The Democratic press. [volume] (Ravenna, O. [Ohio]) 1868-1901, 1875-01-07
THE TRANSIT OF VENUS.
A Most I'm pOrtaut Matter for Astronomer
Great EXDectatiOna.

M Most I'm pOrtaut Matter for A astronomer
Great Expectations.
No person now living has ever, be-
fore the late event, beheld transit OF
Venus. The last one occurred in 1863
when, as Professor Newcomb says,
Napoleon and Wellington were sleep
ing in the arms of their nurses, all
unconscious of the parts they were to
play in the worlds historN Washing
ton, loyal subject of King George,
lived quietly on his Virginia planta-
tion; and American independence was
q dream of few enthusiasts" The
transi!s occur in pairs, each transit
being separated from that nearest it in
time by an interval of eight years,
while more than u century elapses be-
tween one pair and another. Thus,
the transit nearest in time to that of
1869 took place in 1761, eight years
earlier; and the present transit will
be succeeded by another in eight years
hence, in 1882. The next pair will oc-
cur in the years 2O04 and 2012.
The object of the observations made
by no fewer than seventy-five parties
OF astronomers, and at an expense of
| hundreds of thousands of dollars, was
to ascertain the distance of the earth
from the sun, which is not yet accu-
rately known. Our knowledge of the
scale upon which the whole solar sys-
tenn is constructed depends upon the
correct measurement of this distance,
which may be regarded as a vast astro-
nomical standard of linear measure.
The principle involved in measuring
| it by means of the transit of Venus is
quite simple, although it's practical ap-
plicatiOn in actually working out the
problem is extremely complicated. 1t
10 n,NIipd dow N tho mo
operations of surveying, where the
distance of remote and inaccessible
object is to be ascertained. The sur
veyOr measures base line of cOnven-
lent length on which to construct an
imaginary triangle with the specified
object at it's apex. by observing the
direction of the object from each end
of the base line, he finds the two base
angles of the triangle, the length of
one side of which he already knows,
it being the base line itself. With
these known elements of q triangle,
the length of the two remaining sides
in this case the distance of the object
from each end of the base line-can
readily be calculated a
We shall not follow this principle in
its modified application to celestial
measurements. 1t is obvious, howev-
er, that the apparent path of Venus
across the solar disk as seen from the
southern hemisphere will be nearer
the upper edge of the sun and shorter,
than the apparent path of the planet
as traced by an observer in the north
ern hemisphere; as, when a horizontal
rod intervenes midway between a per-
sou sitting in a room and the face of
the clock on the mantel, the rod will
intercept his view of part of the dial,
say between the figures one and eleven,
while, if he rises to his feet, it will APP
parently be lowered and seem to con-
meet the figures nine and three. Of
course, the upper apparent path of the
planet will be traversed in less time
than the lower. The determination of
the distance between such apparent
paths observed from different stations
is the distinctive feature of the method
devised by the eminent English astro-
nomer HALEY for the observation of
the transit of 17Sl, and since called by
his name. When known, it affords
the requisite basis for computing the
distance OF the sun. Delisle's method,
on the other hand, deals solely with
time as an element in the transit, and
involves simply record of the abso-
lutte time of the planets contact with
the SUMS edge, as seen from two diff
ferent places on the earth'S surface, at
one of which this contact happens as
early as possible, while it occurs as late
as possible at the other. The differ
ence in time thus noted will furnish a
measure of the suns distance. The
utility of these methods as applied to
the present transit has been subject
of animated controversy in England,
the names of Richard A. Proctor and
Sir George Airy, the astronomer royal,
being especially prominent i'll the dis
pute.
The importance of the transit of We
nus as a means of accurately determin-
ing the suns distance, once esteemed
transcendant, has been lessened some
extent by the success of other methods
which have been contrived within the
past hundred years. In reference to
the prevalence of the opinion that it
still affords the best means of meas
urement, Prof. George Forbes says: -
" So far as our present knowledge goes,
we are hardly Justified in such state
ment until the observations that shall