Abstract
THE Admiralty has kindly lent to the Science Museum, South Kensington, all four of the pioneer marine timekeepers made by John Harrisori between 1729 and 1759. With these instruments Harriaon was the first to show that it was possible to construct a portable timekeeper which would keep sufficiently accurate time at sea to be of uso in determining a vessel's longitude, and thus solved the problem of ‘finding the longitude’ which had baffled men of science and inventors for more than two hundred years. Harrison's instruments were the first balance-wheel timekeepers to embody any kind of compensation for the effects of change of temperature. In all four of his instruments compensation is provided by varying the effective length of tho balance-spring, tho mechanical details varying in the different individuals. In the first three timekeepers, the effect of the ship's motion is also compensated by employing two balance-wheels connected together by an ingenious but delicate system equivalent to a friction-less gearing; in the fourth chronometer, however, this system is abandoned in favour of a single small balance-wheel the angular acceleration of which is large compared to the stray accelerations due to the ship's motion. The first three chronometers are large clocks each weighing more than fifty pounds, but the fourth is much smaller, being essentially a large watch about five inches in diameter. All four instruments have been cleaned, repaired and put into working order by Lieut.-Commander R. T. Gould, and they are now on exhibition in the Museum, in going condition.
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Harrison's Chronometers at the Science Museum. Nature 136, 216 (1935). https://doi.org/10.1038/136216a0
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DOI: https://doi.org/10.1038/136216a0