ON VARIATIONS IN DIRECTION AND MOTION OF THE AIR. 265 



disposal ; my friend Mr. Hartnup did the same, and furthermore aided me 

 very greatly by allowing his assistants to tabidate, in the manner I required, 

 the observations of the direction and horizontal motion of the air as recorded 

 at the Liverpool observatory. I have worked out the Birmingham observa- 

 tions on the same plan. 



To commence with the horary variations. These extend over a period of 

 nearly eight years at Wrottesley and thirteen years at Liverpool. The 

 amount of motion of each wind for each of sixteen points of the compass is 

 taken note of for every hour, from the daily records, and tabulated for every 

 month. Commencing with the N.N.E. wind, the number of miles of air 

 from this point that passed between midnight and one o'clock in the morn- 

 ing during the month of January in each year is tabulated ; next between 

 one and two o'clock, aud so on through the twenty-four hours of the day. 

 February is then treated in the same way, and thus through every month 

 in the year, for each of the sixteen points of the compass, as shown in 

 Table L, which is given as an example, exhibiting the amount of motion and 

 duration of the south wind during each hour in December for each year. 



From the mean of the seven years thus obtained, the monthly curves of 

 horizontal motion for each hour at Wrottesley are projected. See Plate IV. 

 The means of the separate months are also combined so as to obtain averages 

 for the seasons and the whole year. In Table II. an example of this is given 

 in the horary variations in the S.E. wind at Liverpool. 



Plate V. exhibits the curves projected from tables so arranged for Wrot- 

 tesley, and Plate VI. for Liverpool. 



Beginning with the N.N.E. (Plate IV.), and proceeding through the 

 easterly points to S.E., the curves present no very striking features ; in some 

 months they approach that of temperature, as the N.E. in April, the E.N.E. 

 in February, May, and October, also the E. in February, May, June, Octo- 

 ber, and November. The prevalence of winds having an easterly or north- 

 easterly bearing during the spring and early summer is also seen, but their 

 particular periods and amount are more perfectly shown in the diagrams of 

 "Diurnal Variations" than in those which are prepared for exhibiting the 

 horary variations. 



The S., S.S.W. and S.W. currents, or anti-trade-winds, are the next in 

 order, and exhibit some remarkable features. Independently of the great 

 and sudden increase in the amount of these, especially of the south, when 

 compared with any of those from the east, it will be observed that they 

 exhibit a striking peculiarity in the horary curves ; for while the greatest 

 amount of air passes from the south before noon, diminishing rapidly for 

 several hours after noon, with the S.W. the reverse of this takes place, the 

 greatest quantity passing after noon and the least before — the intermediate 

 wind, namely, the S.S.W. showing the most in the middle of the day. It 

 will be observed that the winds on either side of these three, namely, 

 the S.S.E. and W.S.W., partake of the same peculiarity, but in a less degree, 

 the former having its maximum in the morning, and the latter in the 

 afternoon. 



The west and north-westerly currents present variations that show the 

 greatest difference between the amount of air that passes by day when com- 

 pared with the night, and correspond most nearly with the curve of tempera- 

 ture. The N.N.W. winds in the summer months, and especially in June 

 and July, show the greatest extreme, while the winter months indicate the 

 least difference between the day and night. 



