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Burt's Solar Compass

Solar Compass used to survey lands
in Wisconsin and surrounding areas
during the 1840s and 1850s.

(Museum object #1962.60.2,A)

In 1834, while surveying and subdividing the layout of thirteen townships in land that would one day become northern Wisconsin, government surveyor William Austin Burt of Michigan came to a key realization. High levels of iron ore in the region were disturbing Burt's magnetic compass and garbling readings from the earth's magnetic field, making it difficult to determine north-south survey lines. After a year of experimentation, Burt devised a solution to this problem by inventing a solar compass that did not depend on magnetic readings. It was an innovation that would soon become the standard for surveying in areas with high concentrations of iron ore all over the country. U.S. Army Colonel John Garvin Clark used the compass featured here to survey land in what is known today as Wisconsin, Minnesota, Iowa, and Missouri during the 1840s and 1850s, including the establishment of the Iowa-Missouri line in 1852.

Made of brass, the solar compass used by Clark was built in the 1840s by William J. Young, an instrument maker from Philadelphia, Pennsylvania. Young knew Burt personally and actually built the initial patent model for him in 1835, before continuing to specialize in making the device throughout the mid-nineteenth century. Before envisioning the idea of the compass, Burt had established himself as a skilled craftsman and gentlemen. He held several prestigious positions in the Michigan Territory including postmaster, delegate to the Territorial Council, and Circuit Court Judge.

Aside from his invention of the solar compass, perhaps the most interesting of Burt's life accomplishments was his discovery of the Marquette iron range in Michigan's Upper Peninsula in 1844. After receiving word that a magnetic compass needle was spinning unusually violently, Burt and his company searched the area and discovered that the landscape was rich with deposits of iron. Ironically, this discovery was based on readings from a magnetic compass, not from Burt's own solar compass.

Burt valued his duties as surveyor and considered the profession as a precondition to frontier settlement. Early in his career, he had also worked as a surveyor in New York State before moving to work in Michigan in 1824. From the Upper Peninsula of Michigan down to the northern part of what is today Wisconsin, surveyors quickly discovered the Midwest to be a difficult landscape to plot. In addition to magnetic disturbances, surveyors in the wilderness had to brave swamps, rugged terrain, mosquitoes, and other challenges.

The magnetic north pole is a region of the earth's surface where the earth's magnetic field is most intense. It is close to, but not the same as, the geographic North Pole. The difference - or declination - between magnetic and true north varies from year to year and with location, time of day, and season. For most purposes between the mid 17th and mid 19th centuries, these declinations were not critical. As standards of accuracy improved, however, the weaknesses of magnetic compasses became more problematic. Besides natural magnetic fluctuations, compasses could be deflected by nearby iron pins or chains, the surveyor's buttons or belt buckles, electrical storms or, as Burt discovered, deposits of iron ore. The solar compass, which fixed the location of true north through astronomical observations rather than magnetism, not only allowed surveying to progress through iron-bearing regions, but its greater accuracy soon made it standard equipment for all federal surveys as well.

[Source: Brown, Alan S., "William A. Burt and the Upper Peninsula" (Michigan History, May/June 1980) online at; Smithsonian Institution National Museum of American History online content about the solar compass at Physical Sciences Collection - Surveying and Geodesy; "William Austin Burt" online content at (printed copy in Museum accession file 1962.60).]


Posted on March 08, 2007

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