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Parallel Sailings
Published in Philip M. Smith, Terrestrial Navigation, 2017
Prior to the invention of the marine chronometer, accurate timekeeping being required for the calculation of Longitude, navigators generally had to resort to sailing only due North, South, East or West or not sailing far out of sight of land. The vessel would sail North or South and measure her Latitude daily. When she reached the parallel of Latitude that her destination port was on, she would then sail East or West along that parallel until a landfall was made. This method of sailing is known as Parallel sailing but as there are few ports directly East or West of one another, and apart from short legs of a coastal passage which may require steaming due East or Westerly courses, there is little requirement for this method of navigating nowadays. It should however be noted that there is often a crossover of the mathematics used between different navigational disciplines. The method of calculation of the position of the Intercept Terminal Point (ITP) used in celestial navigation position fixing, is governed by exactly the same mathematical theory, but projected on the celestial sphere as opposed to the terrestrial sphere, the surface of Earth.
Celestial Navigation—Spherical Trigonometry, Spherical Triangles, Azimuth, Sextant Altitude, Amplitude, and Line of Position
Published in George A. Maul, The Oceanographer's Companion, 2017
Ancient cartographers were well aware that latitude could be determined from the sun and stars, and they also knew that longitude was a matter of knowing the correct time difference between two places. At sea, time at a reference longitude, say Greenwich, England, could be determined by the lunar-distance method, but it was cumbersome and often required mathematical skill beyond that of the ordinary seaman. Determining longitude at sea probably was the major scientific problem of the eighteenth century, so much so that the English Parliament offered the longitude prize of £20,000 in 1714. It was won by John Harrison, who invented the marine chronometer just prior to the time of the American Revolutionary War.
The Earth–Sun Relationship
Published in Matt Fajkus, Dason Whitsett, Architectural Science and the Sun, 2018
The lack of a celestial basis for longitude meant that in nautical navigation, mariners were able to determine latitude with a high degree of accuracy using the position of stars for hundreds of years before reliable methods of determining longitude were available. The solution was a highly accurate time-keeping device known as the marine chronometer that allowed sailors to calculate the difference between the time at the prime meridian and local solar time and thus determine their longitude. Today, global positioning systems have largely solved the challenges of determining east-west position at sea, but in the absence of GPS data, the marine chronometer is still the primary means for doing so.
The origins and early years of the Magnetic and Meteorological department at Greenwich Observatory, 1834-1848*
Published in Annals of Science, 2018
At the same 1824 meeting, the Board of Visitors requested the Royal Society Council to consider applying for ‘a proper place’ for the magnetic instruments and observations. This was never acted upon, perhaps because by the mid-1820s, Pond and the observatory had many other problems. The most immediate of these was that, beginning in 1821, the Admiralty requested that the Royal Observatory begin a regular programme of ‘rating’ (testing for accuracy) marine chronometers for use aboard Royal Navy ships. This greatly increased the volume of work for Pond and his assistants, especially as it entailed much tedious paperwork and liaison with chronometer makers as well as the Admiralty.29 In addition, Pond began to be affected by increasingly frequent bouts of serious illness. During his absence, the day-to-day running of the observatory was left to Pond’s ‘Chief Assistant’ (effectively his deputy), Thomas Taylor, who had gained a reputation for drunkenness and was losing the respect of his more junior assistants. The result was that the regular observations of heavenly bodies – the Royal Observatory’s first priority – fell further and further into arrears. Work that had lower priority, such as reviving the magnetic observations, was simply neglected.