When added to glass, thorium dioxide helps increase its refractive index and decrease its dispersion. Such glass finds applications in high-quality lenses for cameras and scientific instruments. The radiation from these lenses can darken them and turn them yellow over a period of years and degrade film, but the health risks are minimal. Yellowed lenses may be restored to their original colourless state by lengthy exposure to intense ultraviolet radiation. Thorium dioxide has since been replaced by rare-earth oxides such as lanthanum oxide in almost all modern high-index glasses, as they provide similar effects and are not radioactive.
This picture shows a yellowed thorium dioxide lens (left), a similar lens partially de-yellowed with ultraviolet radiation (centre) and a lens without yellowing (right).Photograph credit: El Grafo
The Madonna of Loreto is an oil-on-panel painting by the Italian High Renaissance painter Raphael, completed around 1511. The painting shows the Christ Child with his mother, Mary, as well as her husband, Saint Joseph. Just awakened, Jesus is playing a game with his mother's veil. Joseph is shown on the right, looking in from the shadows. Scholars have determined through X-ray analysis that Joseph was added as an afterthought, his image being painted over a window that was previously visible over Mary's shoulder. Furthermore, the change in the position of Jesus's right foot was also revealed via X-ray. These changes align with Raphael's preliminary drawings for the painting. The painting is now in the collection of the Musée Condé in Chantilly, France.Painting credit: Raphael
The Basaltic Prisms of Santa María Regla are tall columns of basalt near Huasca de Ocampo in the Mexican state of Hidalgo, lining a ravine through which water runs from the San Antonio Dam. The walls of the canyon, called the Barranca de Alcholoya, are lined by polygonal columns between 30 and 50 metres (98 and 164 ft) high, with five or six sides each. The basalt columns were created by the slow cooling of volcanic lava. There are two waterfalls at the site. The canyon has been improved by the addition of stairs, walkways and hanging bridges for easier access.Photograph credit: Diego Delso
Albert Aurier (1865–1892) was a French poet, art critic and painter, associated with the Symbolist movement. The son of a notary born in Châteauroux, Aurier went to Paris in 1883 to study law, but his attention was soon drawn to art and literature; he then began to contribute to Symbolist periodicals. He reviewed the annual Salon in Le Décadent, later contributed to La Plume and, in 1889, was the managing editor of Le Moderniste Illustré. From its foundation in 1890, he contributed to the Mercure de France, which published the essays on which Aurier's fame was founded: "Les Isolés: Vincent van Gogh" and "Le Symbolisme en peinture: Paul Gauguin". After a trip to Marseille, Aurier died at the age of twenty-seven in Paris from a typhus infection. The next day, friends, writers and artists accompanied his coffin to the funeral train departing for Châteauroux, where his remains were entombed in the family grave.
Pancuran Tujuh (Indonesian for 'Seven Springs') is a hot spring located on the slopes of Mount Slamet in the Banyumas Regency of Indonesia's Central Java province. Local people believe that the hot spring and its sulfuric waters contain healing properties. According to legend, the springs were discovered by a man named Syekh Maulana Maghribi. Sailing to Gresik on Java to spread Islam, he and a follower spotted a strange light. The legend then tells that they followed the light, landing at Pemalang and continuing overland, but Maghribi fell ill with a strange skin condition and received a vision that he had to climb the southern mountains to treat it. Finding Pancuran Tujuh, he treated himself by bathing in the waters.Photograph credit: Chris Woodrich
The Japanese yen (denoted by the ¥ symbol) is the official currency of Japan. It is the third most traded currency in the foreign exchange market, after the United States dollar and the euro; it is also widely used as a reserve currency. The concept of the yen was a component of the Meiji government's modernization program of Japan's economy, which postulated the pursuit of a uniform currency throughout the country, modelled after the European decimal currency system. Before the Meiji Restoration, Japan's feudal fiefs all issued their own money, hansatsu, in an array of incompatible denominations. The New Currency Act of 1871 did away with these and established the yen. The Bank of Japan was later founded in 1882 and given a monopoly on controlling the money supply.
