Vermont phÅ“nix. [volume] (Brattleboro, Vt.) 1834-1955, 1857-10-17
THE COLD BEFORE SUNRISE.

Amongthe Annoiations of Archbishop Whate
| ly, IN his admirable edition OF Bacon's Essays
We hnd few pointed and interesting observa
tons upon early rising annexed to the essay OF
the "Regimen OF Health" In this essay Bacor
makes no reference TO hours of sleep, and it /.
to supply this deficiency that his editor has col
lecIed few facts upon this much-moot.d sub
| Ject Among these facts he states he iullowinr
"One other circumstance connected with ear.
| ly hours has been hitherto accounted for-name-
" the sudden cold which comes on lust at the
peep Of darn Some say that the earth is grad.
ually cooling after the sun has set, and conse.
quently the cold must have reached its height
Just before the return of the sun.
- his theory sounds plausible to those who
have little or no personal experience of day
break but does not agree with the fact. The
cold does not gradually increase during the
night; but the temperature grows alternately
warmer and colder according as the sky is cloud
ed or clear And all who have been accus,on-
ed to night travelling must have often expercnc-
ed many such alterations in a single nighf. And
they also find that the cold at day-break comes
on very suddenly, so much so, that in spring and
autumn it often happens that it catches the earth
worms, which, on mild nights, lie out of their
holes; and you may often see a whole grasS-plot
strewed with their frozen bodies in frosty morn
they would have had time TO withdraw into their
holes.
"And any one who is accustomed to 90 out
before daylight will often, in the winter, find the
roads full OF liquid mud half-anhour before dawn,
and by sunrise as hard as a rock Then those
who had been in bed will often observe that 1T
was n hard frost last night when in truth there
had heen no frost at all TIL dayb eak Who can
explain all these phenomena?
We think we can, and here is our explana-
ton: Under clear sky the surface of the earth
Is cooled in a manner similar to that in which it
is heated by the sun. Indeed the sky may be
regarded as an immense negative sun, which re,
celvcs back the heat from the earth, or, if we
may so speak, radiates cold upon the earth as
the sun radates heat. Cloud and mists ntercept
the rays Of cold from the sky as they intercept
the heat of the sun while a clear atmosphere
intercepts but little of radating heat, either from
the sun or the earth
A vertical sun looses about one quarter of it's
heating power in the atmosphere, and though at
lower attitudes it looses still MORE yet this lost
heat is scattered through long waste of air,
while the principal part of the heat is received
and concentrated on the surface of the Garth
In the same way the cold rays from the sky have
but little immediate effect upon n clear atmos-
phere, but cool the surface of the earth very
rapidly hence the fall of the dew is like the
condensation of moisture in warm weather, on
cold surfaces, and hence, also, those surfaces re-
ceive most dew which radate their heat most
readily.
Those variations of temperature during the
night referred to by our author, which arise from
the varying mists and clouds, are explained by
the same principles A clear sky cools the sur
face of the earth very rapidly, and this cold is
transferred by eonduction to the incumbent air.
hut when the sky is overcast, he radiation ceases
AMI the chill of the lower air is removed by an
equalization Of temperature so that under these
circumstances the night grows warm, Just as the
day grows cool, when the sky is covered by
clouds, Now these facts will explain the sud
den cold" of the morning by the folio ,ing Gu
rlous paradox 1t is the sun himself that first
cools the earth which he is about to warm. The
first rays of dawn heating those mists of The up.
per air which the cold of the night has collected
dissolves them and opens the sky again on the
earth, and the cold rays renew with vigor their
deadly assault just as they are about 10 yield TO
the life giving rays Of the sun.
Thus the sun, by indirectly cooling and then
directly heating the surface Of the earth aug
ments that rapid change of temperature in the
morning, The geological effect of which we dis
cussed a few weeks ago in connection with Pro-
fcssor Pierce's discovery y. Evening Post