DEW. 
Bafes of the Explanation, 
1. * The leis the ee as g lafs ig elevated, the 
more humidity it attraéts from 
2. Metals attract it very lite ee 
3. * Glafsafenfibly exercifes its aon on the humidity 
of the air, at a diftance, and notwithflanding the interpofi- 
tion of different bodies, fuch as plates of metal, &c.” 
4. “ Metals give to glafs, near which they are placed, 
the property of more f{peediiy atrra@ting caloric from hot 
air, and on the contrary, that of yielding it more fpeedily 
to cold air. 
Nib. When T fay that age give hie this property, I 
* mean that they ad as if they ga 
examination of two ease one of p mercury, t 
a : fa 
€ 
The metallic thermometer arrives much fo 
other to that of the new medium. Its glafs then, if colder, 
muft take up more fpeedily from the medium the caloric 
which it tran{mits to the metal, or, if hotter, it muft more 
cold 
bafis it 
powerfully (bafis r. , ‘eh ther airedlly e glafs, or 
through the a or on the feces pa Cbafi 3.)s ba ‘this 
be in contact; but if 1 it. be at the ce of tome milli- 
metres, ‘Ge humidity not ae the metal on its i ee 
5 rik ee on the oppofite glafs in a ee quantity than 
elfewhe 
If en metal be applied on the cold fide (§ 19.), the 
glafs moft heated does not attra&t fo much humidit 
(bafes 4 and As ), and it accumulates on ie unarmed part 
of the pane.’ 
“Tf, in ave ods the armour be covered hae a Le of — 
fate cools more {peedily than if t tal were no 
the 
eS 
Pp operon is more tee a ae if ms were 
not prefent, there is no effect, and the totality of the double 
glafs armed within, is in the Tame cafe with that unarmed ; 
it, therefore, accumulates neither more nor lefs humidity.”’ 
“A fe Sua armour on the plate of glafs will caufe the phe- 
librio ; but ana 
the heated glafs will not attra humidit 
glafs be armed on both fides (§ 15,), as it vould 
not hes _ ene to the air, either on the cold or warm 
fide, it feems that it ought to attraét as much h 
n the reft of the partition. Butt 
r 
are not onl n im- 
portant a in philofophy ; namely, that Ape exercifes its 
attractio r the humidity (which has a tendency to be 
ieactiea on the air) through metals.” 
The French have, in commoa language, two different 
terms whereby to exprefs the evening and morning dew 
calling the one ee the other ro/ée; and, SS mifled 
by this peculiar nomenclature, or guide accurate 
euferaticn, a modern chemift, C. A. paca fae a very 
~~ 
different account of the matter. § I was well aware,’’ fays 
e, {peaking of the janice which led him to_imvetti- 
ie the {ubje@, “ that the moifture depofited on ‘bodies, 
{oon after fun-fet, is not the fame with that which we find on 
them again at fun-rife. There is confequent/y an interruption 
in the phenomenon, an evaporation of the /erein, or evening 
dew, and a new produétion in the morning. It is ufual a 
from the fun’s place, during the precipitation of this water 5 
nd why does that luminary, in re-appearing on the horizon, 
oie occafion to a ftili Rronger breeze, toa greater degree of 
cold, and a more abundar pe skein “ ?? (Annales 
de Chimie, tom. -28 ome impor points of 
fact, thus taken for ee this ebilst tee oped: to 
give a theory of the dew, confidered generally, and with 
re{peG to the whole furface of the earth, of which we, fhall 
briefly ftate the fubftance. 
If the earth were deprived of its diurnal motion, and 
thus expofed to the ation of the fun, the following might 
be conceived to be the effeéts of that aGion, in relation to 
prefent fubjeG. arge {pace, immediately beneath 
e fun, would be fubje& to continued oo fo mi 
g there remaine ater to dricd The 
aa y> “be a a certain zone, ort reek of the furface, per- 
petually fubjeted to the fall of dew, ale by a win 
There — alfo be a {pace turned 
ever fall, be- 
e 
from the heated {pace, and in which evaporation could never 
take place to produce it. By combining this fuppofed cir- 
culation of the air with the a€tual ftate of things, io other 
the Antillesy and in Me 
wet the bodies peeoey to ia as effc tua 
of rain; which, however, comm appens ie many parts 
of England. This hypothefis, fang eae ganees more 
a 
which it . founde 
peonenegel in Eilace the 
e nt and diftinguifhable than in Britain, 
where we do not find ia their occurrence has been fuffie 
ciently marked. 
The produdtion of dew is admitted, on all = to be a. 
confequence of the nocturnal iad Saber n of the atmofphere, ~ 
Now it is a fact eftablifhed, by the obfervations of different 
meteorologifts, that this ak after a clear day, be-, 
gins near the furface of the earth, an 
o the fuperior atmefphere: for the effe 
is fometimes carried On to a much lower temperature than. 
that of the earth’s furface; and the denfe clouds, which. 
have 
