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



The observations were made iu the summer of 1893, which was 

 abnormally warm all over the north of Europe. In the beginning of 

 July I observed the Fohn at Fort William, and in the latter part of 

 August in the upper Engadin, and more particularly in the valley 

 occupied by the Morteratsch glacier. Besides the observation of the 

 varying temperature of the air itself, the investigation of the tem- 

 pei'ature gradient set up between the melting ice surface of the 

 glacier and the hot winds blowing over it presented considerable 

 interest. The curious fact was observed that while the hot wind was 

 blowing over the glacier and melting the surface in abundance, the 

 temperature of the air, as close to the ice as a thermometer could be 

 applied without touching the ice, was never lower than 5*5 C. 



In the beginning of July at Fort William the weather was very 

 warm, and in the midst of the very warm air still hotter blasts made 

 themselves felt from time to time. The sensation was much the 

 same as is produced when, on the deck of a steamer, the air passing 

 the funnel strikes the face. These hot blasts lasted only for one or 

 two seconds, and repeated themselves every minute or two. Their 

 effect on a thermometer, freely exposed in the shade, was to keep the 

 mercury in a constant state of motion, the temperature rising often 

 more than 1 C. in a minute, and falling again as much. The thermo- 

 meters in the screens were also a good deal affected, though not nearly 

 to the same extent as the freely exposed ones. The recording instru- 

 ments, the clock motion of which was not sufficiently quick to draw 

 the record out into an indented line, showed a broad band which 

 measured the amplitude of the excursions of the instrument, though 

 by no means the amplitude of the oscillations of the temperature of 

 the air. This phenomenon was particularly observed on the 8th July, 

 1893, when I was employed the greater part of the day in making 

 evaporation experiments. It was very warm, as the following obser- 

 vations of the thermometers in the large observatory screens will 

 show : 



It was during the heat of the day, from 10 A.M. to 2 P.M., that the 

 hot puffs made themselves most felt ; but I found it impossible to 

 measure their temperatures, owing to the thermal inertia of the 

 thermometers. The puffs lasted not longer thau one or two seconds, 



