METEOROLOGICAL OBSERVATIONS OF HEX NEVIS. 283 



shine ; fog, in hours' duration ; thunderstorms ; lialos, auroras, and other 

 phenomena. These are collated with the bi-daily weather maps of the 

 Meteorological Council, and also with the hourly observations of the 

 Ben Nevis Observatories. These have been designed mainly to see what 

 light would thereby be cast on the dynamic effects produced by the con- 

 densation and precipitation of the aqueous vapour of the atmosphere. 



Now, among other matters, these maps reveal the existence of two 

 very different types of westerly winds. One type has the wind unusually 

 strong and steady, nearly in the same direction at the top of Ben Nevis 

 as at sea level, with the hygrometer showing a great humidity at both 

 observatories, and continuing long and steadily humid. Under these 

 conditions the accompanying rains are more than ordinarily heavy, and 

 virtually overspread all Scotland. The other type is accompanied by a 

 wind at the top of the mountain, nearly in a direction the opposite to 

 what obtains at sea-level at the time, with the hygrometer at one or both 

 observatories indicating great fluctuation in the amount of vapour. 

 Under these conditions the rains deposited do not penetrate far east- 

 wards, and even in strictly western situations are neither very heavy 

 nor protracted. 



.Somewhat analogous to these westerly winds are the accompanying 

 phenomena of easterly winds, with the notable exception that easterly 

 winds bring with them a rainfall that seldom penetrates to any consider- 

 able distance inland from the east coast. 



Now in the case of districts which are well protected by mountains in 

 the west- south-westerly direction, but well open to the rain-bringing south- 

 easterly winds, it happens that their curves of rainfall for the sun spot 

 period are diametrically opposite to the rainfall curves of strictly western 

 districts. These local climatological considerations have an important 

 bearing on the methods to be employed in collating the spots of the sun 

 with the vaiying phenomena of meteorology. 



The Application of Photography to the Elucidation of Meteorological 

 Phenomena. — Eighth Report of the Committee, consisting of JMr, 

 G. J. Symons (Chairman), Professor R. Meldola, Mr. J. 

 HoPKixsoN, Mr. H. N. Dickson, and Mr. A. W. Clayden (Secre- 

 tary). (Draivn up) by the Secretary.) 



The work has been continued throughout the year whenever possible, 

 and the number of separate observations made in the course of the last 

 three years amounts to more than 200, about 150 of which were observa- 

 tions of high-level clouds. 



It has been found that the low-level cumulus clouds very frequently 

 fail to give any results, as the parallax due to the base line often gives 

 two sucli very different pictures that no corresponding points of the cloud 

 can be identified. For such clouds a base line of 100 yards would be 

 ample. With the present base line of 200 yards it is not possible to be 

 sure of getting a reliable measurement unless the cloud is at a height of 

 at least 2,000 feet. 



Some slight difficulty has been experienced in so drawing the vertical 

 and horizontal lines as to intersect exactly in the centre of the disc given 

 by the image of the sun. This has been especially the case with negatives 



