THE DIURNAL RANGE OF WIND DIRECTION ON BEN NEVIS. 



709 



where E., W., N.E., etc., are the number of cases observed of these respective winds, 

 and 9 is the angle from north round by east of the resultant. The subjoined table 

 contains the result of applying this formula to the summer winds. The first column 

 contains the hours of the day ; the second and third, the north-south and east-west 

 factors ; the fourth, the angle ; and the fifth, the departure of this angle at each hour 

 from the mean angle for the whole day. The mean angle is 256°, that is 14° south of 

 west, or W. by S. \ S., reckoning by points. In the " difference angle " column a + sign 

 indicates that the direction is to the northward of the mean direction, and a — sign that 

 it is to the southward. 



SUMMER WINDS OF BEN NEVIS. REDUCED BY LAMBERT'S FORMULA. 



Hour. 



N.-S. 



E.-W. 



Angle. 



Diff. 

 Angle. 



Hour. 



N.-S. 



E.-W. 



Angle. 



Diff. 

 Angle. 



1 



-13 



-62 



258 



+ °2 



13 



-80 



-43 



208 



-48 



2 



+ 11 



-66 



279 



+ 23 



14 



-65 



-33 



207 



-49 



3 



+ 18 



-68 



285 



+ 29 



15 



-53 



-43 



219 



-37 



4 



+ 28 



-70 



292 



+ 36 



16 



-40 



-58 



235 



-21 



5 



+ 32 



-65 



296 



+ 40 



17 



-22 



-48 



245 



-11 



6 



+ 43 



-64 



304 



+ 48 



18 



-11 



-34 



252 



- 4 



7 



+ 30 



-64 



295 



+ 39 



19 



- 1 



-30 



268 



+ 12 



8 



+ 18 



-49 



290 



+ 34 



20 



- 1 



- 35 



268 



+ 12 



9 



- 3 



-41 



266 



+ 10 



21 







-41 



270 



+ 14 



10 



-31 



-32 



226 



-30 



22 



- 9 



-43 



258 



+ 2 



11 



-47 



-20 



203 



-53 



23 



-13 



-49 



255 



- 1 



12 



-66 



-24 



200 



-56 



Md. 



Mean 



-11 



-12 



-41 



-47 



255 

 256 



- 1 



The values of the difference ancde indicate a considerable diurnal variation in the wind 

 direction, the amount ranging from 48° to northward of the mean at 6 h — equivalent to 

 a N.W. by W. wind — to 56° to southward at 12 h — equivalent to a S.8.W. wind. From 

 l h to 18 h the change is fairly regular, first to the maximum of northing, then back 

 through the mean value to the maximum of southing, and finally back again to near 

 the mean. The directions from 18 h to midnight all closely approximate to the mean 

 of the day. 



The hourly changes in direction are also shown in the diagram (p. 710). In this the 

 thick line shows the mean direction, and the numbered points the places from which 

 the direction for each of the hours would be drawn to the central point. The 

 diagram shows that there is superimposed on the mean direction during the morning 

 hours a N.N. W. component, and during the middle of the day a S.S.E. one, the evening- 

 hours being, as stated before, closely grouped about the mean direction. As no account 

 has been taken of velocity in computing these winds, the length of the lines that would 

 join the hourly points with the centre are merely dependent on the relative magnitudes 

 of the N.-S. and E.-W. components ; but it is of interest to note that the points form 



TEANS. ROY. SOC. EDIN. — VOL. XLIV. 4 X 



