The New York herald., 1874-12-08

viii be ABOUT do not speak with authority. I
have not been IN consultation with them, and, IN
deed, hardly think there has been much consul
taton with regard to the reduction OF the observe
tions; but l think can make some suggestions
which will satisfactorily account for much OF the
delay.
1t must be remembered that in explaining the
principles OF the transit for the sake OF clearness
all disturbing elements were carefully eliminated
and left out OF view. Imaginary observers nave
been located at all conceivable places, from the
North Pole to the South Pole and even at the CEN
ire OF the eartn and centre OF the sun. The eartn
mas oeen Imagined TO stop its rotation upon It's
AXIS. Astronomers have been expected TO meas
ure oy two-ioot rule the distance OF the several
stations, as seen from the or the sun, upon
line drawn through the centre OF the EARTH As 70
sucn silght performances inducing clocks 10 keep
absolutely perfect time, Inducing observers to re-
coro Win absolute precision phenomena which
they may imperiectly see, ana inducing Venus her
self to take the position and to walk the precise
track marked out for her by the ..Nautical Alma
nac," they were, OF course, not worth mentioning
But when our American observers come homo
with their ngures and their photographs they Will
have far different problem to deal with. They
must determine the longttute OF the different STA.
tions and reduce all their observations to Wash.
inRton time. They must determine the effect OF
servation and make allowance for It. as well az for
the several positions They must apply correc.
tons for personal equation OF observers for errors
OF di1erenL instruments OF observattR and for the
error OF the dinerent clocks and chronometers.
In some OF the observations, such as the measure.
ment OF the distance OF the centre OF Venus from
the centre OF the sun, at low altitude the diner-
ence OF rciractlon must be allowed Tor. Tne
photographs must be measured and reduced to
the form OF figures. Alter these and other
preliminary corrections have been applied
the observations themselves must determine
the error OF the Nautical Almanac posi-.
ton OF Venus, the error OF its motion
in right ascension and in declination and the
OF Its apparent diameter, and, II not otherwise
determined, also the corresponding errors OF tho
SUMS place, motion and diameter. These c0rreo-
will be combined with the effect OF the diner
ence OF parallax Of Venus and the sun, while tho
latter will affect each observation differently.
After eliminating oil possible sources OF error
there Will remain especially those depending upon
the positions OF Venus and upon the parallax, and
all these undetermined quantities must be reduced
to equations of condition, the coeficicnts OF which
must be determined for each separate observation.
Then by the method OF least squares these equa-
tions OF condition must pe solved, giving the best
representation possible OF the observations. But
these results VIII only be provisional. The
astronomers OF other countries will, presume
independently to great extent, pursue similar
course and each will arrive at provisional results
from their own observations.
Upon comparison OF the results reached BY
different nations there win be found discrepancies
In all the elements. Then will come the last great
work. combining all. New values Of oil the IN.
determined quantities will be selected, guided by
the several results, and with those values the
III TINA Of non Oha ftOD will ho
puted and compared with the observed time. All
the observations Of all nations will be reduced
either singly or In groups, TO symmetrical
form, for the nnal equations VI condition, to
eliminate, as far as possible. the remaining dis
crepancies between computation and ODserva-
ton. 1t Is not until these final equations OF con.
diton shall have been solved by the method Of
least squares that the final determination can be
said to have been reached.
Whether the general plan which have roughly
outlined shall be followed or widely different
plan there Is royal road py which the LABOR can
be saved and l think 1t viii be found that
/ have undcrrated rather than exaggerated
the difficulties We may hope in few
months to know whether the observations
OF the transit Will sustain the modern de-
termination OF the SUMS distance ninety-two
millions or miles, or the former determination,
ninety.nve millions; although, after the rediscus
sion OF the observations OF 1789 the latter seems
hardly possible. Should the observations every.
where be successful. little would seem to be LETT
Tor the next transit bur 1t Is by no means certain
that the experience in these observations may
develop new methods, SO that. eagerly As the
transit Of tomorrow has been anticipated 1t may
be tnat astronomers, the world over. Will, with
unabated interest and zeal, look forward to the
transit Of December 9. 1882.
HENRY N. PARKHURST.
NEW YORK, Dec. Z, 1874.