OBSERV'ED AND AN EMPIRICAL DEW-POINT. 
145 
Hygroinetrical state of the Atmosphere at Whitehaven, in the year 1848. 
1848. 
Dry bulb. 
Wet bulb. 
Dew-point. 
11 A.M. 
3 P.M. 
Mean. 
11 A.M. 
3 P.M. 
Mean. 
Deduced. 
Observed. 
11 A.M. 
3 P.M. 
Mean. 
11 A.M. 
3 P.M. 
Mean. 
Compt. of Dew-point. 
11 A.M. 
3 P.M. 
Mean. 
o 
O 
o 
o 
0 
January 
35-50 
36-58 
36-04 
33-94 
34-68 
34-31 
31-50 
31-75 
31-62 
31-62 
31-85 
31-73 
3-88 
4-73 
4-30 
February 
43-16 
44-06 
43-61 
41-85 
42-60 
42-22 
40-12 
40-83 
40-47 
40-05 
40-72 
40-38 
3-11 
3-34 
3-22 
March 
43-82 
45-46 
44-64 
41-69 
42-68 
42-18 
39-20 
39-50 
39-35 
39-38 
39-26 
39-32 
4-44 
6-20 
5-32 
April 
48-86 
51-07 
49-96 
45-03 
46-90 
45-96 
40-75 
42-70 
41-72 
40-91 
42-41 
41-66 
7-95 
8-66 
8-40 
May 
57-57 
59-77 
58-67 
52-80 
54-29 
53-54 
49-45 
50-30 
49-87 
49-40 
50-29 
49-84 
8-17 
9-48 
8-82 
June 
60-25 
61-21 
60-73 
55-37 
55-51 
55-44 
52-01 
51-48 
51-74 
52-18 
51-29 
51-73 
8-07 
9-92 
8-99 
July 
61-88 
64-13 
63-00 
57-38 
58-72 
58-05 
54-25 
55-02 
54-63 
54-28 
55-34 
54-81 
7-60 
8-79 
8-19 
August 
59-22 
61-50 
60-36 
54-32 
55-69 
55-00 
50-87 
51-64 
51-25 
50-80 
51-32 
51-06 
8-42 
10-18 
9-30 
September 
58-37 
59-91 
59-14 
54-46 
55-32 
54-89 
51-72 
52-11 
51-91 
51-45 
51-64 
51-54 
6-92 
8-27 
7-59 
October 
51-21 
51-78 
51-49 
48-59 
48-56 
48-57 
46-00 
45-30 
45-65 
45-85 
45-35 
45-60 
5-36 
6-43 
5-89 
Noyember 
43-99 
44-76 
44-37 
42-17 
42-57 
42-37 
40-04 
40-07 
40-05 
40-14 
39-95 
40-04 
3-85 
4-81 
4-33 
December 
42-92 
42-89 
42-90 
41-10 
41-24 
41-17 
38-92 
39-14 
39-03 
39-08 
38-35 
38-71 
3-84 
4-54 
4-19 
Means 
50-56 
51-93 
51-24 
47-39 
48-23 
47-81 
44-57 
44-98 
44-77 
44-59 
44-81 
44-70 
5-97 
7-11 
6-54 
In eight months of the year 184/, the difference between the observed and the 
deduced dew-point is 0°*10, and in 1848 it is but 0°'07, the mean of the two periods 
comprising 1220 observations, amounting to the comparatively evanescent fraction 
of xf^ths of a degree ; and, had the instruments been absolutely perfect, doubtless 
the accordance between the two dew-points would have been still more obvious. 
Hence the results show, in a striking manner, the extreme accuracy of Mr. Glaisher’s 
Tables, and add additional testimony to the value of the Greenwich hygrometrical 
observations, and the resulting formula on which those Tables are founded. Being 
strongly impressed with the utility and importance of these tables, I am induced to 
give my own experimental evidence in their favour, which (coming from a wholly 
disinterested party) may perhaps be entitled to some weight ; and, in the hope of 
giving them greater publicity, and of bringing them into that general use which they 
so well merit, 1 beg to lay that evidence before the Royal Society. 
By means of the tables founded on the Greenwich hygrometrical observations, the 
combination of the dry- and wet-bulb thermometers is converted into a very delicate 
scientific instrument, possessing many advantages over that of Daniell, not the least 
of which is, that its readings may be depended upon, even in the hands of the most 
inexperienced and uneducated person. Thus, observations on the hygrometrical state 
of the atmosphere may be obtained on mountains, at great heights above the sea, on 
the sea itself, in mines, and various other inconvenient localities, by those whose 
occupations or callings lead them to spend a considerable portion of their time in 
such situations. In this way illiterate persons may become truly valuable assistants 
to the meteorologist in his researches, and the observations secured by the shepherd, 
the miner, and the mariner may afterwards be turned to good account by the philo- 
sopher in his closet. 
It is however necessary that the thermometers used for this purpose should be 
essentially good, and, if possible, that their readings should agree with each other, 
MDCCCLI. U 
