Burt's solar compass
Burt's solar compass is a surveying instrument that makes use of the sun's direction instead of magnetism. William Austin Burt invented his solar compass in 1835. It is a device which allows a person to find the north direction from the position of a shadow. The reason for this instrument was to get away from the erratic readings of a normal magnetized compass when in a local land territory of high iron ore content. The instrument was found to be so accurate that it was the choice of the United States government when surveying public lands, state boundaries, and railroad routes. It won awards from various organizations for its technology. It was used by surveyors from the nineteenth century into the twentieth century.
History of Burt compass
Burt became a United States deputy surveyor in 1833 and began surveying government land for a territory northwest of the Ohio River. He and his surveying crew by 1834 were surveying territory in the lower peninsula of Michigan. He was surveying land in the upper peninsula of Michigan by 1835 to be used by new settlers. Here he found that his sensitive magnetic needle compass was fluctuating all over the place. This was being caused by the iron ore deposits in the area. Burt then devised an instrument attachment that worked off sunlight, not magnetism, to find true north. He called the resulting product a True Meridian Finding instrument. It got away from the vagaries of the magnetic compass caused by iron ore deposits in a local land mass district.Burt first used the solar instrument in his Michigan surveys. He found large outcropping deposits of iron ore beds at Negaunee in Marquette County in his later 1844 survey of the upper peninsula of the state of Michigan. This would become known as the Marquette Iron Range. His crew found small deposits of iron ore in the state's lower peninsula at about the same time. Because of his accidental discovery of these iron deposits in Michigan he contributed much to America's Industrial Revolution. The Calumet and Hecla Mine of Michigan's Copper Country was the leading copper producer in the world and discovered with Burt's instrument.
Burt's solar compass uses the location of the sun with astronomical tables and enables surveyors to run more accurate lines, saving the surveyor much time. Burt had a model of his instrument built in 1835 by William James Young, a professional instrument maker. He then submitted this solar compass to a committee at the Franklin Institute in Philadelphia. They examined its characteristics and then awarded Burt twenty dollars in gold and the John Scott Medal for its technology. It was patented February 25, 1836. It has since been referred to as Burt's Solar Compass or Astronomical Compass. He used it in late 1836 to survey the Fifth Principal Meridian in Iowa. Burt improved on the instrument over the years and in 1840 he received another patent on his solar compass. He resubmitted the updated version of the instrument to the Franklin Institute where they found it to be more accurate and easier to use than the first version. Cincinnati Land Office general surveyor E. S. Haines examined Burt's surveying instrument in December of 1840 and reported in a 1841 letter that with its' four year experience in surveying it was found to be superior in technology to the normal magnetic compass then used by most surveyors. The Commissioner of the Federal Land Office sent letters to Surveyor Generals throughout the United States saying Burt's compass was being manufactured by the surveyor Henry Ware and available for purchase.
Renown surveyor Bela Hubbard noted in 1845 that with Burt's solar compass they could survey a straight line through iron rich country, where it would be an impossible task using the normal magnetic compass. The instrument was widely adopted for surveying land in the United States and from the mid nineteenth century until well into the twentieth century it was mandatory for government surveying. Its original impetus was for use where the old fashion magnetic style compass was vulnerable to large land iron deposits that made unusable readings. It was then found to be superior in general to the magnetic compass even when local iron ore deposits were not a problem. A solar compass attachment to the surveyor's transit, was still the recommended method to use for obtaining the true north direction as instructed in the 1973 surveyor's manual of the US Bureau of Land Management.
Burt's instrument invented in 1835 was used to survey 75 per cent of the public lands of the United States, consisting of nearly a billion acres. It had saved the government millions of dollars because of its general inexpensive price tag and the accuracy of the survey. It was vital in surveying mineral lands in many states including Michigan, Wisconsin, Minnesota, Arkansas, and Colorado. Its project expenditure to survey a section of land was only a fraction of what it used to cost before his invention. An example of comparison was the boundary line between Iowa and Minnesota that was surveyed before at $120 a mile with the use of the old fashion instruments, while with Burt's solar compass it was only $15 per mile.
Burt patented his solar compass innovation on February 25, 1836. He used it during two seasons, 1836–1837 and 1842–1843, surveying land in Iowa. When his solar compass original patent of 1835 was about to expire, he went to Washington with his son to apply for a renewal in 1849. The land commissioner committee, who consisted of senators from Michigan and other states, recognizing the value of Burt's solar compass in public land surveys, persuaded him to forego renewal and petition congress for suitable advance compensation. Burt did as was suggested to him on the faith he would get paid for his patent of such a valuable instrument. However the compensation indicated did not materialize in Burt's lifetime or at any time thereafter. Since there was no patent on Burt's solar compass after 1850, instrument makers manufactured and sold "Burt's solar compass" to surveyors as a commercial product. The inventor spent thousands of dollars to perfect his instrument, but only received back eighty dollars in compensation for his labors.
