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  The American Surveyor     

The Compass Meridian Stones of Frederick, Maryland Print E-mail
Written by R. Wayne Twigg   
Saturday, 21 October 2017

A 12.787Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

The Past Is Prologue
This motto of the National Archives of the United States is particularly significant to the profession of Land Surveying. In our daily work, Land Surveyors search for previous Surveyors' evidence. We use it in our surveys and designs, which then stand as introductions to some future surveyor's efforts. Because we routinely straddle the present with one leg in the past and the other in the future, we tend to take the importance of what we do for granted, often not realizing its significance.

But Lawrence Brengle and Thomas Woodrow knew. Brengle first served as Frederick County Surveyor and as a Commissioner in 1817, becoming Mayor of "Frederick Town" in 1820. While surveying the squares, streets and range of lots of the Town back in 1817, it became apparent to Brengle that, despite his careful efforts, mismeasurements were present. His original layout of Frederick Town contained lines that ranged from 5 to 20 feet off. Concerned with accuracy and looking for reasons why, he contacted Woodrow, who by then had succeeded him as County Surveyor and had participated with him in the layout of the boundaries of the town. In 1820, they corresponded over the results of field tests in which Brengle's 12-foot measuring rod proved to be ¼-inch too long and in which compass readings tended to differ by as much as 10 minutes of arc from the effect of diurnal variation on the needle. This helps to explain why the surveys of those two good professionals, Brengle and Woodrow, didn't coincide. Their search for excellence helped to set in motion the conditions that caused Frederick County's Compass Meridian Line to be established.

These two men helped others in Frederick County to realize the vital importance of measurements which were both precise and accurate. Establishing primary reference monuments and survey calibration baselines is fundamental to successful future development.

"Discovery" of the Stones
To any passersby who care to notice, the line between the pair of identical old Stones is not parallel with the public street. Without any identification on them and situated on opposite sides of the old Courthouse (now City Hall) lawn, their exposed granite tops are finished. Each has a copper or bronze rod which has been sealed-in with lead (non-magnetic). To the 1998 stroller, the northernmost one appeared undisturbed, while the south one had several more inches exposed and was leaning. A North-South Baseline? A late visit on a clear Fall evening, with a flashlight on the north Stone and a plumb bob string over the south Stone, there was Polaris, as pretty as you please, shining just above a rooftop over the north Stone. Lawrence Brengle's original field notes indicated that "Courthouse Square" is the southeast portion of original Square No. 47. Combining his courses with a few present-day measurements seemed to confirm that the Stones aligned with North almost perfectly.

The first page in Jim Demma, Esq.'s Annotated Code of Maryland Relating to Land Surveyors quotes Article 25, Sections 123-127, a directive to all County Commissioners to install, at or near their respective courthouses, a True Meridian baseline consisting of two substantial stone pillars, marked with Latitude and Longitude. Every Land Surveyor working in any Maryland county was required to annually check the variation of his compass at the baseline and report it to the Clerk of the Court to have it recorded in the Registry Book. Failure to comply was subject to a fine. This mandate, first passed at the 1870 session of the Maryland Assembly, seems to have never been repealed or annulled. During the next 40 years, out of 23 counties, only 9 responded favorably to the command. These were Baltimore at Towson, Dorchester at Cambridge, Charles at La Plata, Harford at Bel Air, Kent at Chestertown, Queen Anne's at Centerville, Talbot at Easton, Wicomico at Salisbury and, of course, Frederick at Frederick. Interestingly, not all of them were North-South lines. Some of those baselines have been destroyed or disturbed in the ensuing years. Frederick County's may be the only one in Maryland whose Stones still remain and are usable.

A 1999 search for nearby GPS control monuments in the NGS database revealed second-order benchmarks listed as "North Magnetic" and "South Magnetic", part of a 1941 USC&GS level-run, whose descriptions fit each Stone exactly. In 1941, the government survey crew must have known their original purpose, else why label them as they did? Since they were already Agency benchmarks, Roy Anderson of NGS (National Geodetic Survey) agreed to determine the latitude and longitude of "North Magnetic" using GPS.

