The New York herald., 1874-11-30


would would present TO his eye an angle equal to the
l-3yoOO part OF circle, the measure OF the ANGLE
J: But IT Is manifest from the diagram thai the
angie Is the same size as l. 1t Is plain also that
the angle IS the visual angle presented to the
observer aforesaid by the line D. and as TINS line
the distance from the earth TO Venus IN the same
way as 1t Was shown that an observer at
tne th sum sun could Thn estimate his distance from
asserted without proof ana that Is tnar
to an observer At Venus the angular distance
part OF circle that Is, they would appear about
and 81 times as far asunder, the eartn beng
This latter assertion ossea sse as ON Venus ons
OF Kepier's celebrated laws, which demonstrates
That the longer planet takes 70 go round the sun
the Iurtner IL Is from the sun. Hence we only
need ascertain by telescope observation the re-
spectlve periods OF the planets revolutions in
the sun. The law may be thus applied The
earth goes round the sun IN So weeks nearly;
Venus mGyes y round 9.sa in aoous 80 weeks
the about aDa sls io "asss Tae sSs suoe
times thar the distance @ sfe II Venus IS con- 0
tanned IN that OF the earth-viz., about and $40
the p,anets no matter what their distances, the
discovery OF which cost Kepler twenty years OF
labor and study. Kepler demonstrated that the
law actually did apply to the planetary worlds,
and Sir Isaac Newton. not long afterwards, showed
beyond all cavi that It should apply, proving is
OF the universal mutual attractlon OF material
bodies, The reader will now understand now
the solar distance was deduced from the knowi.
edge OF Mars distance that was arrived at in 1862
The only problem remaining, then, according to
haley's method, is the extremely delicate task
OF measuring to nicety the distance be-
tween the two passage lines MIMI and
NM. Tue smallest error In SO doing would
lead to an embarrassing one in the con-
clusion. The measurement on a Photographic
image would involve much uncertainty. TnIs plan
cannot succeed. The distance might be approx
mated by gaugng the planets distance from the
top or bottom OF the suns rim during the transit.
But no scheme can equal the one to De used by
the observers OF 1874, weather permitting. IL Is
this:-rne length OF eacn passage line depends
upon the time occupied Dy the planet In tracing 1t.
Inc more more time me Venus takes up n moving across,
the less the passage line. Knowing the respective
times consumed IN moving over the lines, We can
cal truth that when we know the lengths OF two
such lines We can calculate their distance from
each otner; , Inc more accurate we are IN esti-
tainty OF the latter. Hence the Importance OF
noting the time spent BY Venus In making her
transit. Now, THIS time can be easily found by
fixing the moment at which the transit Degtns
and the instant at which 1t ends All the efforts
OF the astronomers are directed toward this object
The observers OF the last century were about
to signal the decisive moment OF the COM
mencement OF the transit when the mysterious
fhe question now beng universally discussed is
will this strange phenomenon occur agains Many
are o. opinion snati wlll not, IN view Of the mar
Many others expect the recurrence OF the same
deluslve appearance. The chances are that the
obstacle Will again present Itself, though perhaps
In diminished form. There Is an atmosphere OF
great density enveloplng the planet Venus
through which the suns rays, in racing toward the
earth Will undergo reiractl0n, or bending, similar
to that which takes place in our own terrestrial
manifest In the beautiful mirage, or the the
enchanting views or the Fdt1 MorOdnd
Besides this bending OF the solar beams
traversng the airy fields OF Venus, there is the
parallel phenomenon OF an intervening blur be-
tween two gooes at different distances from the
eye during the passage OF one between the OBJ
server and the other. The young students who
were in training Tor several months at Greenwicn
we're furnished with an ARTIFICIAL planet with
which to practise, the better to judge the moment
OF contact on the eventlul day. Even with the
artificial venus slight blur was perceptible
whenever 1t was brought near the image Of the
SUMS rim. The grand secret, therefore, OF the
lab0rs OF the 8tn OF December Will be successful
determination OF the moment OF contact, all the OBJ
stacles Notwithstanding The true moment OF first
contact will be when the centre or Venus passes
the eastern edge OF the sun. But as we cannot
see or determine by visual Judgment where the
centre OF Venus is. we must calculate this moment
rom other observations. Accordingly, the trst
entry made on the records OF the observers will be
the moment when the planers circumference
grazes the suns edge. This Is shown In the ac-
companying diagram (fg 81, which represents
the nrst contact between the two bodies and the
track OF the planet az seen from the southern
station:-