370 Prof. BischofF on the Temperature of' 



to Koch's tables,* that difference would cause a current of air 

 to issue from A, with a velocity of about 100 feet per second. 

 But since the channels of the glaciers are not entirely enclosed 

 from A to B, but have many minor outlets in the clefts 

 D, E, F, H, and I, through which the air escapes in summer, 

 and as they are not contracted at A, but, on the contrary, are 

 enlarged at the lower opening in glaciers which have caverns, 

 and as they have many unevennesses within, a great velocity 

 cannot possibly be supposed to exist. From the smaller clefts 

 D, E, and F, the air will issue in summer as out of A, but it 

 will rush into the clefts H and I, which are situated higher up, 

 in the same manner as it does into B. At a certain height, 

 therefore, there must be a limit between the fissures through 

 which the air enters and those by which it escapes; and this 

 limit must be situated higher than the mean height B C of 

 the glacier, when the upper fissures, and particularly B, are 

 together larger than the lower ones together with the opening A ; 

 whilst, on the other hand, it must be situated below the mean, 

 when the upper fissures are together smaller than the lower 

 ones. From this limit upwards, the various currents will de- 

 scend in summer more rapidly, and will escape more rapidly 

 below, in proportion to their different heights. 



Let us suppose the velocity of the currents to be but one- 

 tenth of that found above, still the volume of warm air intro- 

 duced is very considerable ; and as they must be cooled down 

 during their long course through the glacier, nearly to 32°, it 

 may easily be conceived how great an influence such currents of 

 air must have in melting the glacier away from underneath, as 

 well as in raising the temperature of the glacier- streams. 



If the ice-caverns become completely blocked up in the win- 

 ter, the currents of air under the glacier will be entirely stopped. 

 But even though the glacier be covered with snow, yet all 

 the fissures will not be got closed up so as to prevent the 

 passage of the air ; for many places will still be left, thmugh 

 which currents of air, though perhaps but inconsiderable ones, 



* Experiments and observations on the velocity and quantity of compressed 

 atmospheric air, which issues from apertures of various forms, and through 

 tubes, &c. Gotlingen, 1 824. 



