On October 10, 1767, the Mason-Dixon Line was completed.  It was the culmination of a five year project, beginning in 1763, by English astronomers Charles Mason and Jeremiah Dixon.  They had been hired by the Penn family, who were the proprietors of Pennsylvania, and the Calvert family, who were the proprietors of Maryland.  Being a “proprietor” meant that they owned those two territories.  All of it.  And they ran them like feudal lords, bless ‘em.  And if anyone disagreed, then take it up with the King of England, whomever that happened to be at the time.

 

You see, George Calvert was Secretary of State to King Charles I (1625-1649).  For his loyal service he was made Lord Baltimore and given Maryland, but he died before it became final, so his son, Cecilius, was made the Second Lord of Baltimore.  Regardless, the Calvert family owned Maryland.  Then, in 1681, King Charles II (1660-1685) gave Pennsylvania to William Penn to pay off a debt that the king owed the Penns.  So the Penn family owned Pennsylvania. 

 

The border between the two was set at the 40th parallel.  Unfortunately, nobody knew exactly where the 40th parallel was.  Depending on where the line was finally drawn, Pennsylvania could’ve lost Philadelphia and access to the sea.  And they would’ve had only have one baseball team.  So they tried all sorts of legal remedies, including shooting at each other.  And this went on for 80 years.  During that time there was only one recorded death, though a lot of homes were destroyed, people were beaten, and there was a lot of angry shouting.

 

In the end they all agreed that the best solution would be figuring out just where, exactly, that border should be.  Local surveyors tried to parse it out, but they were stumped.  After all, it’s a bit more than just figuring out the property line for somebody’s farm.  The Mason-Dixon Line runs over 300 miles, making up the present day borders of Pennsylvania and Maryland, and Maryland and Delaware.  That’s 300 miles over hills, through forests and swamps and rivers and all sorts of fun.  So they called in the pros: Jeremiah Dixon and Charley Mason.

 

Both Charley Mason (1728-1786) and Jerry Dixon (1723-1779) were born in England and trained to be surveyors and astronomers.  Pretty much, they learned how to measure things.  Precisely.  They first teamed up in 1761 to travel to South Africa to observe the rare transit of Venus.  A transit is when a planet crosses between the earth and sun, appearing as a dark spot as it moves in front of the sun, which requires looking directly at the sun through a telescope, obviously.  Don’t try this at home.  Among other things, a transit can be used to calculate our exact distance from the sun. 

 

So by the time they got to the colonies, they were ready.  Here’s how they did it, if anyone asks.  First, they started with a point of reference.  Using the stars, they found the point of equidistance from the Chesapeake Bay and the Delaware River.  To do that they first determined the zenith, the spot in the sky straight up from where ever they were, which is really easy.  All they needed was a tripod, string, and a plumb bob, which is a pointy weight.  Then they measured the angle of a reference star using an equal altitude instrument, which is a really cool toy.

 

Based on your zenith, you have the meridian, an imaginary line that runs north and south.  Now pick a star on the east side of the meridian and measure its altitude (or elevation angle) using the equal altitude instrument.  Then wait until that star is at the same (or equal) altitude on the west side of the meridian.  By knowing how long it took that star to move, you now have the exact time, latitude, and true north.  The relative angle of the star will give you the latitude, which gives you true north.  What could be more easier?

 

Then they used a transit, which is the precision instrument mounted on a tripod surveyors use to determine distance and measure angles and changes in elevation.  They also used stuff like spirit levels, sextants, and precision clocks.  But that’s pretty much it.  That’s how they did it.  Now wouldn’t that make a great science fair project?  Comparing what they did with GPS, they were (and still are) amazingly accurate, never off by more than 800 feet, and for the most part dead on.  It truly is a marvel of geodesic cartography.  Go check it out for yourself.  Many of the stones used to mark every mile are still there. 

 

And with that, the border war between the Penns and the Calverts was over, but not the end of the Mason-Dixon Line.  The Missouri Compromise of 1820 used the Mason-Dixon Line as an informal dividing line between slave and free states.  During the Civil War it came to mark a more profound difference between the North and the South, as it still does today.  And, just so you know, Mason and Dixon got along just fine.  They never molested women.  They were kind to children and small animals.  And even though they worked with people who owned slaves, then never owned slaves themselves.

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