ON THE HOURLY OBSERVATIONS OF THE THERMOMETER. 199 
We observe here a considerable approximation to the mean 
in the results of each year, and may therefore conclude that the 
mean daily curve, as exhibited by the yellow line in Plate VI. 
will cross the line of mean temperature about 8 h 9 m a.m. and 
J h p.m., the interval being 10 h 51 m . 
Although these critical times may be greatly influenced by 
latitude, &e., yet the differences in the interval which elapses 
between the morning and evening mean at different places seems 
comparatively inconsiderable. I have arranged in the following 
table the times, &c., of mean temperature for a few places at 
which these elements have been determined, and by which it will 
be perceived that the interval amounts nearly to eleven hours. 
Table X. 
Place. 
Latitude. 
Longitude. 
Height 
| above the 
1 Sea. 
I 
Distance 
from Sea. 
Time of 
Morning 
Mean. 
Time of 
Evening 
Mean. 
Interval 
between 
Morning 
and Even¬ 
ing Mean. 
Leith. 
55-56 
3-13 W. 
feet. 
25 
feet. 
600 
h m 
9 13 
h m 
8 27 
h m 
11 14 
Plymouth ... 
50-21 
4-6 
60 
400 
8 9 
7 
10 51 
Padua . 
45-36 
11-55 E. 
• • • 
II* 
8 41 
7 52 
11 11 
It is to be observed, that of these places the comparison be¬ 
tween Plymouth and Leith is the most accurate, since the ob¬ 
servations are in each case compared with the mean temperature 
of the twenty-four hours, and not with a mean temperature ob- 
, tained in a more general way. 
The hours of mean temperature which we have been just con¬ 
sidering being deduced from the mean results of the whole year, 
do not consequently apply to a less period of time. It may not, 
therefore, be unnecessary to determine the critical hours for 
other periods of time less than a year. The principal of these 
are given in the three following tables. 
Table XI.—Showing the Hours of Morning and Evening when 
theMean Monthly Temperature occurs, as deduced byTableVI. 
Mean 
of1833 
&1834. 
Jan. 
Feb. 
Mar. 
April. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
A.M. 
h m 
9 22 
h m 
9 23 
h m 
8 36 
h m 
7 52 
h m 
7 39 
h m 
7 50 
h m 
7 21 
h m 
7 51 
h m 
8 9 
h m 
8 23 
h m 
8 54 
h m 
9 14 
P.M. 
7 16 
6 39 
6 58 
6 47 
7 25 
7 21 
7 25 
7 23 
6 28 
6 15 
7 20 
5 20 
