The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1875-01-30
study the problem Of irradiasion. he has 9


placed In position q coast survey meridian instru
ment oy which 70 observe the meridian passages
OF tue limos oi the sun and oil Venus ana IN the
Commission transit meridian observations VIII be
made Tor the difference OF defamation OF the SUMS
about mp 40 ,' sec wq'ca w o Soon TO
utilize every member OF ms party small equa-
tollal Oh three inches VIII be used by the 1rst as
sstant astronomer Tor the determination vi con-
facts.
The different chronometers and clock are con-
nected by telegraph lines and the epoehs OF the
different phenomena recorded on cnrono9raph
sheets. Just as the ordinary star transits are.
servers. and for cerrain WORK Il great relief. But
experienced observers have more iaith IN their
"eye ana carr observations than In the "eye ana
naudn
- In order that this centennial appearance OF
venus on the sun might not take the observers
unprepared Tor certain phenomena expected 10
appear an artihcial Venus was set up on Winder's
building, In Washington, ana the observers had
some practlce thereon nom the Navai OoserVa.
tory. AT this NagasaSi station Venus in several
Shapes, as she Will appear crawling on the sun,
mas teen erected on Meridian Hill, ABOUT threc
miles TO the northward and on the same elevation
as the Venus station. Upon these ngures the
cniel and his assistants practise regularly In me
measurement OF cusps. distances, diameters,
&c. In all these artificial Venuses care mas
been taken to have the disK OF the planet appear
OF the same size IN the double image mlcromeler
as she Will actually possess on the 9th. One oil the
curious cases stuaIed Is that wherein Venus IS
painted as she VIII appear wnen only ten seconds
upon tue solar disk With the slightest unsteadiness
OF the atmosphere IT IS almost impossible to make
out this edge OF Venus rms Is a point that can
be studied by ali the parties wnen they return;
and the results will never De satisfactory unil
each observer has adopted similar experiment IA
the field or upon his return from the field. Let
board he painted 10 represent part oil the DISK
and border OF the sun, aud thereon let there oe
painted back Segments representing Venus when
one second, TWO. three &C., 10 ten or nIteen
seconds the limo oil the SUM- The observers
should then pracIise and endeavor 10 ascertain
what Is he smallest segment visible under similar
circumstances 10 those IN which they observed
II the practice with an ARTIFICIAL Venus Is dinicuit
when the observer knows exactly where TO look
for IL. the difficulty Is ten0ld increased when
the exact spot Of her ingress Is not certainly
KNOWN.
members Of the party has been the OCCUPATIONS OF
stars, tina: the different stations may have some
means OF ascertaining their difference OF iongl-
tube. fne Photographic means OF recording the
appearance OF Venus upon the SUMS disk at given
epocns ample Tor the snallness OF the party.
The Photographic telescope is that devised by Pro.
lessor Wnock. OF Cambridge observatory. and
consists OF q six inch object glass. by Clark,
mounted very sodly upon boiler iron pier frmly
lmoedded Jour leet below the surface OF the
ground.
In equatorial instruments the ockwork, geared
into the polar axis moves the telescope, so tnat
when directed TO any given celestial body II will
follow the object pointed upon, and thus enable
the observer to make continued observations with
the star, sun or planet apparently fixed IN the
telescope. In this device OF Professor Winlock,
who Is, by the way, one OF our most mechanically
ingenious ing OF astronomers aa3 ana maLhemaIcans
position. Therefore. u large heiostat, moved by
clockwork. Is placed to the north OF the photo
graphic OBJECT glass I'm :he Dortnern hemispherel,
aud the plane glass mirror OF the instrument is
turned in such manner that the reflected image
OF the sua Is continually directed IN a straight line
through the objective to the reticulated and SEN
sitizsd plates IN the dark photographic room.
The OBJECT glass OF THIS liked Photographic tele.
scope directly IN the merldian OF the transit IN
strument which Is placed to the north. At the
chemical focus OF this lens redetermined AT THIS
staton) IS a reticulated plate OF glass mounted
upon plate similar to tnat used for
the object lens, This plate Is capable, or
but lest minute errors should creep into us
adjustment 1t has q Level upon the TOP, and
plummet, by Which means It's error OF adjustment
can be measured. the chemical local distance OF
the lens Is thirty-eght eet i've inches and at that
distance the image OF the sun Is four and three
elghths inches IN diameter. II gives pictures with
sharp outline under lair circums ancos OF weather.
