The Washington union., 1858-02-20
A NEW DETERMINATION OF THE SOLAR PARAL-
LAX
u. S. NAVAL AsrrososrcAL EXPEDITION,


u. s. NAVAL ASTRONOMICAL EXPEDITION,
Washington, February IL, 1858.
SIR / have the honor to communicate to you tbs re-
suit of the observations specially made by the United
States naval astronomical expedition to determine the
solar paraax the suns distance from the earth
1t will be remembered by the department that DR. Ger
ling-an eminent gcometcr Of Germany suggested the
practicaby of determining this fundamental astronon
cal datum from observations Of Venus the inferior
conjunction instead of awaiting the phenomena Of
trasts of the planet tho sun disc that es
ton to the southern hemisphere proposed to the
department by myself for the purpose Of making these
observations which, in conncxion with similar obscrya
tons be made the Naval Observatory would test the
method and that the earnest commentators of the
measure by physicists, both in Europe and this coun-
try induced Congress to authorize the expedition bya
special grant in the appropriation bill approved Sd Au
gust 1S4s.
We were absent from The United States nearly three
and half years. and the observations constituting the
more immediate object Of the expedition extended through
parts of each of the years from November, 1s49 to Sep
tember, 1852, inclusive.
50 many classes of observations were embraced in the
plan of operations adopted by the department that our
small party was almost constantly occupied in olserva
tory duty proper and not possible to prepare any
the data for the final computations until after the re-
turn of the expedition to the United States. Then our
first efforts to put in proper form for the compue
all the observations of the planets Venus and Mars and
the stars with which they had been compared
Whilst our men of science had been unanimous in ad
vocating the organization Of an expedition because Of the
additional mass of important information certain 70 be
collected by it. there were who entertained opn
ion that the method of determining the paraax proposed
by Dr. Cerlng would not afford result reliable %
had been derived from the ransits of Venus in lI6l and
1863
For obvious reasons therefore, IL proper that the
discussion of the result from observations should be
intrustcd astronomer thoroughly competent to ap
prccatc the problem. yet wholly uncomted as to 'hs
comparative merits OF the two methods.
Under the sanction of the department, DR. B. A. Could
jr of Cambridge Massachusetts,, selected for the
purpose and the elaborate refinement with which he has
executed this difficult and delicate task IL ample proof
that the confidence of the department not misplaced
His report docs him great honor It will fill from $50 to
larger portions of it and all the remainder Of the volume
being already printed
The result obtained by him for the sss equatorial hor
sonol yraax is s'4950 or O"0762 'o than the value
commonly adopted and he concludes that we may ~
with advantage s" 5000 corresponding to distance
for that luminary of 9G, loo, 900 statute miles.
As the information is OF high interest to astronomers,
have the honor suggest that it may be made known
in advance of the publication of the volume
have the honor TO he your obedient servant
j. NJ GILIIss
Superintendent
Hon l. ToucgY,
Secretary of the Navy