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

Professor MITcHELL's 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.
TEN. After giving, while treating on the
inferior planets, some idea Of the manner
Of determining that the orbits Of the pla-
nets were ellipsis, he passed on to consider
the different phases Of those planets and
their courses. He adyerted to The method
adopted by the ancients Of determining the
obliqulty of the ecliptic, by means of a
stylus erected perpendicularly on plane,
the shadow Of which, measured on me.
rdianal line, indicated when the sun had
attained its greatest Northern and when its
greatest Southern declinahpn. II was by
means Of the stylus, also, that they deter.
mined the length Of the year: The line
when the shadow was shortest indicated
the summer solslice; and the longest sha.
dow fell on the winter soIstice. But they
soon found that the stylus was not an &C.
curate index Of time, and that il was ne
cessary to change the stylus, hence the orr
ginal of new style. He next considered
the pecuiarities Of Mars, its phases, al
though a superior planet, and its deep red
color, which might be owing TO an exten.
siye and dense atmosphere, or 10 some pc
culiarity Of its surface. This red appear
ance Of Mars, as caused by its dense almos
phere, has been. controverted, we believe,
by Sir James South, in the Philosophical
Transactions of 1888. The account ei-
ven by Professor Mitchell, Of his own oh.
servations on this planet we're exceedingly
interesting. They confirmed fully the n.y.
pothesis Of Herschell in regard to 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-
tablished fully, that the luminous appear.
ance Of the poles was due to accumua-
tons of snow and ice. Changes Of sea.
son in the planet were followed by changes
At the poles corresponding to the season.
While speaking Of the spheroidal figure Of
the planets, the mode oil determining the
figure Of the earth was gwen, as in our
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 OBSERVE.
tons on the last transit, and alluded % The
use celebrated European astronomer had
Of his observations 10 determining very
important astronomical inquiry.
On Tuesday evening Prof Mitchell took
up the three superior planets, Jupiter, Sa-
turn, and HerscheIl. He began by ex.
planning the elements Of the planeiery or
bits, particulars necessary TO be known
before we can determine the precise posi-
ton Of planet, atany period in lis orbit.
These are the positions Of the line Of the
nodes: the inclination Of the ecliptic; the
periodic fine; the eccentricity; the length
Of the major and minor axes Of the elIipse
The place Of the perihelion, which deter.
mined the direction Of tho major axis; and
the position Of the planet in lis orbit at
particular time. From these elements The
exact position and movement Of planet
could always be ascertained. The mode
Of obtaining these elements, BY finding the
RICH, ascension and decination, from o.
made on the meridian with the
transit instrument and mural circle, and
from these observations dedacing the pIa-
NETS geocenIric longitude and latitude, and
from these data, The heoIicen-
tric Longitude and latitude. involving in|
spherical tfigonomesry, could moi Of course
be given 10 a popular lecture. This IS ~
field which can Ne entered only affer a
Long and profound course of Tmaihematic-
81 studiesi and yet ply sical astronomy
70 the mos' interesting drpat'mort II all.