Mean sea level is an average level of the surface of one or more of Earth's oceans from which heights such as elevation may be measured. MSL is a type of vertical datum – a standardised geodetic datum –, used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and aircraft flight levels. A common and straightforward mean sea-level standard is the midpoint between a mean low and mean high tide at a particular location. Sea levels can be affected by many factors and are known to have varied over geological time scales; however 20th century and current millennium sea level rise is caused by global warming, careful measurement of variations in MSL can offer insights into ongoing climate change. The term above sea level refers to above mean sea level. Precise determination of a "mean sea level" is difficult to achieve because of the many factors that affect sea level. Instantaneous sea level varies quite a lot on several scales of space.
This is because the sea is in constant motion, affected by the tides, atmospheric pressure, local gravitational differences, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point and use it as a datum. For example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. Still-water level or still-water sea level is the level of the sea with motions such as wind waves averaged out. MSL implies the SWL further averaged over a period of time such that changes due to, e.g. the tides have zero mean. Global MSL refers to a spatial average over the entire ocean. One measures the values of MSL in respect to the land. In the UK, the Ordnance Datum is the mean sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the vertical datum was MSL at the Victoria Liverpool. Since the times of the Russian Empire, in Russia and other former its parts, now independent states, the sea level is measured from the zero level of Kronstadt Sea-Gauge.
In Hong Kong, "mPD" is a surveying term meaning "metres above Principal Datum" and refers to height of 1.230m below the average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and offers the longest collapsed data about the sea level, it is used for main part of Africa as official sea level. As for Spain, the reference to measure heights below or above sea level is placed in Alicante. Elsewhere in Europe vertical elevation references are made to the Amsterdam Peil elevation, which dates back to the 1690s. Satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001 and the Ocean Surface Topography Mission on the Jason-2 satellite in 2008. Height above mean sea level is the elevation or altitude of an object, relative to the average sea level datum, it is used in aviation, where some heights are recorded and reported with respect to mean sea level, in the atmospheric sciences, land surveying.
An alternative is to base height measurements on an ellipsoid of the entire Earth, what systems such as GPS do. In aviation, the ellipsoid known as World Geodetic System 84 is used to define heights; the alternative is to use a geoid-based vertical datum such as NAVD88. When referring to geographic features such as mountains on a topographic map, variations in elevation are shown by contour lines; the elevation of a mountain denotes the highest point or summit and is illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both. In the rare case that a location is below sea level, the elevation AMSL is negative. For one such case, see Amsterdam Airport Schiphol. To extend this definition far from the sea means comparing the local height of the mean sea surface with a "level" reference surface, or geodetic datum, called the geoid. In a state of rest or absence of external forces, the mean sea level would coincide with this geoid surface, being an equipotential surface of the Earth's gravitational field.
In reality, due to currents, air pressure variations and salinity variations, etc. this does not occur, not as a long-term average. The location-dependent, but persistent in time, separation between mean sea level and the geoid is referred to as ocean surface topography, it varies globally in a range of ± 2 m. Adjustments were made to sea-level measurements to take into account the effects of the 235 lunar month Metonic cycle and the 223-month eclipse cycle on the tides. Several terms are used to describe the changing relationships between sea level and dry land; when the term "relative" is used, it means change relative to a fixed point in the sediment pile. The term "eustatic" refers to global changes in sea level relative to a fixed point, such as the centre of the earth, for example as a result of melting ice-caps; the term "steric" refers to global changes in sea level due to thermal expansion and salinity variations. The term "isostatic" refers to changes in
Ushuaia is the capital of Tierra del Fuego, Antártida e Islas del Atlántico Sur Province, Argentina. It is regarded as the southernmost city in the world. Ushuaia is located in a wide bay on the southern coast of Isla Grande de Tierra del Fuego, bounded on the north by the Martial mountain range, on the south by the Beagle Channel, it is the only municipality in the Department of Ushuaia, which has an area of 9,390 km2. It was founded October 12 of 1884 by Augusto Lasserre and is located on the shores of the Beagle Channel surrounded by the mountain range of the Martial Glacier, in the Bay of Ushuaia. Besides being an administrative center, it is a light industrial tourist hub; the word Ushuaia comes from the Yaghan language: ush and waia and means "deep bay" or "bay to background". The act creating the subprefecture in 1884 cites the name "Oshovia", one of the many orthographic variations of the word, its demonym is "Ushuaiense". The name is pronounced "u-sua-ia", an exception to the orthographic rules of Spanish, since the's' forms a syllable with the following'u' despite the intervening'h'.
