440 Results of Makerstoun Observations, 1844. 



Table XXXVII. lias been formed from the observations of the motions of the clouds and surface wind 

 given in the Tables, pages 172-308, in the following manner : — When several observations of the direction of 

 the wind have been obtained, at successive hours, with simultaneous observations of the direction of motion 

 of the current of scud, the mean direction of the wind has been taken, and the mean direction of the cloud 

 motion, the direction of the lower current (counted in points from N. by E., S., and W.) has been subtracted 

 from the direction of the upper current, and the difference entered with its proper sign as one result ; when 

 the lower current is from an easterly point the difference is positive if the upper current be most southerly ; 

 when the lower current is from a westerly point the difference is positive when the upper current is most 

 northerly. When in the same day the direction of either current has changed considerably, two or more results 

 have been obtained ; in several cases, especially for the higher currents, a single good comparison has received 

 the value of a result : on the average, each result (the whole number of which is given in the first column for 

 each quadrant, Table XXXVII.) for the differences scud minus wind has been obtained from five pairs of simul- 

 taneous observations, for the differences cirro-stratus minus wind and cirro-stratus minus scud from three pairs, 

 and for the differences cirrus minus wind and cirrus minus scud from two pairs of simultaneous observations. 

 All observations for the direction of the surface wind were rejected for which the force was less than Ol lb., or 

 for which the pressures of 01 lb. were, from variable gusts, due to local causes. All the results for the lower 

 current in the quadrant N. to E., which were positive, were combined, and the mean difference obtained, simi- 

 larly for the negative differences ; and so for the other quadrants. Thus, for the difference of motions scud 

 minus wind in the quadrant N. to E., 57 results were obtained which gave positive differences, the mean dif- 

 ference being + 24° ; 34 were obtained which gave negative differences, the mean being — 34°, and there were 

 3 results without any difference of motion. The mean of the whole 94 results shews that the scud moved from 

 a point 2° south of that from which the surface current proceeded. 



Differences of the Directions of Motion of the Upper and Loiver Currents of Air. — In the three quadrants 

 E. to S., S. to W., and W. to N., the mean direction of the superior current is always positive of the mean direction 

 of the inferior current, and this is true in all the five series of comparisons. In the quadrant S. to W., in which 

 the greatest number of observations were obtained, the law is very distinct. The scud current proceeds on the 

 average (of about 800 comparisons of the motions of the two currents) from a point 21° north of that from 

 which the surface wind proceeds ; the cirro-stratous current (on an average of about 300 comparisons) proceeds 

 from a point 30° north of the surface wind ; and the cirrous current proceeds (on an average of about 200 com- 

 parisons) from a point 40° north of the direction of the surface wind. From these results we might conclude that 

 the cirro-stratous current is 30° — 21° = 9° positive of the scud current, and that the cirrous current is 40° — 21° 

 = 19° positive of the scud current ; the quantities actually obtained from comparisons which are more or less 

 independent are +17° and + 20° respectively, the former differing somewhat in value, though accurate as re- 

 gards sign. Such consistency is only to be expected where the differences of motion have been determined from 

 a sufficient number of comparisons. The results, however, for the quadrant E. to S. are nearly as consistent, 

 though obtained from few observations. In this quadrant the scud is 16° positive of the surface current, and the 

 cirro-stratous is 25° positive of the surface current, whence the cirro-stratous should be 25°— 16°= 9° positive 

 of the scud current ; the result from comparisons which are partially or wholly independent is + 11°. The 

 comparisons in the quadrant W. to N. indicate on the average in all cases that the upper current is positive of 

 the lower, but the differences do not increase regularly with the height of the current. The quadrant N. to E. 

 contains the only exception to the law of the other quadrants ; in this quadrant the cirrous current is not positive 

 of the inferior currents ; the comparisons, however, are very few. The scud and cirro-stratous currents are 

 both positive of the surface current, the former not much, probably because the scud current from the NE. is 

 generally very low. 



Taking the averages for all the quadrants, we have 



Scud current minus surface current, from 347 results, (about 1700 comparisons) = + 13°.9 



Cirro-stratous current minus surface current, ... 223 ( ... 700 )=-t-21°-7 



Cirrous current minus surface current, ... 102 ( ... 200 ) = +31°-9 



Cirro-stratous current minus scud current, ... 217 ( ... 700 )=+16°.4 



Cirrous current minus scud current, ... 106 ( ... 200 ) = + 12 0, 8 



Roughly, then, the direction of the scud current is about 1 point, of the cirro-stratous current about 

 2 points, and of the cirrous current about 3 points, of the compass, positive of the direction of the surface 

 current. 



It happens frequently that comparisons of the motions of two currents are obtained when the other two do 

 not exist, or are not evident, from the absence of clouds within them, or from the masses of clouds in the lower 

 current. It is for these reasons that each of the comparisons of motions above are obtained from observations 

 made partly at the same and partly at different times ; they are therefore to a considerable extent independent 



