New-York tribune. [volume] (New-York [N.Y.]) 1841-1842, 1841-12-29

ed the leavesl Surrounded By warm ar WY
should thev be cold Marx the beautiful concur
sons TO which this inquiry gaze rise. / answer
the question: the first thing was 10 ascertain the
physical circumstances under which iney u'a ho'
become cold il Is not on every summer nisnt 't',,
dew is deposited and. saii he II md orc Of
them, viii see whether TIC plants are tRen cora.
He made the trial. and found that the plants a.'d
mir were ;heu of the same temperature
Aaoiher striking difference between dew and
rain or fog i this thaii, selects the objects %
which /, j. deposited 1t viii not Nli on all ai'Se-
Now Dr. WELLS said that in order "a trace thS
phenomenon to II, oisaal cause II J. necessary l"
see what Is the phrscal character OF the Ooale'
on which it is deposited, to distinguish them 'ro'H
hos. an which r, ! not. It falls by preference on
the flowers. blossoms AMI leaves OF plants Loon
Al the bell Of summer flower. and you lnd hang
ing DEVELOPS Ike pearls upon It, i-ooN ulo'. ~
Earth. tle stones and fses and yoH md there :
none deposired. What IS Tie physical character
isteriric which distinguishes these plants from o'heI
object, Dr.. Wells decided on enquiry ihat
dew fell most copiously upon those objects which
were the best rad ator, II heat; while upon 'nose
which scarcely parted With Iheir heat at all there
ne, .,,i.. p, be-, found Here then another I'M
pof,aat step. and here SAID WELLS, | nave the Key
by which Shall open this secret an'i nnd ont WHAT
Is the cause OF dew.
There VS. another inquiry: Dew NOT only elects
certain object, on which to fall. but certain nights
durin, which i, is deposited. The same body
which i believed this uorang, tomorrow morn
ing shall be perfectly dry. 1t l. found that deW
never falls on cloudy night 1t * absolutely essen
tial that the night he clear. Thus there must De
something IN the clouds which = connected WIN
the depo>i.Ion of dew which the clear ky has not;
and /, ruu,t have reference TO heat Tor tnS Is
the asen, in operation. Agaia thc principle OF IA
iation suggested Itself. The clouds are good RI
dators whre the >ky radiaieS 10 heat al all. We
arr then brought 10 dis; the deposition OF dew re.
oi;ircs that the objects on which II falls be good
radiator. ard mat the heavens above rad'ate not
at all. It IS clear then what makes the plants 20
degrees colder than the air they themselves are
continually throwing Of heat while from the hea''
en-. thev receive none in return OF course they
must fall in temperature; then the vaPor IN tue
air +, condensed upon them Just as It was upon tue
decan,er of iced water. This was the explanation
Of Dr. WILLS of the theory Of dew, ard one more
beautiful Is scarcely to be found in the whole his
tory al modern discovery.
II was necessary however. thar some way os
devised for she tral Of the >--pfrineatam eTncts
with reference 70 this theory. For this purpose
DR. " selected "A silver cup. which i, a bad Fadl-
-;or, and placed it in glass BASIN which Is
GOOD one. He exposed them to a clear sky on
summer nght. In tie morning the glass BASIN
was severed with dew while the silver cup was per
tcctly dry He nest placed glass cup IN silver
basin: in the morning the cup was bedewod wh'e
the silver basin was dry: upon cloudy mght no
dew VAS deposited m either. TINS lett no pesS'-
bic room 'or doubt that ne had discovered the true
bIcory Of Dew.
,'..I r,g,t IN
Colleges or Uni,ersnes. bat IN this way coming
directly from the ordinary pursuits OF business eN-
ampic- OF the extreme rigor OF modern scientific
Investigations. Tres, my lectures will be attended
with one good effect in addition TO the mental dis
cipline every one must receive from listening Ia
such reasoning: | trust 1t will give YOU stronger
tsth in tie wonders every day discovered IN SCI
ence You hear detailed The main facts, the re-
,uits Of scientific discovery and you arc APT,
lcnr To think that such theories must rest on but
slender evidence and that philosophers are In
,uceI bv thoir ardor and enthusiasm give TO the
results of their Investigations greater faith than
th-y are entitled But | trust that IN giving to
YOU examples OF the rigorous method, adopted to
arrirc scientific truth, which are applied To all
Discoveries, you wi see that philosophers do not
credit 4 thing merely because 1t i marvellous but
that ia proportion a, its wonderful nature IL IN
,tration required.
On former evening had occasion to bring be-
fore you some of the wonderful discoveries OF mod
ern Asiroa my. ard gave general outline os tho
kind of reasoning and observation on which these
discoveries are based But found it necessary
10 draw upon your faith for the extreme accuracy
OF which certain observations are susceptible. /
was obliged 10 assume that astronomical instru-
mans could BE- Constructed capable Of making OBJ
ser,ations within CERTAIN limits; and as | then
stared, instruments are capable Of measuring va
ration OF second.
do not propose nov 10 90 into detailed de-
-crpton OF these instrunruis but only 10 give ona
or TWO examples OF the manner in winch Art assist.
Science ia comforting tins extreme accuracy oa phi
losorhical Investigations The instrument with
which nearly all accurate measurements are made,
{. called the nl,rai circis la the great obseryato
RE, a, Greenwich and Paris, the ground is first
cayated until Il solid rock IS found Upon this is
built & towci 81 slid masonry, that it may be
affected By jirfiHg motion OF the earth. Around
this tower IL the buiIslng Of the obser'atory.-
All communication with tue tower OF loors Is cut
off, so that it shall be affected by no motion
but that Of which the whole Earth pattakrs
A;anst the face of this wal the DjsrGi circle is
placed those al Greenwich, and, believe at Pa
ris are brass circles some six feet in diameter nc
curately suspended On an axis, fixed into tae wall,
about which they turn To the crce--thc line OF
~ direction passing through the centre-is liked
large telescope When lhs u brought TO bear upon
u star, acro,. the field OF view, t, extended So
.em Of tine nes-so fine, even, that when masnl-
fed by the power Of th- telescope. they appear like
the finest hairs. !. was long deSlterGtn1a to OBJ
tain some durable substance which should answer
this purpose. The first artist whom application
l.. 10,