The pronunciation "Usuaía" is erroneous: the prosodic accent is on the first'a', why the word is written without an accent mark. Shield The municipality carried out a contest for the election of the image of the City Shield, approving by decree nº28, in 1971, the design of Vicente Gómez. Motto Ushuaia, end of the world, beginning of everything The Selk’nam Indians called the Ona, first arrived in Tierra del Fuego about 10,000 years ago; the southern group of people indigenous to the area, The Yaghan, occupied what is now Ushuaia, lived in continual conflict with the northern inhabitants of the island. For much of the latter half of the 19th century, the eastern portion of Tierra del Fuego was populated by a substantial majority of nationals who were not Argentine citizens, including a number of British subjects. Ushuaia was founded informally by British missionaries, following previous British surveys, long before Argentine nationals or government representatives arrived there on a permanent basis.
The British ship HMS Beagle, under the command of Captain Robert FitzRoy, first reached the channel on January 29, 1833, during its maiden voyage surveying Tierra del Fuego. The city was named by early British missionaries using the native Yámana name for the area. Much of the early history of the city and its hinterland is described in Lucas Bridges’s book Uttermost Part of the Earth; the name Ushuaia first appears in letters and reports of the South American Mission Society in England. The British missionary Waite Hockin Stirling became the first European to live in Ushuaia when he stayed with the Yámana people between 18 January and mid-September 1869. In 1870 more British missionaries arrived to establish a small settlement; the following year the first marriage was performed. During 1872, 36 baptisms and 7 marriages and the first European birth in Tierra del Fuego were registered; the first house constructed in Ushuaia was a pre-assembled 3 room home prepared in the Falkland Islands in 1870 for Reverend Thomas Bridges.
One room was for the Bridges family, a second was for a Yámana married couple, while the third served as the chapel. Thomas Bridges was a fluent speaker. To a lesser extent he was able to communicate in the Ona language, his missionary work was directed at the Yaghans. The word Yamana means "people" in the Yaghan language, he wrote a dictionary of the Yaghan language, the original manuscript of, in the British Museum. As the Yaghans had no ability nor means to write, Thomas Bridges had to construct an alphabet, suited to the phonetics of the language; the original manuscript was lost three times but recovered and published under an incorrect name. More than one alphabet has been used over the years in the rendering of this dictionary; the odyssey of the manuscript covered nearly half a century before it was published. Natalie Goodall was instrumental in reprinting the dictionary in 1987 and providing valuable insights into the history of Thomas Bridges' work. Copies of the dictionary provide material on the letters and pronunciations used which in many respects differ from the alphabet used in the English language..
During 1873, Juan and Clara Lawrence, the first Argentine citizens to visit Ushuaia, arrived to teach school. That same year Julio Argentino Roca, who served as Argentine President twice, promoted the establishment of a penal colony for re-offenders, modeled after one in Tasmania, Australia, in an effort to secure permanent residents from Argentina and to help establish Argentine sovereignty over all of Tierra del Fuego, but only after the Boundary treaty of 1881 between Chile and Argentina did formal efforts get under way to establish the township and its prison. During the 1880s, many gold prospectors came to Ushuaia following rumors of large gold fields, which proved to be false. On 12 October 1884, as part of the South Atlantic Expedition, Commodore Augusto Lasserre established the sub-division of Ushuaia, with the missionaries and naval officers signing the Act of Ceremony. Don Feliz M Paz was named Governor in 1885 named Ushuaia as its capital. In 1885 the territory police was organized under Antonio A. Romero with headquarters in Ushuaia.
But it was not until 1904 that the Federal Government of Argentina recognized Ushuaia as the capital of Tierra del Fuego. Ushuaia suffered several epidemics, including typhus and measles, that much reduced the native pop
Amateur Radio Lighthouse Society
Founded in 2000 by Jim Weidner, K2JXW, the Amateur Radio Lighthouse Society is devoted to maritime communications, amateur radio and lightships. Its members travel to lighthouses around the world where they operate amateur radio equipment at or near the light. Collecting lighthouse QSLs is popular for some amateur radio operators. ARLHS is a membership organization with over 1665 members worldwide as of July 2009. A convention is held in October each year. In 2010 the gathering was in Mississippi. In earlier years it has been held in Solomons, Maryland, St. Simons, Port Huron and other sites. Membership benefits include a newsletter, email reflector, awards program, lighthouse expedition sponsorship, embroidered shoulder patch, a list of every known light beacon in the world capable of supporting a ham station, a web site at; the ARLHS has been featured in national magazines, such as WordRadio. Jim Weidner is its founding President; the club call sign is W7QF and the website is The ARLHS maintains a catalog of lighthouses called The World List of Lights.
