The Bay itself has no concept of time. The measurement of time is a human construct that enables us to schedule events, coordinate activities and meet deadlines. It is also a road map for history, placing events and artifacts in context and sequence. Yet most of us take for granted all of the timepieces that regulate our lives.

Methods of reckoning time have included how long a pierced vessel took to be drained of water, how long a lamp or candle took to gutter or how long it took sand to pass through an hourglass.

The movement of the sun was also used to measure time. Sundials go back 5,500 years. There were even portable versions: Eleanor of Aquitaine gave a ring-sundial to Henry II in 1152 to wear as neck pendant. He, in turn, bestowed on her a bejeweled version inscribed with carpe diem-seize the day.

A colonial era gnomon-the upright shadow vane of a sundial-was found at Historic St. Mary's City, MD. It dates from the 1650s and was probably mounted atop a compass for quick alignment with North, a requirement for timekeeping.

Sundials work almost anywhere but are most accurate when they are designed to correspond to a particular latitude, so that the resulting shadow falls along a rim marked with the hour gradations. Curator Silas Hurry said the St Mary's City gnomon was made for Jerusalem, the point that many 17th century navigators reckoned zero degrees longitude.

It is likely that Capt. John Smith had such an instrument, because during his capture in 1607 by the Powhatan Chief Opechancanough, Smith used a pocket compass to amaze his captor, showing him the glass face through which he could see the needle and not touch it. Smith also gave a quick lesson in geography and astronomy. I can't see how he could have done this without the sundial's help.

Smith's cleverness may have saved him from the terrible fate of his two companions, Master Jehu Robinson, who was shot through with 20-30 arrows, or Thomas Emry who died under excruciating Powhatan torture.

Weight-driven clocks turning gears of some sort go back to the 1200s, when some early models had only an hour hand. Near the middle of the 17th century, though, Dutch physicist Christiaan Huygens (1629-93) began to analyze the pendulum -likely inspired by Galileo.

The swinging of a pendulum is one of the most regular, repetitive motions in nature. Placing a weight or "bob" at the end of the pendulum gives it the momentum to continue swinging a long time. The "period" or time for a complete cycle-to and fro-is constant, depending only on the length, mass of the pendulum and gravity.

Clock makers have determined that a length of about 39 inches constitutes a "seconds pendulum" because it swings one second in either direction. A bob that is supported on a threaded rod can be adjusted up and down slightly-changing length-so it will keep accurate time. The trick is to keep it going.

Huygens licensed Salomon Coster, of The Hague in the Netherlands, to make clocks based on this principal. The earliest known example of a Huygenian timepiece is dated 1657 and can be seen in Leiden in the Netherlands.

Huygens' work on pendulums was published in 1673. His mechanisms, though, were unreliable on a moving ship where the gyrations of wind and wave disturbed a pendulum's swing. With an accurate timepiece, mariners would be able to tell, by measuring speed, how many miles east or west they had travelled and thus determine, and record, longitude. This was vital information for those who wanted to avoid running into land during the night or a storm.

Huygens thought that it was possible to build a spring-driven clock that could be taken to sea. He did build such a clock, but it was not accurate enough.

Spring-operated clocks were not new, and Huygens drew upon the work done by Peter Henlein of Nuremburg in 1509. (The Cosmolography of Pomponius Mela, published 1511, noted that "In these days of ingenious things, Peter [Henlein]...performs works that astonish...for with a little iron, he makes timepieces...that no matter how they are turned about both indicate time and beat 40 hours even though carried on the chest or in the pocket." These were arguably the first "pocket watches," although tension on the spring grew less as it unwound, slowing the clock, a problem that was not solved until much later.)

In 1675, Huygens took out a patent on his own version of a pocket watch and the use of a spring-wound movement allowed for the miniaturization of time pieces so they could be portable.

At sea, there were still no functional clocks, and "time" aboard was kept using a (half-hour) hourglass which at each turn, day and night, was marked by the ringing of the ship's bell. Each half hour, the number of strokes on the bell was increased by one until at eight bells, or four hours, the watch-a seaman's work shift-was changed.

Mariners could only estimate speed through the water and-factoring in time-the distance travelled. A traditional weighted chip or "log" of wood was tossed overboard attached to a cord, which was let run out as the ship sailed away from the stationary log. The cord had knots every 47.3 feet and those passing through a seaman's hand were counted while a little "hourglass" running 28 seconds, ran its course. The number of "knots" felt by the seaman was the vessel's speed through the sea.

