120 



Chemical and Physical Notes 



by the sensations and at the same time so rapid as to elude almost every 

 other method of estimation or measurement. It has also, I believe, not 

 been before remarked that the true Fohn occurs in our own country and 

 with its characteristics quite as well marked as in Switzerland. It is 

 sometimes supposed that a great absolute height of mountain chain is 

 required for its production ; but this is not so. A relative height of 1000 

 to 1200 metres is quite sufficient for its production; and this is equally 

 available on the west coast of Scotland and on the northern slopes of the 

 Alps. 



"Some observations were made in 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 Engadine, 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 temperature 

 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 very warm air still hotter blasts made them- 

 selves 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 thermo- 

 meter, 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 thermometers in the screens were also 

 a good deal affected, though not nearly to the same extent as the freely 

 exposed ones. The recording instruments, 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. It was very warm, as the following observations 

 (Table XXI) 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 temperature, owing to the thermal inertia of the thermometers. The 

 puffs lasted not longer than one or two seconds, 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 Table XXI, it will be seen that 