Its main feature is a short, transmitted identification number for each lighthouse. The WLOL lists any lighthouse, or was an Aid to Navigation and can reasonably accommodate an amateur radio operation. Lights that are no longer in existence, but were once an ATN show up on the list, designated as historical. With over 15,000 entries, the WLOL is one of the most complete lighthouse catalogs in existence. Amateur Radio Lighthouse Society Website ARLHS Convention web site India's First ARLHS activation in Mahaballipuram, India Aug 2008 Kadalur Lighthouse Centenary and ILLW operation Aug 2009
The Lighthouse at the End of the World
The Lighthouse at the End of the World is an adventure novel by French author Jules Verne. Verne wrote the first draft in 1901, it was first published posthumously in 1905. The plot of the novel involves piracy in the South Atlantic during the mid-19th century, with a theme of survival in extreme circumstances, events centering on an isolated lighthouse. Verne was inspired by the real lighthouse at the Isla de los Estados, near Tierra del Fuego and Cape Horn. Although not as well known as Verne's other novels, it is considered as good by Verne's fans and the literature critics; the novel was adapted into The Light at the Edge of the World. Vasquez and Felipe are the three lighthouse keepers stationed at the Staten Island lighthouse off the southern tip of Argentina. Two of them are murdered by a band of newly arrived pirates led by one Kongre. Vasquez, the only survivor, spends several months until the dispatch boat Sante Fe is due to return, surviving off the pirates' hidden stores of food in a cave.
After the Century, an American ship from Mobile, crashes on the island due to the light's having been put out by the pirates, Vasquez bands with the sole survivor of the wreck — First Officer John Davis – to stop the pirates from escaping into the South Pacific. They manage to scavenge a cannon from the wreckage and shoot the pirates' ship, the Maule, as it is about to leave the bay they are situated in; the shell only causes minor damage and the pirates' carpenter is able to fix it in only a few days. The night before the ship is about to attempt to leave again, Vasquez swims to the Maule at its mooring and plants a bomb in the rudder; this causes, yet again, only minor damage, is fixed in only one day. The next day however, the second-in-command of the pirate ship, spots the Sante Fe on the horizon. For the pirates, it will not arrive until nighttime, the Sante Fe can't get into the bay without light from the lighthouse; this will give the pirates the perfect chance to slip out and sail around the southern side of the island, which they know quite well by now.
Vasquez and Davis, return to the lighthouse and turn the light back on. The troop of pirates tries to regain the lighthouse and kill the two, but they find the bolted iron door to the staircase too reinforced to break down. Kongre, the band's leader, orders Carcante and the carpenter to climb the side of the lighthouse and murder Vasquez and Davis at the top, but they are shot as soon as their heads peek over the banister. Kongre and the remaining pirates realize it flee to the island's interior. Most surrender afterward, a few starve, Vasquez watches as Kongre commits suicide. Vasquez returns home with the Sante Fe after making sure the island is safe for the new lighthousemen. Verne, Jules & Butcher, William. Lighthouse at the End of the World. Nebraska University Press. CS1 maint: Multiple names: authors list Verne, Jules; the Lighthouse at the End of the World. France: Jules Hetzel. Dehs, Volker. "The Complete Jules Verne Bibliography X. Apocrypha"; the Complete Jules Verne Bibliography. Retrieved 19 December 2006
Tierra del Fuego
Tierra del Fuego is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla Grande de Tierra del Fuego, with an area of 48,100 km2, a group of many islands, including Cape Horn and Diego Ramírez Islands. Tierra del Fuego is divided between Chile and Argentina, with the latter controlling the eastern half of the main island and the former the western half plus the islands south of Beagle Channel; the southernmost extent of the archipelago is at about latitude 55 S. The earliest known human settlement in Tierra del Fuego dates to around 8,000 BCE. Europeans first explored the islands during Ferdinand Magellan's expedition of 1520. Settlement by those of European descent and the great displacement of the native populations did not begin until the second half of the 19th century, at the height of the Patagonian sheep farming boom and of the local gold rush. Today, petroleum extraction dominates economic activity in the north of Tierra del Fuego, while tourism and Antarctic logistics are important in the south.
