35.
A
RNOLD'S CHRONOMETER.
Joshua Romer. London. 1807.

Meriwether Lewis purchased a “Gold Chronometer” from Thomas Parker in Philadelphia for $250 and paid an additional 75 cents for a winding key. This may or may not have been an Arnold’s chronometer, which was a very rare and expensive instrument. Lewis described the chronometer thus:

her ballance-wheel and [e]scapement were on the most improved construction. she rested on her back, in a small case prepared for her, suspended by an universal joint. she was carefully wound up every day at twelve oclock. Her rate of going as asscertained by a series of observations made by myself for that purpose was found to be 15 Seconds and a 5 tenths of a second too slow in twenty-four howers on Mean Solar time.

The ”small case“ that Lewis mentions was a mahogany box; the ”universal joint“ was a set of gimbals which held the chronometer in a horizontal position. Before the expedition began, Andrew Ellicott recommended that Lewis secure such a box and a set of gimbals. Lewis paid Henry Voigt of Philadelphia $6.75 for the box and gimbals and for cleaning and adjusting the chronometer.

On the Lewis and Clark Expedition, the most important attribute of the chronometer was not whether it kept perfect time but rather whether its rate of going—the daily rate of time gained or lost—was known, predictable, and consistent. In the field, Lewis measured a rate of going for his chronometer that closely matched the rate that Ellicott had determined for the chronometer before the expedition began.

During the expedition Lewis sometimes carried the chronometer in his watch pocket which led on two occasions to the chronometer getting soaked. The watch also stopped several times because Lewis neglected to wind it; on other occasions it stopped for no apparent reason. When it was necessary to reset the chronometer, Lewis could stop the timepiece by inserting a “hog’s bristle” through a hole in the watchcase.

The watch on display in this exhibition was made by Joshua Romer of London in 1807. Although it is not an Arnold’s chronometer, it is typical of the pocket chronometers of its day.

This watch is on loan from the National Museum of American History, Smithsonian Institution.


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