A new and accurate method of finding a ship's position at sea, by projection on Mercator's chart ...: The principles of the method being fully explained and illustrated by problems, examples, and plates, with rules for practice, and examples from actual observation (Google eBook)

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T. Groom & co., 1845 - Navigation - 88 pages
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Page 47 - Greenock, a series of heavy gales from the westward promised a quick passage. After passing the Azores, the wind prevailed from the southward, with thick weather, after passing longitude 21 W., no observation was had until near the land, but soundings were had not far, as was supposed, from the edge of the bank. The weather was now more boisterous, and very thick, and the wind still southerly. "Arriving about midnight, 17th December, within 40' by dead reckoning, of Tuskar light, the wind hauled...
Page 47 - It then at once appeared that the observed altitude must have happened at all the three points, and at SmalPs light, and at the ship, at the same instant of time; and it followed, that Small's light must bear ENE, if the Chronometer was right.
Page 22 - , crosses the second Sumner line will be the position of the ship at the time of the second observation, and a, her position at the first observation.
Page 47 - Irish coast a lee shore; the ship was then kept close to the wind, and several tacks made to preserve her position as nearly as possible until daylight, when, nothing being in sight, she was kept on ENE under short sail with heavy gales. At about 10 AM an altitude of the sun was observed, and the Chronometer time noted; but having run so far without any observation, it was plain the Latitude by dead reckoning was liable to error, and could not be entirely relied on. Using, however, this Latitude,...
Page 50 - If any plane or fiat surface pass through the sphere, the intersection of the surface of the sphere by the plane is the circumference of a circle. A great circle of a sphere is one whose plane passes through the centre of the sphere, and so divides the sphere into two equal parts, called hemispheres. A small circle of a sphere is one whose plane does not pass through the centre of the sphere, and consequently divides the sphere into two unequal parts. The pole of any circle of a sphere is a point...
Page 79 - ZZ' is greater than 180 (or must be subtracted from 360) when the great circle which passes through the positions in the heavens,, in which the bodies were observed, passes also below the elevated pole., the bodies being also observed on different sides of the meridian. In all other cases ZZ
Page 47 - ... light, and at the ship, at the same instant of time ; and it followed, that Small's light must bear ENE, if the Chronometer was right. Having been convinced of this truth, the ship was kept on her course. ENE, the wind being still SE, and in less than an hour, Small's light was made bearing ENE }^E., and close aboard.
Page 47 - E., and close aboard. The latitude by dead reckoning, was erroneous 8 miles; and if the longitude by chronometer had been found by this latitude, the ship's position would have been erroneous 31 i minutes of longitude, too far W., and 8 miles too far S.
Page 47 - December, within 40 miles, by dead reckoning, of Tusker light, the wind hauled SE true, making the Irish coast a lee shore; the ship was then kept close to the wind, and several tacks made to preserve her position as nearly as possible until daylight, when, nothing being in sight, she was kept on ENE under short sail with heavy gales. At about...
Page 12 - The latitude, longitude, and apparent time being uncertain, and one altitude of the sun being observed, at any hour, when sufficiently high above the horizon, the chronometer time being noted, and declination given; it is required to project, on Mercator's chart, a line, diagonal to the parallels of latitude, and meridians of longitude, called a parallel of equal altitude, which shall pass through the position of the ship, and show by inspection, 1st. The bearing of the land. 2nd. The errors of longitude...

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