AT NIGHT, FROM THE EARTH, ETC. 
197 
The numbers contained in this table show very clearly that, under the same state 
of the sky, the excess of the reading- of the thermometer in air above that in the 
reflector is the same at all times of the year, and they as clearly show that the amount 
of the excess varies with every variation of the quantity of cloud. These results are 
exhibited in each year ; and they are very decidedly shown in the last column of each 
division of the table, which contains the mean results for every month derived from 
the four years’ observations, excepting in January, which was deduced from three 
years only. 
Table C. is formed from the numbers in Table XCIX. by taking their yearly values 
for each state of the sky. The last column of this table contains the mean result 
from all the observations which were spread over 1419 nights ; in the year 1841 there 
was one observation lost ; in 1842 there were fifteen ; in 1843 there were nine, and 
in 1844 there were six. These observations were lost chiefly from the instrument 
being out of repair, or the having omitted to set the index the previous day. The 
result in the last column is therefore deduced from 1389 nights, and include those 
from all states of the sky and weather. 
Table C. — Showing the mean results in each year, with the different states of the 
sky, and for the whole time derived from all the self-registering observations of the 
thermometer whose bulb was placed in the focus of a metallic parabolic reflector. 
The mean yearly excess, according to the state of the sky with respect to the quantity of cloud, of the readings of a self- registering thermometer placed in air at 
the height of 4 feet and protected from radiation, above those of a similar thermometer placed in the focus of a metallic parabolic reflector fully exposed to the sky. 
1841. 
1842. 
1843. 
1844. 
1840 February 10, to 1844 December 31. 
of the sky. 
Whole 
Whole 
Whole 
Whole 
Whole 
Whole 
Whole 
Whole 
Mean 
sum of 
number 
Mean 
sum of 
number 
Mean 
number 
Mean 
sum of 
number 
Mean 
number 
Sum of 
Mean 
number 
Sum of 
excess 
excesses. 
of 
nights. 
excess. 
excesses- 
of 
nights. 
excess. 
excesses. 
of 
nights. 
excess. 
excesses. 
of 
nights. 
excess. 
of 
nights. 
excesses. 
excess. 
of 
nights. 
excesses. 
per 
night. 
o 
idy 
97-3 
66 
1 47 
177-8 
72 
2-47 
281-4 
86 
3-27 
322-9 
97 
3-33 
321 
879-4 
2-74 
cipally I 
oudy... j 
203-9 
70 
2-91 
118-8 
30 
3-96 
258-2 
49 
5-27 
237-4 
49 
4-85 
198 
818-3 
4-13 
'-cloudy . . 
396-0 
78 
5-08 
430-5 
82 
5-25 
394-9 
62 
6-37 
336-4 
60 
5-60 
282 
1557-8 
5-52 
1389 
7826-4 
5'6o 
cipally 1 
270-8 
43 
6-30 
578-4 
81 
7-14 
5911 
78 
7-58 
374-4 
55 
6-81 
257 
1814-7 
7-06 
adless . . . 
535-9 
66 
8-12 
682 1 
85 
8-03 
768-1 
81 
9-48 
770-1 
99 
7-78 
331 
2756-2 
8-33 
By considering that the cloudy nights in this table are represented by 10; the 
principally cloudy by 8 ; the half-cloudy by 5 ; the principally clear by 2 ; and the 
cloudless by 0, the following particulars may be deduced from this table. 
The sum of the products of the above numbers into the number of nights of each 
class in each year, divided by the number of nights in the year, gives the mean state 
of cloudiness during the nights of that, year ; and the yearly sum of the excess of the 
reading of the thermometer in air above that placed in the reflector, divided by the 
number of nights in the year, gives the excess, corresponding to the mean state of 
cloudiness ; and thus we find 
