In researching older property deeds you will encounter strange measurement terms such as Chain, Perch, Rod, pole and furlong. These are based on a Gunter Chain which is a surveyor’s tool named after Edmund Gunter who in 1620 described it. It is an actual chain that is made up of 100 links and the total length is 66 feet. The links are 7.92 inches long. From this we have a quarter chain equals 1 rod (16.5 ft) also 1 pole and 1 perch, 10 chains (660 ft) equals a furlong, 80 chains equal one mile (5280 ft) 10 square chains equal one acre. It is interesting that road right-of-ways and railroad right-a-ways are sometimes 66 feet or one chain in width.
In 1763-67 Charles
Mason and Jeremiah Dixon surveyed and marked most of the boundaries between
Maryland, Pennsylvania and the Three Lower Counties that became Delaware. Mason had brought along state-of-the-art
equipment for the survey. This included a “transit and equal altitude
instrument,” a telescope with cross-hairs, mounted with precision adjustment
screws, to sight exact horizontal points using a mounted spirit level, and also
to determine true north by tracking stars to their maximum heights in the sky
where they crossed the meridian. Mason
and Dixon also brought a Hadley quadrant, used to measure angular distances;
high-quality survey telescopes; 66-foot long Gunter chains along with a
precision brass measure to calibrate the chain lengths; and wood measuring rods
or “levels” to measure level distances across sloping ground. A large wooden
chest contained a collection of star almanacs, seven-figure logarithm tables,
trigonometric tables and other reference materials; Mason was skilled at
spherical trigonometry. Mason had
acquired a precision clock so that the local times of predicted astronomical
events could be compared against published Greenwich times. Each one-minute
local time difference implies a 15-second longitude difference.
They started out with a team of five people but by the time they
got to the end of the survey they grown to 115 people. A classic outcome of having a government
contract. Included in the team were
axmen to clear a line of sight, pack mule drivers to get the trees out of the
way as well as cows for milk, chain carriers, instrument bearers and tent
bearers. It was like a small army moving through the woods. They didn’t travel light.
Mason described their journey to Middle Point in their Journal:
"1764 June 18 The waggons set out from Newcastle.
19 Joined the waggons and arrived at Dover at night.
20 At Esquire White's. 21 At Mr. Brown's.
22 At the River Nanticoke; pitched our Tents on its Banks.
23 Engaged axmen, etc. The whole company including Steward, Tent
keepers, Cooks, Chain carriers, etc. amounting to 39. Two Waggons, Eight
Horses, etc.
24 (Sunday) 25 Crossed the River Nanticoke in canoes and went to
Middle Point, fixed up the Transit instrument and began to produce an arch of a
Great Circle in the direction last run."
So in 1764 at the end of June Mason and Dixon were in the Delmar
area. They would return to the area in
September to make adjustments to their line.
Measuring with the
Gunter chain and levels they had a team of axmen clear a line of sight about nine
yards wide the entire way. The open view
and clear skies were necessary for astronomical observations, a key component
of the survey work. The team would walk
the boundaries and identify current property owners and significant
landmarks—often trees or streams. With the chainmen, the surveyor would then
identify the starting and ending points of a particular line. The two chain
carriers would take hold of either end while the surveyor used a compass or
theodolite to mark the distance along a particular line of latitude. As they
moved along, the leader marked the ground with an “arrow,” or metal pin, and
the follower walked in that direction. Upon reaching the leader, the follower
picked up the “arrow” and replaced it with a wooden stave. Together, they would
determine if their line was straight, and if not, with the help of the
surveyor, they would adjust it before moving forward. When the leader was less
than one chain’s length away from the final point, the chain carriers would
stop and count the links between the last stave and the final station to
determine the exact measurement.
The 1751 Transpeninsular
line that runs from Fenwick Island to slightly west of Delmar required the same
effort. A farmer however that just want
his land surveyed would have a
lot less workers but
most of the same technique would be employed.
No comments:
Post a Comment