Recently, I wrote about a navigation game people play called geocaching. Here’s my next lesson in familiarizing myself with the world of GPS. Afterward I’ll tell you about a book that explains the origins of one of the components of navigation.

First, chapter two in “Geocaching with Jeff” or “Learnin’ GPS by the Seat of Your Pants.”

If you recall, to play the game you go to the geocaching Web site, punch in your zip code and up pops the geographic location of numerous hidden caches listed in ascending order of miles from your home. The latitude-longitude coordinates are listed, along with a few hints about finding the location and the scenery you’ll see getting there.

The caches I’ve found have been plastic containers filled with any number of items and a logbook to record the experience of finding the cache.

The premise is simple. Grab a GPS, punch in the coordinates, and let the machine lead you to the spot. Take along the helpful hints and locating the prize should be a piece of cake, right?

Well, yes and no. Of the four I’ve tried to find, I’m batting .500. But I don’t think it’s because I’ve not been at the right spot. On my forages I’ve been accompanied by friend and fellow guide Karen Francoeur, who is using a more sophisticated GPS unit than mine.

We’ve tracked down two spots, one which seems to be on a train trestle in Bangor and another off a trail on Eliot Mountain in Northeast Harbor that did not seem to have the rewarding final find. We were successful, however, in finding one at Blagdon Point Preserve at Indian Point on Mount Desert Island and another a mile in the woods near Seal Harbor. The train trestle trove may in fact be located near the trestle, it’s just that when we went in search of it a few weeks ago, there was so much snow on the ground it could have been buried.

Since then, as you know, we’re back to bare ground.

Last Saturday’s balmy temperatures provoked us to try the game again. Francoeur picked out three of the listed locations, and we were off around noon.

By the description on the first location, I knew right where to go – at least I knew where to find the parking lot of the Nature Conservancy property at Blagdon Point. My guess, without a map in hand, was the cache was hidden down near the shore. Our GPS units told us otherwise, and sure enough we located the plastic container in short order. Several parties had found it last August. One, David and Tammy, wrote in the logbook in memory of “Bad Monkey who couldn’t make it.” There was a note from an Agawam, Mass., couple visiting Acadia National Park and another from a couple from Newton, Mass. In October, an Evanston, IIl., couple logged in as did a couple from Atlanta, Ga. The last entry was from a Vermont couple on Feb. 17.

We left a note on the log, did a high-five for our first successful find, and headed off to Northeast Harbor’s Thuya Gardens to find our second cache. It’s not in the gardens, by the way, it’s off a trail up Eliot Mountain – well, it’s supposed to be, anyway. We looked and looked to no avail. At one point we were within a few feet of each other, the GPS units agreeing we were on the right spot, yet there was no cache. Maybe it was moved?

A little disheartened, we headed for the third location. We were relying on the map programmed into Francoeur’s GPS.

At Seal Harbor we began our third treasure hunt. If we’d had a topographical map, our mile or so walk would have been a little quicker. The trick is to plot your coordinates on a map, and then you can follow existing trails to the general area. Following the arrow on a GPS can get confusing because it gives you a straight-line heading. Trails wind around so you tend to get a tad confused at intersections. A map would come in handy.

For example, at the first trail intersection the GPS pointed to the right fork, but the better way to have gone (according to the map) was to the left. Anyway, after a few fits and starts, we arrived at the scenic trail clearing described in the geocache description and began our hunt for the plastic container. By now it was getting dark and we only had one small flashlight between us.

At 6 p.m. I stumbled down over some rocks and literally kicked the cache! By the glow of the mini-flashlight we flipped through the log and the several bits of memorabilia. This cache had been found by only a few people, the last being a couple from Plymouth, Vt., on Feb. 18. We signed our names in the logbook, sealed the container, put it back in its hiding place and headed back to the car in the dark.

Next time I think I’ll take along a headlamp – or get an earlier start!

Measuring longitude

Now for some history.

In this age of instant information and hand-held navigation tools that position you on earth in a square of less than 30 feet on a side, it’s hard to imagine what it must have been like long ago.

Navigation is knowing where you are, where you want to go, and how to get there. To do that modern cartographers rely on numerous mapping systems and datum, but the one known to most of us is latitude and longitude.

By drawing a pattern of squares on the earth’s surface and assigning a means of measuring where those squares are in relation to a beginning point, cartographers are able to pinpoint places on earth.

Simple, right? Yeah, but it’s easy when you’re looking at a modern globe or map. How did our forefathers who had no accurate maps deal with this problem?

Put yourself on a sailing ship in the early 1700s and set sail. How would you know where you were after a day? A few months? You’d be able to measure the angle of the sun or the moon above the horizon to establish your latitude (north-south), but how about your longitude (east-west)?

To measure that you’d need an accurate chronograph. But none existed. Clocks of that era relied on pendulums that were of no value on a pitching, rocking ship.

In her book “Longitude” (Penguin Books ISBN 0 14 02.58795) Dava Sobel explains: “The measurement of longitude meridians … is tempered by time. To learn one’s longitude at sea, one needs to know what time it is aboard ship and also the time at the home port or other place of known longitude – at the very same moment. The two clock times enable the navigator to convert the hour difference into geographical separation. Since the earth takes 24 hours to complete one full revolution of 360 degrees, one hour marks a 24th of a spin, or 15 degrees. And so each hour’s time difference between the ship and the starting point marks a progress of 15 degrees of longitude to the east or west.

Every day at sea, when the navigator resets his ship’s clock to local noon when the sun reaches its highest point in the sky, and then consults the home-port clock, every hour’s discrepancy between them translates into another 15 degrees of longitude.

With no way of measuring longitude accurately, ships and lives were lost.

Sobel masterfully tells the story of the race to come up with an accurate measure of longitude and how one man, John Harrison, devoted most of his life to building a chronometer that satisfied the needs of mariners. Actually, between 1730 and 1770 he built and revised five models.

If you like science and history with some politics of the times thrown in, get your hands on this book. It’s a quick and informative read.

Jeff Strout’s column is published on Saturdays. He can be reached at 990-8202 or by e-mail at jstrout@bangordailynews.net.