1894.] Atmospheric Temperature, especially during Folm. 113 



temperatures varying from 10'5 to 11'2, the mean being 10'8 C. 

 Swung in my own shadow, but exposed to the wind, the temperature 

 was 9 0- 8. The wet bulb was 4 0- 7, 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 

 temperatures were : dry, 6'6 C. ; wet, 3 '7 ; relative humidity, 58'5. 

 The exposure of the thermometer was as good as could be desired, 

 and, with the fresh breeze blowing, it was thoroughly ventilated. I 

 was again much struck with the highness of the temperature of the 

 air almost in actual contact with the ice. The observations at 1 m. 

 and 2 cm. from the ice were repeated, giving substantially the same 

 results at 1 m., dry bulb 10'2, wet 5'l ; at 2 cm., dry bulb 6'8, 

 and wet 3'2. The hot Fohn puffs were more striking on the ice 

 than on the land, owing to the greater difference between their tem- 

 perature and that of the surrounding air. At 4 P.M. I left the ice 

 and returned to the station of 1 o'clock on the hill-side, and took the 

 temperature at 4.35 P.M. dry bulb 16'0, wet 8 0- 0, relative humidity 

 24 0> 5. At the station in the valley below the glacier the temperature 

 was at 5.45 P.M., dry bulb 16'4, wet 11'8, and relative humidity 

 56. These observations, besides showing the remarkable conditions 

 of the air over the glacier, indicate the fineness and warmth of the 

 weather which prevailed. 



On the 21st August another series of observations was made 

 at the stations on the land and on the ice. The breeze on the 

 ice was not so steady or so strong as on the 19th, and about 5 o'clock 

 in the afternoon there was a heavy squall of rain and thunder. 

 The same hot Fohn puffs made themselves felt as before, without 

 there being any means of measuring their temperature. Their 

 duration at their maximum temperature was never more than 

 a few seconds, during which but little effect was produced on the 

 thermometer. It occurred to me that the only way of gaining a 

 knowledge of the temperature of these puffs of air would be by com- 

 paring the rapidity with which the thermometer moved when exposed 

 to a known difference of temperature, with that observed in th e puffs. 

 A number of observations was made with this view, by warming the 

 thermometer and noting its rate of cooling in air of known tempera- 

 ture. The reverse procedure was also followed on the ice. The 

 thermometer was cooled by being laid close to, but not touching, the 

 ice, it was then quickly raised to a height of 1 metre, and its rate of 

 change of temperature observed. In this way it was found that for an 

 initial difference of 4 the thermometer required 10 seconds to rise 1, 

 for a difference of 3 12 seconds, and for a difference of 2'5 16 seconds. 

 These ratios were observed in the open air, and under the circum- 



VOL. LTI. I 



