New-York tribune., 1841-12-10
Dr.. Lardner's Fifth Lecture.

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Dr.. Lardners Fifth Lecture.
Tho Fifth Lecture of Dr. LARDyER, delivered
ON Tucsday evening at Niblos, vas listened to by
sill larger audence than have formerly attended
and possessed higher degree of interest than the
previous, portions Of the course. He commenced
by ,uyng that those present at bis former lecture,
would remember that he had pointed out nrhe plan
crary motions, certain peculiarities which charac
terizc them, and that there rcghed among them
All order aud harmony which render them i.i lab-
i,alions for social, rational and intelligent beings
He had eften remarked, moreover, tina, this princ
pie oforderwas called for by any the essential
properties Of mater, which only demand tina; these
revolutions of the planets be performed around the
Sun in certain paths called Comic Sections which
may be infinite in the variety of their forms. De-
spite all tho mere physical laws Of material nature
The planets might move in circles, or in oysls Of
any conceivable elongation or again, they might
pass around the Sun, and then leave the bounds Of
the Solar System TO return. All these sup
positions contradict none OF the requirements OF
nature; but we see that these varieties do not ex.
list in the conduct of the planets. They do non
avail themselves of the extended license granted
by the laws of matter. You what order and
regularity prevail in all their motions, revolving a
they do in orbits nearly circular in the same plane.
and all, with their satellites, in the direction
1t may be said, as il often has been that all this
beautiful regularity is the result of natural laws
Descartes maintained that they were all floating in
fluid, having vertical motion, ard this keeping
them in the same direction. But the question in
stantly rccurs, even adopting this theory what
gives 10 the fluid this whirling motion and ;he
naterialist can answer it no more easily than the
former.
This voluntary respect for order and regularity,
which have shown 10 prevail among the planets
and which is not enforced by the strict letter Of the
laws of Nature, does not exist among the Comets.
These are exceedingly hayward and rregularly
conducted persons. They do not, like the planets
reyolyc in circles; but in extremely oval orbits
with tbs Sun near one end OF the curved path
Now ii may be asked what charm there is in cir
cular orbit which renders it more respectable for
the planets to move in them than in ovals like their
wavward companions. The Sun, il the first place,
being in the centre of the circular orbit is always
nearly cqui-ds;an, from the planet, that the
temperature of lis surface, Gar is affected by
distance, IS nearly uniform; there beng SX,ra-
ordinary augmentation or diminu,ionof distance
50 tina; there are no very serious extremes OF heat
and cold
But with respect to the Comets, they move il
orbits which at one time cause them TO appronct
very near the Sun, aud at another drive them oil
10 an inconceivabe distance into the realms OF
space Thus the extremes Of heat and cold which
prevail at the extreme points of their orbits E'u,
be OF intense severity. Newton, who first deliver
ed an intelligent and clear theory Of cometary mo
ton, about the time OF the publication of his Pm
cipia in the year $780, witnessed the aPPearascc
of splendid come, which spread alarm through
ont Europe, and claimed the most careful observa
ton of astronomer, throughout the world. He
calculated accurately Its course around The Sun
and found that after rushing into the Solar System
from the remote regions OF the Universe it passed
round the Sun, approaching it 50 nearly tina, the
distance between them AT its nearest pom, was l66
times less than the distance of the Earth from the
Sun. The heat which the Come, at this point re-
ceived from the Sun, he sscertaiacd to he 80 .0OC
tines greater than tina, OF our hottest summer
supposiug that 1t. calorihc rays act by the sam,
laws as upon the surface OF the Earth. He .howec
that the temperature Of the Comet in thu; position
must lie nearly the same that OF 1 hot iron. :,
thar no ordinary substance could remain solid FOL
u moment, while all organic substances must be
Instantly destroyed. Indeed is the oPihion o
many mat the constituent parts OF The Comet
themselves necessarily pass through the three
stale, OF liquid, solid, and yaPor. While al tlei
PessdclioR they may be, ; We Snow many OF thea
are, mere vap5r: as they recede they gradual
~ converted 10 liquids unpl at their GpAtfio'
they become s7diicd: just water exists IN th'
three state, OF steam. water asd ice
Ban we are not hastily TO assume that when
Comet gets to IL extreme distance from the Sun
which as will be hereafter shown, i, inconcriyaby
great, the cold Is 50 very intense. as this depend
entirely os the magnitude Of the comet. For in
stance Newton calculated. in 1880. ,sa, II the vol
ume Of the Comet be equal 20 that Of The Earth