Time and timekeepers: by Thomson Adam

Author:Thomson, Adam
Language: eng
Format: epub
Tags: Clocks and watches, Time
Publisher: London, T. & W. Boone
Published: 1842-03-25T05:00:00+00:00

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To the honour of those whose genius and labour were directed to horology, timekeepers have been found to give the longitude with so much certainty, that other methods are now chiefly applied to verify the correctness of the observation. Huy-ghens is supposed to have been the first who thought of constructing timekeepers for this par-pose ; but at that period, 1664, sufficient attention had not been paid to the effects produced on metals by the variations of temperature in different climates, and he unfortunately failed in his experiments.

CHRONOMETERS USED AT SEA.

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The first was invented by John Harrison—Hardships avoided by means of the Chronometer—Its complete success— Obtained the Prize.

The first chronometer used at sea, was invented by John Harrison, and after many years of study completed in 1736. It neither varied from change of temperature, nor the motion of a vessel. This timekeeper was first placed on board a ship of war going to Lisbon, the captain of which attested, that Harrison had corrected an error of about a degree and a half upon their return to the English channel.

In 1739 he produced one upon a smaller scale,

which from experiments made, promised to give the iongilude with even greater accuracy. In 1741 he finished another smaller tiiun either, which appeared io the members of the Royal Society more simple, and less likely to be deranged ; and in 174!) he received the gold medal which is annually awarded by the Royal Society to the originator of the most useful discovery.

Having much improved and corrected this third chronometer, Harrison applied to the comniis-rs of the Board of Longitude, in order to :i a trial, according to the Act of Parliament; this, after much delay, was granted, and his son : as allowed to take a, voyage to Jamaica instead f himself. William Harrison embarked at Portsmouth on e lfith of November, 1761, after eighteen days' wvigation the vessel was supposed to be 13° 50' pest of Portsmouth, while the watch marking 15° 19'was condemned as useless. Harrison, how-maintained, that if Portland Island were wrrectly marked on the chart, it would be seen 1 the following day ; and in this he persisted so rongly, that the captain was induced to continue . the same course, and accordingly the island as discovered the nest day at seven o'clock. This raised Harrison and his watch in the estimation of the cre«', who otherwise would nol have

been able (o procure the necessary stores during the remainder of the voyage.

In like manner Harrison was enabled by hie watch to announce all the islands in the order in which they would fall in with them. When he arrived at Port Royal, after u voyage of eighty-one days, the chronometer was found to be about live seconds slow; and finally, on his return to Portsmouth, after a voyage of five montiis, it had kept time within about one minute, five seconds, which gives an error of about eighteen miles.

This whs much within the limits of thirty miles prescribed by the act of 1714, yet several objections being; raised, (chiefly it is supposed by Dr.

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