By May, the crew was mired in mud deep within the Pocomoke Swamp. (Pocomoke is an Algonquian word that means “black water.”) The crew waded around cypress knees and pushed aside clingy tangles of aquatic plants. They warded off snakes and snapping turtles, scratched itchy insect bites, and pulled off sucking leeches. The closest dry ground where they could pitch their tents was a two-mile hike away. Fed up, the disgruntled men went on strike. In a journal entry for May 8, 1751, John Emory and Thomas Jones, the surveyors and bosses, wrote, “This morning our Workmen combined together to Exhort higher Wages from us and . . . [would not] work longer with us unless we would enlarge their wages.” Threats to the strike leaders and discussion with the rest of the men resulted in all returning to work with no pay raise. The men continued under grueling conditions working “till late at night often to the mid-thigh in water.” In fact, water so inundated the exact spot where the twenty-five-mile marker was to be placed the crew couldn’t set the sixth (and last) crown stone. Instead they marked the line’s halfway point — dubbing it the Middle Point — with another crown stone. Despite nasty conditions, the crew completed the job, marking a straight line across the peninsula, a distance of almost seventy miles. But that only provided the peninsula’s southern boundary line between Maryland and Pennsylvania.
Between 1760 and 1763, another team of surveyors attempted several times to run the peninsula’s eighty-mile-long eastern boundary line, referred to as the Tangent Line. By the terms of the Chancery Suit, the Tangent Line was to extend northward from the Middle Point until it reached a point tangent to, or touching, the circle drawn around New Castle. If the line had run straight north along the meridian, it would have been much easier. Instead, to reach the tangent point from the Middle Point, the Tangent Line had to run at an angle of 3 degrees 32 minutes 5 seconds northwest from the Middle Point. That made the survey a lot harder — maybe even impossible. Imagine trying to draw a straight line from your home to the doorway of one specific building located eighty miles away with no reference points in between to guide your direction. That’s a bit what running the Tangent Line was like.
The surveyors’ northwestward trek from the Middle Point was fine for the first few miles. By June 16, 1762, conditions must have deteriorated, since Pennsylvania surveyor John Lukens wrote to Pennsylvania commissioner Richard Peters to inform him that he was aware of errors between his attempt at running the Tangent Line and earlier attempts. Frustrated, Lukens ended his letter, “I pray to be released from Trying to Do what I now Conceive to be Impossible, Viz. Run a Straight Line of ye Lenth of 80 miles.” His crew struggled on. At the end of August, Lukens informed Peters that navigating uneven, swampy areas near the Choptank River had greatly delayed his crew and caused them to have to make “three different offsets of the line.” (Under the instruction of the boundary commission, Lukens and his crew were to stop if they found the Tangent Line off course by more than ten feet for every five miles.) Optimistically, Lukens concluded the note with his hope that his crew would finish the Tangent Line within ten days to two weeks.
Unfortunately, by the time they reached the area where they expected to find the tangent point (the spot where the Tangent Line touched the circle drawn around New Castle), the line was too far east. The surveyors made yet another attempt during the summer of 1763. That line ended up 346½ feet too far west. The surveyors’ attempts had failed. Boundary bickering continued. And everyone wondered if the trouble would ever end.
FREDERICK CALVERT (the sixth and latest Lord Baltimore) and William Penn’s sons Richard and Thomas (John died in 1746) were as fed up with boundary-line hooliganism as the colonists were. Then they heard about Charles Mason and Jeremiah Dixon, two men who had scientists buzzing about their recent success with important astronomical observations. Glowing reports about the pair’s precise observations of the transit of Venus, as well as additional celestial observations they had made in South Africa, had traveled through the scientific community. And what was more, Dixon’s surveying skills were equally lauded. If any two men could use the stars to direct long survey lines across uncertain colonial territories, it was these two.
