110 On Dove's Lata of the 



We see by these results that the mean direction moved 

 round from N.E. to S. by W. during the year; and if we 

 recollect the number of revolutions during the different sea- 

 sons, as given in the early part of this paper, we are struck 

 with the fact that the least number of revolutions occur when 

 the mean direction for the quarter nearly coincides with the 

 mean direction for the year, and that the number increases 

 as the former recedes from the latter, in the sense of the 

 direct revolutions. 



After having given the results of the yearly observations 

 bearing upon the subject before us, I have thought it also 

 advisable to examine the mean direction of the wind for each 

 day in a certain month, with the view of illustrating still 

 further the law of the turning of the wind. 



The quantities used are those given in the first column of 

 Table IV. [Vide page 120, and Plate L] 



The month of April, 1859, was selected, because it is an 

 average month ; with regard to the number of revolutions, 

 which were 3 "72, this number closely corresponds with that 

 for April, 1858, viz. : — 4"0, and the latter number is nearly 

 the average number of direct revolutions per month through- 

 out the year. 



If we analyse the directions given in Table IV., and divide 

 them into positive and negative, according to the principles 

 laid down above, when speaking of the motions of the vane 

 in general, and taking, as jumps, all those changes in direc- 

 tion which are within 5° of 180° distant from each other, we 

 obtain the following results ■ — Positive sense, 990° 26' ; 

 negative sense, 686° 25'; and one jump between the 19th 

 and 20th of the month, consequently if a? represents the jump, 

 we obtain as the result 304° 1' + x direct revolutions of the 

 wind more than negative ones. On examining the nature of 

 the jump we see that the wind went around from N.E. to N., 

 N.N.W., S.W. by S., S., and S.S.E., consequently, the motion 

 of the mean direction could not have been retrograde. The 

 jump being therefore considered positive, we have 490° 54' as 

 the total number of degrees through which the mean direction 

 veered in the sense S.E., N., W., S., in advance to the revo- 

 lutions in the sense S.W., N.E., or 1-36 revolutions, which 

 will be as nearly as possible the mean value of the revolutions 

 of the mean direction in tbe course of a month. 



Having given these facts, which directly support the law of 

 the turning of the winds for the southern hemisphere, I now 

 proceed to a second and indirect mode of proof; but allow 

 me first to make a few explanatory remarks. 



