Burt's solar compass

The solar compass works on the principle that the direction to the Sun at a specified time can be calculated if the position of the observer on the surface of the Earth is known, to a similar precision.

These angles are set on the compass for a chosen time of day, the compass base is set up level using the spirit levels provided, and then the sights are aligned with the Sun at the specified time, so the image of the Sun is projected onto the cross grating target.

[1] Burt became a United States deputy surveyor in 1833 and began surveying government land for a territory northwest of the Ohio River.

[4] It overcame the vagaries of the surveyor's compass caused by interference from iron ore deposits in a local land mass district.

[6] He found large outcropping deposits of iron ore at Negaunee in Marquette County in his later 1844 survey of the upper peninsula of the state of Michigan.

[8] His crew found small deposits of iron ore in the state's lower peninsula at about the same time.

[11] Burt's solar compass uses the location of the Sun with astronomical tables and enables surveyors to run more accurate lines, saving them much time.

[13] They examined its characteristics and then awarded Burt twenty dollars in gold and the John Scott Medal for its technology.

[16] Burt in 1849 went to Washington with his son to apply for a renewal of his solar compass original patent of 1835 that was about to expire.

It was then found to be superior in general to the common compass, even when local iron ore deposits were not a problem.

[18] Surveyors can locate true north by viewing the Sun or other astronomical objects like stars or the Moon, which have a direction from any given point on the surface of the Earth.

It can be calculated precisely for a given date and time, and is not influenced by local variations in the magnetic field due to local deposits of minerals such as iron ore. Burt's instrument allows surveyors to determine the true north direction in reference to the Sun rather than being influenced by the Earth's magnetic field.

An understanding of the latitudinal and seasonal declination and the longitudinal variation with time of day are necessary, as the compass has specific sub-assemblies to take each of these variables into account.

It varies predictably throughout the year, increasing and decreasing smoothly at a calculable rate, and is constant for everywhere on Earth at the same time.

[22][26] The operation is as follows: Burt improved the instrument over the years and it won awards from various organizations for its technology as being simple, rugged, inexpensive, reliable and accurate and was used by surveyors from the nineteenth into the twentieth century.

[11][29] He then received another medal for his simpler, more accurate version by jurors of Astronomical Instruments with a personal compliment by Albert Edward, Prince of Wales, on October 15, 1851, at Hyde Park, London, England.

[30] This instrument was invented to get away from the highly variable and unreliable readings given by the common compass of the day in a locality with a magnetic field anomaly caused by large iron ore deposits.

[31] Burt's instrument was used to survey 75 per cent of the public lands of the United States, consisting of nearly a billion acres.

[20] It had saved the government millions of dollars because of its general inexpensive price tag and the accuracy of the survey.