National Republican. (Washington City (D.C.)) 1872-1888, 1874-01-12
CELESTIAL DISTANCES.
PROF. NEWCOMERS EIGHTH LEcTUR

PROF. NEWCOMERS EIGHTH LECTURE.
Prof. Ncwcomb delivered the eighth lecture Of
his interesting course on astronomy before the
Columbian University on Friday evening.
The lecturer announced his subject to be the
measurement of distances in the heavens, and es-
pccially Of tho distance Of the sun. The usual
method OF making such measurements is BY de-
terminng the paraIlax Of the body to be meas
ured. 1t was therefore necessary to begin by ex-
planning what parallax is. The definition Of this
word is the difference between the directions of q
body as seen from two different points. Illustra-
lions were given to Elbow how this depended on
the proportions between the distance Of the body
which it is seen. The nearer the body the greater
the paraliax, if the distance between tho points
from which 1t is viewed remains the same. This
distance is called tho base line. Two base lines
are used in astronomy, one being the distance be-
tween two points on the surface OF the earth, the
other the diameter OF the earth's orbit. By the
latter all distances outside of the moon have, in
the tirst place, to be measured. If, for example,
We observe . planet when the earth is on
one side Of the sun, and again a six mo- months
see it In different direction owing to the change
in the position of the GARTH II the planet did not
would give the exact proportions between the
diameter Of the earth's orbit and the distance Of
the planet But since the planet always moves
during the interval We must determine and allow
for this motion, and to do this accurately needs
long series Of observations, made when the earth
and planet are in various points OF their orbits.
portions between the distances Of the planets and
that Of the sun are learned, and 1t is thus found
that the distances are determined from the times
Of revolution by Kcpler's third law, as explained
in q previous lecture. These results, though ex-
tremely accurate, do not give distances in miles,
but only proportions. or distances in which the
rcd. This distance is the unit Of measure COM
monty employed by astronomers in stating dis
tanccs in the celestial spaces 1t IT, for instance
found that Mercury is about at the distance one
third, Venus nearly three iourths, Mars one and
hall, and 50 On.
DISTANCE III MILES.
These distances cannot be expressed in miles
until we know tho length OF our base line. To
measure This We must take the distance between
points the earth itself as the base line, and
when do this The parailax oil the sun is 80 small
that hardly more than o century has elapsed since
Il has been doEe with any certainty. Indeed, the
parallax to be measured was not directly that Of
nearest the earth from which the parsllax and
distance OF the sun could be found by the known
proportion between them. ......
TRANSIT or VENUS.
The lecturer then explained how transitS of
this purpose The observers at distant stations on
the surface Of the earth would see Venus follow
different paths over the disc Of the sun by measur
the two bodies would be determined. Various
ways Of making these measures would be en-
ployed In the transit OF next December, among
which that Of taking Photographic OF the sun with
American astronomers. 49,
In conclusion, the lecturer illustrated the I'm
mensity Of the suns distance by saying that II his
hearers had friend in the sun whom they wished
TO sec, and could travel thither by . train which
went at the rate Of $50 miles an hour, il would
still be vain to start on the journey. Though the
without making single stop, they wouIi all die
Of old age before reaching their Destination.