Nashville union and American. [volume] (Nashville, Tenn.) 1868-1875, 1870-03-03

band Of astronomers viii be on the alert
for the same thing At Aleppo, Smyrna, OF
Alexandria. These four sets of places,
1t will be seen on reference to q map OF
the world, are far apart from each
other, and the difference in time between
the moment of ingress, as also OF
egress, as noted BY the observers having
each of those stages of the transit in
charge, and the differences in the appar-
emit paths of the planet across the sun,
viii be considerable-suficient to furnish
a sound basis for the subsequent calcnla-
tions. The number of observing places
and parties may be multiplied almost in
definitely; and the more there are the
better, if observers are equally skillful,
the instruments equally good, and the
latitude and longitude of the stations de-
termined with equal exaetness. Numer-
Gus observations thus taken wonld serve to
verify or correct each other; and from
the mean of all of them, the suns parai-
lax and distance could be ascertained with
great precision.
At present the suns distance is thought
to be only proximately known. 1t was
estimated at the last transit of Venus in
1863, by the imperfect instruments of
that period land without the fullness Of
preparation which will be bestowed upon
observations of the next transit), and was
then figured out at 95, 3os, $50 miles mean
distance from the earth). AT the opposi-
ton of Mars in 1862, which gave anothe.
chance of solving the problem, the mean
distance of the sun was estimated at 81,
4S0, 900 miles. Curiously enough, too,
Mr.. Stone, of the Greenwich Observatory,
| in looking over the recorded observations
of the last transit, finds that the calcula
tors who used these data made certain or
rors of computation, the correction Of
which places the mean distance of tht
sun according to the amended calculations
at 81, 74O, 900 miles, which agrees remark
ably with the distance deducible from thu
opposition of Mars. The observations O
the transit of 1874 may be expected II
decide the interesting question whethe
we have been putting the sun off som
4, 900, 600 miles further than be ought b
be.
Photographers are expected to rende
valuable aid to the astronomers in catch
ing the precise moment of ingress an
egress, and also the path of the plane
over the body of the sun. Mr.. De L
Rue, the eminent English photographer
has called attention TO the close agreemen
between the micrometrical measurement
applied to the eclipse photographs take
by him in 1860, and the elements of tina
phenomenon calculated by Mr.. Farley i
the Nautical Almanac. As the transit o
Venus is a leisurely operation, occupyin
several hours, the photographer woulC
not be so much hurried as in attending t
an eclipse, and results of the highest &C
curacy may be expected from his labors
Photographers will undoubtedly accom-
psny all the English expeditions.
Observers of the last two transits O
Venus remarked penumbral appearance
about the edge of the planet. This wa
supposed to indicate the presence of al
atmosphere of considerable height AM
density, equal at least to those of the at
mosphere of this earth. The more pow
erful instruments and finer tests to b
employed at the next transit may settl
this point conclusively, and supply an
other link in the chain of proof that thi
nearest of our planetary sisters is a fl
habitation for q race of sentient being
living under conditions not widely differ
ent perhaps from those experienced here
The last transit of Venus, as we hay,
said, took place in 1869. The phenome
non occurs at alternate intervals of an,
105. and and 1911 years. The mex
one after 1874 will happen in 1882.
The French, German, and perhap
other governments of Europe, will sen
out expeditions TO observe this rare pho
nomenon; but none of them will probabl
surpass, if they equal, the enterprise an
lavish expenditures of England in the mat
ter. Our Government has not yet take