Appalachian Chapter, MSS
Serving 2 counties (Frederick and Washington) in central Maryland, Chapter surveyors discussed the situation at their next meeting. "North Magnetic" appeared to be undisturbed, but its southern partner would have to be re-aligned and stabilized. A celestial observation seemed the answer. While it is true that one can still see Polaris from "South Magnetic" with the naked eye through the trees when the leaves have fallen, there was too much foreground illumination to actually view the star through a theodolite's objective lens. The Chapter decided to establish an observation station in nearby Baker Park and conduct a Polaris observation from there. Astronomic North could then be transferred via traverse to the Stones.

Station "Compass Ref" was installed on a Saturday morning by two Chapter members at a convenient place in the park within sight of City Hall's weathervane. Set 0.33' below ground level using a ground plate and driving rods, centered inside an 8-inch PVC pipe collar, the FENO rod with stamped bronze cap was stabilized with compacted sand inside the pipe and a heavy concrete collar outside.

Roy and Rob: NGS and GPS
February 24, 1999, 9:00 a.m.; Day 055.375 of 1999 A.D.; Julian Day 2451233.875. Roy supplied three 2-meter poles, three Ashtech choke-ring antennae and a battery-powered psychrometer for determining relative humidity. Rob Farrar, then of Spectra Physics, brought four dual-frequency Geotracer Model 2204 receivers, one Geotracer choke-ring antenna and one Seco fixed-height pole. Chapter members Gordon Conner and Matt Crouse started Session One at the receiver on "Compass Ref". Simultaneously Bill Orsinger switched on at "Patrick", Rob at "Strip", both at the airport, and Roy at "North Magnetic". Roy kept everyone busy during each of the 2-hour occupations with station rubbings, relative humidity and barometric pressure readings, Observation Log sheets and Obstruction Diagrams (skyplots). In addition "Compass Ref", a new City GIS station, needed a complete site diagram with witness measurements. Next day, same crews, same equipment conducted another session between 1:00 and 3:00 p.m. Preliminary processing of the downloaded data revealed good-looking plots with no apparent glitches. Disks with observational data in raw and RINEX formats were delivered to NGS headquarters, along with the borrowed equipment, soon after.

A Long Look Back
Let's pause to discuss some of the conditions that helped to bring about the establishment of Frederick's Compass Meridian Baseline. Survey lines "laid in" with a Compass are difficult to consistently and accurately reproduce with a Compass, due to such various and varying factors as local attractions, mineral deposits, diurnal variation, vernier scale limitations and the variations of annual magnetic declination. The compass' scales and verniers must be precise; needle's pivot point must be undamaged and sharp; and levelling bubbles in adjustment and vanes true. The Surveyor's Compass is a delicate instrument, requiring proper handling, usage and care. If not respected, it will not yield the accuracies of which it is capable.

That's not all. Magnetic North is everchanging. Density of mass creates magnetic attraction. Gravimetric studies, which began for Land Surveyors back in the 1700s, have indicated that the density of Earth's mass under any given location will change during relatively short time periods. This is a major factor that causes the Surveyor's Compass Needle to vary from "True" North. This change is referred to as secular variation and is illustrated by the wavy lines on an Isogonic Chart. Daily variations of the compass' magnetic needle occur from the effects of diurnal change as well as from solar geomagnetic storms. Local variations can occur from geologic iron deposits and from many sorts of artificial disturbances. All of these factors, and a few more, must be compensated for. Therefore it isn't difficult to understand how precise and accurate "survey-grade" angular measurements with a compass are, in essence, impossible in many settings. Loss of accuracy becomes assured when the Surveyor using the compass doesn't recognize and apply these factors properly.

In the spirit of objective fairness and genuine respect, it should be noted that excellent, reproducible rural compass surveys have been conducted in various places throughout the U.S., often in forestry applications. In fact, if you can still find it, F. Henry Sipe's book Compass Land Surveying is a highly recommended addition to any Land Surveyor's library of reference material.