The earliest human settlement occurred around 8,000 BCE. The Yaghan were some of the earliest known humans to settle in Tierra del Fuego. Archeological sites with characteristics of their culture have been found at locations such as Navarino Island; the name Tierra del Fuego was given by the Portuguese explorer Ferdinand Magellan while sailing for the Spanish Crown in 1520. He believed he was seeing the many fires of the Yaghan, which were visible from the sea, that the "Indians" were waiting in the forests to ambush his armada. In 1525 Francisco de Hoces was the first to speculate that Tierra del Fuego was one or more islands rather than part of what was called Terra Australis. Francis Drake in 1578 and a Dutch East India Company expedition in 1616 learned more about the geography; the latter expedition named Cape Horn. On his first voyage with HMS Beagle in 1830, Robert FitzRoy picked up four native Fuegians, including "Jemmy Button" and brought them to England; the surviving three were taken to London to meet the King and Queen and were, for a time, celebrities.
They returned to Tierra del Fuego in Beagle with FitzRoy and Charles Darwin, who made extensive notes about his visit to the islands. During the second half of the 19th century, the archipelago began to come under Chilean and Argentine influence. Both countries sought to claim the whole archipelago based on de jure Spanish colonial titles. Salesian Catholic missions were established in Dawson Island. Anglican missions were established by British colonists at Keppel Island in the Falklands in 1855 and in 1870 at Ushuaia on the main island, which continued to operate through the 19th century. Thomas Bridges learned the language and compiled a 30,000-word Yaghan grammar and dictionary while he worked at Ushuaia, it was considered an important ethnological work. An 1879 Chilean expedition led by Ramón Serrano Montaner reported large amounts of placer gold in the streams and river beds of Tierra del Fuego; this prompted massive immigration to the main island between 1883 and 1909. Numerous Argentines and Croatians settled in the main island, leading to increased conflicts with native Selk'nam.
Julius Popper, a Romanian explorer, was one of the most successful entrepreneurs in the region. Granted rights by the Argentine government to exploit any gold deposits he found in Tierra del Fuego, Popper has been identified as a central figure in the Selk'nam genocide. Following contact with Europeans, the native Selk'nam and Yaghan populations were reduced by unequal conflict and persecution by settlers, by infectious diseases to which the indigenous people had no immunity, by mass transfer to the Salesian mission of Dawson Island. Despite the missionaries' efforts, many natives died. Today, only a few Selk'nam remain; some of the few remaining Yaghan have settled in Villa Ukika in Navarino Island. Following the signing of the Boundary Treaty of 1881, Tierra del Fuego was divided between Argentina and Chile; the gold rushes of the late 19th century led to the founding of numerous small settlements by immigrants such as the Argentine settlements of Ushuaia and Río Grande and the Chilean settlements of Porvenir and Puerto Toro.
In 1945 a division of Chilean CORFO engaged in oil exploration made a breakthrough discovery of oil in northern Tierra del Fuego. Extraction began in 1949, in 1950 the state created ENAP to deal with oil extraction and prospecting; until 1960, most oil extracted in Chile came from Tierra del Fuego. During the 1940s Chile and Argentina formulated their Antarctic claims; the governments realized the key role of Tierra del Fuego's geographical proximity in backing their claims as well as in supplying their Antarctic bases. In the 1950s, the Chilean military founded Puerto Williams to counter Ushuaia's monopoly as the only settlement in the Beagle Channel, a zone where Argentina disputed the 1881 borders. In the 1960s and 1970s, sovereignty claims by Argentina over Picton and Nueva Islands in Tierra del Fuego led the two countries in December 1978 to the brink of war. In response to the threat of an Argentine invasion, minefields were deployed and bunkers built on the Chilean side in some areas of Tierra del Fuego.
The threat of war caused the Chilean Pin
Jules Gabriel Verne was a French novelist and playwright. Jules Verne was born in the seaport of Nantes, he was trained to follow in his father's footsteps as a lawyer, but quit the profession early in life to write for magazines and the stage. His collaboration with the publisher Pierre-Jules Hetzel led to the creation of the Voyages extraordinaires, a popular series of scrupulously researched adventure novels including Journey to the Center of the Earth, Twenty Thousand Leagues Under the Sea, Around the World in Eighty Days. Verne is considered a major literary author in France and most of Europe, where he has had a wide influence on the literary avant-garde and on surrealism, his reputation is markedly different in Anglophone regions, where he has been labeled a writer of genre fiction or children's books because of the abridged and altered translations in which his novels have been printed. Verne has been the second most-translated author in the world since 1979, ranking between Agatha Christie and William Shakespeare.
