Public ledger. [volume] (Memphis, Tenn.) 1865-1893, 1882-12-04
gHE TRANSIT or VENUS
The Phenomenon to bs Seen by
Any One Through Smoked
Glass.
The Astronomers and Their Prepa.
rations to See the Transit at
Various Points.
The Government Appropriation
Other Ira nsits of Venus.

sun Ior the nrst time since 1874, and
for the last time before the year zoos.
The planet has for some time been
brilliant in the evening sky. As she
swings round her orbit she is rapidly
nearing the line between the earth
and the sun, setting closer behind her
hery lord every evening; and when the
transit" occurs she will appear as a
small spot on the suns bright disk,
moving from edge to edge in about six
and a halt hours-fram 8 am. until
3;2l pm. A piece Of smoked glass
will enable any one along the Allan
TIC coast 10 see the phenomenon
which = pair of common opera
glasses will make more distinct. Care
should be taken to have the glass
which is to protect the eye from the
sun well smoked. Better than smoked
glass, on which the loss of a fake Of
SCOT might injure the eye, would be a
piece OF colored glass, dark brown or
blue.
A transit of Venus is due to the
simple fact that her orbit about the
sun is inside that described by the
earth. If her orbit were in the same
plane as that of the earth there woul.
be a transit every time Venus com
pleted her revolution in respect to the
earth. But sometimes she passes above
and sometimes below the sun, and the
translts are rare events, occurring in
pairs, eight years intervening between
those of a pair. The pairs are sepa
rated bv periods alternately of 1851
and 1914 years. The transit this month
il the second of a pair, the first of
which occurred in 1874.
THE IMPORTANCE OF THE TRANSIT
There is no display of interest to
the unseientific eye in the transit of
Venus. The thousands of observers
who will cranet their necks and dirty
their noses with smoked glass on De-
cember s will see nothing but a little
round black spot moving slowly over
the sun. But the scientific value OF
the transit lies in the fact that it can
Nc made to measure the distance from
the earth to the sun, which is itself
the astronomical unit Of measurement
in the vast distances of space. The
mathematical process by which this is
lone is very complicated. But it can
readily be seen that two observers at
distant points on the earth would see
the planet at different points on the
suns disc at the same moment. 1.-THE
exact distance between the two points
can be measured, the suns diameter
can be calculated, and its distance
from the earth directly follows. The
details OF this work are so complica
ted that the result OF the transit of
1874 are not yet fully known, and
years will pass before anything definite
will be known of the deductions from
the observations Of December. So
tar the only transits. observed are
those Of 1851, 176l, 1863 and 1874.
After the transit of 1863 the distance
from earth to sun was reckoned al
from 100000 to IS, 000, 600 miles.
This was so wide a margin that over
a million dollars were spent in obsery-
ing the transit of 1874, and the calcu-
lations SO far made vary from $4,000.
0OO to $3.50, 600 miles. 1t is hoped
that the observations of next month
will reduce this immense margin.
HOW OBSERVATIONS ARE MADE.
Observations are made in three
ways. The simplest is merely to oh.
serve the moments when the edge OF
the planet just touches the edge OF the
sun-the contacts" as they are
technically called. Another method
Is to measure as often as possible the
apparent distance of the planet from
the edge of the sun. A third method is
to make asmany photographs of the sun
with Venus upon it as can be obtained
during the transit. The pictures are
afterward carefully measured. The
photographs Of 1874 we're for the most
part failures, but the American pho,
tographs were exceptionally good. 1t
is difficult TO avoid distortion in
photographs, and. moreover, the scale
OF the plates must be SO accurately
liked that errors shall not exceed
l.lOOth Of an inch on a four inch
picture.
The difficulty in the observation Of
contacts" is caused by the atmosphere
Of Venus, which causes a band Of
darkness which seems 10 Join The
planet to the edge Of The disc for
several seconds after it has really
passed. This atmosphere was first
observed by David Rittenhouse, Of
Philadelphia, at the transit of 1863
when enus was half on the sun, be
saw a ring Of light surrounding the rest
OF the planet, so that its whole
outline could be seen. This statement
was doubted until confirmed by the
observations of 1874. Another point
of interest 10 observers will be the
possibility Of discovering a satellite "a
Venus (which would probably be
named Cupid. Supposed discoveries
Of a moon TO Venus have been often
made, but more than a century hai
passed since the last announcement
If the discovery is again made, the
lost satellite will appear as a small
black speck near the planet.
WIDELY SCATTERED TELESCOPES.
The transit OF next month will b,
widely observed. Congress at the las
session appropriated S75, 600, which
will put eight parties in the field, pro.
yided with the same apparatus used
in 1874. The transit will be yisibl,
from beginning 70 end all owe
South America and the Atlanti,
! slope Of North America. Professol
Newcomb's party has sailed for th,
, Cape Of Good Hope; Professor Boss
goes 10 Santiago, Chill; Assistan
Smith, Of the coast survey, to New
Zealand, and Lieutenant Very, of tn
J navy, 10 Santa Cruz, Patagonia; Assis
tant Davidson, Of the coat survey
; will observe at Fort Thorn, NeI
: Mexico, and Prois. Hall, Harknes
I and Eastman will observe, respective
I ". AZ San Antonio. Tex, Washington
ID. g., and Cedar Keys, Fla, France
. Germany and England have also sen
: ont parties and besides all these
observations viii be made at all tn
o~bgeryatnries which command th
e%clipse, aud the rebults collatea a
Washington. Prof. Sharpless, Q
Hayeriord College, will observe "con
facts"
II h hardly likely that the hest re-