In the preface to his Key to Solar Compass and Surveyor's Companion published in 1858 by his associate William S. Young, Burt refers to the many requests for such a book on how to use his solar compass. He explains a magnetic compass had problems with the true meridian at different localities. It also had problems from day to day with different readings from that expected as a constant or from previous readings. It was determined that a magnetic compass used as a surveying tool was interfered many times from the local attraction of iron ore making it inaccurate. A much better guide for the surveyor than the magnetic needle compass was desired. Burt's diligent hard work, persistence and perseverance ultimately paid off in the invention of the Solar or Astronomical Compass.
Description of Burt's solar compass
Burt's instrument is made of brass and therefore has no magnetic characteristics.It was initially a small telescope solar attachment to a normal surveyor's magnetic compass instrument. The sun's image was projected onto a silver plate and used for bearings. The instrument allows surveyors to determine the true north direction by reference to the sun rather than being influenced by the earth's magnetic field. Surveyors can then locate true north through viewing the sun or other astronomical object like stars or the moon. It is not influenced by magnetism or iron ore or any other mineral deposits in a land district. The United States government required land surveys to be done by Burt's solar compass. In many cases the cost to accurately survey land territories with heavy mineral deposits that interfered with the normal surveyor's instrument would exceed the value of the land.
Burt's precision surveying instrument consists of three arc settings: one is for the latitude of the land; another for the declination of the sun; and a third for the hour of the day. The instrument has two main plates, the upper and the lower. On the lower plate is placed the sights. This plate revolves underneath the upper plate on a centre. The upper plate remains stationary. The lower plate may be clamped in any position to the upper plate.
There is a graduated ring on the lower plate which covered by the upper plate, except two openings at opposite points. Here there are verniers to read angles. On the upper plate is placed a needle box, having divisions for the north end the needle only of about 36 degrees, with a vernier to read the needle's variation. Upon this plate, is placed the solar apparatus. It consists of a latitude arc, declination arc, and an hour arc. There are also two levels, placed right angles with each other, together with other necessary fixtures.
The latitude arc is that which is attached by screws to the plate. It stands nearly vertical to the plate. The hour arc lies partly horizontal over the levels, and the declination arc placed upon a revolving limb, above the plate, and other fixtures of the solar apparatus. On this revolving limb is placed another movable limb, which turns on a joint at one end, and the other end, with a vernier, moves over the declination arc, with a clamp screw, to clamp it to the sun's declination for the time being. At each end of this described limb, there is attached to it a small brass plate standing out at right angles with the limb, and into the upper side of one and the lower side of the other, is set a small convex lens. Opposite to each lens on the brass plates there is attached a small silver plate, by means of three small screws and on each of these, lines are drawn at a suitable distance apart to embrace the sun's image, which falls upon each from the lenses. This part of the instrument is used with one end towards the sun and then the surveyor can determine the north declination.
To gain a better understanding of the set of parts of the solar apparatus just described one should pay particular attention to the apparent motion of the sun or stars, around the earth, regarding the earth as lies center of their daily revolutions. A distinct view of the probable conical motion of the sun, when it has north or south declination, is necessary, in order to understand how the movable parts of the solar apparatus may be adjusted to trace the sun, in its apparent course, while the sights of the sun compass remains stationary.
If one imagined he was at the Earth's equator and the sun had no declination, the sun would rise to him due east, and set due west. At noon the sun would be at the highest point, and in the lowest point at midnight. In other words, when the sun has no declination, its apparent revolutions are in a perfect plane with the Earth's equator.
If a straight line were drawn from the rising sun to the setting sun, and from the sun at noon and at midnight, both of these lines would pass through the Earth's center and the equator would intersect these lines. This is not so when the sun has north or south declination because its apparent motion will have an angle to the above described plane or lines, with the Earth's center, equal to the amount of the sun's declination north or south. Then it will be seen, that when the sun has north or south declination, and the earth is regarded as the center of its revolutions the plane just mentioned becomes conical.
This conical motion of the sun can be further explained by the spiraled branches of the wheels of a covered wagon. The rim representing the sun's apparent path, the hub, the earth, and the spokes, lines drawn from the sun's path. Then it may be seen that a line drawn from the sun to the Earth's center would pass north or south of the equator, equal in degree to its declination north or south. The instrument has an equatorial movement, with a small lens and collaborator for adjusting it by an image of the sun's disc. It also has a mechanical attachment for sighting a star as a reference.
The operation is as follows:
- Set the sun's declination for that day, obtained by means of tables, on a scale attached perpendicular to the time dial.
- Set the latitude on a scale in the alidade.
- Set the approximate local time on a dial that rotates on a polar axis.
- Orient the instrument, while remaining level, so the image of the sun appears between scribed lines on a screen below a lens. The time dial is fine adjusted to bring the image between lines perpendicular to the first set. The time axis will then point to the pole.
- The pinnula may then be pointed to a terrestrial object and its bearing read from the angle scale.
- The magnetic declination may be read from a compass attached to the base plate.
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