Controversies arising from the differences in adjoining or connecting surveys made necessary the establishment of (to quote Mr. Richard Cooper, Wicomico County Surveyor) "...an unquestioned place where the deviation of the magnetic needle could be checked against the true meridian..." and where land surveyors could check their chains. [As an aside, the widely-respected Mr. Cooper wrote an interesting article about the Salisbury Stones that was published in the Maryland Society of Surveyors Newsletter, Volume 20, No. 3, 1993] In short, the granite markers were installed to provide a local standard for both an angular check and a measurement check, a calibration baseline, if you will. Many of the orders for the surveys of lands that were issued by no-longer-existing Courts of Equity (a.k.a. Chancery) required that the court's Surveyor first check his compass' declination at the meridian baseline and register his instruments before he started each court-ordered survey.

Astronomic or Magnetic?
At the time of the Chapter's 2003 observations, the Frederick area's Local Magnetic Declination was approximately 11°07' West of Astronomic North (see Calculation Sheet). As an aside, the Surveyor should record the magnetic bearing of his backsight line at the same time he determines the astronomic bearing of it. Subtracting the two yields the current amount of Local Magnetic Declination. In retracement matters, knowing how to perform any of these easy surveying tasks, and using the actual or approximate date of a deed's compass survey gleaned from research, will help the Surveyor to estimate what the Magnetic Declination was at the time of the original compass survey. From an original survey property marker, calculating the Astronomic North bearing and comparing it with the magnetic bearing given in the deed will closely yield the original survey's magnetic declination. A wise Surveyor will check that declination against other original markers or good markers in original locations, if they can be found. Applying that correction to the rest of the deed's bearings will greatly aid a modern Surveyor to "walk in the [original] Surveyor's footsteps".

An Astronomic North observation takes approximately 15 minutes for two experienced field personnel and 20-25 minutes for one competent office person, much less if he has a good software program. Elgin, Knowles and Senn, Inc. are the ones who, until 2008, provided the excellent data, instructions and charts used by Chapter Surveyors for this observation. Prior to 2008, EKSI's data was published annually in Sokkia's booklet Celestial Observation Handbook and Ephemeris.

Personnel time is essentially the same whether for a sun shot or for a star shot. A sun shot is nearly as easy to do as a star shot and has the distinct advantage of being able to be performed at any convenient time during the normal daily run of traverse and locations. If you're using an electronic theodolite or total station, sighting directly on the sun requires a solar filter, a fairly low-priced item. Like the star shot, the hour-angle solar method requires precise time and does not require corrections for temperature, barometric pressure, curvature and refraction, as does the Altitude Method. However, the Altitude Method's results for sun sighting aren't quite as accurate as those of the Hour-Angle Method. You should be familiar with the advantages of each of the 3 methods in order to choose which one would be the best for your application. All three of these common methods for determining Astronomic North from Station "Compass Ref" to City Hall's weathervane were used during 2003. A brief comparison of the three independent results is included on the Calculation Sheet, shown farther on. To obtain acceptable results, any method of celestial observation requires a precise instrument in good adjustment with sensitive leveling bubbles. The steep zenith angles demand it.

"...A Man with a Measuring Line in His Hand"
As previously mentioned, the City of Frederick had already experienced the discomforts of ill-fitting compass surveys as far back as 1820 and probably before. Something had to be done to establish a local, easily-accessible Standard for deciding which Surveyor was right. Evidence from Maryland Geological Survey archives indicates that the Frederick County Compass Meridian Stones were installed by the authority of the 1870 mandate during the fall of 1896 by Dr. L. A. Bauer, as were the two stones installed that year in the City of Salisbury, Wicomico County, Maryland. Records further note that a U.S. Coast and Geodetic Survey (USC&GS) Magnetometer, an Altazimuth precise transit and a Meantime Chronometer were used to accurately determine both the Magnetic Bearing and the True Bearing.

In the 1894 picture of these celestial observation instruments, note in particular some of the special characteristics of the Altazimuth instrument used for celestial observations. It had a large, extra-sensitive level bubble at the top, a very large vertical circle with eyepiece, and several other attachments for celestial observations including a right-angle eyepiece.

