PRESSURE OF THE WIND. 289 
TABLE XXVI.—Means of the Maximum Pressures of Wind between the Hours of Observation for 
each Month and Quarter of 1843. 
Period. 
January 
February 
March 
April 
May 
June 
July 
August 
September 
October 
November 
December 
Spring 
Summer 
Autumn 
Winter 
The Year 
The observations in the first week of January were not made use of in obtaining the hourly means for that 
month in Tables XX VI. and XXVII. No observations haying been made at 18" in the second week, a cor- 
rection was applied to the mean for that hour of —0-11 in Table XXVI., and of —0-14 in Table XXVIL., 
obtained from Tables XXIII. and XXIV. as follows :— 
{Mean pressure, January 9—31 = 2:21 minus mean pressure, January 16—31 = 2°32} = — 0-11. 
Mean pressure, January 9—31 = 1:43 minus mean pressure, January 16—31 = 1:57 = — 0-14. 
P ry P y 
The means for January in Tables XXVI. and XXVII. are further corrected by —0:15 and — 0-10 re- 
spectively, in order to render the means for that month equal to those obtained Tables XXIII. and XXIV. 
Diurnal Variation of the Maximum Pressure of Wind.—The means for the months of January, F ebruary, 
and December are very irregular, presenting two or three maxima and two or three minima within the nine daily 
observations ; in the other months only one maximum is evident, occurring between 11 a.m. and 2 p.m. The 
minimum occurs after 9 p.m. and before 7 a.m. The following are the interpolated hours for the maximum for 
the mean meteorological and astronomical seasons, obtained on the assumption that the means correspond to 
the middle of the interval to which they belong ; for example, that the mean of the maximum pressures occur- 
ring betwixt 0* and 2 correspond to 1» :—* 
Seasons. Mean Meteorological. Astronomical, 
Spring, : : 15 20” p.m. 1 40™ p.m. Makerstoun mean time. 
Summer, . } 1+ 10™ p.m. 15 20™ p.m. 
Autumn, . A ills al@ ares 11" 30™ a.m. 
Winter, 2 0" 10™ p.m. 112 30™ a.m. 
The maximum pressures occur latest in the day in Spring, and earliest in Autumn and Winter. 
A secondary minimum and maximum occur in Winter of the meteorological group about 2" p.m. and 44 p.m. 
respectively, and in Winter of the astronomical group about 4" p.m, and 6" p.m, respectively. 
The maximum in the diurnal variation for the year occurs at 02 30™ p.m. ‘he value of the maximum 
pressure increases regularly from 8" 10™ a.m. till 0 30™ p.m. at the rate of 0:08 1b. per hour, and it diminishes 
from 0" 30™ p.m. till 8 10™ at the same rate. 
* This assumption is obviously inexact, as the means of the maximum pressures, while the pressure is increasing, will most pro- 
bably belong to nearly the termination of the periods in which they occur, but since, while the pressure is diminishing, they will 
probably correspond to nearly the commencement of the periods, the interpolated time of maximum will not be affected by the error 
of the hypothesis. 
MAG, AND MET. oBs, 1843. 4D 
