Up until the 18th century, amethyst was included in the cardinal, or most valuable, gemstones ( along with diamond, sapphire, ruby, and emerald ).

Traces of this hidden agenda of the city's history is found in the 18th century guidebooks to Aachen as well as to the other spas ; the main indication for visiting patients, ironically, was syphilis ; only by the end of the 19th century had rheuma become the most important object of cures at Aachen and Burtscheid.

Overall, his contributions are considered the most important in advancing chemistry to the level reached in physics and mathematics during the 18th century.

However, in the 17th and 18th centuries Bern encouraged industrial development in Unteraargau and by the late 18th century it was the most industrialized region in the city-state.

When the office of Lord High Admiral was in commission, as it was for most of the 18th, 19th and 20th centuries until it reverted to the Crown, it was exercised by a Board of Admiralty, officially known as the Commissioners for Exercising the Office of Lord High Admiral of the United Kingdom of Great Britain and Northern Ireland, & c. ( alternatively of England, Great Britain or the United Kingdom of Great Britain and Ireland depending on the period ).

The remaining ones were defined in the 17th and 18th century ; the most recent ones are found on the southern sky, defined in Coelum australe stelliferum by Nicolas Louis de Lacaille ( 1763 ).

Among those major Protestant Christian traditions that employ congregationalism are those Congregational Churches known by the " Congregationalist " name that descended from the Anglo-American Puritan movement of the 17th century, the Baptist churches, and most of the groups brought about by the Anabaptist movement in Germany that immigrated to the U. S. in the late 18th century.

The congregationalist theory of independence within a union has been a cornerstone of most ecumenical movements since the 18th century.

Dragoon regiments were established in most European armies during the late 17th and early 18th centuries.

The double bass as a solo instrument enjoyed a period of popularity during the 18th century and many of the most popular composers from that era wrote pieces for the double bass.

The Ecuadorian economy, like that in the mother country, suffered a severe depression throughout most of the 18th century.

From flamenco's beginning in the 18th century most performers were professional.

Despite some military attempts by the Spanish to retake it in the 18th century, most notably in the Great Siege of 1779 – 1783, the Rock has remained under British control ever since.

A Protestant church, St. Mobhi's, was built in the mid 17th century and most of it was rebuilt in the mid 18th century.

During most of the 18th century Spain had arrested its relative decline of the latter part of the 17th century.

The Hittites were an ancient Anatolian people who established an empire at Hattusa in north-central Anatolia around the 18th century BC, which reached its height during the mid-14th century BC under Suppiluliuma I, encommpassing an area that included most of Asia Minor as well as parts of the northern Levant and Upper Mesopotamia.

Since most Episcopalians had given their support to the Jacobite rebellions in the early 18th century, they also suffered a decline in fortunes.

In the 18th century, a group of writers, most notably Ferenc Kazinczy began the process of language renewal ( Hungarian: nyelvújítás ).

History painting was the dominant form of academic painting in the various national academies in the 18th century, and for most of the 19th ; in France artists such as Henri Jean-Baptiste Victoire Fradelle, Antoine-Jean, Baron Gros, Jacques-Louis David, Ingres, Claude Joseph Vernet, Carle Vernet, Pierre-Narcisse Guérin were among the leading figures.

Since the 18th century the writ has also been used in cases of unlawful detention by private individuals, most famously in Somersett's Case ( 1772 ), where the black slave Somersett was ordered to be freed.

The privilege of habeas corpus has been suspended or restricted several times during English history, most recently during the 18th and 19th centuries.

In the late 18th century the harpsichord was supplanted by the piano and almost disappeared from view for most of the 19th century: an exception was its continued use in opera for accompanying recitative, but the piano sometimes displaced it even there.

Since at least the 18th century Freemasonry has incorporated Templar symbols and rituals in a number of Masonic bodies, most notably, the " Order of the Temple " the final order joined in " The United Religious, Military and Masonic Orders of the Temple and of St John of Jerusalem, Palestine, Rhodes and Malta " commonly known as the Knights Templar.

A 1998 study of the Stony Brook University Algorithm Repository showed that, out of 75 algorithmic problems, the knapsack problem was the 18th most popular and the 4th most needed after kd-trees, suffix trees, and the bin packing problem.

As the 20th century approached, most of 19th-century Africa had been carved up among the various European powers.

Although 19th-century ethnologists saw " diffusion " and " independent invention " as mutually exclusive and competing theories, most ethnographers quickly reached a consensus that both processes occur, and that both can plausibly account for cross-cultural similarities.

Unlike most of the visual arts, opera was commercially profitable, accessible to most classes of society, and thus an effective means of reaching the 19th-century public.

The modern sophisticated instrument spanning 6½ octaves in virtually all keys was perfected by the 19th-century French maker Sébastien Érard and because of its pedal-driven ability to play all sharps and flats of all notes within its range, it continues today as the standard style of most large professional concert harps.

The emancipation of the serfs in 1861 was the single most important event in 19th-century Russian history.

The study of hypnotism subsequently revolved around the fierce debate between Jean-Martin Charcot and Hippolyte Bernheim, the two most influential figures in late 19th-century hypnotism.

The 19th-century French painter Edgar Degas was a most prolific user of pastel and its champion.

During most of the 19th-century in fact, the term " tennis " referred to real tennis, not lawn tennis: for example, in Disraeli's novel Sybil ( 1845 ), Lord Eugene De Vere announces that he will " go down to Hampton Court and play tennis.

The most famous of 19th-century Tolstoy politicians was Count Dmitri Andreevich ( 1823 – 89 ), successively the Minister of Education, Minister of Interior and President of the Academy of Science.

The villanelle has no established meter, although most 19th-century villanelles have used trimeter or tetrameter and most 20th-century villanelles have used pentameter.

The most thoroughly tonal language is the 19th-century constructed language Solresol, which consists of only tone.

The 19th-century nation-states developed an array of policies — the most important was compulsory primary education in the national language.

Clark was the most important 19th-century Attorney-General of Tasmania.

The 19th-century belief that matriarchal societies existed, a belief now abandoned among most scholars, was due to the transmission of " economic and social power ... through kinship lines " so that " in a matrilineal society all power would be channeled through women.

Theodor Fontane (; 30 December 1819 – 20 September 1898 ) was a German novelist and poet, regarded by many as the most important 19th-century German-language realist writer.

The most important monuments of the Kuzbass include the 18th-and 19th-century historical and architectural museum at Kuznetsk Fortress in Novokuznetsk, a group of monuments and historic sites on the former Siberian Highway ( Moscow-Irkutsk ), and the Shestakovsky historical and cultural complex of archeological monuments and paleontological sites in Chebulinsky District.

Before the Civil War, settlers reported up to 50 mounds in the area that became East St. Louis, but most were lost to 19th-century development and later roadbuilding.

One of the most famous pieces of 19th-century salon music was the " Fifth Nocturne " of Ignace Leybach, who is now otherwise mostly forgotten.

The Flatiron Building ( c. 1830 ), constructed as a business building in thriving 19th-century Brownsville, is one of the oldest, most intact iron commercial structures west of the Allegheny Mountains.

The mid 19th-century Greensboro stoneware potteries were among the most productive in the eastern United States.

It was named for Belgian Father Pierre De Smet, a 19th-century Jesuit missionary who worked with Native Americans in the United States and its territories for most of his life.

Like many 19th-century American towns, Roslyn experienced a major fire in 1888 that destroyed most of its commercial district.

For example, for the 19th-century fin de siècle, the most radical changes to the cultural and social order occurred more than a decade after the 20th century had started ( most notably as a result of World War I ).