In measuring the quantity of local mass/ density attraction, the Magnetometer was used to determine the amount of magnetic secular change. Sensitive or not, all level bubbles represent the perpendicular to the local gravity vector, which can visually be indicated by a plumb bob string line. However, the string/vector can be pulled away from the true vertical by a phenomenon that varies in magnitude depending on the amount of Earth's density and the proximity of mountain masses to the site. This small angle of deflection is known as the LaPlace Correction and is added to the Astronometric Azimuth to create the Geodetic Azimuth.

The 1896 celestial method to determine the True Bearing of this Meridian Baseline was the Solar Altitude Method, averaging the results of two observations on the sun, one in the morning and one in the afternoon. Using USC&GS methods and this advanced equipment, the monuments were set to the minimum accuracy of a minute of arc. Nathaniel Bowditch's (recall the Compass Rule a.k.a. Bowditch Method of traverse adjustment) Altitude Method, as explained in the book Practical American Navigator, adapted for land use, remained the solar computation method of choice for Land Surveyors until recent times' common availability of ultra-precise time made the more accurate Hour-Angle Method practical and easy.

Observations
An answer to the question "Which one is Polaris?" is "It is the end star in the tail of the Ursa Minor (Little Bear) Constellation, a.k.a. The Little Dipper." But in 2003, because of all the modern background lighting, Chapter Surveyors couldn't see enough stars in that constellation to identify it. In addition, Polaris, at Magnitude 2.0, doesn't shine brightly enough in the heavenly canopy to draw attention to itself. But it is handy for Northern Hemisphere Surveyors (Polaris can't be seen from the Southern Hemisphere locations because of Earth's curvature) to observe this particular star for several good reasons. It has the distinction of being close to the North Celestial Pole, seeming to track about a 1° radius around Astronomic North. Because of the star's proximity to the Pole and because the Earth's polar axis and equator are projected onto the Celestial Sphere, the Surveyor's own Latitude becomes another way of locating Polaris. By subtracting his position's Latitude angle from 90°, i.e., Co-latitude, and using his compass for approximate direction, the Surveyor will see that the resulting zenith angle is close to where Polaris sits in the heavens. The zenith angle, while steep, is within range of a theodolite's eyepiece. Polaris can be observed without using a diagonal eyepiece attachment. Although other stars in your ephemeris can also be used, if not masked by the local horizon or vegetation, Polaris is, for most, the star of choice.

If those facts aren't enough to influence the Surveyor-Observer, his Great Creator has provided two heavenly markers just for the Surveyor's own personal convenience in locating the "Pole Star". Ursa Major, the "Big Dipper" is easily recognized and provides 3 stars for alignment. Cassiopeia, the "lazy W" constellation, lies on the other side of the Celestial Pole and provides one star.

Now please refer to the Chart to Locate Polaris. The Chart has been rotated around until the label "Northern Sky at Eastern Elongation" is at the left. Rotate the chart 90º counterclockwise and you are now looking at the approximate configuration of the sky at the North Celestial Pole as it was on the night of October 11, 2003, between 8-10 p.m. Eastern or Western Elongation events are good times to sight Polaris because the star appears to be traveling in north-south directions in a counterclockwise rotation. The Surveyor doesn't have to use the tangent screw very much, and it is much easier to record the instant of time that the star appears to move onto his instrument's crosshair. Note the words "appears to". For all intents and purposes, we are moving, not the star. But for ease of understanding and for calculations, some of Earth's characteristics, such as the equator, the axis, etc., are projected outward onto an imaginary surface called the Celestial Sphere. So celestial observation methods assume that the Earth is fixed in space and the stars are rotating around us.

Truth be told, to make our celestial observatory functional, we cheated. Having previously performed both an Altitude Method and an Hour-Angle Method Sun Shot from "Compass Ref" in order to establish a Grid Azimuth to City Hall's weathervane, we knew exactly in the daytime where Polaris would appear in the heavens before the Hut was erected. In fact, we had to know because the celestial observation slot in one of the roof panels is only a few degrees wide. Therefore, the users of this particular celestial observatory must accurately align the slot during the daylight erection so that the subject star will appear in the roof panel opening when darkness has fallen.

