The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1878-05-07

The appearance Of Mercury ON the was black,
but NOS dark as had been expected.
Mercury nor Was there any appearance of satellite
the planet. No solar observed neitnor
were solar protuberances observed
LOCAL OBSERVATIONS BY PROFESSOR PARK
HURsT--A COMPLETE EXPLANATION OF THE
PHENOMENA OF THE TRANSIT AND THE OBJ
JEcrs OF ASTRONOMERS IN OBSERVING IT.
TO rHE EDiroR rHE HERALp:-
Tho great popular interest in tho transit OF Nor
curry, which has taken place to-day arises from its
repeating reduced scale, the phenomena Of the
transit Of Venus which will be visible here in four
| years from next December. In the transit
Of 1874, the only one that has occurred
within tho lifetime Of this generation, astronomical
expeditions sent out by the principal civilized
nations those parts OF the world where would DO
best SEEM and from that day to this many compuors
have been at work reducing the observations then
taken, without having yet Cleaned from them all tho
Information which they could give with regard to the
earhs distance the sun, the elemental measure
of the planetary spaces.
A phenomenon precisely similar In kind is to-day
expected to yield results entirely different in their
character. In observing the transit OF Venus The
object is to determine the SUMS distance from The
paraax and this best DO done from observations
of planet which IL near Us. which has as largo
orbit as possible and from points the oartEs
acc where the parallax will be greatest. On tho
rary in tho observation OF the transit Of Mercury
whose distance from is much greater and whose
orbit is so much smaller tho main object is to deter
mine the absolute position Of tho planet In It's orbit
This planet so difficult OF observation and Its orbit
is SO mpcrectly known, that there Is difference Of
about seventy seconds between the British
and tho American predictions OF tho time OF tho
transit position OF the planet best be obtained
by observation from points on tho ear.h's surface
where the paraiax Is least. Tho very best position
for observing other contact would be that at which
tho would DO vertical at the time OF tho con-
tact. for there would DO no parallnx But as
there interval OF moro than seven hours betwcon
the first and the last contact one place give
this condition, even approximately, Tor the whole
transit Any point within tue United States will d.
vide interval between the ngress and the egress
showing the whole transit we'll without leaving home,
therefore American astronomers have had to-day as
good an opportunity TO reach useful results
observation OF the transit as II they had travelled
thousands OF miles TO vii ness IT,
OBSERVATIONS
The primary object OF the observations has been to
determine the position or Mercury in It's orbit: but
the main object The position OF
the orbit ise ana this, not for It's own sake, but
for tho purpose Of ascertaining whether there is
a planet revolving around the sun interior 10 tho
planet Venus. The search tor this interior planet
winch has been by common consent named Vulcan.
has proved In vain Astronomers have come to the
conclusion that II s almost impossible that such an
interior planet could exist without having been
fixed. Lsverrier considered IL probable that such
planet zoos exist and urged special search Tor II,
relying TO great extent upon the facts that the perl
heon OF the orbit Of Mercury advances rapidly
than be accounted Tor by the action OF the known
pianes or OF some zone Of planets or meteorites or
other matter revolving around the sun within the
orbit OF MerSary rho question o. To-day, nen, ~ ~
the advance Of the perhclon OF the orbit OF Mercury
THE PLANETS ORBIT.
1t Is to be remembered that tho orbit OF planet Ia
not material ring; It 10 simply the path through
which tho planet moves, having no more actual ex-
stence than the path OF bird IN The arr Tho action
plane; ss The change o. Tho ), orbit .
Object nanse The I psn Of ' Mercury ny
ro 50 ins. a. certain point Mercury is nearer the
than at other but t Is found that the next
time t5as Mercury reaches ina. point moves orwara
further before u begins 10 reccde. AS Mercury APP
proaching IFS apneion the eject OF large motion
IT the perinellon would DO to cause the planet TO DO
further advanced III It's orbit ana therefore to hasten
the time OF the transit H. therefore, Mercury should
servations TO have appeared earlier than can be
counted TOR by the action Of the sun and the known
planets It Will make probable that there Is other
attracting matter yet undiscovered
We not to conclude that this attracting matter
In the proiuberancos ana 10 the around the
OF which may hope to learn more In the total
Light, or IN streams o. moleorio matter, such as
give TO mecoric Showers may be all that - re.
Quired to account for the motion oil Mercury.
OBSERVATIONS THROUGHOUT rHE COUNTRY.
In accordance with tho invitation OF the National
Observatory amateur observers have today, doubt
less In many places carefully observed Tins tran
Al some the clouds must have interviewed and pro-
vented recording tho times oil ngress and e2ress but
although the sky covered with clouds most Of
day, had clear sky at both Of these Important
times. Our only trouble was the com motion tho
atmosphere preventing distinct image oil tho planet
The modes OF preparation have been various, but
Will ocscribe that which adopted the more fully
cause believe it will be the beat method for amateur
oh q no nm.
preaching transit OF Venus.
II has been my experience from careful comparison
that can obtain satisfactory Wow of tho sun
by receiving its image upon q screen than by
direct VISION The screen ! employed was about
IA loot In diameter ana was supported by wirc
framework. BY prism the light rel ectcd at
right angles, 80 That The screen aid not face tho
sun, but stood with its edge toward II. This made u
easy exclude the direct sunlight from falling upon
without the necessity Tor enclosiDg H. as 10
not necessary. and almost useless III the afternoon
from tho high wind, provided curtains TO exclude
the observatory nearly oil the direct sunlight
reducing the aperture OF the object glass TO eight
inches ana applying u power suhiciont 10 make The
image OF the entire sun circle oil forty inches In
meter and the image OF Mercury oDe.quartcr OF
irch rs shown IN tue above diagram, the ciocKwork
motion kept The telescope pointed ut tho sun. with
that part OF tho eastern limb OF tho where
Mercury expected TO appear near n line drawn
across The screen tangent TO tho limb. There were
three observers any observatory in Brooklyn and
an assistant count the time from tho
tho computation from the formula IN the American
splc indicated that the external contact would
take place Ion. ,6m $685.. New York time,
thero being probable delay OF SIX OF
eight seconds before the indentaton would
DO sufficient 10 be pcrceptible. Al I'm. As.
ali the indcnaiion upon the limb Of tho sun,
clear AID distinct, Notwithstanding Tho trcmulous
motion caused by tue atmospheric disturbance, al
though ut tunt moment the length OF the indcntaton
did not appear exceed four seconds OF space. As
the plane; entered further upon The DISK the from
uiousness seemed to increase, ana the 'bIack DROP
SO often seen III traDsts oil Venus, became PLAINLY
visible before the internal contact At 10 min. 36 sec
two OF the observers saw the first unduaton Of light
across this black Drop but we dd not catch another
glimpse OF tins g untl seconds later and In
The third observer, at forty seconds
caught the distinct glimpse the light. Shortly