New-York tribune., 1878-04-27
ACADEMY OF SCIENCES.
urAsIrpIvc THE SIMS DISTANCE.

IN MEASURING THE SIZED VI
CHEMICAL ELEMENT.
irRoM A srAPF CORRESPONDENT OF THE TRIBUSEJ
WASHINGTON, April 22.-There were so
many excellent essays presented at the meeting last
week. that space could be found at that time to do
Justice 10 all Of them IN this correspondence The dis
cussOns and essays respecting the means OF ascertain
ing the suns paalax with precision are OF special In
teres in view OF the fact that astronomers are think
ing Of abandoning observations on future translts OF
Venus.
MEASURING THE SUNS DISTANCE.
Professor H. f. Peters delivered an interesting es-
say, entitled Remarks the Value Of the Result OBJ
tanned for the Solar Paraax from the English Tee-
scopc Observations" Professor Peters began by giving
q rapid review Of the various values obtained for the
solar paralax since Haey's method was put In prac-
ce the defects and merits Of these calculations were
also briefly alluded TO- The estimate obtained by Pro-
fessor Newcomb from consideration OF all the values
from different methods spoken of with Approval 1t
gives the probable figures s"sis, with plus or
minus error OF O".013. CGhis is in miles, FOR the
suns distance 92.3S 900 miles. with the provso
that ii may be much 025l70O0 or as little rs o.
245,GOO) sir George b. Airy, tho Astronomer Royal.
has recently promulgated his results obtained from
sIdy OF the British telescope observations made at the
last transit OF Venus lie dcduces parallax Of s"7G
This extraordinary result. which would carry us back
toward estimates that have been largely discarded by
astronomers has yced general surprise. Nt is equiv
acnt to a distance of 033l0O00 miles) The Astronomer
Royals method of reaching this conclusion was cllbor
atcly reviewed by Professor Peters, and 1t was
SHOWN TO lie dependent upon II peculiar selection
OF phases which regarded as OF equal value. But
these phases had each been reduced separately, the
probable error in te different results would have been
than It s in combining them; but some Of the
results would have been nearly similar to The estimate
adopted by Professor Ncwcomb. In short. II may be
properly stated that the British elescOpc observations
have really given no data Tor the plrauX. They
are not ncomp pitibc VITA previous estimates hut they
prove nothing either way. Undue weight has been
given BY Professor Airy 10 minor and very imperfect OBJ
servatOEs. Some curious Instances were given One Of
the observers Lad written Professor Peters We got
noihing;" yet the indefinite notes taken by
that observer incorporated into Professor Airy ca
culaiOns We mayas well admit that IN The present state
Of knowledge observations on contacts do n sup
ply with accurate data than have been already
attained. IL is quite possible that tie edge o tie sun
the outline OF varying figure; the circumference Of a
hall OF which portions may at any time b. expanded
or diminished. Photographs may bring greater ac-
curacy Of observaton but the phenomenon is itself OF
complicated character and nothing nearer than
have Il certain TO be obaiEcd by noting aud studying
the transits OF Venus.
REMARKABLE CoINCrDENCEs ~ ESTIMATES.
An exceedingly interesting discussion followed. Pro
fessOr Davidson pointed Uut other sources OF error In
the calculations OF the Astronomer Royal. Professor
Newcolnb said that extraordinary fatality had at
tended all determinations Of tho pardllax. Hansen,
after framing elabuIate tables Of the moons motion.
dcduced ticrefrom value for This constant Of '96.
Ic Verrier from an elaborate computation Of an entcy
different kind, and taking the equatorial bulge OF the
earth into cbCf considerations obtained value Of 90.
This near agreement Of such distinguished mathcmatl
clans might have been accepted as conclusive hut II was
afterwards found that there III Le vcrricrs
.. a
be s"s5 while modern observations on the moon
showed the uracy Of anscus tables aud stones cor
rcctious applied them brought down the estimate by
that theory %, while errors yet remained In them,
though the dispute about them had almost become an
international question Professor Ncwcomb gave rea-
sons for thinking that SIS might he the figure ultt-
Inatey adopted. Uhis would make the distance 92Oie,
600 mles Professor Young stated that lie had Just re-
cevcd information which he believed entirely new
in this country; that Mr. stone taking the data
Professor Airy had used has arrived az value OF
So precisely he Professor EecoonL hdd jaSt
dssigHcd. This announcement created marked scnSa-
tion among the academicinns, aud was followed
y round Of applause. Professor Young also confirmed
the statement Of Professor Peters that the outline
OF the SUMS disk IL varying factor, having himself no
ccd a change In II while under observation, aud IN one
instance making careful note OF difference III the coi-
vcxity Of portion, determined 10y using the wire Of his
Ell ,e rhc "buup that Was there shown the outline
OF the sun not lees ihnn 1000 miles high Professor
Langley testified TO similar stat" OF tnings, an he
equally d-trusIed asutcmeuts that depended on the
assumption that the outline Of the sun l. uniform aud
unchanEng.
THE MEASURE or THE VELOCITY OF LIGHT
THERE'S strong probability that Professor Newcomb'-
suggestion will carry weight To substitute more trust
worthy determination Of the speed Of lt for cSpcn-
sive transit observations in order to obtain the suns
parallax A this subject is likely 20 enlist wide Gttcn-
ton the following portions OF the report OF Professor
tf. f. -
intcfeet rhey were omitted from a previous r'tef)
He mad mentioned some Ol tdc Onsiarcs thEt must be
~ order TO secure accurate results iiOi the
great difficulty is with the revolving mirror which
create vortex OF ar, avoid which the mirror must
be in vacuum, and OF course ihcos"d ia box win
Meeting from both its back and front. Eu the ccnri
mgal force may disort the mirror when rapidly fe'oN
ing and there are many minor obstacles III mdnHSiE
such revolution In yacuO. II the material be too light,
the mirror or its frame, or both may hy IA pieces III
ployed, the mirror be turnci by gai-
vanic circuit, but more elaborate inacHneIy si
duration OF each actual experiment need not bc over
two minutes. dhe amount ,Oi 0i IG."rn ~ ig Z VIII % ~
be nearly bright as the portion of the full moon That
could through slit of the same SIZE ~ that
used In the apparatus. Perhaps four five mirrors
might DE used Foundations and hNtlrcs WIIl
need to he very firm. In preliminary experiment no
difficulty was found in obtaining return ray at the
window from which the lisht was sent To the distance
mentioned
Professor Stephen Alexander, in commenting upon
the foregoing plan, mentioned that he had estimated the
difference between the velocity OF light space and In
the atmosphere NJ 3,0JOth. Professor Pickering
discussed the uncertain element which might be
introduced If springs were used In the apparatus
to check or regulate the velocity The change
OF shape in the mirror by centrifugal motion
also consdc red. Professor Peters inclined to think
that the alteration OF light will need TO be fully
determined before the proposed method can supcrsedc
the necessity of transit OF Venus observations The
tHA nfnt a
alteration was discussed between Professors Peters and
kcWcOmh the latter telling curious facts To the
uncertainty Of D'AlembertS method, and pressing
preference for Strives. Professor Langley thought
that the measurement Of velocity could be attained
through the use of electric light which flashed
every four seconds ne had been giving some attention.
10 tile subject Professor Young asked how the IncO
sure OF the rapidly resolving mirror could be kept
liz VII would be leakage arnnnd the