

1894.] Atmospheric Temperature, especially during Fohn. Ill 



and their temperature, to judge by the sensation, was rather higher 

 than that of the body. The thermometers had only begun to rise 

 when the heating ceased, and they fell back again. From the 

 figures in the above table, it will be seen that the temperature 

 of the air at noon reached 24'9 C., a very high figure for a station in 

 nearly 57 north latitude. Along with the great rise of temperature 

 there is a fall of absolute as well as of relative humidity, indicating 

 that the air has come from a greater altitude. Attempts to measure 

 the actual temperatui-es of the hot puffs gave no satisfactory result. 

 I am much obliged to Mr. Omond and the staff of the Fort William 

 Observatory for their courteous assistance while making these 

 observations. 



Later in the year, in the middle of August, I visited the upper 

 Engadin, and stayed for some weeks at Pontresina. Here, as else- 

 where the weather was very warm, and I was much struck by 

 observing the same blasts of hot air as I had experienced in Scotland. 

 The general characteristics of the weather were the same, and the 

 temperature of the air in the valley rose nearly as high as it had 

 done at Fort William. 



On the 18th August I went for an excursion on the Morteratsch 

 glacier with a guide. On my remarking the hot puffs of air, which 

 were much more striking on the ice than on the land, he said it was 

 the Fohn, of which he considered them a characteristic. The sun and 

 the hot wind were causing an enormous amount of surface melting of 

 the ice, and having a thermometer with me, I took the temperature 

 of the air by whirling at a height of about 1 m. from the ice, and 

 found it 12'0 C. ; the wet bulb was 5*0, so that the vapour tension 

 was 2'3 mm., the relative humidity 22, and the dew point 8'6 C. 

 The great dryness of the air will be remarked. I then swung the 

 thermometer in a conical path as close to the ice as possible, and the 

 temperature of the air was 10'0 C. Being astonished to find so high 

 a temperature so near the ice, I put the bulb of the thermometer into 

 a crack in the ice, so as to be below the level of the surface of the 

 ice, and its temperature only went down to 7'5 C. 



All the temperatures were taken with a mercurial thermometer, 

 which was whirled at the end of a string so that its velocity was 

 about 6 m. per second. It was not protected in any way, so that 

 the temperatures observed with it are not free from a certain 

 error due to radiation and reflection, although it was always shaded 

 from the direct sun. These errors are not usually great with a 

 whirled instrument, and most of my observations have to do with 

 differences of temperatures observed with the same instrument and 

 under similar circumstances. On the glacier the thermometer, when 

 whirled, was not apparently affected by radiation or reflection from 

 the ice, and only very slightly by that from the sun. On land I 



