1 METEOROLOGY OF BEN NEVIS. 



other observations seem in favour of the idea that tornados and the most 

 destructive gusts in storms, which are analogous to tornados, are the im- 

 mediate effects of uprushes of warm moist air-currents and downrushes of 

 colder and drier air to take their place. Now, to this important inquiry Ben 

 Nevis contributes invaluable data, with its observations of sudden, rapid, and 

 often short-continued changes of temperature and humidity, many of which 

 are strictly limited to the upper region of the mountain, as first shown by the 

 observations made by Mr Wkagge in 1882 at the eight stations on the slopes 

 of Ben Nevis, from sea-level to the top, and since confirmed by the observa- 

 tions at the Observatory. 



If there be conjoined with an unusually rapid rate of decrease of tempera- 

 ture with height a lower sea-level pressure, calculated from the Ben Nevis 

 Observatory readings, than what is actually observed at Fort- William ; that is 

 to say, when the barometric observations indicate a more rapid decrease of 

 temperature with height somewhere in the aerial stratum between sea-level 

 and the top of the mountain than the thermometric observations alone show, 

 then the indications of a coming storm become more decided. Conversely, 

 the absence of any abnormally rapid decrease of temperature with height, as 

 may be ascertained from all the observations, is rarely attended or followed by 

 storms of wind. 



On the other hand, abnormally high temperatures are observed at the top, 

 when the temperature is occasionally even higher than at Fort-William ; these 

 are always restricted to the higher parts of the mountain, are not associated 

 directly with storms, but are the accompaniments of anticyclones and the fine 

 weather which characterises them. Indirectly, however, owing to their de- 

 pendence on the cyclone with its adjoining anticyclone, it is impossible to over- 

 state the value of these Ben Nevis observations in any serious investigation of 

 the weather changes of north-western Europe. 



Since 1868 the Scottish Meteorological Society has, through the courtesy 

 of the Commissioners of the Northern Lighthouses, been favoured with meteor- 

 ological observations from all the Lighthouses, each keeper of a lighthouse being 

 thus a regular observer of the Society. An important part of the keepers' 

 duty is to record the hour of beginning and ending, and varying force of all 

 strong winds, gales, and storms that occur. The observations made at the 

 Lighthouses since December 1883, when the records of the Observatory com- 

 mence, have been plotted on monthly sheets, which show graphically when and 

 where storms occurred round the Scottish coasts ; and on the same sheets 

 have been entered, for the respective Meteorological Districts, all cases when 

 storm signals have been hoisted and kept up, under direction of the Meteor- 

 ological Office. The investigation is still in progress, but the following results 

 may be provisionally stated. 



