122 Chemical and Physical Notes 



the general temperature of the air is above that of melting ice, 

 and the effect of Fohn is observed in the increased melting of 

 the ice. From the observations of Mr Bernacchi, there seems 

 to be reason to suppose that the surface of the ice which forms 

 the great barrier does not usually rise to its melting-point even 

 in the warmest month, February.- Apart from the indications 

 of the thermometer, in Greenland the occurrence of Fohn was 

 made most evident in spring and autumn by its producing 

 melting of the ice, which without it did not take place. 



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

 Engadine, and stayed for some weeks at Pontresina. Here, as elsewhere, 

 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 1 8th 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 i m. from the ice, and found it i2'oC. ; 

 the wet bulb was 5-o, 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 io'o C. 

 Being astonished to find this high temperature close to 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 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 or two degrees, 



