The times. [volume] (Richmond, Va.) 1890-1903, 1893-11-05
THE MERIDIAN LINE.
onicia'ly and Core thy Established at
Rartou ffef1bs

haFto tietZhls
II will be OF interest to engineers and
surN eyors in this locality 10 know that
a meridian line has been lately estab-
lished by Messrs. James T. Redd & sons
at Barton Heights, near the city. II IS
a Nell-known fact that the magnetic
needle although generally supposed TO
point TO the north, does not indicate a
true rorth and south lire. 1t not only
varies greatly In different parts OF the
world. but at the same place II varies
slightly from year to year. so that a
given line shows different course to-day
from what IL did ten or twenty years
ago. This constant change Of direction
is called the Magnetic Variation" and
Il is obvious that every surveyor ought
10 knew or be able to ascertain its
amount at any time in order to make
surveys of different dates tally.
a State law requires that a meridian
line shall be esta blished I'm every county,
and ttat every surveyor shall test his
Instruments by the same once a year,
and ascertain the amount OF variation
for that year AS no line had ever been
established In Henrico county, the Board
OF Supervisors OF the county recently de-
termined 20 comply with the law. The
line just established, then, is the legal
and official meridian for HenricO county.
The method Of finding the meridian
line is attended with considerable diff
Guilty. 1t Is found by observations OF the
North Star and Of course has to be done at
night The chief difficulty lies I'm the
fact that the North Star itself Is not eX-
actly on the North Pole or prolongation
Of the earths axis. but revolves around
1t just as the stars OF the Great Bear and
other consultations do, only In a very
small circle. The star thus eliminates
or crosses the meridian twice in twenty
four hours and II the exact moment OF
its elimination were known and the
time-piece of the observer were correct,
an observation at that moment would
give the true meridian. But the star
rcvolves around the pole in twenty-three
hours and hfty-six minutes, SO that the
time Of it's elimination is constantly
changing, being four minutes earlier every
night. This, and the uncertainty Of time
pieces. render this plan yalueless for
obtaining exact results The observation
must be made, then, when the star is
at it's eastern or western elongation.
The instrument, transit or theordollte,
being firmly set and well levelled up.
is directed TO the star a short while
say half an hour-before the elonsation.
the time Of which can be approximately
determined by the position Of the Great
Bear; then as the star moves eastward
COR westward as the case may be) the
direction OF the instrument is changed
so as TO keep the vertical hair-line con-
tinually on the star. When the star
ceases 10 move away from the vertical
line. II has reached its elongation, and
will soon begin TO move in the opposite
direction. The line Of elongatlon as shown
by the instrument being now projected
on the earth's surface, simple calcula-
ton of angular distance Will give the
true north.
Messrs. Redd & Sons made two obser-
vations OF the star using well-adjusted
transit. The first was made about the
beginning Of October, catching the star
at its eastern elongation about o'clock
in the evening. The line thus found was
secured by means Of two hubs" stout
wooden blocks driven firmly into the
ground. About three weeks later they
made a second observation, when the
star was at it's western elongatiOn, about
$3.50 I'm the morning, the line being secured
I'm the same way as the first. The All
muth. or distance OF the star from the
pole, having been previously calculated
from data entirely Independent OF
the present observations and found
to be one degree and thirty-five minutes
for the latitude OF Richmond, the angle
between the lines OF elongation described
above was measured with the transit and
found TO be three degrees ana ten min
utes. exactly double the Azimuth angle
showing that both observations were abb
solutely correct. The remainder OF the
operation consisted In bsecting the angie
between the eastern and western elonga-
lions OF the North Star and planting a
substantial granite post firmly In the
ground at each end OF the line.
The line which measures 1913 IL feet
between the stones, is situated on Mil
Ter avenue Of Barton Heights, two
squares west Of the street car line on
North avenue where there will probably
never be any interference from railroad
tracks or strong electric currents. The
north stone, designated IN" is on the
west side OF the avenue near Wickham
street The south stone. marked IS" Is
on the east side OF the avenue at its inter
section with York street.
The needle had not been used at all
I'm the operations above described, but
after the line was fixed the needle
was set free with the instrument on the
meridian. and the variation found to be
three degrees and seventeen minutes
west-that is 10 say. the magnetic needle
al the present time, and In the vicinity
~ Richmond. indicates a line three degrees
and seventeen minutes TO the west or
the true north.
A Valuable Secret
INV friend" said the fiashily dress
- h. approached the unsODhiStl-