Green-Mountain freeman. [volume] (Montpelier, Vt.) 1844-1884, 1874-05-06
The Approaching Transit of Venus.


At the end of May OF the beginning of
June the first of the parties who are to
observe the transit of Venus will leave
England for Kergueen's Land and Rodri-
guez. The scientific world-the astro-
nomical portion of it more especially
says the London Telegraph, will watch
with intense interest for their safe arrival
with al their instruments in good order.
inasmuch as on the success of their obSer-
vatons in Il great measure will depend the
determination of the true distance of the
earth from the sun This problem has
been one which astronomers from very
early days have been eager to attack. So
far back rs twenty centuries ago Arist;lr-
chus Of Samos endeavored to solve it. but
with the rough instruments of those times
he came no nearer to the truth than one
twentieth part. Hipparchus and Ptolemy
were also unsuccessful, whilst Tycho Brahe,
keplcr and Galileo gave measurements
which vary immensely from what is now
considered to he approximately correct.
In the seventeenth century, however, Flam-
stead, our first Astronomer Royal, amongst
others, turned his attention to the subject,
and from that date no considerable varia-
ton in the supposed distance has been re-
corded.
1t is worthy of remark that, rs the me-
cllanical nicetieS of telescopes and astro-
nomical instruments were developed, the
sun had apparently receded from us. The
observations recorded during the transit
of Venus in the last century made us some
ninety y-fiVe millions of miles away from it !;
but. owing 10 some unforeseen optical
phenomena, the figures have been open to
suspicion More recently, the measure
ment of the velocity of light by a purely
mechanical method. and its application to
determine the suns distance by timing the
! disappearance of Jupiter's satellites, has
! caused astronomers to more thar think that
81 l-2 millions of miles is nearer the mark.
70 settle this question beyond dispute lit
is to he hoped) the present expeditions
have been organized by the Admiralty. To
the uninitiated this may seem to be of but
! little consequence excepting rs securing
! the solution of IN astronomical problem
not worth the f20,0 900 or $4,000 that will
be spent upon it. When. however, it is
explained that this large sum of money
will contribute to the lessening of the dan
gers of navigation by increasing the facil-
tiles for Obtaining correct longitudes in
anv part of the globe, the most ardent ad-
yocate of economy must admit that Il
larger sum could not represent the true
value of the benefits to be gained. The
results obtained through the organizing of
these expeditions will hold n prominent
place in future nautical almanacs. The
correct distance of our earth from Venus
is established. and Il little reflection will
make it evident that, far away as she is
from us, when she passes between us and the
sun (Which she only does at long intervals
of time) she will appear to cross, at places
of different latitudes, in different paths. AT
a high latitude she will appear to move
much lower down than if observed at a
low latitude If. then, from some one
place of low latitude, and another of Il
higher, of both of which the correct longl-
tude is known, the respective times she
takes to pass over the sun be noted, mathe-
maticians will be able to tell us the real dis
tance he is from us. 10 judge of the accuracy
of observation necessary for this calcula-
ton. it may be of interest to state that an
error of one second of time, though the
total time of passage in some places will
be over four hours, will very materially
affect the results At the last transit the
accumulated errors were not much more.
but they were sufficient to create doubt
as to three and a half millions Of miles.
This year the limits on the globe for favor
able observation of the phenomenon lie
between the antarctic circle and parallel
of latitude running through the middle Of
Siberia. Unfortunately for us, night shuts
out the opportunity of observing it from
England; hence one of our parties will bt
, sent to Egypt, where the last third of il
!. will he seen after sunrise. This is tn,
most northerly station which we shall at
. tempt as the Russians have undertaken Il
hold a line across their Asiatic dominion
? The Americans will occupy the Macdonald
islands in the far south, if they can edec
| landing. The Astronomer Royal. ST
George Airy. who is the organizer and d.
| rector of our English parties, has, wit
the concurrence of the Admiralty, wisel
determined that no party of astronomer