civ General Results of the Makerstoun Observations. f 



It appears, then, that if we take the mean direction of the surface-current as W. 21° S., the directions of the 

 four currents will be nearly as follow : — 



Resultant direction of the surface-wind (No. 207), W. 21° S. 



scud-current, W. 7° S. 



cirro-stratous current, W. 2° N. 



cirrous current, W. 9° N. 



The mean resultant direction for the three cloud-currents, giving each an equal value, is W. 1° N. The mean 

 resultant direction of all the currents, giving each an equal value, is W. 4° S. 



221. If we neglect the distinctions of the upper currents, and consider merely the differences of all the 

 results for the cloud-currents compared with the surface-wind, we obtain the following numbers : — 



Quadrant N. to E., 499 results, mean upper current minus surface-current, = + 5°-8 



E. to S., 179 = + 19°-l I 



S. to W., 1393 =+26°-6 f 



W.toN.. 466 = + 10°-6 ' 



The mean upper current, therefore, is least positive of the surface-current in the quadrant N. to E., and it is 

 most positive in the quadrant S. to W. ; the mean result for each couple of opposite quadrants is nearly the 

 same, namely, 15° and 16°. 



222. If we compare in a similar manner the mean cirro-stratous and cirrous current with the scud-cui-- 

 rent in each quadrant, we have, — 



Quadrant N. to E., 157 results, mean cirro-stratous and cirrous current minus scud-current, = — l°-2 



E. toS., 88 = + 15=-9 



S. toW.,437 = + 16°-l 



W.toN., 340 =+ 3°-2 



In the quadrant N. to E. the mean of the two upper currents seems to differ nothing from the scud-current, and 

 nearly the same seems to hold for the quadrant W. to N. ; but in the southern quadrants the mean upper cur- 

 rent is positive of the scud-current 1 6°. 



223. It appears, then, from the previous numbers, that the mean upper current always proceeds from a point 

 positive of the direction of the surface-current, and that the motion of the mean of the higher currents, compared 

 with the motion of the scud-cuiTent, obeys the same law in the southern quadrants. These results are in accord- 

 ance with the conclusions from the causes of the oblique motions of the aerial currents. Currents of air pro- 

 ceeding northwards from more southerly positions retain a portion of the excess of eastward velocity of the places 

 from which they start ; hence the south-easterly winds become more southerly, and the south ^vinds become more 

 south-westerly, as they proceed northwards ; the extent of the change of direction depending on the gTeater or 

 less rapidity with which they lose their excess of eastward velocity and acquire that of the more northerly lati- 

 tudes on which they move. Tliis loss of eastward velocity will depend upon the proximity of the aerial stratum 

 to the surface of the earth, and therefore the lower currents of air vnW lose more of their eastward velocity than 

 the higher currents, and the upper current of southerly -snnds will become more westerly than the lower cur- 

 rents. If, in considering the currents of air wliich proceed southwards from more northern latitudes, we re- 

 member that the lower currents, from their proximity to the surface of the earth, acquire the greater eastward 

 velocity of the lower latitudes more quickly than the upper currents, it will be evident that the lowest current 

 from the north-west should become less northerly than the upper current, and that the lower current from the 

 north should become less easterly than the upper current. This, it will be observed, agrees with the results 

 previously obtained ; we find, however, in the northern quadrants, that the scud-current differs less from the 

 surface-current than it does in the southern quadrants ; this, it is conceived, is due to the fact that this current 

 is nearer the surface in the northern than in the southern quadrants : it may, however, be due also to the 

 greater proximity of the origin of the currents. We find also that the mean upper currents differ little or 

 nothing from the scud-current in the northern qviadrants ; it is only necessary to examine the numbers in Table 

 97 to see that this is not due to the smallness of the differences of motions of these currents, but to the num- 

 bers of positive and negative results being more neai'ly equal. It has been frequently observed that when the 

 lower current of scud is from a north-easterly point the current of cii'ri is from a north-westerly point ; these 

 currents could not have had the same origin, and therefore the explanation of the difterences of motions given 

 above cannot apply ; this difference of origin occurs in all the quadrants, and diminishes the apparent effect of 

 the variable velocity of the earth's surface ; it occurs seldomest in the south-west quadrant. 



