New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1882-12-04
THE TRANSIT or VENUS.


If the weather is clear on Wednesday
next anyone in this city who cares to
nroyide himself with bit of smoked
glass can watch the transit of Nenus-the
passage of a black spot across the brightness
of the sun-an event which Will not occur
again until june S, 20O1. At the last transit,
in 1874, Venus traversed the northern limb of
the sun, while on Wednesday the planet will
pass across the southern limb. 90 The first
or external contact will occur by local
time at 9 o'clock minutes and 40 sec
onds, the second or internal contact at
o'clock 2S minutes and 4S seconds, the third
contact, also internal, mt o'clock 81 minutes,
and the fourth, or external, at 3 o'clock -
minutes and seconds, at which instant Venus
finally leaves the sun. The beginning OF the
transit will be visible in England, Western
Europe and Africa and the end over most of
the Pacific Ocean. The whole of the transit
will be visible from the Eastern and Middle
States, and from Mexico, Central and South
America.
The scientifi c problem, for the partial sOu-
ton Of which nearly all the civilized nations
of the globe have sent out trained Observers, is
the measuring of the parallax of NenuS-that
is the angular difference between the direction of
Venus as it would appear from the centre of
the earth and the direction seen by an observer
at the surface of the earth-the consequent de-
termination of the parallax of the sun from the
known proportion between the respective dis
tances of Venus and the sun from the earth,
and the ultimate verifying with greater accu-
racy Of the distance of the earth from the sun.
The Importance of these observations has been
well stated by Professor NewcOmb: "ThC
measurement of the heavens involves two dis
"tnct operations. The one consists in the de-
determination Of the distance between the earth
"and the sun which is made to depend on the
"solar parallax, or the angle which the semi
"diameter of the earth subtends as seen from
"the sun and which is the unit of distance in
celestial measurements. The other consists in
"the determination of the distances of the stars
"and planets in terms of this unit, which gives
"what we may call the proportions of the uni
"verse. Knowing this proportion we can de-
"terinine all the distances of the universe
"when the length of our unit or the distance OF
"the sun is known, but not before" Aud
again: " 1t may be asked how the parallax of
"the sun can be found from observations of
"the transit of Venus, if such observations
"of Venus and that OF tho sun. We reply that
"the ratio of the parallaxes of the two bodies is
@known with great precision from the propor-
tons of the system" But the problem to be
solved is one practically So delicate and nfni-
tcsimaI as to appear to the lay mind almost
hopeless. The solar parallay is considered to
be between S.7j" and S.s5". This doubtful
tenth of second is the cause of tie outlay and
toll which have placed scientists at posts of
observation throughout the Western IIemi-
sphere, equipped with the best products of
mechanical skill Yet this tenth Of a second.
SAWS Professor Young. is no more than the
angle subtended by a single hair at the distance
of 500 feet. Taking the solar parallax to be
$500, the suns distance is 81, SS5, 900 miles,
while divergence of a twentieth of a second
either way changes the result half a million
miles. The most hoped for in these observa-
tions is to reduce the error 10 4 quarter of a
million miles Professor Hardness saws: ain
"lS74 as in 1761 exaggerated views prevailed
respecting the value Of transits Of Venus. but
"no competent authority now supposes that
"the solar paraliax can be settled by them alone.
" The real argument for expanding 50 much
"moncv upon transits of Venus is that, being an
" important factor III determining inc solar
"parallax, their extreme rarity renders it un-
"pardonable to neglect any opportunity of OBJ
serving them"
As to the best methods OF securing accurate
results in tho ACKNOWLEDGEMENTS, astron-
Omers arc at variance. The French and Eng
lish rely on the observation of contacts at the
instants of ingress and egress. This is tho
simplest, given perfect observers, but it is sub
ject to serious errors owing to atmospheric dis
turbances caused by the fluctuations Of the air