METEOROLOGICAL OBSERVATIONS ON BEN NEVIS, G3 



be tested by persons engaged in tlie practical work of forecasting day by 

 day ; your Committee or any other body of scientific men can only 

 indicate the lines on which results of value in forecasting may be looked 

 for. 



The first work the Directors of the Observatories set themselves to do 

 was to prepare the meteorological ' constants ' for the positions on the 

 summit and at the base of Ben Nevis. This has been done, based on 

 twenty years' observations on the summit and thirteen years' at Fort 

 William. The constants for these periods will appear in vol. iii. of the 

 Ben Nevis observations, now in the press, and to be published durin" the 

 coming winter. 



In your Committee's previous Reports other lines of investigation 

 have been frequently referred to and reported on, along which researches 

 connected with the Ben Nevis observations are being carried on by 

 Dr. Buchan and Mr. Omond. Some of the results have a special bearino- 

 on forecasting. One or two illustrative cases may be here added. 



1. The occurrence of small diflFerences of temperature between Ben 

 Nevis and Fort William, associated with very low humidities at Ben 

 Nevis and great dampness at Fort William, and the relations of this 

 state of things to the stability and continuance of an anti-cyclone, and 

 also to thunderstorms and those heavy local rains commonly denoted as 

 thunder-showers, have been reported on. 



2. The occurrence of long -continued periods of saturation of the air at 

 the top of Ben Nevis, as indicative of a condition of the atmosphere 

 favourable to the development and continuance of stormy weather. 



3. A marked difference in the direction of the wind on the summit 

 from that at surrounding low-level stations. Such a difference most 

 •commonly occurs when Ben Nevis lies between a cyclone and an anti- 

 cyclone, and may be indicative of the direction of movement either of 

 the cyclone or the anti- cyclone. 



4. The predictive a.spects of very strong winds on the summit of 

 Ben Nevis accompanied, notwithstanding their great force, with very low- 

 temperatures there and great differences of temperature between the 

 summit and Fort William, and the intimate connection of the whole with 

 cyclonic weather, have been pointed out. Recent kite observations have 

 made us tolerably familiar with this remarkable phase of the cyclone, and 

 to Ben Nevis we may look for important contributions of illustrative 

 data. 



5. The difference between the Ben Nevis and Fort William barometers 

 when both are reduced to sea-level. This difference, when it amounts to 

 several hundredths of an inch, clearly points to an abnormal condition of 

 the air between the summit and Fort William in respect to the vertical 

 gradient of temperature or humidity, or both. 



The investigation of some of the points raised in this discussion has 

 been a chief subject of inquiry during the past eighteen months. The 

 inquiry is a discussion of the hourly observations of pressure, temperature, 

 humidity, sunshine, winds and rainfall at the two Observatories in their 

 inter-relations, more especially as regards the bearings of the results on 

 weather changes 



The principal point to be kept in view is the relation of the differences 

 of temperature at the two Observatories to the differences of their sea- 

 level pressure at the time. An illustration will explain this. During 

 the last three days of September 1895, the sky over Scotland was clear^ 



