An Octant is a doubly reflecting navigation instrument used primarily by sailors to measure the angular distance between two visible objects and was a forerunner of the sextant. The name comes from the Latin octo, or “one-eighth of a circle,” for the Octant’s arc which spans 45°, or one-eighth of a circle. The primary use of an Octant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation. The estimation of this angle is known as sighting or shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical chart (latitude), for example, sighting the Sun at noon or Polaris at night (in the Northern Hemisphere) gives an angle by which the latitude can then be estimated. Sighting the height of a landmark on land can also give a measure of distance. History: The principle of the Octant as an instrument to measure ones latitude was first implemented around 1742-present but was superseded by the improvement of the octant to a sextant, a very similar instrument, better made and able to measure bigger angles 120°, allowing the measurement of Luna distances to give longitude when used with an accurate chronometer. The sextant started to appear around 1730 and had been attributed to by John Hadley (1682–1744) and Thomas Godfrey (1704–1749), but reference to the sextant was also found later in the unpublished writings of Isaac Newton (1643–1727). Earlier links can be found to Bartholomew Gosnold (1571–1607) indicating that the use of a Sextant for nautical navigation predates Hadley's implementation. In 1922, the sextant was modified for aeronautical navigation by Portuguese navigator and naval officer Gago Coutinho. Henry Hemsley was a lesser-known instrument maker and optician working in London in the late 17th and early 18th century. However, it should be noted that there were two Henry Hemsley opticians and instrument makers around this period. (Henry Hemsley 1, 1786-89, who had premises at 85 Fleet St London and Henry Hemsley 2, 1828-56), whose workshop was at 135-138 Radcliff Highway London. Therefore, based on the inscribed workshop address Henry Hemsley 2 is responsible for making this example.The octant is representative of its type and although not fully complete it demonstrates how 18th and 19th-century mariners determined their latitude on a chart to navigate their way across the world's oceans in the 18th and 19th century. It also demonstrates the skill and workmanship of the early instrument makers that operated from London at this time and provided most of the navigational instrumentation use by commercial and military navies of the time.Octant, ebony wooden frame and handle. Scale is missing from recess in frame. "H. Hemsley 135-138 Ratliff Highway, London", no box"H. Hemsley 135-138 Ratcliff Highway, London"flagstaff hill, warrnambool, shipwrecked-coast, flagstaff-hill, flagstaff-hill-maritime-museum, maritime-museum, shipwreck-coast, flagstaff-hill-maritime-village, navigation, navigational instrument, instrument used for navigation, sextant, henry hemsley, instrument maker, london, octant

An octant is an astronomical instrument used in measuring the angles of heavenly bodies such as the sun, moon and stars at sea in relation to the horizon. This measurement could then be used to calculate the altitude of the body measured, and then the latitude at sea could also be calculated. The angle of the arms of an octant is 45 degrees, or 1/8 of a circle, which gives the instrument its name. Two men independently developed the octant around 1730: John Hadley (1682–1744), an English mathematician, and Thomas Godfrey (1704–1749), a glazier in Philadelphia. While both have a legitimate and equal claim to the invention, Hadley generally gets the greater share of the credit. This reflects the central role that London and the Royal Society played in the history of scientific instruments in the eighteenth and nineteenth century's. There were also two others who are attributed to having created octanes during this period, Caleb Smith, an English insurance broker with a strong interest in astronomy (in 1734), and Jean-Paul Fouchy, a mathematics professor and astronomer in France (in 1732) In 1767 the first edition of the Nautical Almanac tabulated lunar distances, enabling navigators to find the current time from the angle between the sun and the moon. This angle is sometimes larger than 90°, and thus not possible to measure with an octant. For that reason, Admiral John Campbell, who conducted shipboard experiments with the lunar distance method, suggested a larger instrument and the sextant was developed. From that time onward, the sextant was the instrument that experienced significant development and improvements and was the instrument of choice for naval navigators. The octant continued to be produced well into the 19th century, though it was generally a less accurate and less expensive instrument. The lower price of the octant, including versions without a telescope, made it a practical instrument for ships in the merchant and fishing fleets. One common practice among navigators up to the late nineteenth century was to use both a sextant and an octant. The sextant was used with great care and only for lunar sightings while the octant was used for routine meridional altitude measurements of the sun every day. This protected the very accurate and pricier sextant while using the more affordable octant for general use where it performs well. The invention of the octant was a significant step in providing accuracy of a sailors latitude position at sea and his vessels distance from land when taking sightings of land-based landmarks.Octant with metal handle, three different colored shades are attached, in wooden wedge-shaped box lined with green felt. Key is attached. Two telescope eyepieces are in box. Some parts are missing. Oval ink stamp inside lid of box, scale is graduated to 45 degrees. Ink stamp inside lid of box "SHIPLOVERS SOCIETY OF VICTORIA. LIBRARY"instrument, flagstaff hill, warrnambool, shipwrecked coast, flagstaff hill maritime museum, maritime museum, shipwreck coast, flagstaff hill maritime village, great ocean road, octant, navigation, nautical instrument, navigation instrument, john hadley, sextant, astronomical instrument

