Pressure of the Wind. 431 



from the maxima between the hours of observation. From both Tables the diurnal variation for each month 

 shews some irregularities ; neglecting the means for December, the maximum force of wind (from Table XXXI.) 

 occurs between noon and 2 h p.m. and the minimum occurs between 9 h p.m. and 6 h a.m. ; in December the maxi- 

 mum pressure occurred about 10 h p.m. and the minimum about 10 h a.m. The approximate epochs of pressure 

 of wind from Tables XXX. and XXXII. for each of the astronomical quarters and the year are as follow : — 





From Table XXX. 



From Table XXXII. 





Minimum. 



Maximum. 



Minimum. Maximum. 



Winter, Nov., Dec, Jan., 



5 h 10 m A.M. 



h 40 m p.m. 



6 h 40 m A.M. l h m P.M 



Spring, Feb., March, April, 



12 50 ... 



2 ... 



12 10 ... 1 40 ... 



Summer, May, June, July, 



3 ... 



1 40 ... 



9 40 p.m. and 3"a.m. 2 10 ... 



Autumn, Aug., Sept., Oct., 



3 10 ... 



1 10 ... 



4 50 ... 1 40 ... 



The Year 1844, 



4 10 ... 



1 50 ... 



12 40 a.m. 1 40 ... 



The epochs from Table XXXII. are most to be depended on. The differences between the two sets are 

 chiefly in the times of minimum pressure, and these times are not well marked. In the winter quarter, con- 

 sidering the means from Table XXXII., the pressure varies little from 9 h p.m. till 8 h a.m. : there is the appear- 

 ance of a secondary maximum about midnight. In spring the minimum occurs at midnight, but there is again 

 a minimum about 5 h a.m., a secondary maximum occurring between these times ; in summer the pressure is 

 nearly constant from 9 h p.m. till 4 h a.m., and in autumn it is nearly constant from midnight till 6 h a.m. In the 

 mean for the year the pressure of wind varies little from 9 h p.m. till 6 h a.m. ; there is a slight indication of 

 a secondary maximum about 2 h or 3 h a.m. : the maximum pressure occurs almost exactly at the time of the 

 maximum temperature of the air. 



Annual Variation of the number of times which the Wind blew in 1844. — From Table XXXIII. the num- 

 bers of times which the wind blew with a force of 0*1 lb., or upwards, at the hours of observation in 1844 were 

 for each month as follow : — 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



233 



308 



382 



371 



275 



400 



306 



434 



442 



459 



459 



176 



The average numbers a-day out of 24 observations are 



8-6 12-3 14-7 14-3 10-2 16-0 11-3 16-1 17'7 17'0 177 6-8 



The wind blew most frequently in the months from August to November, and with least frequency in 

 January and December. On the whole the wind blew seldomest about the winter solstice and oftener about 

 the equinoxes than about the summer solstice : this result is the reverse of that for 1843. 



In 7536 observations, the wind blew 0-1 lb. or upwards 4245 times, or 13*5 times a-day of 24 observa- 

 tions, or 563 times in 1000. 



Annual Variation of the number of Points of the Compass in which the Wind blew. — The following are the 

 numbers of points in which the wind blew in each month of 1844 : — 



Tan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



19 



28 



29 



19 



26 



29 



32 



30 



26 



31 



28 



22 



Neglecting the points in which the wind was observed to blow less than four times, the numbers of points are 

 16 19 22 13 22 20 23 24 20 28 23 15 



The wind blew from the fewest points in January, April, and December, and from the greatest number 

 about October. 



If we divide the number of points from which the wind blew by the number of times which it was observed 

 blowing, the quotient will represent the variability of direction. The quotients for each month are as follow : — 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



0-082 



•091 



•076 



•051 



•095 



•072 



•105 



•069 



059 



•068 



•061 



•125 



The direction of the wind was most variable in December and July, and least variable in April and Sep- 

 tember. 