Having an experienced astronomer as one of the Maryland-Pennsylvania boundary surveyors would be critical. Plotting the boundary lines’ directions would require locating the specific positions of stars at precise times during the night. The coordinates of the stars’ positions, when mathematically triangulated with the surveyors’ instruments, could be used to pinpoint locations on the earth’s surface.
COLONIAL NAVIGATORS looked to the night sky and the celestial sphere as they sailed the Atlantic Ocean to the New World. The word celestial comes from the Latin word caelestis, meaning “sky” or “heaven.” The celestial sphere completely surrounds Earth. Imagine Earth as a ball inside an infinitely larger ball. Now, mentally push Earth’s equator straight out into space, and it becomes a celestial equator that divides the celestial sphere into the northern and southern skies. A meridian, a north-south line, is another imaginary celestial line that astronomers and navigators use. A meridian is a line that encircles the celestial sphere in a north-south manner and crosses through the zenith, a point directly above any location. For example, someone in Philadelphia looks up and sees a zenith specific to his or her location and therefore would establish a specific meridian based on it, while someone in London would have his or her own zenith and meridian.
Since the earth beneath your feet prevents you from seeing the half of the celestial sphere on the opposite side of the planet, your view of the celestial sphere is never more than half. And your horizon always limits your view of the stars.
For countless centuries, people have grouped certain stars into constellations that remind them of figures, real and mythological. There are eighty-eight officially recognized constellations: twenty-eight in the northern sky, forty-eight in the southern sky, and twelve in the swatch of the sky that lies within the path that the sun appears to travel during the course of a year. The sun’s apparent path is called the ecliptic. (The constellations in this path are called the zodiac.) Constellations are named after animals or mythological heroes, such as Cygnus the Swan and Orion the hunter. Constellations always remain in the same positions relative to one another.
During the course of a night, constellations seem to travel slowly westward across the sky. In reality, it’s you moving as the earth rotates daily on its axis from west to east.
These are the constellations visible in the Northern Hemisphere. The specific ones you can see when you look at the sky depend on your location and the season.
Mathematician and astronomer Charles Mason, born in 1728, knew the night sky as well as he knew his own neighborhood. As a boy growing up in Sapperton, England, Mason greatly preferred calculating the locations of stars to helping his father mill wheat and bake bread. At that time, Robert Stratford, a local mathematician who served as the village schoolmaster, generously encouraged Mason’s love of mathematics and taught him the math skills he would need to become an astronomer. In 1756, Charles Mason, who was by then married and had two sons, joined the staff of the Royal Observatory at Greenwich, England.
Jeremiah Dixon was born in Bishop Auckland, England, on July 27, 1733. His father was a Quaker and the owner of a coal mine. As with Mason, mathematics and astronomy interested Dixon from an early age. John Bird, a famous maker of mathematical and astronomical instruments, also lived in Bishop Auckland and was one of Dixon’s friends and mentors. Dixon studied surveying and was a skilled draftsman. According to family legend, Dixon often wore a long red coat and a three-cornered hat. If this was true, he certainly world have cut a striking figure striding across the countryside with his surveyor’s equipment.
Mason and Dixon made newspaper headlines in 1760, when the Royal Society in London, a scientific academy of distinguished scientists, hired them to observe an astronomical event called the transit of Venus. Periodically, the orbital path of a celestial body — a planet, for example — carr
ies it in front of a larger one. During the transit of Venus, the planet Venus passes between Earth and the sun. While doing so, it appears as a black dot moving across the surface of the sun. The Royal Society wanted the transit observed and recorded because astronomical data collected during the transit would enable them to calculate the distance between the earth and the sun. From that, they could calculate the size of our solar system. But a transit of Venus is a very rare event. It happens only twice in a century. And one would occur in 1761.
