The New York herald., 1874-12-09
than Bessers number. I sup,oin these dinerent
methods In tabular form:-

-. Ps.a,as s4H'. Dstana S.u
Opposition OF Mars ...............s sH g. 1900
Lunar Lunar theory theory sa.oa. sSo
jupisers satellites and velocity Of - -
Absrrat,on and velocity ci light. :. sss ssio0oOt
From mere inspection oftne above table 1t IS al
once seen that the psrasx ~ found by the transit
OF l7oe-nAmely asf seconds-was too small, ana
all the other methods substantially agreed there
must have been &C error either in the observation
or the subsequent collation.. Indeed, astronomers
had begun to lose sn confidence In finding the
SUMS distance by transit oil Venus Till but lev
years ago Mr.. Stone rcdiscussed the ooservatloDs
or lTe9. He focnd that by taking into account the
remarks OF the different observers the oDserva-
solar paraIlax thus deduced was proved TO De 50
seconds, agreeing with the values given 10 our
tae tae'e Observers -" but 10 Encke ana Besse
VINO JAILED to take into account all the
remarks OF the Observers AS thus corrected. sse
81 $50 900 miles, but we have no right TO say tnat
1t affords more accurate means than any OF
one OF the most interesting problems OF this
transit 10 see how near the paralax Will come 10
wnat is known from other methods, and we may
De sure that II it is found 10 diner much it VIII not
be relied on. The remarks made by the observers
OF 60 which Stone was the first to duly appreciate
had reference to the .'Dack DROP" ana tnls Is tue
next matter and perhaps the most Important 10
be looked for In this transit.
known as the "blacE drop" ..igament" or ..nine.
pln," as described by direrent observers DID u
occur again IN ls74 and VIII we now learn lts true
nature such are the important questions we
nope were solved yesterday. That we may under-
stand the answers soon TO come TO as, permit me
TO briefly explain what Is meant by the BLACK
drop" 1t was OF the greatest consequence
to the observers OF 1859 to determine
the exact instant that Venus toucnea tae
the instant it lett the edge internal contact, and
was seen completely as black spot on sne sun;
not leave the sun Sharply. but appeared length
ened out ike ninepln. or with black drop ap-
na e assas
with precision; they did the best they could, now
ever, and left the remarks when. stone took into
account. and thus arrived at an approximately
correct result
Various causes have been assigned for this re-
clined to believe, was due to what is known to
physicists as irradiation, which very simple ex-
amy one OF readers can m
the same size, one black, the other white; they
may be OF any shape. but It would
resent the solar disc; assure yourself that they
are oil the same size by placing one over the DINER
paper and the WnIe circle on piece o. black
paper or black CLOTH On looking AZ them now
the white circle, though just the same SIZE as the
black, Will appear the larger. In = word. toe white
object appears larger than 1T really Is. This pne-
nomenon Is known as irradiation, and Is quite
two Or three e DAYS G ia the brightly Illuminated
crescent seeming to extend beyond the darker
portion OF tue disc and hold II In It's grasp In
tine same way the bright sun projected on the CON-
paratively dark heavens seems larger than he
really is. Now when Venus comes in contact
leave it.. sne shuts out part OF the light from i'm
meaasey AFTER ner which would fTrm %na
occurs Just behind the planet, and the 'oack
drop" appears. The SUMS light also encroacnes
smaller than II really is But when the edges are
almost IN contact, there Is ne light Just after the
s5d 80 % nese 1 can 9e no ana
Father Hell. one OF the observers in 1869. as
scribed the phenomenon to the sensible size which
visible. Both these suppOsitions are probably cor
rect but they 90 not fully account lor All the pne-
is hoped the observations and photographs OF this
present transit will throw more light
Third-These photographs VIII. OF course, form
one Of the most interesting features OF tns tran
sit. They VIII be taken, as we have SAID, at eacn
second and will afford reliable picture OF all that
occurred and one wnlcn the astronomer can study
at his leisure. The 'black drop'' VIII be faithfully
photographed ana we may thus 0e able TO solve
this mystery ana settle the question whether or
Fourth-Eesides these advantages OF the position
OF Venus ana the SUMS distance oelng known, we
shall be able to determine longltudes with much
greater accuracy than at present How impor-
tant this Is Tor navigation and commerce your
should prove uniavoraDle or the reoccurrence o.
the .sblack DROP render the observations uncer
taken In vain, nor the million or dollars appro
prlaeed by the various governments uselessly EN-
ployed. AS We have said before, TO solve the
necessary to accurately determine the longitude
oil the various stations. As there are some sew
enty-nve stations IN all, we shall thus have. as =
result OF the observations on the transit, the
longitude or large number OF places Gil over the
globe more accurately determined than could
have been possible without these expeditions.
From these as centres the longitude OF neighbor-
ing places may be computed, and thus the ac-
ofn mn rotff n m IN m n
Fyth-Again, meteorological and magnetical in
struments have been taken out with nearly all the
expeditions. observations will be taken during
the voyage and at the various stations, and that
by some OF the first scientific men and best trained
observers OF the world. More will thus De accu.
and valuable facts collected to be hereafter col
lated leading eventually to more certain
knowledge OF the laws OF storms, IN which 80
great an advance mas been made during the past
twenty-five years. Naturalists too have been ap.
pointed to accompany some OF the expeditions,
and special funds have Deen granted them Tor the
collection OF specimens. AS the natural history OF
many OF the stations Is but little known our
museums and cabinets will be thus enriched with
new and valuable treasures. SO there can be but
little doubt that, besides astronomy, science In
general will profit largely from these expeditions.
such then, briefly, are the main results TO be
looked for rom the observations on the transit OF
Venus and some OF the advantages certain 10 ac-
crue 70 astronomy and TO science. Permit me
to place them here all together -First-A more ac-
curate knowledge OF the SUMS distance from us
and the other planets. Second-An explanation
of the .sback dropn appended TO Venus when
leaving the internal contact Third-The preserv-
ing OF the appearance OF the results by photogra-
phy never before applied TO so great extent TO
the solution OF any scientific problem. FOURTH
The advantages to navigation and astronomy from
q more accurate determination OF the longitude.
Filth and lastly-The collateral advantages to
science in general from the meteorological obser-
vatlons and collection OF rare and valuable speci-
mems. Hoping that these and many other results
and advantages will accrue from this transit o
Venus rsma'O' very IesgSsiHiay ggSHHHy {Iufs r. FsIsBEs
ST. FRANCIS xAvIRR's COLLEGE, Dec. 8, 1874