He has sometimes been called the "Father of Science Fiction", a title, given to H. G. Wells, Mary Shelley, Hugo Gernsback. Jules Gabriel Verne was born on 8 February 1828, on Île Feydeau, a small artificial island on the Loire River within the town of Nantes, in No. 4 Rue Olivier-de-Clisson, the house of his maternal grandmother Dame Sophie Allotte de la Fuÿe. His parents were Pierre Verne, an attorney from Provins, Sophie Allote de la Fuÿe, a Nantes woman from a local family of navigators and shipowners, of distant Scottish descent. In 1829, the Verne family moved some hundred meters away to No. 2 Quai Jean-Bart, where Verne's brother Paul was born the same year. Three sisters, Anna and Marie would follow. In 1834, at the age of six, Verne was sent to boarding school at 5 Place du Bouffay in Nantes; the teacher, Mme Sambin, was the widow of a naval captain. Mme Sambin told the students that her husband was a shipwrecked castaway and that he would return like Robinson Crusoe from his desert island paradise.
The theme of the Robinsonade would stay with Verne throughout his life and appear in many of his novels, including The Mysterious Island, Second Fatherland, The School for Robinsons. In 1836, Verne went on to École Saint‑Stanislas, a Catholic school suiting the pious religious tastes of his father. Verne distinguished himself in mémoire, Greek and singing. In the same year, 1836, Pierre Verne bought a vacation house at 29 Rue des Réformés in the village of Chantenay on the Loire River. In his brief memoir "Souvenirs d'enfance et de jeunesse", Verne recalled a deep fascination with the river and with the many merchant vessels navigating it, he took vacations at Brains, in the house of his uncle Prudent Allotte, a retired shipowner, who had gone around the world and served as mayor of Brains from 1828 to 1837. Verne took joy in playing interminable rounds of the Game of the Goose with his uncle, both the game and his uncle's name would be memorialized in two late novels. Legend has it that in 1839, at the age of 11, Verne secretly procured a spot as cabin boy on the three-mast ship Coralie with the intention of traveling to the Indies and bringing back a coral necklace for his cousin Caroline.
The evening the ship set out for the Indies, it stopped first at Paimboeuf where Pierre Verne arrived just in time to catch his son and make him promise to travel "only in his imagination". It is now known that the legend is an exaggerated tale invented by Verne's first biographer, his niece Marguerite Allotte de la Füye, though it may have been inspired by a real incident. In 1840, the Vernes moved again to a large apartment at No. 6 Rue Jean-Jacques-Rousseau, where the family's youngest child, was born in 1842. In the same year Verne entered another religious school, the Petit Séminaire de Saint-Donatien, as a lay student, his unfinished novel Un prêtre en 1839, written in his teens and the earliest of his prose works to survive, describes the seminary in disparaging terms. From 1844 to 1846, Verne and his brother were enrolled in the Lycée Royal in Nantes. After finishing classes in rhetoric and philosophy, he took the baccalauréat at Rennes and received the grade "Fairly good" on 29 July 1846.
By 1847, when Verne was 19, he had taken to writing long works in the style of Victor Hugo, beginning Un prêtre en 1839 and seeing two verse tragedies, Alexandre VI and La Conspiration des poudres, to completion. However, his father took it for granted that Verne, being the firstborn son of the family, would not attempt to make money in literature but would instead inherit the family law practice. In 1847, Verne's father sent him to Paris to begin his studies in law school, secondarily to distance him temporarily from Nantes, his cousin Caroline, with whom he was in love, was married on 27 April 1847, to Émile Dezaunay, a man of 40, with whom she would have five children. After a short stay in Paris, where he passed first-year law exams, Verne returned to Nantes for his father's help in preparing for the second year. While in Nantes, he met Rose Herminie Arnaud Grossetière, a young woman one year his senior, fell intensely in love with her, he wrote and dedicated some 30 poems to her, including
United Kingdom Hydrographic Office
The United Kingdom Hydrographic Office is the UK's agency for providing hydrographic and marine geospatial data to mariners and maritime organisations across the world. The UKHO is a trading fund of the Ministry of Defence and is located in Taunton, with a workforce of 900 staff; the UKHO is responsible for operational support to the Royal Navy and other defence customers. Supplying defence and the commercial shipping industry, they help ensure Safety of Life at Sea, protect the marine environment and support the efficiency of global trade. Together with other national hydrographic offices and the International Hydrographic Organization, the UKHO works to set and raise global standards of hydrography and navigation; the UKHO produces a commercial portfolio of ADMIRALTY Maritime Data Solutions, providing SOLAS-compliant charts and digital services for ships trading internationally. The Admiralty's first Hydrographer was Alexander Dalrymple, appointed in 1795 on the order of King George III and the existing charts were brought together and catalogued.
