HOURLY OBSERVATIONS OF AIR TEMPERATURE AND PRESSURE. 
G27 
The annual variation of the values of P 3 and Pg will be represented, with a fair 
degree of approximation, by the expressions 
P3 = 1-08 + '20 cos (X + 126°) + Al cos (2X - 2°) 
Pg = *42 + -16 cos (X + 260°) + *10 cos (2X - 172°), 
in which X is the Sun’s longitude. The term involving cos 2X gives rise, in the 
value of Pg, to the two ^maxima at the equinoxes, and in the value of Pg to the two 
min ima at the same seasons. The comparison of the observed and computed values of 
the two components for the several months is given below. 
Montli. 
P-2- 
P3- 
Observed. 
Calculated. 
Difference. 
Observed. 
Calculated. 
Difference. 
Jamiaiy . 
•94 
•91 
- -03 
•36 
•37 
+ -01 
February 
1-26 
1-22 
- -04 
•30 
•30 
•00 
March 
1-34 
1-38 
+ -04 
•18 
•29 
+ ‘11 
April .... 
]-21 
1-17 
- -04 
•48 
•40 
- -08 
May .... 
•71 
•76 
+ -05 
•63 
•54 
- -09 
June .... 
•56 
•51 
- -05 
•61 
•62 
+ -01 
July .... 
•66 
•70 
-r "04 
•65 
•58 
- -07 
August . . 
1-11 
1-18 
+ -07 
•55 
•46 
- -09 
September . 
1-71 
1-57 
- -14 
•29 
•37 
+ -08 
October . . 
1-51 
1-55 
+ -04 
•29 
•34 
+ -05 
November . . 
M7 
117 
•00 
•40 
•39 
- -01 
December . 
•76 
•85 
+ -09 
•33 
42 
+ -09 
Sum . 
•63 
•69 
]\[ean . 
± -05 
± -06 
It has already been remarked that the epoch of the maximum phase of the first 
three components appears to be earlier in the summer and later in the winter. 
In the first order the mean value of p, is 214°, corresponding to 2 h. 26 m. p.m., the 
variation due to season being about 12°, or 48 minutes of time, by which amount the 
maximum is earlier in June and July than in December. 
In the second order the first maximum in June is 20°, or 1 h. 20 m. earlier than in 
January. In the third order the difference in the same direction is 63°, or 4 h. 12 m, 
of time. 
In the fourth order, as before noticed, there is some doubt as to the manner in 
which the change of positions of the summer and winter maximum is brought about. 
From March, when the first maximum occurs about 60° after midnight, or at 4 A.M., 
there is no doubt a retrogression, as in the other components, till June, when the 
maximum occurs 16° after midnight, or at 1 h. 4 m. a.m. ; this is followed by a 
progression between June and October, when the maximum having become later, is 
4 L 2 