Ralph Donnelly, former president of the Maryland Society of Surveyors, built the "Hut", with the help of NGS' Ralph Poust, in 1984. He based his design on clues found in Mason's and Dixon's own notes and reports and finished the rest from the prompts of his own genius. Ralph's resulting full-scale transportable model kit has 4-foot wide, 6-foot high wooden panels which connect to form a circle approximately 12-feet in diameter. The 8-foot long triangular roof panels rise in the center, converging in a cone-shape. Once in place, the Hut's composite roof's design and heavy wooden weight make it impossible to rotate in place. Also, remember that the Surveyor's celestial observation requires not one but two lines, one to the star, of course, and one to his own traverse backsight. The Hut's door has to be aligned toward the backsight, because this alignment is usually the real reason for the Surveyor's activity in the first place.

Observing Polaris
October 12, 2003. The Hut had been set up during the day under high solid cloud cover, which had been prevalent throughout the day. Clouds began to clear in the southern sky as the sun set. Seven o'clock; then seven-thirty; then darkness. Clouds still obscured our northern heavenly target. Chapter Surveyors familiarized themselves with the instrument and experimented with a technique in precise timing. By calling Station WWV (303)499-7111 on a cell phone and turning up the volume, all within the Hut could hear the time ticks and the announcer's voice calling out UTC (Coordinated Universal Time, a.k.a. Greenwich Civil Time). The double tick came on the 12th second, indicating a DUT correction of -0.4 seconds. This DUT correction is applied to UTC to yield UT1 time. UT1 is also known as Earth Rotation Time and is recommended for celestial observations. Several calls were necessary to begin the stopwatch at exactly zero seconds. To maximize their vision's ability to recover during the blackout conditions inside the Hut, the Surveyors drew on their military training experience and used several red lanterns and lights.

Eight o'clock. The clouds still refused to give up their position. Then, with the coolness, came the clearing. Miraculously, the clouds began to dissipate from east to west, as if the Hand of God was drawing aside the curtain. Having first studied star charts, the Chapter Surveyors knew that Cassiopeia would be located on the east side of the Celestial Pole between 7:30 and 8:00 p.m. The stars of the "Lazy W" constellation appeared, one by one. Polaris was next. The Surveyors entered the Hut to take their place at the instrument, which had already been set up over "Compass Ref". They had the angle clockwise from the weathervane as well as the calculated zenith angle. The Polaris observations had finally begun. Standard direct-and reverse sets were turned by nearly everyone, with Surveyors switching between the roles of Instrument Operator, Note Keeper and Time Keeper.

Where in the World is "South Magnetic"?
Specifically, it now sits at North Latitude 39°24'55.9013", West Longitude 077°24'43.9930", having a new orthometric height of 295.6 feet. Its northern partner "North Magnetic" rests undisturbed at North Latitude 39°24'57.3913", West Longitude 077°24'44.0017". Listed in the NGS database as PID JV2529, "North Magnetic" is listed as a Second Order, Class 0 benchmark with an orthometric height of 297.38 feet. For Maryland grid users, the convergence angle is ­00°15'44" and the Geoid99 height is ­107.37 feet. To convert from astronomic orientation to geodetic in this vicinity, the LaPlace Correction is +0°00'04".

Armed with Kundrick's comps, Bob Pasley, Bob Banzhoff, George Nagel, Barry Hoyle, T. J. Frazier and others met again on April 9, 2005 to dig up and reset "South Magnetic". With a little apprehension, George removed the first shovelful of dirt. After all, Surveyors are inclined to hold monuments as they exist, not to dig them up.

We were very surprised to see that the granite stone control monument was shorter than we had expected and was not broken off at all. Below the finished 4-inch square, 6-inch long tip, the stone has a rugged, straight-from-the-quarry look. Weighing more than 100 pounds and measuring 24-26 inches long, the shape tapers to a 12-14 inch square base. Those of us who can barely remember our solid geometry days may recall that this geometric solid shape is referred to as a "truncated square pyramid". The design is used in this type of application to provide stability by evenly distributing downward and lateral stresses of soil settlement and surface disturbances.

