Chemical and Physical Notes 123 



according as the sun shone on the grass or was obscured by a cloud. The 

 effect was immediate the moment the sun came out; sunlight reflected 

 from rocks and light-coloured surfaces did not produce the same effect. 



"On the i gth August I returned to the glacier. At u a.m. in the 

 valley below the glacier I found the temperature of the air 22 C., and 

 the wet bulb I2'5, whence the vapour tension is 5'o mm., and the relative 

 humidity 26. In determining the temperature of the air by whirling the 

 thermometer I found variations of as much as 2. The hot puffs of air 

 made themselves felt most markedly, and showed that the real variations 

 of the temperature of the air were much greater than the thermometer 

 showed. At i p.m., on the hill-side, to the west of the tongue of the 

 glacier, and at a height of about 2100 m. above the sea, four good 

 observations of the temperature were made, giving I7'5, i8 0- o, I9'5, and 

 I9*o; they are all equally trustworthy, and represent the average tem- 

 peratures of the air during the minute, or minute and a half, that the 

 thermometer was whirled. The mean of these values, i8'5, is taken as 

 the temperature of the air. For determining the temperature of the wet 

 bulb, the bulb of the thermometer was wrapped round with one thickness 

 of Swedish filtering paper thoroughly moistened, and the thermometer 

 was whirled as before and until the temperature ceased to fall ; it then 

 stood at 9'5. Still higher up the hill at an altitude of 2250 m., the 

 temperature of the air at 2 p.m. was i8'5 C. Having returned to the 

 spot where the observations had been made at i p.m. the following air 

 temperatures were observed : between 2.40 and 2.46 p.m., I7'5, i8'o, 

 l 7'Si I 7'> 1 7'3> I7'i 5 mean, i7 - 4; and between 2.50 and 2.54 p.m., 

 i6 '5, i6'5, i67, and i6 0> 5 ; mean, i6'55. The mean of the two sets is 

 I7'o6. It must be repeated that each of these individual observations 

 is a faithful indication of the average temperature of the air in which the 

 thermometer was whirled, and in so far as its sensibility enabled it to 

 assume the same temperature as the air. From this spot I descended 

 to the glacier and went up it until I got to a position which, judging by 

 the eye, was at the same height as the station just left on the mountain 

 side, and about one kilometre distant from it in a straight line. The 

 weather was rapidly getting colder, the sky being covered with the 

 characteristic Fbhn cloud. The wind was fresh down the glacier, which 

 made the exposure of the thermometer easy and good. The hot Fohn 

 puffs were also very striking. The thermometer was first swung exposed 

 to sun and wind, showing temperatures varying from io'5 to il'2, the 

 mean being io*8 C. Swung in my own shadow, but exposed to the wind, 

 the temperature was 9'8. The wet bulb was 47, showing a relative 

 humidity of 37. The thermometer was now exposed, both wet and dry, 

 in a horizontal position with the bulb at a distance of about 2 cm. from 

 the ice, on the top of one of the superficial ridges of the glacier, and fully 

 exposed to the wind, though shaded from the sun. The observed tempera- 

 tures were : dry, 6'6 C. ; wet, 37 ; relative humidity, 58-5. The exposure 



