WINDS OF BEN NEVIS. 



547 



shows no appreciable changes, even in fine summer weather, when the power of the sun 

 is greatest, and such changes might be looked for. To make certain of this, the number 

 of observations of each of the four cardinal points were tabulated for each month of the 

 seven years, 1884-90, and the difference of the total number at each hour from the 

 mean of the whole day taken out. Combining the E. and W. winds into one table, 

 we find that there is no regular diurnal change, except a very slight tendency to an 

 excess of W. at night and of E. in the forenoon. The table of N. and S. winds 

 shows a rather more marked variation, most pronounced in the summer months : from 

 1 to 9 a.m. the N. is in excess, from 10 a.m. to 6 p.m. the S., and for the rest of 

 the day both are rather below the mean of the whole day. 



This result is substantially the same as that arrived at by a more elaborate examina- 

 tion of the summer winds of Ben Nevis for two years, communicated to this Society in 

 1886 (see Proc. Roy. Soc. Edin., vol. xiii. p. 839). We see no reason to alter the 

 explanation of this very slight diurnal variation given in that paper, viz., that it is 

 entirely due to radiation on the N. and S. sides of the hill, and is not connected 

 with any general system of land and sea breezes. It is rather remarkable that on Ben 

 Nevis there should be practically no diurnal variation in the direction of the wind, 

 situated as it is near the Western Sea, and with the elevated plateau of the Moor of 

 Rannoch, and the great mass of the highest hills of Scotland to the E. of it. At any 

 sea-level station in the neighbourhood, doubtless a diurnal change of marked character 

 would have appeared in a similar set of observations. 



Table I. — Hours of Each Wind. Ben Nevis Observatory. M> eans 1884-89. 





















Calm or 





N. 



N.E. 



E. 



S.E. 



S. 



S.W. 



W. 



N.W. 



Var. 



January, .... 



120 



67 



43 



96 



104 



118 



103 



78 



15 



February, 



124 



79 



65 



86 



83 



101 



67 



52 



15 



March, .... 



138 



105 



76 



109 



81 



87 



68 



56 



24 



April, .... 



133 



87 



85 



103 



94 



65 



61 



48 



44 



May, .... 



79 



89 



71 



135 



115 



88 



73 



48 



46 



June, .... 



112 



57 



60 



90 



89 



99 



89 



59 



65 



July, .... 



130 



34 



53 



111 



102 



88 



91 



68 



67 



August, . ... 



151 



38 



34 



78 



121 



99 



101 



59 



63 



September, 



133 



33 



34 



86 



113 



103 



102 



61 



55 



October, 



188 



68 



61 



90 



73 



94 



72 



54 



44 



November, 



149 



56 



66 



100 



74 



111 



84 



62 



18 



December, 



190 



68 



30 



63 



83 



113 



92 



84 



21 



Year, .... 



1647 



781 



678 



1147 



1132 



1166 



1003 



729 



477 



February (Leap year), 



129 



81 



68 



89 



86 



104 



70 



54 



15 



