New-York tribune., 1841-12-03
Or. Lardner's Third Lecture.


The subject this evening, said DR.. Lardner in
commencing BIS lecture, IS a review of the individ
aal bode. which compose The Solar System, aad
IN Pursuing ii wish 10 call yeur especial attention
to the two points which indicated in my first
Lecture They form the n.9rals of all these Lee
lures and relate 10 circumstances which would be
Observed b. none but scientific men. You are all
aware thai there prevails, among scientific m-n and
especially among men pretending to science. to
great extent, the vice Of rva;eriasnl the origin Of
this tendency. Ike tina; CT any other vices. is no
doubt the natural .auity OF nan. They are accCs-
toned to believe tha: all the phenomena ob=erva-
bic in body can be traced 70 the imnediate and
necessary properties OF matter. and il say they.
the question o. 2 experimenting Providence, Is a;
once cut of. Even granting their premises We
might at once silence their caviIs by asking them
wiz conferred upon matter these necessary proper
tlesl
Bl, this il not the course choose 70 take. l
.hall endeayor 10 show you ;hat some. nay all OF
the most important provisions Of this Earth and
the ether bodies OF the Solar System, on which de-
peuds the wsll-beins Of all VINO dwell upon the
Earth and the other planets. entirely indepen9-
ent OF the properties OF matter. These conclu-
sons however are not TO be arrived a; per salteN.
Like the -eriic,s OF iuries, they collected from
a great number of small but most interesting
circumstance which all Converge 10 the same
point This poiat the aim of all these lectures. i.
to -ho. that there is and must be 4 experimenting
Providence presiding over all these bodies and ea-
dowed with infinite wisdom. goodness and power
This is the grand proposition TO whlch all the
rays of ligh; 90 10 speak) from ihi. stage shall
converge.
In examining the different bodies of the Solar
system | shall begin with Mercury, the one
est the Sun. Tins planet Is rarely seen by the
naked eye but it does occasionally come into view,
sometimes rising some three hours before the Sun.
and sometimes setting "a long after it. Thus tie
Ancients saw It and recognized it a. belonging to
the Solar System. The distance of Mercury frum
the Sun i forty millions ei miles. while that OF the
Earth in round numbers j. one hundred millions.
Upon a close telescope examination Mercury pre-
sents a change in It's appearance similar TO that
presented by the moon; IN one position us visible
disc has the form OF crescent, in another OF
nalf circle, and in another 1t Is full. These ap-
pearances and their cause are so well understood
that -hall not stop to explain them farther. On
submitting Mercury 10 a strict and careful exam
nation with powerful telescopes. several very IN
teres,ing circumstances unfold Themselves. The
surface of its disc, observe in th- irst place Is
not OF uniform brightness ii does not appear like
plain circle of light as does the Sun but its face
is ottled,-strcaked and subject TO continue
change. Indeed these spots themselves are sub
ect TO perpetual mutation,-the dark ones some
times becoming light and rice rersa. We all
know how important the vcissitudes OF day
and night to existence we naturally inquire,
therefore, when the habita,ion of the planets is
brought into consideration whether they have these
vicssrudes
Were these spots upon the face of Mercury per-
mancnt, so that we could distinguish accurately the
times of their appearance and disappe irance, We
might ascertain this point with regard to Mercury
but 30 chsngcable the light and shade, that we
nave from this quarter clue IN our inquiries.
But there Is another feature of the planet that dis
closes the secret When IT has the form OF a cres
cent, if the surface were gobular and perfectly
smooth the inner line OF the crescent would be
regular curve. But when examined by powerful
telescopes the line is found be Irregular and
broken, and on particular occasions the Poiat OF
the crescent is suddenly broken oil. Now this
phenomenon could only be produced by mountains
on the surtace OF the planet.
But if this be the cause an intelligent auditor
would saw how i it that the outer edge j. not
ike The inner, rough and irregulari This is sus-
ceptibe ef an easy explanation. The oughness
observed is caused by the natural nights of the
mountains. The inner line is the boundary be-
tween the parts Illuminated by the Sun and those
on which he does shine the light that falls
there falls upon this boundary; Just there the Sun
either just rising or setting and all know that at
time OF day elevated objects cast long shadows.
The extended shadows of the mountains then pro-
duce this rough, inner line, while the mountains
themselves which upon the outer edge.
are relatively so small as to leave it smooth aud
regular. By carefully noting the tine when the
point of the crescent is thus cut of, and also the
moment when 1t Is agon cut OIL by the same
mountain, shall lnd that the interval is nearly
lwen,y-tour hours in other words. we have the
development of this extraordinary analogy betweco
Mercury and our Earth: the days OF both are OF
me same length.
Again. we naturally wish to know whether Mer
curry has the pleasant variety of the seasons that
xe ENJOY. Ii W. could ascertain the causes OF the
seasons the Earth, and inG that the same causes
-xist IN Mercury, should at once conclude
mat the inhabitants of that planet are blessed with
me same succession of summer and winter. Now
the simple cause of the seasons the Earth l.
inclination of h~r axis TO the plane o. her orbit,
hat the North Pole may point toward the sun one-
1aif the year, and away from him the other. As
tronomers nave not yet been able TO discover the
the inclination Of Mercuty's axis to the plane OF his
orbit ii any exists its proximity 10 the Sun pre-
vents their ng this. Some German astrono-
ners and others have arrived what appears to
be probable conjecture, that Mercurys axis Is ia
;liued, and to greater degree Than the Earths,
and that, therefore, it has greater variety OF sea-
IONS than ours. That Mercury mas atmosphere
IS shown bY the mntabty OF the spots ON her