The New York herald., 1874-11-30

10 In less than the ten minutes previously esti-
maticisn. VINO knows wen now g estimate the
rate at which his station Is carried forward to
involved In the assertion tnat the velocity OF the
station diminishes IN proportion 70 ,5s prTCx:
TO me et6ss pss sos the sr'
the nearer does his velocity APPROACH Log miles
AZ hour II Is scarcely necessary 70 say tnas me
earth, inasmuoh as the light emanatlng from tho
unconcealed portion OF the SUMS disc Is suficengi
imperceptible shadow strikes the station at A, ~
the same instant a. which the observer sees sne
But the middle OF the sun cannot be seen, cam
lts position be well judged BY the astronomer.
can only see very small portion OF It at tune aol
must nave resource TO the plan OF observing tho
adgs tnu ~ ,ass contacts OF the planet WIN tne
aalleys method Hall way between she nrst PAIR
Of contacts as and the second pair. the planet wiz
central point OF the sun.
In IKE manner the Observers at B, by noting
che contacts at the left and right edges OF the
SUMS rim can calculate the moment at which
Venus crosses between and the middle OF tho
Many other df1ncultles arise in the process OF
the work, which involve problems in the higher
fields OF mathematical science. Venus does not
always move with the Same velocity; neither does
the earth, because they rev0ve IN paths that are
sey - are the SHs oWes
when they are at the most remote points OF their
respective orbits rne eartn Is so0o0o o. miles
ana Venus. ct some times is 100000 OF miles
nearer TO the sun than she Is st other periods It
WILL be necessary, then after the observauons OF
the stn OF December to ascertain the average dis
lance ana the greatest and least distance
as the particular distance at which each VIII
stand from the grand central luminary on thas
day. Even these obstacles iall 70 daunt the Keen
mathematicians, BY measuring the apparent size
OF the sun and OF Venus, from time to time, tney
those orbits. II the sun looks one-thirtletn larger
IN January than in June then we are assured thas
he Is one-thirteth nearer in the former than IN
mate our relative distance from the sun at any
part or the year. II remains to determine the
day. Tnis can be deduced rom another law
discovered BY Kepler. whereby tue precise
may accurately he iound the law Is that .
line drawn from the sun to any planetary orb
passes over equal spaces In equal times. FUR
tner discussion OF this topic ana the numerous
other tasks involved In the calculations would
dernessss OF diagrams and trlsonometricai caicu-
lations that would tend 10 prejudice very strongly
the popular mind against the beauties Of abstracts
science. Tnus far We nave steered GEAR OF sines,
rangents, dilrerentlal and integral calculus, norl-
zontal paralaxes and other mathematcai NsIil mob
snail leave them undlsturbed for the present.
Sufice It to say that tue stupendous difficulties TO
be met with IN the solution OF the great problem
are not more numerous or formidable than tho
preparations by which It IS fondiy hoped to sur
But by this time We can understand the impa-
ttence OF the reader to know why II is that Venus
scribed, overtaking the earth every 5s4 days, and
yet let's 100 years pass by without once comin0
between the earth and the sun.
WHY TRANsITS so RARELY OCCUR.
II Venus and the earth travelled III the same
plane, on the same level. round the sun. then, az
surely as Venus overlook the earth, so surely
would she pass between IT and the sun, and there
would be transit OF Venus every nineteen
Venus travels is tilted 50 that one hall OF it lies
above the plane Of the earth's path and the other
rspressstaon nal esi0M of this, 0Oen let a crcuar
vessel, i've feet wide be filed with water. on
sci circular sheet OF timber three and half feet
In diameter. Then tilt the sheet OF wood so that
one,nalI Of II may remain % somewhat an0Ye the Inc
pressed beneath 1t. The circumference OF the
timber now resembles the track IN which Venus
travels ana the circumference OF the pond repre-
seuts the path OF the earth's movement the
SUMS position being the central point OF the board.
given In hg. 8. One-halt OF Venus orolt Is sup,
posed 10 be lifted above the plane OF the eartn's
It, The amount OF Inclination between the orbits
is equivalent TO the hundredth part Of circle,
other 1I' at % the line NJ the eartn passes the
point & L on the 7tn OF every December: ana!
Stations oa1 oH ae are 1a ranss
When the earth is in any other part OF It's orbis
Venus cannot pass between II and the sun, be.
cause she Will appear to be either above or below
the solar globe. In order that transit occur
Venus must oyertake the earth at or very near
the point or l.. On the 8th OF December the
earth. Venus and the sun will be in the positions
mapped on this diagram. The arrows snow the
direction Of the planetary movements. While the
earth makes clrcut round the sun Venus per-
forms one and fye-eighths nearly, and conse-
quently when the earth returns to this same
position year hence. Venus VIII DOT be In
the same pace, put wlll appear IN tne
Sin' S have Ae made one and aseelsS.ns .aadI
tonal rounds, and so on, until At length in
December OF tue year 1852 she G WilI occupy nearly
coming transit and the phenomenon Will again
be observed. The phases which Venus would
In the diagram, and her position IN December OF
each year until iss2 II is plain. then, tnat the
out transit taking place. During the same
period Venus VIII perform thirteen. II thirteen
OF the earth's we should have transit every eight
years. But this not being the case, after eight
n9 70 ne ns has us
from the position 'S2. After eight years more
this amount Of departure VIII be doubled:
u becomes SO great as to equal whole length OF
Venus orbit. This takes place after 235 years.;
at Intervals Of eight and 2s5 years. it is now 2ss
years ago since trausit took place while the
1850. Eight years previously Q6ap a similar
one had taken place. But SINCE transits can also
occur at N in the month OF June, 1t wln not oe
In the meantime q transit will occur at and
another eight years thereafter Nor None can take
place at that point Afterwards Tor 235 years.
DATES OF THE TRANsITs.
Translts have been known to take place as
acknowledgements q, 1851; December 4, 1889;
sans saae Is on
SO. 1874: December 0, 1882; June I. 2oo4;
June 8, 2012; December TO- 2l17; December 8,
1850; December 10, 1868. II may hence be OBJ
served that thew take place in pairs eight years
apart, and that the intervals Of years between
them are respectively 8, l2lH,s, 104H, g. 121 u and
30 on this beng the order OF succession for long
duration Of time.
The photograph instrument will be employed for
determining the contacts, and the electric battery
for ascertanlng the l0ngitudes OF the stations.
THE sPEcTRosCorE.
This wonderful appliance, unknown to former
observers, Is likewise 10 be employed In ascer-
tanning the moments of contact 1t Is known
upon the spectrum, hnes different from
those presented by the sun itself. When
Venus is about to Craze the suns edge
before the first contact the light from this eR-
velope makes an impression on the spectrum IN