AS the principal measures OF the photography are
intended to determine the distance ana direction
OF the centre OF the planet IRON the centre OF the
sun during the progress oil the transit, certain
instrumen tai conditions must exist. II detective
In a small degree the correction can be deter
mined by reading the level with Tn. plumb line in
two Positions one wnen a little more than half
the sun Is photographed with the reticulated
plate In direct position aud hall OF 1t screened,
and then when IN a reversed position.
All the details OF these instrumental errors and
their deter minaiion have been iully studied out
the first contact at ingress can be seen by the eve
the photograph Will be used TO determine, as
nearly as practlcaDle the instant OF contact. AS
1t cannot 40 SO directly series OF rapid pnoto-
graphs will be made rom the computed time OF
contact Tor the next nve minutes; the time Of
eacn exposure VIII be noted on the cnronograpn
by electricity and after the planet Is vel ad-
vdnced on the soar disk 1t Is believed that by
these times and the SIZE OF the segme1ts OF Venus
limb the epoch OF contact can be derived directly
by proportion. In pfacnce tue parry mas taken
ten vi these many seconds. several me nods
for executing this were tried The one adopted
gave the most RAPID woIk.
REMARKABLE DEVICE OF A FRENCH ASTRONOMER.
The French parry under Jansen have great
faitn IN this method and ne has perfected con-
trivance Dy whica ne OBTAINS forty eight pictures
OF tue suns border at lngress in one minute.
During the progress OF tue transit winch lasts
four hours and lorty-slx minutes, 1t Is expected
at beginning and ending. not less than two hun
dred Iull sized photographs OF Venus position on
the suns DISK. 1t viii De seeA that the American
parties are lairy prepared 10 observe all the
phenomena Of this tran-it by the Photographic
and astronomical methods; and TINS Is the case
generally with all otner parties But still more
beautiful method will ne essayed by some OF the
parties OF other nations, and PROBABLY by the
American party at PeklD. The means by which
Jansen ana LocKyer determined the epocns OF
totailty in solar eclipse with the speciloscope
can probably be used here. IL is now well estaD-
nsned that just outside the solar pnotosphere,
aud between II and the cnIomospnere
bright coored lines or bands wnicD indicate the
presence OF glowing or luminous vapors or gases.
solar eclipse OF that year. when the direct light OF
the philosophers was cut OF by the nterposng
body vi tne moon. BY proper InstrumeD tai con-
trivances, these bright lines can be seen at any
time. So long as these bright cOlOred lines are
instant their brightness disappears the observer
knows That the lmD o a solid body. such as the
planet venus, mas been In terposed between INN
anu tue border the sun and Al tnat Iustans Is
apparent contact. The temperance OF these
bright lines on the SUMS iinD as the outer limb or
the planet draws upon the sun, announces the IN
slant when Venus has July entered upon the SUMS
DISK. similar pnencmeua, IN reverse order, Will
occur at the time OF the egress contact several
difficulties ODtrude themselves Tor the accurate
determination oil the FIRST ingress contact, espe-
caily that OF knowing exactly at what point on the
suns llInD the first contact occurs, although
the position can be computed with sufficient
curacv lor eye observations; but II will he essdyed,
nevertheless, and probably the reported ingenious
adjustable ring SIT devised by Mr.. Locxyer VIII
give satisfactory results, II we can Judge from the
tests to which IL has been submitted. At any rate
the observation Ui external contact at egress bv
this me nod Is very useful as supplementary 10 the
two internal contacts; ana by comparison OF the
tunes by the three means-astrOno,Llcd photo
graphic and spectroscOplc-we shall derive some
valuable uata by wnlcn TO uomolOgate the results
oil ali the observers. IL would have been well to
attempt this method in all the American parties;
but the Comm ssion did not place latin in us
success.
having given the means to be employed IN this
transit OF Venus to determine tile distance OF the
rom the sun, IL may not be Inappropriate TO