¥vapora- 
tion. 
— 
’ 
220 
tained, and also the mean evaporation from a surface of 
F water, for three succeeding years. 
eA el PS 
two 
| Bean! Rain. | frou. | from. 
1796 | 1797 | 1798 Ground.) Water. 
F Inch. | Inch. 
ora 1.90 
\February | 1. 
‘March 4 
‘A i 
May 2.03) 2. 
June Pu ieee 
July 15) 
‘August —_—|— 
‘September} — | . 
October | —| . 
[November — | 1.04 
December | .20, 3.08 
6.88'10.95 
Rain $0.63)38.79 
Evapor, _23.75/27.84/23.87 
Experi- The writer of this article, employed the following 
ment to as- method of discovering, by evaporation, the tity of 
ss tay latent caloric existing in steam or v A quantity 
Process of 
forming ice 
on the pri 
ciple of eva- glazed 
poration. 
water, equal in weight to 550 grains, was pla- 
of p 
eae con intinmi ness anh wishing 4distsionmina, comp 
with a pocket , the weight of which was 
59.32 grains, png Whe anes! Cesponeel as in the ex- 
periment described under the article Coin, p. 732 ; and 
on exhaustion was then pg age weaty tone cautious- 
ly, to prevent any part o water kling 
by too violent an ebullition. In foul eiioaher 
over, 
t be 
considered as equal to 550 + 130 — 12.75, or 667.25 
grains. "This gives Gh=72, or as the ratio of the 
524 
of water , to that cooled down from 
47° to 804° or 164°; and as this quantity must have 
combined with a dose of caloric, the abstraction of 
which was sufficient to reduce the temperature of 
667.25 grains of water 164°, the vapour must have com- 
bined with 52+ 16}, or 8634°. A slight correction 
must be applied to the result, to make allowance for the 
es caloric ing the time of the experiment, 
which was observed minutes, 
EVAPORATION. 
ascribing the reduction of 
tion of the water ; and that this must, i 
i 
a 
hs 
ah 
: 
F 
cE 
ib 
gz 
owing to radiation. 
similar to those 
z 
_ 
73 
ES. 
BSE 
poration, became, in some cases, de sence Por pg 
—— of — the 380 ~ rege 
such instances, the e evaporation in cooling the 
water, must have been more than counteracted by the 
caloric imparted by the condensed vapour. One expe- 
riment on this subject which he relates, was 
on the evening of the 16th of October. With the view 
Vt Baby teers hry 2 
next placed a number of small shallow earthen pans, a 
part of which were glazed, and a unglazed. In 
the last place, all the were filled with soft water, 
which had been boiled on the same ing. On the 
night alluded to, ice ap in the when the 
temperature of the air, at the height of 55; feet, was; 
according to a naked thermometer, 37°. A dry earthen 
pan was placed among those which contained water, and - 
the inside of its bottom was found to be as much colder 
than the air, as the water was in the other pans, before 
ice appested in them. Moisture was attracted by this 
pan uring the night, which was afterwards converted 
nto “f J ere 
a film of ice. aie) 
In the course of his i Dr Wells observed, 
that water ex in the evening in the open 
air to the sky, lost a li 
water had been cooled en to condense the vapour 
of the atmosphere, and to the weight gained afterwards 
being insufficient to com vious loss. ' He 
exposed, therefore, water to the influence 
until it was cooled to 34°; of this he put 
into each, of two china ‘saucers, which had also bee 
grains in weight. prota 
t. At a naaivedad 6 
of the straw-bed 12°, colder 
air. F - 
~- Dr Wells the result of these experiments as Qpjections 
a * that the cause of the formation of ice, to DrWell’s 
‘in such circumstances, cannot be evaporation ; but be- theory. 
fore coming to this conclusion, he ought to have shewn, » 
that, during the experiments, there was no e 
from the surface the ground, as well as from the was 
i 
‘9 ter in the pans. For it is easy to conceive, that the 
evaporation from the extensive surface of the fibres of 
the grass, might be sufficiently great to cool the air in 
contact with them below the freezing point, ar 
this temperature might afterwards be conimunicated to 
the air immediately above the pans, either by conduc- 
of air. Taking this view of we can 
che yousush OB paiva teks pore pans, the 
water which they contained suffered no loss by evapo- 
