Soldier using a prismatic compass to get an azimuth A prismatic compass is a navigation and surveying instrument which is extensively used to find out the bearing of the traversing and included angles between them, waypoints (an endpoint of the lcourse) and direction. Compass surveying is a type of surveying in which the directions of surveying lines are determined with a magnetic compass, and the length of the surveying lines are measured with a tape or chain or laser range finder. The compass is generally used to run a traverse line. The compass calculates bearings of lines with respect to magnetic needle.
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Least count means the minimum value that an instrument can read which is 30 minutes in case of prismatic compass. It means compass can read only those observations which are multiples of 30 minutes, 5° 30', 16° 00', 35° 30', for example.
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A prismatic compass and local map are essential companions to aid route finding. There are relatively few walkers on the Black Mountain, even when the weather is good and clear, so the walker must rely on his or her own resources to complete a circuit.
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He is considered as the inventor of the prismatic compass, patented a year later by Charles Schmalcalder. He also studied compass needles, his Bakerian lectureOn the Best Kind of Steel and Form for a Compass Needle; Phil. Trans., 1821. containing the results of many experiments.
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The included angles can then be calculated using suitable formulas in case of clockwise and anti-clockwise traverse respectively. For each survey line in the traverse, surveyors take two bearings that is fore bearing and back bearing which should exactly differ by 180° if local attraction is negligible. The name Prismatic compass is given to it because it essentially consists of a prism which is used for taking observations more accurately.
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Charlie Douglas (left), Arthur Paul Harper, and Douglas' dog Betsey Jane in the valley of the Cook River in 1894 From 1889 Douglas agreed to work for the survey department full-time for a wage of eight shillings a day. He was provided with: a prismatic compass, a survey chain and drawing tools. For five months, in 1891 Douglas travelled up the Waiatoto River. He climbed Mount Ragan and reached the Therma Glacier at the head of the Waiatoto.
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As in all mountains care is needed when the weather is poor, especially when visibility falls due to mist, fog or driving rain and snow. Navigation can become difficult when landmarks disappear, and is particularly dangerous when walking along the edge of the escarpment. A prismatic compass and local map are essential companions to aid navigation. There are relatively few walkers on the Black Mountain, even when the weather is good and clear, so the rambler must rely on his or her own resources to complete a circuit.
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Points have been located with a prismatic compass > all around the Lake. A man stands on the shore with a compass and takes a > bearing to the man in the Boat as he drops the lead, giving a signal at the > time. Then a man in the Boat takes a bearing to the fixed point on the shore > where the first man is located and thus the soundings will be located on the > chart. Henry Elliot and Mr. Carrington have just left in our little boat, > the Annie.
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Except in areas of extreme magnetic declination variance (20 degrees or more), this is enough to protect from walking in a substantially different direction than expected over short distances, provided the terrain is fairly flat and visibility is not impaired. By carefully recording distances (time or paces) and magnetic bearings traveled, one can plot a course and return to one's starting point using the compass alone.Johnson, p. 149 Soldier using a prismatic compass to get an azimuth Compass navigation in conjunction with a map (terrain association) requires a different method.
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Lieutenant Pennell with a prismatic compass Commander Harry Lewin Lee Pennell (1882 – 31 May 1916) was a Royal Navy officer who served on the Terra Nova Expedition. He was responsible for the first sighting of Oates Coast on 22 February 1911, and named it after Captain Lawrence Oates. He only spent short periods in Antarctica, returning with the Terra Nova to wait out the winters of 1911 and 1912 in Lyttelton, New Zealand. Due to the absence of Robert Falcon Scott on land, Pennell assumed the role of command on the Terra Nova, which would bring fresh supplies back to Antarctica with each voyage.
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Three days later at Ganderi, he joined his three associates "our party then consisting of forty, including muleteers, and fifteen baggage animals," loaded with articles for trade: "cloths of English manufacture, musical boxes, binoculars, time- pieces, a spare revolver or two with a few rounds of ammunition, salt, glass beads, shells, needles, country-made looking-glasses, shoes, and lungis, as well as several phials and galipots of medicines," and for provisions "nothing but sugar and tea."J.E. Howard, ed., Memoir of William Watts McNair: The First European Explorer of Kafiristan (London: D.J. Keymer, 1890). Prismatic compass As McNair explained, > In addition to these I had secreted a prismatic and magnetic compass, a > boiling point and aneroid thermometer, and a plane-table which I had > constructed for the occasion. . . .
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