An Octant is a doubly reflecting navigation instrument used primarily by sailors to measure the angular distance between two visible objects and was a forerunner of the sextant. The name comes from the Latin octo, or "one-eighth of a circle," for the Octan'ts arc which spans 45°, or one-eighth of a circle. The primary use of an Octant is to measure the angle between an astronomical object and the horizon for celestial navigation. The estimation of this angle, is known as sighting or shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical chart (latitude), for example, sighting the Sun at noon or Polaris at night (in the Northern Hemisphere) gives an angle by which the latitude can then be estimated. Sighting the height of a landmark on land can also give a measure of distance. This fine octant once belonged to Captain Farquhar Chisholm and was donated by his granddaughter, Margaret Ruth Greer (nee Chisholm, born 1914). The label inside the Octant's box reads “Thomas L. Ainsley, Instrument Maker … etc”. Farquhar Chisholm was born in 1832 in Inverness, Scotland. He regularly sailed on perilous voyages between Quebec, Canada and the Baltic ports of Europe. In 1854 he migrated to Australia during the Gold Rush, to a place called Fiery Creek (near Beaufort Victoria) where he was fairly successful in his quest for gold. In the years of the Great Gold Rush, it was said that there were over 40,000 diggers in the goldfields of the Beaufort area! In 1857 having made sufficient money, he hired another crew and returned to Clachnacuddin, Inverness shire, Scotland and in that same year, he studied and obtained his Master Mariner Certificate (which would have included the use of an octant for navigation). He was appointed to Mr George (or James) Walker, as commander of his sailing ship, the 3-masted ELIZABETH, built 1859 and known as “The Walker barque”. In 1870 he married, then in 1887 returned to Australia with his wife and children (Kenneth Chisholm (1871), Mary Bremner Chisholm (1873), Margaret Hood Chisholm (1874), Farquhar Chisholm (1878)). They arrived in Port Melbourne, Victoria and sadly, only six weeks after landing, his wife Caroline passed away (in Geelong,1888). In 1900 Capt. Chisholm lived in Camperdown (Victoria) and not long after this his daughter Margaret died of consumption. In his later years, he went to live in the manse of St. Paul’s Presbyterian Church, Wangaratta, with his son, Rev. Farquhar Chisholm. He died there on Sat, 23rd March 1912, 80 years old. He was known as “… quiet, unobtrusive and competent, respected by all with whom he came in contact”. Some other members of Captain Chisholm’s family are; his older son Kenneth Chisholm, who was a contractor in Camperdown; a nephew Donald Macintosh (of 23 Douglas Row, Inverness); a grandson Brian Jones (son of Caroline Belle-Jones nee Chisholm, who lived in Camperdown in the earlier part of her life).The octant, the forerunner of the sextant, was a significant step in providing accuracy of a sailors latitude position at sea & his vessels distance from land when taking sightings of land-based landmarks.Octant, once belonging to Captain Farquhar Chisholm. Wedge shape (the size of an eighth of a circle), made of wood, glass and metal. Used in the 1880s. Maker’s name across centre “L. SIMON - - - SHIELDS”. Three (3) light filtering, coloured glass shades. Two (2) eyepieces. Scale attached for measuring angles. Label inside the fitted, wedge-shaped case "Thomas L. Ainsley, Optician"Label inside case "Thomas L. Ainsley, Optician" Maker’s name across centre “L. SIMON - - - SHIELDS”.flagstaff hill, warrnambool, shipwrecked-coast, flagstaff-hill, flagstaff-hill-maritime-museum, maritime-museum, shipwreck-coast, flagstaff-hill-maritime-village, maritime navigation, navigation instrument, migration, captain chisholm, farquhar chisholm, sailing ship, the elizabeths, thomas l. ainsley, l. simons, shields england, octant, john hadley, chisholm

German Brass Octant. Early 19th century octant, serial number: M2218, with attachable brass lens and comes in a wooden box with a brass handle attached to the back of the box. Octant is comprised of a wooden handle, a brass arc and lenses and black metal body. Octant is a triangular shaped, with brass attachments joined to the top including a brass lens, a mirror, and several other mirrors and lenses. Also called reflecting quadrant.

