Dartmouth Engineer - The Magazine of Thayer School of EngineeringDartmouth Engineer - The Magazine of Thayer School of Engineering

Invisible Hands of Science

Historic instruments bring engineering’s past alive.

By Matthew Forman ’11
Photographs by John Sherman

When Thayer School of Civil Engineering was founded in 1867, surveying was a key component of the skills Thayer students were required to master. In fact, surveying was so crucial to the establishment of property boundaries, the westward expansion of the nation, and the development of railroads, canals, bridges, and other infrastructures of commerce that until the 1880s all Dartmouth students — not just engineers — studied the subject. And though Thayer School broadened its focus beyond civil engineering — and dropped the term from its name in 1941 — Thayer students continued to study surveying until 1962.

Thayer students

Many of the surveying instruments used by Thayer students during the 19th and early 20th centuries now reside in Dartmouth’s Scientific Instruments Collection. Assembled by the late Dartmouth physics professor Allen King, the collection, housed in the physics department in Wilder Hall, is one of the largest in North America. It is now curated by history professor Richard Kremer, who regularly brings the instruments into his history of science classes for students to examine and research.

Thayer School

“Using the collection is a new way in the history of science to go beyond texts,” he says. “Knowledge is being produced with these objects. They’re the ‘invisible hands of science.’ ”

The following is a close-up look at tools Thayer students used in the school’s early decades.

This circular slide rule, 3 inches in diameter, belonged to Professor Robert Fletcher, Thayer School’s first director. It was made by J. Halden & Co. of Manchester, England, in the early 1900s.

Halden Calculex

Consisting of a telescope and bubble level, the Wye level was a basic tool for measuring elevation. In an early topography exercise, Thayer students used Wye levels to determine the contours of Bridge Street in West Lebanon. William J. Young of Philadelphia, Pa., one of the most prolific American instrument makers in the 19th century, constructed this level. It cost about $150 in the 1860s.

Wye level

Dip circles, also known as dip needles or inclinometers, measure slope — a.k.a. “dip angle” — with respect to gravity. Used in surveying, mining, and prospecting, dip circles also served as demonstration instruments in physics classes. The Phelps & Gurley Co. of Troy, N.Y., manufactured this brass and glass dip circle around 1848. Dartmouth purchased it in 1862 for $20.

Dip circle

In the 19th century, as now, engineering students were expected to execute complex calculations with ease. They could increase their speed and accuracy with the Thacher calculator. Placing the logarithmic scale on a drum and series of crosspieces, the Thacher functioned like an 18-meter slide rule for calculations up to five significant digits. Inventor Edwin Thacher patented it in 1881. This one was manufactured by Keuffel & Esser of New York around 1887.

Thacher's calculating machine

Students used the optical square for sighting along two lines at right angles. This optical square was made around 1885 by a local instrument maker, J.N. Brown, whose shop was located just off Main Street in Hanover.

Optical square

The sextant was designed to determine the angle between the moon and stars to calculate longitude at sea. On land, surveyors used sextants to determine angles between fixed locations. In an early class, Thayer students used sextants to measure angles for triangulating the height of a local church spire. This sextant, manufactured by Blunt & Nichols of New York, dates from between 1866 and 1868.


Measuring horizontal and vertical angles, transits were integral to surveying. As a culminating project in the September 1869 course on surveying and engineering, Thayer students had to use triangulation to calculate the distance from the Dartmouth Green to Mount Ascutney in Vermont. They used transits to obtain the angles they needed for the calculation. This transit was manufactured by William J. Young of Philadelphia, Pa., in the mid 19th century.


Categories: Features

Tags: curriculum, faculty, history, patent, students

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