Today, we measure America. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
created them.
In 1807 Thomas Jefferson put
a Swiss engineer named Ferdinand Hassler in charge
of a new government agency. It was the Coast
Survey, later called the U.S. Coast and Geodetic
Survey. When I did road surveying 150 years later,
we called it the "USGS," and we did so with a
certain awe. We normally measured 100 feet within
1/8 of an inch. From the start, the "USGS" refined
measurements to ten times that accuracy.
Jefferson charged Hassler with staking out our new
country as accurately as anyone could. For 35
years, Hassler did just that. He began by placing
two benchmarks, one in western Connecticut and the
other in eastern New York. Then he worked away from
these markers, up to Maine, and down toward
Florida. Every two kilometers, he set a stone
monument that located a position and an elevation.
He worked with maddening care. He spent 45 days
running one eight-mile base line on Fire Island. He
got only as far as southern New Jersey during his
lifetime. But the work has gone on ever since.
Today you're never more than a few miles from a
small bronze marker, embedded in stone or concrete,
with a warning that you'll be fined if you disturb
it. One sits on top of Mt. Whitney, giving its
elevation as 14,494.777 feet, give or take a few
thousands of an inch.
The vision of Jefferson and Hassler is reflected
today in a great spider web of 500,000 benchmarks.
The whole system refers to one primary marker on a
ranch in Kansas, near the center of America. The
precision of the network takes account of
variations in gravity and changes in the earth's
curvature.
The system is nearly invisible until you face a
problem of making ends meet in the middle. We need
such precision when we build a railway, highway,
bridge, pipeline, or communications system. And woe
betide the surveyor who doesn't tie his
measurements to this fine network.
Pennsylvania highway department engineers used
their own benchmarks for a bridge in 1969. They
built outward from either side and learned how
imperfect their markers were only when the two
halves missed each other by 4 feet. The New Jersey
turnpike is marred by corrective S-curves, because
the various stretches of highway were tied to
inferior benchmarks.
The "USGS" system was begun with the same old
telescopic transits and levels that I still used
when I was young. Now they're very nearly museum
pieces, and I'm left to wonder: How could Jefferson
have seen it all coming? How could he and Hassler
have known? What trick of vision ever let them see
so far?
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Wilford, J.N., A Continent Beneath the Ice. The
Mapmakers. New York, Vintage Books, Random
House, 1982, Chapter 20.
I am grateful to Albert E. Theberge, Jr., Librarian
with the National Oceanographic and Atmospheric
Administration (NOAA), for providing the following web
sites that recount the dramatic history of NOAA,
and its various earlier incarnations (which include
the Coast Survey and the USGS). He points out that
it was actually the United States Coast and Geodetic Survey
that placed the markers we sought out during my old road surveying days.
http://www.history.noaa.gov/
http://www.photolib.noaa.gov/
http://www.photolib.noaa.gov/historic/c&gs/
http://www.lib.noaa.gov/edocs/CONTENTS.htm
From the 1832 Edinburgh Encyclopaedia
Early-19th-century surveyor's transit
The Engines of Our Ingenuity is
Copyright © 1988-2004 by John H.
Lienhard.
