ON METEOROLOGICAL OBSERVATIONS ON BEN NEVIS. 71 



other points, the great height in the atmosphere the squall reached, bear- 

 ing in its train totally changed conditions of temperature and moisture. 

 Mr. Mossman has been engaged in discussing the remarkable series of 

 observations made by Mr. Wragge in 1882 at eight stations well dis- 

 tributed up the slopes of Ben Nevis from Fort William to the top. The 

 work is so far advanced as to indicate the important bearing of the re- 

 sults as regards the vertical distribution of pressure, temperature, and 

 moisture during the changes of weather of that year. 



Steps have been taken to make the observation of dust particles in the 

 atmosphere part of the regular work of the Observatory. Eight observa- 

 tions are made daily, and as each of these eight is the mean of ten, there 

 are really eighty of these observations made every day. The observa- 

 tions now accumulated amply confirm the tentative results given in your 

 Committee's last year's report, as showing a well-marked diurnal varia- 

 tion. Further, dry, thick fog is shown to contain a great amount of dust, 

 but thin, wet mist very little. It is when a tbin drizzling mist envelops 

 the summit that the lowest values are obtained, and the all-important 

 observation has been made, after consulting the daily weather maps of 

 Europe at the time, that the winds differ in direction 90°, or even more, 

 from the winds then prevailing near sea-level. In other words, the 

 drizzling and practically dustless winds blow out from a shallow cyclone 

 overspreading this part of Europe at the time. The significance to 

 weather forecasting of these different types of wind, as regards dustiness, 

 or dustlessness, to the cyclones and anti-cyclones prevailing is too evident 

 to call for further remark. 



In your Committee's last report, expression was given to a desire that 

 a system of special observations on the hygrometry of the atmosphere be 

 instituted at the two Observatories, with the view of arriving at some 

 accurate knowledge of the absolute amounts of aqueous vapour at differ- 

 ent heights under the different weather conditions. With reference to 

 this, the Directors of Ben Nevis Observatory report that the University 

 of Edinburgh has awarded the Scholarship placed at their disposal by the 

 Commissioners of the Exhibition of 1851 to Mr. A. J. Herbertson ; and 

 that the research to which he will devote his attention during the two 

 years he holds the scholarship is the hygi'ometry of the atmosphere, and 

 it is understood that the investigation will begin at Ben Nevis Observa- 

 tory, and will proceed on the lin'es indicated by the Directors. 



During the past year Mr. Omond has been engaged in an important 

 inquiry into the relations of the Ben Nevis High and Low Level Observa- 

 tories to the cyclones and anti-cyclones, or the weather changes of the 

 British Islands. In this large inquiry the instances dealt with are 

 arranged into eight groups, according to the direction, N., N.E., E., &c., 

 of the gradient from Ben Nevis in the direction of the cyclone or anti- 

 cyclone. To these are added two groups, first when Ben Nevis is inside the 

 highest isobar; and second, when it is inside the lowest isobar; in other 

 words, when the Observatories are approximately either in the centre of 

 an anti-cyclone or of a cyclone. 



Dr. Buchan is investigating the observations at the two Observa- 

 tories during February and September, 1891, in their relations to the 

 changes of weather. These two months have been selected owing to the 

 exceptional character of the weather which prevailed, and the admirable 

 illustrations afforded of the more striking meteorological conditions, and 

 meteorological contrasts of the two Observatories, and other striking 



