532 



Mr. J. A. Bronn on the Directions ^c. of [Feb. 1^ 



6 A.M. to 6 p.:\r. ]S'ow at Makerstomi during the four 3-ears 1843-1846 

 the mean of the resultant directions for the hours 6 a.m. to 6 p.m. was 

 243°. Hence we have 



-0=277° -248°= + 29^ 



So many causes may affect the direction of the surface current in 

 certain pLaces that it cannot fail to appear possible, if not probable, that 

 we hare here a result depending on local conditions, contour of the 

 country, or accidental causes. This possibility it is essential to consider. 



In the first place it will have been remarked that the mean direction 

 of the wind from the four years' observations, 27° south of west, is the 

 same as has been deduced from the Greenwich observations. In the 

 next place, the mean direction of the wind for Scotland, deduced from 

 eleven years' observations (1857-1867) at 9 a.m. and 9 p.m., made at 

 fifty-fiv& stations, was 32° south of west*, while at Makerstoun, from 

 observations at the same hours in the four years, 1843 to 1846, it was 

 29° south of westt — a difference of only 3°, w^hich would go to increase 

 that of i// — 0. 



Fortunately I have been able to confirm the result for the difference 

 of directions of the cloud and surface currents by observations made in 

 a very different locality. M. Quetelet observed the directions of the 

 cloud-motions (without distinction of species) at the Brussels Observa- 

 tory during the years 1833 to 1846, and he found the resultant directions 

 by Lambert's formula as follows J: — 



In the 7 years 1833 to 1839 (;^)=258 53 



Do. 1840 to 1846.... „ =255 21 



In the 14 years 1833 to 1846. . . . „ =257 50 ; 

 whereas by the \^'ind-vane of Osier's anemometer (which was erected 

 in 1842) the direction was found 



In the 5 years 1842 to 1846. .. .0 = 225° 49' 



A comparison of the numbers of times the clouds and surface-wind 

 had moved from each point of the compass in the five years 1842 to 

 1846 induced Quetelet to think that the clouds, as well as the re- 

 sultant surface-wind, had really proceeded from a more southerly point 

 than in the preceding years. Had the eminent director of the Brussels 

 Observatory sought the resultant directions for each year, he ^ ould have 

 found that marked differences of the direction of motion existed in each 

 of the five years. I have calculated these directions from Quetelet's 

 numbers ; they are as follows : — 



* This result I hare clecliicecT from Table II. of Mr. Biiclian's paper alreadj- cited, 

 Trans. Eoy. Soc. Edinb. toI. xxt. p. 616, 



t *' Eesults of Makerstoun Obseryations," Trans. Eoj. Soc. Edinb. vol. xix. pt. 2, p. c. 

 \ Sur le Climat de la Eelgique, 2^^^ parti e, p. 8. 



