sive observations on the snow-line of the Himalaya. By the term 

 snow-line should be understood the lower limit of perpetual snow, that 

 is, the highest limit to which the snow recedes in the course of the 

 year, or the boundary-line of the snow which resists the effect of sum- 

 mer. In describing one portion of his observations he says, " I con- 

 clude, then, that 15,500 feet should be assigned as the mean elevation 

 of the snow-line at the southern limit of the belt of perpetual snow in 

 Kumaon, though this will be rather under than above the fact." At 

 the head of the Pindur, near the glacier from which that river issues, 

 he considers that the ground was free from snow in situ up to a height 

 of 15,000 or even 16,000 feet in October. With reference to the 

 snow-line in the northern part of the chain of mountains, he thinks 

 that 18,500 feet must be nearly the average height, at least on the 

 Jainti ridge. These observations were mostly confined to that por- 

 tion of the Himalaya lying between the northwestern frontier of Nipal 

 and the River Sutlej ; this is extending from about the 77th to the 81st 

 degree of east longitude, while the breadth from the plains of India on 

 the south to those of Thibet on the north is about 120 miles. Jame- 

 son's Journal, Oct. 



