Mississippi Democrat. (Carrollton, Miss.) 1844-18??, 1846-04-15
The Planets.

Professor MITCHELLs last two lectures
were devoted to the examination OF the
planets and satellites with the exception
of the Earth and moon) OF our solar sys
tenn. Alter giving, while treating on the
inferior planets, some idea of the manner
of determining that the orbits OF the pIa-
nets were ellipsis, he passed on to consider
the different phases of those planets and
their courses. He adverted to the method
adopted by the ancients of determining the
obliquity of the ecliptic, by means of a
stylus erected perpendicularly on a plane,
the shadow of which, measured on a me
ridiana line, indicated when the sun had
attained its greatest Northern and when its
greatest Southern declnation. 1t was by
means al The StytuS, also, lnat they deter
mined the length of the year: The hne
when the shadow was shoGtest indicated
The summer solstice; and the longest sha
dow fell on the winter solstice. But they
soon found that The stylus was not an ac-
curate index Of time, and that il was ne
cessary to change the stylus, hence the ORR
qinaI Of nelo style. He next considered
the peculiarities of Mars, its phases, al
though 4 superior planet, and ITS deep red
color, which might be owing 10 an extern
sve and dense atmosphere, or 10 some pc
cuIarity of its surface. This red appear
ance Of Mars, as caused by its dense atnlos.
phere, has been controverted, we believe,
| bv Sir james South, in the Philosophical
Transactions of 1888. The account gi-
ven by Professor Mitchell, OF his own OBJ
selvations on this planet were exceedingly
interesting. They confirmed fully The n.y.
pothesis of HerscheI in regard 10 the
course Of the luminous appearances Of the
poles of the planet. Professor Mitchell
stated that he had seen distinctly changes
going on at the poles of Mars, which es-
tabished fully, that the luminous appear.
ance of the poles was due to accumula
tons of snow and ice. Changes of sen
son in the planet were followed by change,
1T The poles corresponding TO the season
While speaking of the spheroidal figure Of
the planets, the mode OF determining The
figure of the earth was gwen, as in ou
ordinary text books. The transit of Mer-
curry, as Illustrating the necessity for OBJ
servatories in all parts Of the world, form
ed very interesting part of the lecture
Professor Mitchell gave his own observa
tions on the last transit, and alluded 20 thC
use a celebrated European astronomer hat
of his observations in determining a very
important astronomical inquiry.
On Tuesday evening Prof Mitchell TOOL
up the three superior planets, Jupiter, Sa
turn, and HerscheIl. He began by ex
planning the elements Of the panetery OF
, bits, particulars necessary to be knows
before we can determine the precise posi-
ton of planet, at any period in lis orbit
These are the positions Of the line of tn
T nodes: the inclination of the eclptic; th
periodic time; the eccentricity; the lengt
of the major and minor axes OF the ellipse
. the place of the perihelion, which deter
mined the direction of the maj or axis; an
the position of the planet in lis orbit at
? particular time. From these elements lh
exact position and movement of plane
5 could always be ascertained. The mod
$ of obtaining these elements, by finding tn
E right ascension and declination, from oil
: servations made on the meridian with th
d transit instrument and mural circle, an
e from these observations deducing the pl'
: nets geocentric longitude and latitude, al
y afterwards, from these data, The heoIice
trio longitude and latitude, involving
spherical trigonometry, could not Of cour'
k be given in popular lecture. This is
o field which can be entered only after
n long and profound course of malhemati
ST al studies; and yet physical astroneu
is the most interesting department of a