The Toledo chronicle. [volume] (Toledo, Tama County, Iowa) 1873-1924, 1874-11-05

unequal periods of time BY noting the
exact time and duration of the transit
at these two stations and after
ward comparing them, the difference
between the parallaX of the sun and that
of Venus can be obtained, and from this
the parallax of the sun and then the
suns distance from the earth. 1t is, Of
course, impossible to obtain stations on
directly opposite sides of the earth, to
watch the transit, yet places are selected
as far apart as possible, and the neces-
sary allowance made in the calculations
II may at first seem very easy thing
to take these observations; but in reality
it is very difficult to make them accu-
rate. The instruments may not be exact
in every particular, and small error in
measuring an angle at so great distance
rs the sun will make a great difference
in the result. Clocks may differ by one
or two seconds, and the state Of our at
mosphere will affect the distinctness with
which the planet is seen. Then it is OK
tremely difficult to tell the second when
the edges of Venus and the sun meet,
for, rs they approach, the dark edge of
the planet appears drawn out toward the
sun before it really touches it; and the
difference between the real and apparent
contact may occasion 4 serious error.
Hence the great importance that every
thing be prepared with the utmost care
and that, so far as possible, there be uni
formity in the methods Of observing at
the different stations.
Another science aids the astronomer in
this work by giving him new method Of
measuring small angles in the heavens
1t is that of photagraphin@ the object
and then making the desired measure
ment on the plate by an instrument
called IA micrometer. The sun has been
photographed for the purpose ofstudying
the solar spots for many years, and the
process has been perfected and used with
great success. 1t is thought that by this
method a much more precise measure
ment can be obtained than by the simple
eye observations.
For the past two years preparations
have been in progress for the coming
transit. Our own Government has APP
propriated for this purpose Sl5000o.
Eight stations arc to be occupied
three northern and five south
ern. The northern stations are
near Pekin, Yeddo, and place in the
neighborhood Of the Caspian Sea. The
southern stations are upon the island of
Mauritius; kerguelan's Land; Hobart
Town, southern part Of Australia; some
point in New Zealand and Chatham
Islands, east of New Zealand
These stations are occupied several
months before the transit in order
that the instruments may be well mount
cd and tested and the latitude and
longitude of the place determined, and
every preparation thoroughly made.
Other nations, especially England,
Russia and Germany, have made extern
slve preparations for observing the tran
sit, choosing different stations favorable
70 the purpose.
Another transit of Venus will take
place in 1892, which will be in some re
spects more favorable than this. 1t will
be visible in the Atlantic States, and
more generally in the inhabited parts of
the earth. The various instruments now
used will be kept for that transit, and it
Will he observed with the same interest
and thoroughness as the present one
After these the next will be in 2OO4; SO,
If my Atlantic readers would see tran
sit OF Venus at all, they must travel
where it can be seen in 1874, or have
their smoked glasses ready for the one
that will occur Dec 6, 1SS2-St. Nicholas
'or NocemJer.