OBSERVED AND AN EAJPIRICAL DEW-POINT, 
147 
least, I have not met with more than two or three instances in which some daily loss 
was not appreciable to a finely graduated metre. In severe nights, the depth evapo- 
rated in twenty-four hours will sometimes, though very rarely, reach i%ths of an inch. 
On the 22nd of May, 1844, 0*430 was measured, and on a freezing mixture being 
applied to Daniell’s hygrom.eter, the dew-point was found to be 24° below the 
temperature of the air, which was 63°. The evaporation for the month was 6*280 
inches, with only a quarter of an inch of rain. 
Amount of Evaporation at Whitehaven, Cumberland, in the six years ending 
with 1848. 
Month. 
1843. 
1844. 
1845. 
1846. 
1847. 
1848. 
in. 
in. 
in. 
in. 
in. 
in. 
January 
•78.') 
•940 
•935 
1-015 
•860 
•743 
February ... 
1-178 
1-190 
•905 
1-335 
•843 
*792 
March 
1-620 
1-835 
1-862 
2-085 
1-821 
1*397 
April 
1-718 
2-610 
3-400 
2-575 
2-181 
2-728 
May 
3-045 
6-280 
3-645 
4-375 
2-950 
4-580 
June 
4-690 
3-820 
3-760 
6-645 
4-506 
3-749 
July 
3-125 
4-495 
5-455 
3-450 
4-726 
3-935 
August 
3-305 
2-520 
3-250 
3-875 
3-751 
3-686 
September ... 
3-745 
3-405 
3-225 
2-980 
2-793 
2-896 
October 
1-940 
2-270 
2-360 
1-780 
1-688 
1-549 
November ... 
1-030 
1-554 
1-760 
1-.360 
1-107 
1-129 
December ... 
•800 
•800 
1-875 
1-025 
1-005 
1-019 
Inches 
26-981 
31-719 
32-432 
32-500 
28-231 
28-203* 
The mean amount of evaporation for the six years is 30*011 inches, and the average 
quantity of rain for the same period is 45*255 inches, so that the depth of the water 
precipitated exceeds that taken up by evaporation at the coast, in the latitude of 
54^°, by 15*244 inches. 
The evaporation gauge with which the above experiments were made, is a copper 
vessel 8 inches in diameter, and rather more than an inch and a half in depth. Half 
an inch of water is accurately measured and poured into the dish, and the daily loss 
ascertained each morning at 9 o’clock, by means of a carefully graduated tube read- 
ing to the thousandth part of an inch-f-. 
The evaporation dish receives a fair proportion of wind and sun, and is always ex- 
posed in the open air during the day, except when rain is falling. At night, and in 
wet weather, it is placed under a capacious shed, 9 feet in height, and open in front. 
Thus, it is conceived, that the evaporating surface is freely acted upon by all the 
circumstances concerned in promoting this natural process. 
Mr. Howard found the evaporation near the surface of the ground in the neigh- 
bourhood of London to be about 20 inches, or 5 inches under the average fall of 
* Evaporation in 1849, 28-699 inches, 
f Till the close of 1846, the dish was placed on a stool, 8 inches above the ground ; since that period it has 
been placed on a stand 4 feet 4 inches in height, and just large enough to hold it. 
U 2 
