National Republican., 1875-07-09
rHr PLANET MRS.
Results Of Observations made by Professors
Stafford and Colbert at the Dearborn observ-

Results Of Observations made BY Professors
Stafford and Colbert NJ the Dearborn 0bserv-
atory.
lFrom the Chicago, July1.l
The observations on the planet Mars, made BY
Professor Stafford at the Chicago Observatory,
Tuesday night, proved to be entirely satisfactory.
Professor Colbert has been industriously laboring
for some time past getting the place in readiness
for the occasion. The main object Of the ohserva-
tion was to ascertain by actual measurement
the exact angle made by lines from the planet
Mars and o certain fixed star, and from this angle
and known distance TO another point on the
earth's surface, to calculste the distance Of the
planet from the earth. The fixed star taken for
the observation was the one known ss star No. 8,
In the constellation of Sagittarius. The star is
practically an inhnite distance from the earth;
that Is to say, lines from any two points, however
widely separated on the earth's surface, to this
star would make no perceptible angle with each
other, and would be parallel for all intents and
purposes.
Taking this fact as basis two points are select
lines from the star and the planet to the eyeof the
observer accurately measured. This gives tri-
angle formed by lines from the planet 70 the points
themselves The latter distance being known,
and the angles made by the lines from the planet
star being also knowH, IL becomes matter Of SIM
pie trigonomety to hnd the remaining sides of the
triangle, or the distance Of the planet from the
earth. According to calculations made the star
would appear to be exactly covered by the planet
at point in $50 south latitude, while In this lati
from direct liI tothe star. The angle between
the lines Is measured by micrometer inseated in
front Of the eye-piece Of the telescope. This MI
crometer consists Of strip of glass, on which are
marked two exceedingly fne lines. The strip is
moved by tangent screws, and the distance moved
Is marked on the circumference Of wheel at
tached to the tangent screw The lines on the
micrometer are first made to bisect one Of the
objects, and then moved till the lines bisect the
second, the distance being accurately measured
by the divisions on the circumference Of the wheel
showing the revolutions Of the tangent screw.
These divisions are afterward converted into arcs
Of circle, giving the angle between the liae.
The result Of the revolution by Professor Sat-
form was that the angle between the two lines
was $50 seconds Of degree. Before the final
calculation can be made, however, 1t will be
which observations were made. The distance
from one planet being known, the other distances
are calculated by the third law Of Kelyer, which
is the squares of the times Of revolution are pro-
portional to the cubes Of the mean distances.
The distance from the earth to the sun is used
as the unit In nearly all the calculations regard
ing the heavenly bodies and hence arises the
necessity fer great accuracy in measuring the dis
tsnce, and it is for this reason that astronomers
embrace every opportunity to test the accuracy
of previous measurements by new observations.
The previously accepted distance of the earth
from the sun was % 600 600 miles, but the calcu-
lations made from the observations of he recent
transit of Venus by the French astronomers in
creases this distance by &C, 200 miles, The result
of the present observations is, therefore, looked
for with considerable interest.