The first chart Dalrymple published as Hydrographer to the Admiralty did not appear until 1800. He issued Sailing Directions and Notices to Mariners. Dalrymple was succeeded on his death in 1808 by Captain Thomas Hurd, under whose stewardship the department was given permission to sell charts to the public in 1821. In 1819 Captain Hurd entered into a bi-lateral agreement with Denmark to exchange charts and publications covering areas of mutual interest; this is thought to be the earliest formal arrangement for the mutual supply of information between the British and any foreign Hydrographic Office. Hurd developed the specialism of Royal Navy hydrographic surveyors. Rear-Admiral Sir W. Edward Parry was appointed Hydrographer in 1823 after his second expedition to discover a Northwest Passage. In 1825 some 736 charts and coastal views were being offered for sale by the Hydrographic Office. In 1828 Captain Parry and the Royal Society organised a scientific voyage to the South Atlantic, in collaboration with the Hydrographers of France and Spain, using HMS Chanticleer.
In 1829, at the age of 55, Rear-Admiral Sir Francis Beaufort became Hydrographer. During his time as Hydrographer, he developed the eponymous Scale, saw the introduction of official tide tables in 1833 and instigated various surveys and expeditions. Several of these were by HMS Beagle, including one to Tierra del Fuego and Patagonia in 1826. In 1831 Captain Beaufort informed Captain FitzRoy that he had found a savant for the latter's surveying voyage to South America, Charles Darwin. After completing extensive surveys in South America he returned to Falmouth, Cornwall via New Zealand and Australia in 1836. By the time of Beaufort's retirement in 1855, the Chart Catalogue listed 1,981 charts and 64,000 copies of them had been issued to the Royal Navy. In the 1870s, the Royal Naval Surveying Service supported the Challenger expedition, a scientific exercise that made many discoveries, laying the foundation of oceanography; the cruise was named after HMS Challenger. On her 68,890-nautical-mile circumnavigation of the globe, 492 deep sea soundings, 133 bottom dredges, 151 open water trawls and 263 serial water temperature observations were taken.
The Challenger crew used a method of observation developed in earlier small-scale expeditions. To measure depth, the crew would lower a line with a weight attached to it until it reached the sea floor; the line was marked in 25 fathom intervals with flags denoting depth. Because of this, the depth measurements from the Challenger were at best accurate to 25 fathoms, or about 46 metres; as the first true oceanographic cruise, the Challenger expedition established an entire academic and research discipline. During the late 19th century, the UKHO took part in several international conferences, including the International Meridian Conference to determine a prime meridian for international use and other conferences working towards the establishment of a permanent international commission concerning hydrographic matters. Hydrographers to the Admiralty Board during this period included: Rear-Admiral John Washington, Rear-Admiral George Henry Richards, Captain Sir Frederick J O Evans and Rear-Admiral Sir William J L Wharton.
During Rear-Admiral A Mostyn Field's term as Hydrographer to the Admiralty Board, the Hydrographic Office lent instruments to the Nimrod Expedition of the British Antarctic Expedition led by Ernest Shackleton in 1907. Following the RMS Titanic in 1912, the Safety of Life at Sea convention was established, as well as the introduction of ice reporting and forecasting. During World War I, while Rear-Admiral Sir John F Parry was Hydrographer of the Navy, the Hydrographic Office produced numerous new charts and products to support the Royal Navy. Following the war, the First International Hydrographic Conference was held in London, it led to the establishment in 1921 of the International Hydrographic Organization. In the 1930s, the systematic and regular collection of oceanographic and naval meteorological data started. In the Second World War, while led by Vice-Admiral Sir John A Edgell, chart printing moved to Creechbarrow House in Taunton in June 1941; this was the first purpose-built chart making factory, was designed by the Chief Draughtsman, Mr Jowsey.
In 1968, compilation staff were transferred from Cricklewood to Taunton, thus bringing together the main elements of the Hydrographic Office. A purpose-built office, named after Alexander Dalrymple, was opened. Metrication and computerisation of charts began in the 1960s and early 1970s under the leadership of Rear-Admiral Sir Edmund G Irving, Rear-Admiral George Stephen Ritchie