126 Chemical and Physical Notes 



ice, the air actually in contact, which alone comes under consideration, 

 is first cooled to o C., which reduces its saturation tension to 4*6 mm., 

 and the difference is only i -4 mm. We see, however, that this has been 

 sufficient to increase the absolute humidity of the air in close proximity 

 to the ice. At i m. above the ice the air had an average temperature of 

 10 C. ; at 2 cm. from the ice its temperature was as high as 6'65 C., and 

 the air in actual contact with the ice must have been at o C. Many 

 observations have been made of the temperature of the air at different 

 heights above glaciers, and, as might be expected, considerable differences 

 have been observed ; but I am not aware that any observations have been 

 made on the air almost but not quite in contact with the ice, as are those 

 which have been made at 2 cm. from the ice. The bulb was perfectly 

 shaded from the sun but freely exposed to the wind, it was also fully 

 exposed to any cold radiations from the ice. There is, therefore, no doubt 

 that 6'65 was the temperature of the air passing the bulb of the thermo- 

 meter. The vertical distribution of temperature shown by these figures 

 is remarkable. From a height of i m. to within 2 cm. of the ice there is 

 a gradient of 3'4 per metre; in the remaining 2 cm. there is a gradient 

 at the rate of 33 per metre; and, from various observations and con- 

 siderations, it is probable that the moderate gradient is continued to 

 within a millimetre of the ice, when it becomes precipitous. It is to be 

 noted that the absolute humidity, as shown by the vapour tension of the 

 air, has increased from 3^4 mm., at i m., to 4*1 mm., at 2 cm. ; showing 

 that ice is being evaporated and transferred from the glacier to the 

 atmosphere. The wind was blowing freshly down the glacier, and its 

 velocity was measured by noting the time which pieces of paper allowed 

 to drift took to reach the ice, and then pacing the distance. The mean 

 velocity was found to be from 8 to 10 ktloms. per hour. 



"The observations made on the 2ist and on the 22nd confirmed those 

 of the igth. The same variability of the air temperature at the land 

 stations was noticed. Between 12.55 an d 1>o P- m - the following tempera- 

 tures were observed by whirling: 16'2, i6'2, i6'o, I5'5, i6'o, I5'5, 

 i5x>, i4'2, i3'8, i4'o, i3'5, I3'5. These are all good observations, 

 and represent real variations of the temperature, or rather they indicate 

 real variations of greater amount. Taking the mean of the last five 

 observations, we have the temperature of the air I4'o. The wet bulb 

 was found at 1.15 p.m. to be 7'5, giving a difference of 6 -5. On the 

 glacier the air felt closer than on the previous occasion. The temperature 

 at i m. was ii'5, and at 2 cm. from the ice 7'3. The difference 4'2 is 

 less than on the previous occasion. The wind was much less strong, and 

 yet the temperature close to the ice is higher. The wet bulb under the 

 same circumstances showed 4'o. Five minutes later the dry bulb was 

 observed at i m., io'2 and 9'4, mean 9'85. Another observation of the 

 dry bulb at 2 cm. from the ice gave 6'6. The interval between the bulb 

 and the ice was now reduced to the smallest possible distance, about 



