112 Mr. J. Y. Buchanan. On Rapid Variations of [May 31, 



remarked that the greatest disturbing effect is produced by sunlight 

 reflected from grass. If the thermometer was whirled in the shade 

 of a north wall with a grass field or hill- side close by, the thermo- 

 meter would be immediately affected to the extent of one to two 

 degrees, 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 19th August I returned to the glacier. At 11 A.M. in the 

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

 and the wet bulb 12'f5, whence the vapour tension is 5'0 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 1 P.M., on the 

 hill-side, to the west of the tongue of the glacier, and at a height 

 of about 2,100 m. above the sea, four good observations of the 

 temperature were made, giving 17'5, 18'0, 19*5, and 19'0; they 

 are all equally trustworthy, and represent the average tempera- 

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

 thermometer was whirled. The mean of these values, 18 '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 2,250 m., the temperature of the air at 2 P.M. was 

 18'5 C. Having returned to the same spot where the observations 

 were made at 1 P.M. the following air temperatures were observed : 

 between 2.40 and 2.46 P.M., 17'5, 18 0< 0, 17'5, 17'0, 17'3, 17'l ; 

 mean, 17'4 ; and between 2.50 and 2.54 P.M. 16'5, 16'5, 167, and 

 16'5 ; mean, 16'55. The mean of the two sets is 17'06. Again 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 Fohn cloud. The wind was 

 fresh down the glacier, which made the exposure of the thermo- 

 meter easy and good. The hot Fohn puffs were also very striking. 

 The thermometer was first swung exposed to sun and wind, showing 



