, 1875-06-15
Hoonp1o.

mathematics 10 soe that II wn can obtain Tho
value Of tho angular displacement l,ore TO with
tain tho distance Of tho sun from tho earth to
within 100. 700 miloa of tho truth, which is not
lnore tllan half tho limit Ut probable orror ot-
snding tho comparison Of the observations OF
Vct,us aud tho sun. IA tho varying distance Of
tho planet from tue star can be measured with
tho uicromator pk short intotvala during groat
pnrt' Of tho night, 1t tho woathcr 10 tlnc, from
liked obHeryntorias furnfated with ilrst-onss iu-
proper r combination OF all tho on}crYod angular
tiietan OH will give tho tsno valno to wthin tho
above named quantity.
.upourAscE og TIE PHENOMENON.
Tho pin not MA,s hAs bceu observed ut prev!ous
opposisftns for tho ptlrnose OF indng Ills raral-
lax and tito observations mnda thirtaon yeara
ago enAbhet astronomers to d8clde that tue did,
ta,lco Of tho sun. ~ calculated by Enckc, ~aa
thus month will present mems Tor ftding tho
dtstauco n,2te accurately tllau was posatblo
III 1862. THO reason 10 TINT tho star No. 8 tn
Sagittnrus, Mill furn!af fkcd roint Of light to
Which the ohs.,rvera 10 both hemtHpllercs Gun d.
rectly rotor tla position Of Mars. TAcy will thus
ret til of Boyer.t clements OF uncertainty Wlllol,
attend obsoryatit,l's nada With the meridian or.
clio. for. the doATlnination Of a1titudc, and
thence fnaing til q destination: Among these
NO mar me,tl Oh probable Irregularities
in refraction At dl nicni at,tudos; the difference
OF reirnctlon for $40 points very nqaf caotl
other boing susceptible Of much moro accurate
other point: Thsu there ARC oscillations OK tho
oartla'H crust, ulch CO uSo minute doha9sipns Ok
tho instruments from stse mcan position, the OK
tent Of which can nev e.: bo accurately known,
| mixud tip with orrors in tho graduation OF
| tho circles md IN tho reading Of tho arcs.
Tho oscillation Of l.hu instrument belng
tho SAME at ati atationa FOR the planet nnd tor
tho star, Its extent will ona1eo no error III tho
| measure Of tho angular tlh5tance between, the
| two. hut there iB anothoy most important ad-
vantage Obsorvatons OF nltltudo, with tAs
meridian cilots Or trauait IN ai!imelt, cap ouy
bo mado during the fow aeco lhls III each twenty-
! four hours wien tho p@nnat Is very near TIC
| plano Of tbs meridian. But i,r using tue GrAnd
! Equatorial, tho dstanco Of the planet ftom the
star can bo measured to within tonth part OF
| second Of arc, gr0at many tasuoa during tho
one ngLt In whlch tho appulao occurH. We arc
tnua aDle 10 obtaiu meau OF loHu'ta which ~
comparatively FREQ from tho errprs tnctdoht to
M equal number Of obseryhtIonss g. sprcad over
| several nights, In the course or which minor
perturbatl0ns may occur OF which wo eau KNOW
nothing. BESIDES all tlte, tho astronomer can
| take rnUre precise measures OF the ApRuttr dis
tsnoo hotween two points with Tue mlor9meter
| obtain by the moaauEo OF alutldoa on tle de-
| ollnkton aiso1e, .-....-
Tho Chicago Astronomical II Society determined.
/ should 10 put 10 hrsL-c.ass working order, 10
thai tho Grand Equatorial telescope could bo uBetl
to tako thcBe moasntos In this city, for coDpari-
sou NTH thoso made ut other points. In order
to this, IL rms recogHary to rebuild tho dome.
wlic4 WAS complataly rotten, and to aco11ra lho
services Of tho makers OF tho Instrument to ro-
ndjust It's aeyera parts after soYcral years OF in-
glorious disuetudo. Of cosa1sc tho Observatory,
onco put in tr,n. will DO available Tor other
work after that IL accomplished. And there
IL plenty 10 bs done. Previous to- tho
Great Fire the transit instrument u
smaler telosconu) did good aoryiea in tho hAnds
Of Prof. Stafford, in helpiug to tlx tho precise
positions OF III the !ixpd stars OF creator than
the teut, ,psgnituda. But t4ere Ii host Of
other Important problcnla, 10 tho solution 81
which tho great telescope Ia peculiarly adapted,
whicI have boou lstt untouched IN thla city for
1ua,lY yeaIa. 1t will noH ba in order to taka tlom
up. Nothing moro ts wanted, than sufficient
endowment for the Observatory, to enable chi.
atelar zeeo4rcE, and vie With tho otias of Europe
ID the noat Bublune industry that can oncsgo
the attention Of uaortala.
Tho t,no IL I'D shost In proportion to tha az
tent Of renovation required, thst tho a4juat-
tnonts a1e not Jet conlplotal.. hut thsro IL
reason to hope that they nlll al have boon made
by tho 2gth instant II that hope DO fnlalletl,
aud the sk,ea bo proptlous, Chicago will take asi
problems oi tho nluotoontl, oentury. Even II
this b not possible thoro IL still the same grand
future opou 10 tho Observatory, Though t4o
initial labor may DO wanting. Wo need scarcely
add that no effort will bo npasot by those
charged with tho work to begin With &he pAonom-
onon Of tue 2otl. Instant, aud to. mako thst ~
earpest Of future Labor aud futuro snecoHs.
IL II SHOULD 10 borna N mind thAt tho Qbsosya-
Ftory ......... .......
WILL NOT NJ oYEa .,
to vieItors, nor oven to members OF tho Society,
on that evening. Therp will bo no tin1o 10 waste
| III explAnation, kud uothing to Reo Which capuot
/ 10 sean Just u well at anotter tlmo- The mem.
bera OF tho Society will have opportunities for
studying tho outlines OF tue seas aud continents
i'll tic plaues- Mars On subsequent evenings ant
/ lle changes Of position OF tho plalses With TO-
though not measured. Just IS we'll through al
OF vfa.gaaasss through 4lo Great E4uAtoriAl tato,
scope. We may add TINT tue nov lckasa q
,nel uherHhtp ,promiso tkat tho Observatory vii
ha pa,n to members and th0lr families on Tucs,
day ss4d YhusedAy evenings af.er July 1. IN Till
year.