Have recently read a short, engaging book entitled Longitude, by Dava Sobel. From the book cover's flap: “Anyone alive in the eighteenth century would have known that 'the longitude problem' was the thorniest scientific dilemma of the day — and had been for centuries. Lacking the ability to measure their longitude, sailors throughout the great ages of exploration had been literally lost at sea as soon as they lost sight of land. Thousands of lives, and the increasing fortunes of nations, hung on a resolution.”

Finding latitude, on the other hand, was simply a matter of measuring the angular height above the horizon of Polaris, the North Star. But lines of longitude, which run from pole to pole, are not parallel and vary in distance from one another according to one's latitude. Starting precisely at the pole, if one were to walk three feet in any direction and turn left or right, walking a small circle while keeping three feet from the starting point would achieve passage through all the Earth's time zones and degrees of longitude. Achieving the same feat at the equator would entail a voyage of nearly 25,000 miles.

For an example of the perils of premodern oceanic sailing, the book tells the story of England's Admiral C. Shovell, returning home from Gibraltar in October of 1707 in persistently foggy weather. “Fearing the ships might founder on coastal rocks, the admiral summoned all his navigators to put their heads together.” The wisemen agreed that their planned course would take them safely west of danger. But a common crew member approached the admiral and claimed to have kept his own reckoning, and the danger appeared so enormous by his calculations that he made his concerns known to the officers. Admiral Shovell had the man hanged on the spot, for mutiny. But the admiral and his navigators had miscalculated, and four of the five ships were wrecked on the tiny, rocky islands off the Cornwall coast, with the loss of almost 2000 men. The poor sailor who'd been hanged was thus denied even the pleasure of being able to cry “I told you so” as the ships went down. Advances both in precision clock making and celestial observation and mathematics eventually solved the longitude problem near the end of the 18^th century.

For off-trail exploring in a place such as the Shawangunk pine barrens, a USGS topographical map and compass have long been the tools of choice. The compass, of course, points not to true geographic north, but to the magnetic pole, which during historical times has been situated in the northern reaches of Canada's Arctic Archipelago but at present has drifted to about 86º north and longitude 157º east, over the Arctic Ocean. The magnetic declination (variation) of the compass becomes extreme from locations in the Arctic region significantly off to the side of that longitude. When I was in Thule, Greenland in the early 1960s, I was aware that Thule lay almost due east of where the magnetic pole was then located. However, the compass gets less and less reliable in those regions, for the needle is drawn almost vertically down rather than laterally. Declination declines to zero along those meridians of both east and west longitude where the magnetic and geographic poles are in line with one another.

I once decided to test my orienteering skills by crossing the Shawangunk Badlands in a straight line from near the Five-Mile Post on the Smiley Road to my cabin. On my topo map, I first used a protractor to determine the angle of my route relative to geographic north and south, then determined the compass azimuth I must follow relative to magnetic north/south (approximately 12½º of declination). Once this azimuth had been calculated, I could simply follow it while keeping the red needle of the compass pointing to magnetic north, without the need for any further arithmetic. As I proceeded through the pine barrens, I would repeatedly site on the farthest easily distinguishable tree that stood at the desired azimuth, and walk to it (typically about 20 to 40 yards). Or, if I arrived at a particularly prominent tree, I would walk along my approximate route to where I could turn around and still see that prominent tree, and adjust my position so that the tree was at the same azimuth, but with the other end of the needle pointing north (i.e. 180º from my original azimuth). I proceeded thus for just over a mile through this rugged terrain, and came out within 100 feet of my destination. If one is with a companion, one can take turns siting on each other, which eliminates the possibility of losing track of the correct tree.

On my Wallkill Valley property, I routinely use my siting compass for identifying trees, as far as a couple of hundred yards distant through the woods, whose tops are starting to block my view of the ridge, and which must be marked for felling and adding to my woodpile (usually the tree disappears from view soon after I descend the hill behind my house).

For a simple exercise in orienteering, proceed with a siting compass to near the southwest corner of a large, open meadow. Mark the spot and follow at the azimuth of magnetic north (zero degrees on the compass) for 100 paces, more if the meadow is large enough. Then turn right and walk for the same number of paces at an azimuth of 120º, then turn right again and proceed at 240º for the same distance. This should bring you exactly to your starting point.

Hikers and campers today rely increasingly on the GPS to find their way in wilderness areas. While this has certain advantages, it also puts one at the mercy of a gadget that can suffer breakage, loss of electrical charge or loss of a signal. Just as importantly, it robs the user of the geographical knowledge and understanding that comes with map study and acquisition of orienteering skills.

Back in 2006, I was engaged in trying to determine the architectural and proprietary history of a stone mansion known as Brykill, along the Shawangunk Kill in the township of Gardiner. The dwelling had been radically altered and reconstructed in the early 20^th century, but from my research I knew the property had been acquired from the original 17^th century patentee by one Benjamin Smedes Sr. during the first decade of the 1700s. The big break in the puzzle came when I was able to determine that a 1736 inscribed stone embedded in a wall of the reconstructed house was not a builder's datestone at all, but rather the gravestone of a Smedes child who had died in infancy, and whose stone had been removed from the gravesite at some point. I'll quote from my article published in the fall, 2006 issue of de Halve Maen, the quarterly journal of The Holland Society of New York:

“With the riddle of the inscription at last solved, I was spurred to reexamine the various [property subdivisions and] complex boundary descriptions contained in the will of Benjamin Smedes Sr. and the deed record. I focused on one parcel of land within the large...[original tract] that seemed as though it might correspond to the plot of ground where the Brykill dwelling stands. Using a protractor and graph paper, a calculator to convert chains and links into feet, and the map legend to convert feet into inch fractions on the face of my USGS topographical map, I determined with certainty that the parcel of land that includes the dwelling is part of a 29-acre lot granted by Benjamin Sr. in his will to his youngest son, Nathan. There is reference in the boundary description to a family burial ground of two square rods — which tells me where the gravestone undoubtedly came from.”

Such a determination would scarcely have been possible without all I had experienced while learning to find my way in the Shawangunk wilderness using the venerable tools of map and compass.