Being chosen for the mission was a tremendous honor. Thirty-two-year-old Mason and twenty-seven-year-old Dixon eagerly accepted the job of tracking and timing Venus’s path across the solar disk. Since the sun must be visible to see this event, nighttime observation is impossible. In some locations, the entire transit can be seen. In others, depending on when sunrise and sunset occur, only part of the transit is visible. Mason and Dixon’s commission was to observe the entire transit. The Royal Society decided that the best place for them to do that was on Sumatra, one of the Indonesian islands in the Indian Ocean. Sea travel during the 1700s was a serious undertaking, yet the adventurous astronomers willingly risked danger in their quest for new scientific information. To arrive in time for the June 1761 transit, the Royal Society advised them to leave England six to seven months beforehand.
Making arrangements for the trip took time. Mason and Dixon gently packed delicate astronomical instruments, cushioning them against the rigors of sea travel. Since Mason’s wife, Rebecca, had died the previous year, he arranged long-term child care for his sons, Doctor Isaac and William. The possibility that Mason would never see them again was very real.
By November 1760, the Seahorse, a twenty-four-gun ship in England’s Royal Navy, was ready to leave for Bencoolen, a British military post on Sumatra. Mason and Dixon were ready, too. “We wait for nothing but a fair wind,” they wrote. But business snafus prevented the surveyors (and the Seahorse’s impatient captain) from departing until January 8. Less than forty-eight hours after they set sail, a crewman sounded an alert: a French warship was approaching. Cannonballs flying toward the Seahorse chased thoughts of Venus from Mason’s and Dixon’s minds.
LATITUDE AND LONGITUDE were critical lines for Mason and Dixon’s work, as were another set of invisible lines. This other set of lines is located on the celestial sphere.
A star’s altitude is its angular distance above the horizon relative to the person observing the star. But knowing only a star’s altitude wouldn’t help an observer in a different area locate the star. So astronomers divided the celestial sphere into a grid of lines, similar to the latitude and longitude lines used by mapmakers. Each star is assigned two coordinates that pinpoint its location on the celestial sphere. People anywhere on Earth can locate a star once they know these coordinates, known as right ascension and declination. (Note that while the celestial meridian, discussed earlier, is subjective — dependent on one’s location — right ascension and declination are set grids, like longitude and latitude.)
When Mason and Dixon observed a star, they always recorded its right ascension. Right ascension is like a meridian of longitude, except it’s a point on the celestial sphere rather than on Earth’s surface. A star’s right ascension is determined by measuring its position along the celestial equator. Its location is measured as an angular distance, a portion of the 360 degrees that make the full circle of the celestial equator. Instead of starting at the prime meridian, as is done with longitude, the starting point for right ascension begins at the vernal, or spring, equinox. The vernal equinox occurs on or about March 21, when the sun’s position in the sky begins to move from south to north across the celestial equator. That point on the celestial sphere is considered zero degrees. Moving from east to west, right ascension is measured in hours, minutes, and seconds along the celestial equator. The hours increase from zero to twenty-four — the number of hours it takes Earth to rotate completely on its axis once. Each hour is equal to an angle of fifteen degrees. (15 × 24 = 360, the number of degrees in a circle.) When looking at Earth, it helps to think of right ascension as divisional lines, or coordinates, that go from left to right.
The other imaginary celestial grid line is a star’s declination, which is similar to a parallel of latitude. A star’s declination is its angular distance north or south of the celestial equator. Declination is measured in degrees, minutes, and seconds. The celestial equator has a declination of zero degrees. The celestial north pole is expressed as +90°; the celestial south pole is −90°. Mason carried a star table, given to him by the Royal Society, that listed the declinations of all the stars he and Dixon would see.
Antares is the brightest star in the zodiac constellation Scorpius. Mason and Dixon often observed Antares while they were in Africa. Antares’s coordinates are: right ascension 16 hours 29 minutes 24 seconds, declination −26 degrees 25 minutes 55 seconds. The minus sign in the declination lets the observer know that the star is located south of the celestial equator.
Right ascension and declination form an invisible grid of lines and points on the celestial sphere, similar to longitude and latitude on the earth’s surface.