The Stone rests on a multiple layers of carefully chosen, deliberately-placed flat stones. We had to remove the layer nearest the ground surface so that only the finished top 4 inches of the stone monument would be visible. As is seen in the "Before" picture, the Stone was excessively exposed, undoubtedly due to the contact with the truck axle and to the re-grading of City Hall's front yard during its 1985 transition from Frederick County Courthouse to Frederick City Hall. When one considers the extent of multiple landscapings performed here in the past, it is a near miracle that the Stones have survived for us to view and ponder. Some extraordinary person surely must have known that the Stones possessed an extraordinary importance and took action to prevent their obliteration. But they kept theirs' and the Stone's identities silent. The Chapter is grateful to that anonymous protector.

From the look of things at the bottom of the hole, there were more layers of foundation stones, but we curbed our curiosity and left them in place, undisturbed. "South Magnetic" was repositioned Due South from "North Magnetic". We rested the Stone directly on the flat-stone foundation, just as the original USC&GS surveyors did. Chain ties were set. A large concrete collar was poured in-place. The final alignment was checked and double-checked.

Chief Justice Roger B. Taney's bronze bust looked on approvingly from its nearby vantage point near the old Court House entrance. Brother-in-law to Francis Scott Key, Taney had established a thriving law office here in Frederick just across the street from "North Magnetic", eighty-four years before the setting of the Meridian Stones. His law practice thrived to some extent because a portion of his business dealt with the consequences of land surveys that had been performed to individual standards and therefore were relatively precise but not accurate.

Frequently, Taney dealt with the problems of property ownership and land issues, such as apparent gaps and gores, appearing before the Court of Equity. He had seen the effects of conflicting land surveys in the courtroom and tried as best he could to deal with them. He routinely issued Orders to Survey to the County Surveyor, as part of Court proceedings. The Surveyor and Taney would have discussed the necessity of conducting the resurvey of lands according to professional standards so that the work would "stand up in court". Surely the two of them would have agreed that it is far better to be accurate in the right place than to be precise in the wrong place. Nearly a century later, the Stones' Baseline was installed with just that premise in mind.

Right is [Still] Right and Wrong is [Still] Wrong, But How Can You Tell the Difference?
Today, seemingly more than at any other time in our history, there are too few basic reminders to help keep us from straying from the truth. Standards that served us so well for so long are now being disdained as if they are not relevant or true. Toleration is a social rule of the day. It is greatly disturbing. Passive toleration is revealed as both foolish and harmful in the light of unchanging truth. It may even be precise at times but it is not accurate.

A professional standard for our work is really not much of a different concept than a standard for living, right? Let's face it, the worst possible scenario for professionals is everyone doing that which is right in his own opinion. So just how can a Land Surveyor know his measurements are correct and another professional's measurements are wrong? Come to the Baseline. There aren't many different standards of measurements for us, just one. We have to conform ourselves to it, not the other way around. Do not misinterpret this to imply that Surveyors should conform to each other. That is what the Standard is for.

By necessity, however, we Land Surveyors are a calibrated people in a seemingly uncalibrated world. Adjusting ourselves and our equipment to the Standard is crucial to enable Land Surveyors to perform to at least a minimum standard of practice. Come to the Baseline is the lesson the Compass Meridian Stones of Frederick County teaches, and we professionals would do well to heed that reminder. You have the power to be extraordinary, by participating in this great Land Surveying profession of ours, right where you are, as you measure your life according to our standards.

I lovingly dedicate this story and work to the memory of my son Christopher Wayne, who helped me run the first traverse through the Stones.

Note: A video prepared by the City of Frederick about the stones can be found at https://youtu.be/wQFa0qCCWyQ.

Wayne Twigg lives in the mountains of central Maryland. He has worked in and practiced all aspects of the profession of land surveying for 50 years, earning a college degree and numerous certificates. Several of his articles have been published. He has served as an officer in the Appalachian Chapter, MSS for the past 35 years. He gives presentations on "The Mason & Dixon Line", "The Colonial Land Patent System in Maryland" and "Celestial Observations", as well as participating in historical events featuring land surveying. He is a member of the Maryland Society of Surveyors, National Society of Professional Surveyors, American Association for Geodetic Surveying and a charter member of the Mason Dixon Line Preservation Partnership.

A 12.787Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

 
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