www.ucls.org 22 Early American Surveying Equipment By Dr. Richard L. Elgin, PS, PE, Rolla, Missouri America’s Requirements Much of America’s surveying practice descended from the English, but our early surveying equipment did not. The Old World used the delicate, expensive theodolite to divide its lands, sighting on points and measuring angles on a divided, graduated circle. American surveyors needed to establish boundaries over vast wildernesses that were difficult to traverse, and they needed to do it quickly and cheaply. Enter American innovation, technology and craftsmanship to improve a device used by mariners for hundreds of years, a form of which was being made in England: the magnetic compass. The result was the rugged, inexpensive standard American compass. One commentator said of the American compass: “Where accuracy can be sacrificed to speed and cheapness.” The Compass Rugged, the compass with its body of wood or brass, two sight vanes, a leveling device and placed on a staff or tripod, it required only a balanced magnetized needle resting on a sharp point. The needle aligned itself with the earth’s magnetic field and pointed to magnetic north. Magnetic north was known to move and hence was a poor direction with which to reference boundaries. This movement was well known, noted in some 1746 instructions that it “. . . may in time occasion much confusion in the Bounds . . . and, Contention.” Variation, the angle between True Meridian (a line of longitude) and Magnetic North was known to differ at different locations on earth, and the angle was known to change in amount over time and location. True North was a better reference direction, and in 1779, Thomas Jefferson wrote that the plats of surveys were to be drawn “protracted by the true meridian,” and the variation noted. The first standard American compasses were “Plain” compasses. They used magnetic north and had no mechanism for applying the variation angle, converting magnetic direction to true direction. David Rittenhouse (1732-1796) was an American man of science. He is generally credited with adding a vernier to the plain compass so one could “set off” the variation, the needle still pointing to magnetic north, but the bearing to the object sighted read on the compass circle being the true bearing. Thus the “plain compass” became the “vernier compass,” a great advancement in the American compass. The Land Ordinance of 1785 specifies that all lines be surveyed “by the true meridian . . . the variation at the time of running the lines thereon noted.” Tiffin’s Instruction of 1815 (the first written instructions issued by the GLO to its Deputy Surveyors) specified “a good compass of Rittenhouse construction, have a nonius division . . .” This is a vernier compass, “nonius division” meaning a vernier. Thus, the vernier compass became the standard instrument for surveys of the USPLSS. Until . . . WilliamAustin Burt and his Solar Compass William Austin Burt (1792-1858) was a GLO Deputy Surveyor who, in 1835, while laying out townships in Wisconsin, noted unusual deviations in the lines surveyed using his compass. He began work on a method and form of compass that would determine the direction of the true meridian independent of magnetic north. He invented an ingenious device that uses the observer’s latitude, the sun’s declination and local time to determine true north. The device mechanically solves the PZS (Pole Zenith Star) Triangle. The prominent Philadelphia maker, William J. Young (1800-1870), built the device, and Burt was awarded Patent 9428X on Feb. 25, 1836. Burt made improvements to his solar compass, and an improved version was patented in 1840. In 1850, Burt’s patent expired, which allowed other makers to produce the solar compass. (The circumstances of the expired patent are a sad story.) There are about 12 known post-1850 makers of solar compasses. All the solar compasses made before 1850 are marked “Burt’s Patent” and “W.J. Young” or “Wm. J. Young,” as he made them. They are not dated or numbered. Those made by Young after about 1852 are numbered. Is it a transit or a theodolite? Generally, theodolite refers to an instrument with divided circles to measure both horizontal and vertical angles to high precision; the telescope is relatively long and will not transit (rotate 360 degrees) about its horizontal axis. The more common term “transit” refers to an instrument with both horizontal and vertical circles (only horizontal on early transits), a four screw leveling head, bubbles for leveling and a telescope that will transit. William J. Young is credited with building the first dividing engine in America. That allowed him to cut circles, and he is credited with building the first American transit in 1831.
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