It wasn't until 1765, that the first reliable maritime chronometer-an accurate shipboard clock that would keep time though a long voyage-was developed by John Harrison of England. It was the size of a grapefruit.

Ashore, other clocks proliferated. The Astronomer Royale at Flamsteed Observatory in Greenwich, England, had timepieces calibrated to the movements of celestial bodies, with long pendulums and extremely accurate periods. These were enclosed in cases to protect them from drafts.

In the early 19th century, thousands of clock makers and sellers were working throughout Europe and the British Isles. A popular model was the long-case clock-now called a grandfather clock. It was large enough to have a seconds pendulum and had enough vertical room for its weight-driven mechanism to run for a week or more.

There were clockmakers in the United States as well, but for a long time, they built only the cases or cabinets, using domestic woods. The movements were still imported-often from the British Isles. Models burgeoned with almost unlimited variety. The basic clock had a face of sheet steel coated with zinc, which prevented paints and enamels from flaking off. The dial with hands was usually ornamented and the numerals added by an artist. Options for a seconds dial, displays of day and date, or phases of the moon, appeared in every conceivable fashion, with chimes and animations added, driven by additional weights.

Simultaneously, the technology for watches was also developing. In 1687, David Johnson in Boston was taxed as a 'watchmaker,' although most believe he only repaired them. The obituary for Thomas Harland 1735-1807 noted that he made the first wrist watch in America. Philip Sadler of Baltimore sold watches in 1806, although they are believed to have been imported.

Watches have been machine-manufactured since about 1850. They were, for men, almost exclusively pocket watches. Wrist watches, called "wristlets," were generally women's fare.

This changed during World War I, when wristwatches were used in combat to time maneuvers and coordinate artillery fire. They were much more handy on the wrist. In 1926, Rolex introduced a truly waterproof watch: the "Oyster."

When our neighbors, J. Russell and Margaret McQueen, died in the early 1980s, their old grandfather's clock was put up for sale by their son, John. My wife, Nancy, wanted the clock, but I balked at the price.

A little research revealed that this timepiece had been made by T. [Thomas] Barclay, who made and sold clocks from 1811-1822 in Montrose, a town in southeastern Scotland. It appears that Barclay was personally responsible for the assembly, its painted face and likely its hardwood cabinet.

The works themselves-the brass gears, shafts, vanes and frames-were made by B. Wright and Company. Efforts to locate a record of this exact firm were unsuccessful. There was a "B. [Benjamin] Wright, who made clocks in London in the late 1600s. Could this clock have been made by one of his descendants?

Eventually, the clock's history led me to loosen my purse strings and it began ticking in our great-room at Catchall.

It didn't tick for too long, though, and I trundled the works up to Richard Slama, an Annapolis clock maker. On my first visit he looked at the clock awhile then said that he remembered the clock from years earlier. "A lady came in and liked it, but the man stamped out wanting nothing to do with such a frivolous thing. The lady came back the next week and bought it anyway, and off it went." The couple was the McQueens.

Slama was puzzled why it wouldn't run. It had ticked and kept time in his shop for a couple of weeks. When he learned where it had been placed in our old house, he said the problem was likely vibrations in the weights. Walking on our rickety 100-year-old floors would set the 13-pound pieces of iron running the bell and pendulum slowly swinging. This will eventually stop the clock

Huygens had already figured this out in the 17th century: Two pendulums swinging from a common support will come to swing in opposite directions, which will eventually stop the clock. He called this phenomenon "odd sympathy," today it is described as resonance. Securing the clock case to the wall solved this problem.

Later, the nearly 200 years of ticking-the constant stop and release of gears as the pendulum swung to and fro-eventually began to wear down little brass teeth in parts of the mechanism, as well as loosen the bearings where the shaft of each component turned, which made the fit between gear teeth even worse. It was necessary for Slama to make a gear or two from scratch.

At sea, both on the Bay and worldwide, mariners have gone beyond mechanical timepieces and increasingly rely on satellite-based time and three-dimensional location signals from the Global Positioning Network encircling Earth.

These devices are easy to use and extremely accurate, but are subject to failure, which puts a mariner in danger if he or she is not trained to fall back on some of these older technologies.

Traditional clock-makers (and repairers) are scarce today. Of the four I've known, only Paul Corn of Waldorf, MD remains. I hope he and his colleagues will go on preserving the many ancient clocks still functioning. It is a comfort for me to awake at 2 a.m. and hear the old Montrose clock striking as it has for almost the last 200 years.