The Wichita daily eagle. [volume] (Wichita, Kan.) 1890-1906, 1897-09-14

portion TO its actual size that two straight,
lines passing from the eye 20 the opposite
sides Of the disk may be said 20 be prac-
tically parallel. The perfection OF the
visual figure here noted constitutes one
OF the most wonderful. as il is valuable,
results Of successive Improvements IN
the art Of telescope construction. The
writer has seen more than one telescope
of the older makes that gave an image
Of bright star OF such irreglar outline
that it might not be unfairly be compar-
ed to a spadeful Of soft mortar thrown
70 .he sidewalk from height Of several
feet. OF course such an instrument as
that would not be tolerated today except
as curiosity, but even now there are
many in use in the observatory which
are far from perfect in this particular.
ACCURATE MEASUREMENTS.
A very large part Of the work done
with the equatorial telescope, that be-
ing the class 10 which the forty-inch in
strument beIonsg, consists in measurin
apparent distances and angular positions
between two or more objects that are
nearly in the same line Of sight. That
is, they seem 10 be very near each other
farther away than the other, and 1t is for
the telescope TO furnish Us with the
means Of determining whether the near
ness is actual or only seeming. Owing
TO poor definition, and imperfection in
the measuring apparatus used-some-
times one Of these and sometimes all
three-the results obtained not only by
different observers with different instru-
ments but by the one observer with the
same instrument, often differ so widely
that but little value can be attached to
the result deduced from comparison OF
all the measures. So difficult is this class
Of work that astronomers have been OBJ
serving and measuring for many years
the parallaxes-that is. the changes in the
apparent positions Of stars due TO change
Of place Of the earth from one side of its
orbit TO the other-they only know ap-
proximately the distances Of about ten
of the uncounted millions that deck the
armament (only few thousand Of which
can be seen with the unaided eye), and
have guessed at the distances Of perha ps
fifty others. In hardly any one case can
it be truely said that the distance is
known to within less than ten per cent,
and in some instances the comparisons
indicate a negative parallax," which
owuld mean that the star is at more than
an infinite distance if it did not mean
an absurdity. OF course such a dilemma
would not be encountered by scientific
workers IL 1t were not that the differ
ences of angular measurement involved
are exceedingly small. How many they
are may be inferred from the statement
that probably not more than ten stars
have paralaxes exceeding a tenth part
Of setond Of arc in each case, and in
the great majority OF instances the par
ajax Is far less than that. The angle nam
edmay be represented by the breadth Of a
disk one foot in diameter placed at dis
lance OF 400 miles. The angle formed by
two straight lines meeting az q point and
separated by a single foot a. the distance
OF 400 miles from the junction is but a
very small fraction more than one-tenth
Of second.
VARIATIONS IN MEASURES.
Professor Barnard showed to the writer
the following results of a series OF six
angular measures made oneach Of the
dates noted for the distances Of the stars
known as Atlas and Pieione in the well
known group Of the Pleiades:
Aug. 27............. 80. ...300.65 seconds
Aug. 29............... go. 300.6o seconds
Sept. 2. ....... ... .... 300. Sc seconds
Sept 3...... ... 300. 70 seconds
Sept. 4.... 800. 800. ...3 800. 81 seconds
To those who know something Of the
| subject, and are able TO Judge the Stature
of Hercules by observing the size Of his
foot, this small array OF figures tells VOL
| umes, and the information conveyed is
almost startling. Here Is a degree Of IN
| ifo-mity never before attained, and espe-
cially wonderful considering the extent OF
| the arc me2 sured. II means not only
| that we may hope for vast improve
ment upon the work OF other observato tor
| lee. but may anticipate a supersading OF
| the results obtained by them in a very
| lagre field Of work with the telescope.
| with the cutting down Of probable error
| 70 very small fraction, instead OF hav-
| ing il sometimes exceed ne total guam
| tity involved, as is the case now. The
term probabls error means the unce--
| tainty which attaches % the given value
| of a quantity. and Is function OF the
! by computing from different sets OF OBJ
servations which do no: agree. And the
! actual uncertainty often IS far greater
! than that claimed by the persons stat
| ing II. this for the reason that he does
not take into the account all the work
! that some others may deem valuable.
/ For instance, Harkness. the presen. sup
/ erintendenc OF The American Nautical
/ Almanac, gives the constan: OF Mutation
as 9-22 seconds. with probable error OF
! less than OF second. while his pre1eces-
scr, Newcomb. gives The constant as 9 2I
seconds, these being la,e results in each
/ case. and both determinations made from
considering a vast mass OF material Two
resent determinations OF the diameter %
/ TIE planet Jupiter differ by jabou: one-
six,ieth part OF the :ocai. ana numerous
! other instances might De cited in which
| god authority gives wide margins % IN
! certainty in regard 20 numerical values.
BASIS FOR COMPUTATION.
I: looks now as II very large part &c
/ this uncertainty Is - be done away with
/ n the near future by the adoption % ne
| measures made with the great Ye-kes
/ equa ;or.aI as the bass of couputa ions
I Of parallax Q. stars, distances and posi-
I tiors % componen;s OF binary sys-eTa.,
and angular diarse.e-s ot planets ana
/ lur,ins-ies. 20 say nothing Of re nsw de-
partu-e OF finding ne paraIlsx ct nsbuia.
I o. The IA more precise results ila- fairly
may Re looked in Cor the work Tita ~
! spec;rc=co7e and IN the participating
s.a- feds and ether greater das-i7cnes.
% DEAN than Il attempted elsewhere
( ]: perhaps is not 100 much 20 exfect ma.
7 very much - he WORK done a. osTse-Tz-
& .o-.es will % -ea5e-ei comparatively