The cannon fire lasted for more than an hour. Shaken, Dixon reported news of the attack to the secretary of the Royal Society: “Our loss amounts to 11 killed and 37 wounded, (a great many of which are mortal) our Riging and Masts are very much damaged being rendered quite unfit for service, and her Hull much wounded.”
Dixon and Mason worried that repairs would “take up so much time that it will be impossible for us to reach India soon enough to make the Observations upon the Transit.” They suggested the Royal Society consider a closer place for their observation. The society threatened them with legal action if they didn’t resume travel as planned. So Dixon and Mason waited while carpenters repaired the Seahorse.
Once travel resumed, it became clear that the ship could not reach Sumatra in time for the transit of Venus. Mason and Dixon disembarked at the Cape of Good Hope, South Africa, at the end of April 1761. There they paid the Seahorse’s carpenters to build a circular observatory, from which they would observe the transit. Bricks provided a level floor. A conical roof capped the observatory’s five-and-a-half-foot-tall canvas wall with an opening “easily turned to any part of the heavens.” To shield the instruments from wind and weather, the carpenters tarred the top of the observatory and filled the joints with putty.
Mason and Dixon’s observatory at the Cape of Good Hope was constructed of canvas, wood, and bricks and did more than just shelter their instruments. It also provided them with a stable base from which to make their observations and measurements. The observatory pictured here is similar to the one they built.
A pendulum clock affixed in a wooden case was crucial for Mason and Dixon’s astronomical observations. To assure accuracy, it had to be absolutely level on top of an unshakable, immovable base. The carpenters set the base’s wooden posts four feet deep in the ground. With the clock wound and ready to go, each swing of the pendulum brought June 5, the date of the transit, closer.
At last the big event began. Mason and Dixon observed the transit with two telescopes and an astronomical instrument called a Hadley’s quadrant, which is used to measure angles. They recorded the time when Venus first touched the outer rim of the solar disk and the moment when it became visible on the solar disk as a complete black dot. They also recorded Venus’s exit off the disk — when it first touched the other edge of the solar disk and the moment when it completely passed off the solar disk.
The most recent transit of Venus occurred in June 2012. As the transit progressed, Venus (the black dot) slowly traced a path across the face of the sun. (Progression moves clockwise from top left.)
The successful observation elated Mason and Dixon. The Royal Society was pleased, too, especially since cloudy skies had thwarted their other authorized mission, attempted by Astronomer Royal Nevil Maskelyne on Saint Helena Island, in the South Atlantic.
Mason and
Dixon’s excellent results established their reputations and impressed the Penns and Frederick Calvert. The lords proprietors met with the astronomer-surveyors in 1763 and found them “Persons intirely accomplished & of good character” who would “settle & Determine” the boundary lines once and for all.
The job was immense — a surveying commission the likes of which the eighteenth-century world had never seen. With eyebrows skeptically raised, geographers, landowners, politicians, and scientists waited to see if Mason and Dixon would succeed where so many others had failed.
BY SEPTEMBER 3, 1763, Lord Baltimore’s agent (and uncle), Cecilius Calvert, had informed Maryland’s governor Horatio Sharpe of the surveyors’ imminent departure from London.
Mason and Dixon boarded the Hanover Packet and left for Pennsylvania in mid-September. After sixty-four days at sea, the two men welcomed the sight of salt-marsh grasses rippling along the fringe of Delaware Bay. Eager to be on land, they disembarked as soon as the ship dropped anchor at Marky’s Hook, the first port of call for Philadelphia during colonial times, located about twenty miles south of the city. Eager to complete their journey, Mason and Dixon hired two horses — this would be the first of many horseback rides on American soil — and arrived in Philadelphia on November 15. They saw the steeples of Christ Church and the State House towering above the city’s center. It was at the State House where they would formally meet with boundary-line commissioners from both provinces.
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