The sun., 1898-12-25
BIG ARC ACROSS DELAWARE
Coast Survey Which is Measur.
ing the Earth Began at
Cape May.
ACCURATE FIGURE OF EARTH


Hence to California the Arc
Was Traced in Feet
and Inches.
A gigantic arc commencing at Cap,
May, intersecting Delaware in the lowel
part of Sussex county, and stretching
across this continent due west to Cali
fornia has just been accurately measured
by the Coast and Geodetic Survey in ar
effort to ascertain the true shape of the
globe.
From these valuable measurements q
corps of skilled mathenaticians will
shortly determine for the first time,
with any degree of accuracy, the figure
and size of the earth. 1t will soon be
known just how large a mass The earth
is and whether it is, in truth, fattened
at the poles.
The great arc now completed extends
from Cape May, intersecting parts OF
New Jersey, Delaware, Maryland, Vir-
ginia, West Virginia, Ohio, Indiana,
Illinois, Missouri, Kansas, Colorado,
Utah, Nevada and California, merely
touching the northernmost corner of the
District OF Columbia. The work was be-
gun at the two ends of the line and the
worked toward each other.
A few weeks ago they closed the gap
between them, the last stone being
placed in the earth in Colorado. The arc
was found to be 1925 statute miles in
length. The actual area covered by the
transcontinental chain of network OF tri-
angles. for the marking off OF which the
surveyors have spent % years, does not
cover the line OF the parallel at every
point. In some places, where obstruc-
lions occurred, it was run alongside,
which method gave accurate results
The great arc has also been measured
astronomically; that is to say, in degrees
of longitude. There is, of course, an
agreement between longitude and time,
;he one being readily estimated from the
'ther, since the 800 degrees comprising
! circle around the earth equals "a hours
II time. Hence the number of degrees
which the arc measures could be readily
earned by comparing clocks along the
inc. Consequently 35 c.ronometers
we're put in place at various points and
by telegraph.
Accuracy was carried to such a fine
,oint in this longitude measurement that
wen the time required for a telegraphic
lash to skip across the continent between
he stations was taken into consideration.
The arc was found to be 4S4 degrees
ong.
These measurements, considered in
onnection with the great arc newly sur
eyed, will, when simple formula is
pplied, give the distance from either
nd to the centre OF the earth. The angle
Which would be formed at the centre of
he great sphere by two lines, one from
he Cape May and the other from the
'alifornia end of the arc, is of the same
umber of degrees as the arc is long.
'ow, anyone conversant with trigonom-
try can find the radius of a sphere when
he angle to the length OF the arc are thus
wen.
The most trying work connected with
,e triangulation for the great arc was
lcountepd in Illinois and Indiana,
here the country is so fiat that the
lrvature OF the earth prevents long. dis.
nee signalling. To overcome this giant
ipods, sometimes 100 feet high, were
rried about and erected at each sta.
IN. These supported the instruments,
1t the surveyors stood upon inclosing ,
ames, like windmill towers, built
'out but not touching the giant tripods
lree hundred and eight stations OF all
nds were established throughout the
tire trans-continental work, each of +
lich is indicated by q permanent :
ark. !
In the mountains a copper bolt, loaded
TO the solid rock, was left, while in
e plains or elsewhere, when possible, a
urface stone is always accompanied by o
other buried beneath it. All such >
mes have copper bolts loaded into
I'm, and sometimes go wedged that -
~ secure themselves more and more
htly as an effort is made to extract
I'm. There are some people mean
ough to dig for these stones in order
get the copper, but nature has effaced
re of the surveys marks than has hui .
nifty. The original stones laid near F
} coast OF Cape May have already been A
ioured by the waves. M
Is soon as the leveling accompanying M
8 work is entirely completed we will G
We some figures as to the relative D
ghts of the Atlantic and Pacific Z
cans. Some claim that the Pacific P
l. be found higher than the other. In j,
t, this is a question much mooted by H
entitic men. If difference in the j.
ghts are found the survey can tell "
h reasonable accuracy whether the D
is due to errors in leveling or j,
ether too great to be explained in Js
t way. W
.eveling done by the survey across D
rida some time ago, and repeated Je
ee different times, indicated that the CT
II of Mexico was foot higher than l..
Atlantic, and it is still an open ques- f,
whether this is really true at these W
nts, or whether the same error was A.
eated thrice by the carefully-manipu- o.
d instruments. w
his tremendous feat OF surveying Just Sa
shed is the most extensive and valu- P.
, contribution toward the solutions of Gt