A sextant is an astronomical instrument used to determine latitude and longitude at sea by measuring angular distances, especially the altitudes of the sun, moon, and stars. It is a doubly reflecting navigation instrument and used mainly by sailors to measure the angular distance between two visible objects. The name comes from the Latin sextans, or “sixth part of a unit,” because the sextant’s arc can be 60° or 120° of a circle depending on the model used. The primary use was to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation. The estimation of this angle is known as sighting or shooting the object, or taking a sight. This angle and the time when it was measured is used in order to determine Greenwich Mean Time and hence longitude. Sighting the height of a landmark on land can also give a measure of distance from that object. History: The development of the sextant was as an improvement over the octant, an instrument designed to measure one's latitude. The octant was first implemented around 1731-present but can only measure angles up to 45°. As larger angles were needed to allow the measurement of lunar objects - moon, stars and the sun - at higher angles, the octant was superseded by the sextant. The sextant is a similar instrument but better made and allows larger angles from 60° to 120°. This improvement allows distances to be accurately calculated thereby giving longitude when used with a chronometer. The sextant was derived from the octant in 1757, eventually making all previous instruments used for navigational positioning obsolete. The sextant had been attributed to by John Hadley (1682–1744) and Thomas Godfrey (1704–1749), but reference to the sextant was also found later in the unpublished writings of Isaac Newton (1643–1727). Earlier links can be found to Bartholomew Gosnold (1571–1607) indicating that the use of a sextant for nautical navigation predates Hadley's implementation. In 1922, the sextant was modified for aeronautical navigation by Portuguese navigator and naval officer Gago Coutinho. It should be noted that the octant and quadrant are in the same family as they were, and all are, regarded as sextants. The sextant is representative of it's type and although not fully complete it demonstrates how 18th,19th and 20th century mariners determined their latitude and longitudinal to determine their position on a chart, allowing them to navigate there way across the world's oceans. It also demonstrates the skill and workmanship of the early instrument makers that operated scientific instrument businesses from London and other areas of England to provide most of the navigational instrumentation used by commercial and military navies of the time.Sextant with square, fitted box of polished wood, "Hezzanith" brand. Box contains many parts for the sextants use. On certificate "Heath & Co, London. Sextant Number Y 822". Catch on lid "DEFIANT LEVER" and "PATENT NUMBER 187.10". Maker's certificate is attached to the inside of the box.flagstaff hill, warrnambool, shipwrecked-coast, flagstaff-hill, flagstaff-hill-maritime-museum, maritime-museum, shipwreck-coast, flagstaff-hill-maritime-village, sextant box, sextant, hezzanith, heath & co, navigational instrument, george wilson heath, astronomical instrument, instrument manufacturers, scientific instrument, navigation, celestial navigation, octant, quadrant, lunar navigation

This representative example demonstrates a mariner’s astrolabe. Historical examples are rare. There are less than one hundred known to exist and most of these have been recovered from shipwrecks, many from Spanish and Portuguese vessels. An astrolabe is a measuring device once used to navigate the seas by observing the sun and stars to measure their altitude. The measurement of altitude could then be used to calculate the ship’s latitude but at that time in history there was no means of measuring longitude. The body of the navigational astrolabe was cast brass and much heavier, and less complicated than the variety used on land. The heavier weight and cut-away shape reduced the effect of the wind and waves when trying to use it at sea. A mariner’s astrolabe or ‘star finder’ is a simplified version than that used by Arabic astronomers to find the altitude of the sun and stars above the horizon, and time of the sunrise and sunset. It is a forerunner to the quadrant, octant and sextant and was popular for about 200 years over the 1500s and 1600s to find the latitude of a ship at sea. The user held the astrolabe at eye level and, usually with assistance, aligned the stars through the two small sights (pinnules), then read the altitude indicated by the pointer on the arm. It could also be used to sight the sun by holding it lower down, aiming it at the sun, and adjusting it until the sun shone through both pinnules. This astrolabe is an example used to demonstrate the mariner’s astrolabe, which was navigational tool of the 1500s and 1600s, in the time before longitude was able to be determined. It is a forerunner to modern navigation technology. Mariner’s astrolabe – a representative example. A gold painted, disc shaped object with cut outs and revolving arm in centre. The arm has two sights attached at right angles. The top has a ring attached. Measurements are marked in degrees in a circular scale around outer edge.flagstaff hill, warrnambool, maritime village, maritime museum, flagstaff hill maritime museum & village, shipwreck coast, great ocean road, navigation instrument, navigation tool, navigation, astrolabe, mariner’s astrolabe, measure latitude, measure altitude, arabic navigation, measuring device, star finder, astronomy, marine tool, marine instrument