Hamilton Chronometer Model 21 Up-dn With Mint Inner And Nice Outer Box Running For Sale

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Reprinted from H. A. A. Journal August 1946.

One of the very latest achievements in the persistent progress of horology is the hairspring and balance wheel assembly of the Hamilton marine chronometer. This assembly has contributed to the history of the marine chronometer records of performance never previously attained,-- records of performance which have been repeated not just once or twice, but thousands of times. Its success was the result of an intensive, modern engineering analysis which depended, for its execution, upon the traditional craftsmanship and skill of the horological industry. A detailed description of this balance unit and an explanation of the many features which contribute to its remarkable properties are being given her for the first time.

Before the days of Christopher Columbus and down through the years until the latter part of the eighteenth century, whenever man ventured out of sight of land he had at his command only crude methods of dead reckoning to determine his location at sea. This method of navigation involved computation of the course of a ship on the basis of the known location of the starting point and estimates of direction, speed, drift and so forth. It was only as precise as the observation of these variable factors. Its inaccuracies not only caused endless inconvenience, but introduced hazards of shipwrecks on voyages of long or short duration.

Following the period of discovery, as colonial expansion and sea commerce continued to develop, the need for a better solution to the paramount problem of navigation became even more critical. Early mariners, for the determination of their latitudes (or north-south positions) at sea, had employed a method satisfactory in principle but only approximate in execution. About 1730, by the invention of the sextant, this method was defined to nearly its present state, Determination of longitude, however was found to be a much more difficult problem. Its solution was regarded so important that during the seventeenth and eighteenth centuries many leading nations offered immense financial rewards for the "discovery of the longitude." The most classical of these was that posted by England through the especially created Board of Longitude.

At that time, various methods of determining longitude were being advocated. The most feasible of all appeared to be that one requiring these three factors: an almanac, a sextant, and an accurate source of time.

By means of the almanac and sextant, both already at his disposal, a navigator could readily determine his local time at sea. If he could only know by how much hi local time differed from that at the zero meridian (Greenwich) at the moment of observation, he could readily establish his longitude through the relationship: 24 hours equals 360 degrees of longitude. Hence, the development of an accurate, portable timepiece became a challenge to the horologists of the period.

The man who successfully met this challenge was John Harrison. His was a long struggle. He face many obstacles in proving the excellence of his chronometer. But finally, by his genius and persistence, he qualified for the prize of 20,000 pounds sterling offered by the Board of Longitude. He had created a timepiece that would assure determination of longitude within half a degree,--thirty nautical miles. Through this achievement marine navigation became an exact science and an invaluable instrumentality in man's ever-growing conquest of the seas.

Succeeding generations of horological craftsmen refined and improved the chronometer. They contributed steadily to its value and importance to the sea-faring men of all nations, making it the most treasured and carefully guarded piece of equipment aboard ship. And even now, in our own era of advanced scientific development, the marine chronometer remains an indispensable implement of marine navigation. This is a tribute to the art and science of horology.

However, down through the years until the entry of this country into the recent war, the production of chronometers was conducted on a small-volume basis. Skilled chronometer makers, individually or in small groups, produced and assembled the parts and adjusted the instruments. Sources of supply were confined almost entirely to England and Switzerland.

As the participation of the United States in the war became imminent in 1940 and 1941, plans were laid for the building of history's greatest navy. And out of this program sprang history's greatest demand of marine chronometers. Existing sources of supply were hopelessly inadequate. Some were threatened with extinction, others with virtual isolation. How was the United States Navy to get these chronometers-- vast quantities of them--in the shortest possible time? Could dependability of performance be assured? Could greater accuracy be attained to meet the precise requirements of the modern warfare? This was the challenge issued by the United States Navy through the United States Naval Observatory.

The Hamilton Watch Company accepted that challenge and, with the fine cooperation of the Naval Observatory, designed and produced a marine chronometer which fully met the Navy's requirements. The success of that venture is attested by the performance records of 10,000 Hamilton chronometers delivered to the Navy and the Maritime Commission since early in 1943, sometimes at the rate of 500 per month!

At first glance, the Hamilton marine chronometer is conventional in appearance. However, a detailed examination will reveal many innovations. Some were created for the benefit of volume production, but other were deemed necessary for the sake of excellence alone. Characteristic of the former are the essential interchange-ability of the parts and the accessibility and service conveniences. Of the later, the most outstand are those incorporated in the hairspring and balance assembly. These also constitute the most significant departures from previous chronometer construction. Just how these improvements came about can be understood best by first analyzing the problem that existed before their development.

An appraisal of the various elements of a chronometer movement revealed that although the mainspring, fusee, train and escapement all contribute to the performance and serviceability of the instrument, these elements had already been developed to a stage bordering on perfection; that the inherent qualities of the hairspring and balance wheel were the limiting conditions affecting its precision of performance.

From analysis of an extensive series of tests on a variety of chronometers, the principal faults in rating were summarized as follows:

1. Instability of rate. After the balance wheel has been stopped or after a change in in temperature, the recovery of rate is not immediate or not exact. After service or overhaul, an appreciable running-in or settling period is required before the rate becomes stable.

2. Large isochronal error. Slight changes in amplitude of balance wheel motion caused by variations in the driving force are usually accompanied by a significant change in rate. As a rule, the rate increases when the motion decreases.

3. Temperature compensation error. This is appreciable and definite middle temperature errors exist, particularly when wide ranges of temperature are encountered. Compensation devices are varied and complicated in construction. Adjustment of compensation error is rather difficult with these constructions and usually affects other performance characteristics.

Hence, in the design of a new marine chronometer balance unit, the prime objectives were maximum stability of rate and minimum isochronal and temperature compensation errors. Furthermore, it was imperative that these characteristics be achieved, in so far as possible, through inherent qualities of the various components. Arduous and time-consuming application of personal skills in adjustment could not be tolerated because of the necessity for rapid and large volume production and the limited supply of highly experienced personnel.

In considering how these objectives were accomplished let us first view the balance as it appears in the assembled movement (Figure 1) and then discuss the various components in the following order:

HAMILTON MODEL 21 14 JEWEL FUZEE CHRONOMETER RUNS GREAT

Very nice inner and outer boxes. Up and down indicator works as it should. Nice dial and black hands . Detent escapement and chain fuzee drive.

Running strong. Please not the escape wheel will be blocked for shipping. Rare Hamilton ships chronometer

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