HOURLY OBSERVATIONS OF AIR TEMPERATURE AND PRESSURE. 
633 
The values of accord very closely with those at Greenwich where the mean 
yearly value is 41°, the mean yearly values at the seven observatories ranging 
between 37° and 43°. The variations of the epochs of maximum from winter to 
summer are at all stations well marked, and at Aberdeen, as was the case with the 
component of the second order, pg shows an exceptionally low value in the summer, 
differing about 70°, or nearly five hours of time, from the winter epoch. 
The expressions for the annual variations of the values of P 3 and Po, derived from 
the means of the observations at the seven observatories, differ little from those 
before given for the Greenwich values, allowance being made for the smaller ampli¬ 
tude of all the components. They are as follows ;—■ 
Pj = -68 + -14 cos (\ + 105°) + -21 cos (2X - 8 °), 
P 3 = -30 + -13 cos (X + 260°) -f ‘07 cos ( 2 \ - 166°). 
The comparison of the observed and computed monthly values of the components 
for several months is given below.' 
Months. 
Ps- 
Observed. 
Calculated. 
Difference. 
Observed. 
Calculated. 
Difference. 
i 
[ January 
•62 
*62 
•00 
• GO 
•22 
•00 
February . 
•78 
•78 
•00 
•17 
•18 
+ •01 
March . 
•93 
•85 
-•08 
•12 
•19 
+ •07 
April 
•75 
•63 
-12 
•32 
•30 
-•02 
May . . . 
■42 ♦ 
•49 
+ •07 
•53 
•41 
-•12 
June. 
•33 
•33 
•00 
•43 
•46 
+ •03 
July . . . 
•35 
•40 
+ •Ob 
•42 
•41 
-•01 
August . 
•66 
•65 
-•01 
40 
•33 
-•07 
September. 
•97 
•90 
-•07 
•27 
•25 
-■02 
October. . 
1-02 
•94 
-•08 
•15 
•23 
+ •08 
November . 
•79 
•78 
-•01 
•24 
•28 
+ •04 
December . 
•59 
•63 
+ •04 
*22 
•26 
+ •04 
' 
Sum . 
•53 
Sum 
•51 
Mean . . 
•04 
Mean . 
•04 
On the whole it may be regarded as well established by the substantial consistency 
of these results, that they truly indicate the chief characters of the diurnal inequality 
of temperature in the British Isles; and they leave no room to doubt that the 
variations which recur with such remarkable regularity from year to year, and are 
observed at so many different places, extending to quantities so small as those 
represented by the third and fourth order of harmonic components, are due to the 
operations of determinate physical causes, the effects of which this system of analysis 
enables us to distinguish and i-ecord with remarkable and unexpected precision. 
MDCCCXCIII.—A. 4 M 