Minnesota is a state in the Midwestern United States, carved out of the eastern half of the Minnesota Territory and admitted to the Union as the 32nd state on May 11, 1858. While the state's residents are primarily white and northern European, substantial influxes of African, Asian and Hispanic immigrants have joined the descendants of European immigrants and of the original Native American inhabitants. Nearly 60 percent of Minnesota's residents live in the Minneapolis–Saint Paul metropolitan area, known as the Twin Cities. The remainder of the state, often referred to as Greater Minnesota, consists of western prairies now given over to intensive agriculture; eastern deciduous forests, also heavily farmed and settled; and the less-populated North Woods. The state, known as the "Land of 10,000 Lakes", is known for its moderate-to-progressive politics and social policies, its civic involvement and its high voter turnout.
This picture is a depiction of the historical coat of arms of Minnesota, illustrated by American engraver Henry Mitchell as part of State Arms of the Union, published in 1876 by Louis Prang. The escutcheon features a Native American riding on horseback in the background, while a farmer plows a field in the foreground, with his rifle resting on a stump nearby; these represent the state's peoples and industries. The French motto below the shield reads L'Étoile du Nord, meaning 'The Star of the North'.Illustration credit: Henry Mitchell; restored by Andrew Shiva
This picture is an oil-on-canvas portrait of Duvivier by the French painter Antoine de Favray from the second half of the 18th century, titled Portrait of the Countess of Vergennes in Turkish Attire. She is portrayed on a divan in oriental costume, shortly before she married Gravier. The painting now hangs in the Pera Museum in Istanbul.Painting credit: Antoine de Favray
In firearms, rifling is the helical groove pattern that is machined into the internal (bore) surface of a gun's barrel, for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting. This spin serves to gyroscopically stabilize the projectile by conservation of angular momentum, improving its aerodynamic stability and accuracy over smoothbore designs.
This picture, taken in 2016, shows the conventional rifling of an Austro-Hungarian 90 mm (3.5 in) M75 cannon, manufactured in 1891, on display at Ljubljana Castle in Slovenia.Photograph credit: Petar Milošević
The King of Brobdingnag and Gulliver is a satirical print produced in 1803 by British caricaturist and printmaker James Gillray, executed in etching and aquatint. It is based on the fictional land of Brobdingnag from Jonathan Swift's 1726 novel Gulliver's Travels, which is inhabited by giants. The print shows a profile of George III of the United Kingdom, representing the Brobdingnagian king, holding a miniature Napoleon, representing Gulliver, while observing him through a spyglass. It was published on 26 June, five weeks after the breakdown of the Treaty of Amiens, which precipitated the Napoleonic Wars. The king's speech balloon in the top half of the print reads "My little friend Grildrig, you have made a most admirable panegyric upon Yourself and Country, but from what I can gather from your own relation & the answers I have with much pains wringed & extorted from you, I cannot but conclude you to be one of the most pernicious, little-odious-reptiles, that nature ever suffer'd to crawl upon the surface of the Earth". This copy of the print is in the collection of the Metropolitan Museum of Art in New York.Print credit: James Gillray; restored by Chris Woodrich
Cerastes cerastes, commonly known as the Saharan horned viper or the horned desert viper, is a venomous viper species native to the deserts of northern Africa and parts of the Middle East. It commonly has a pair of supraocular "horns", although hornless individuals do occur. The colour pattern consists of a yellowish, pale grey, pinkish, reddish or pale brown ground colour, which almost always matches the substrate colour where the animal is found. Dorsally, a series of dark, semi-rectangular blotches runs the length of the body. The belly is white and the tail, which may have a black tip, is usually thin.Photograph credit: Holger Krisp
The North American B-25 Mitchell is an American twin-engine medium bomber manufactured by North American Aviation (NAA). The design was introduced in 1941 and named in honor of Major General William "Billy" Mitchell, a pioneer of U.S. military aviation. Used by many Allied air forces, the B-25 served in every theater of World War II. After the war ended, many remained in service, operating across four decades. Produced in numerous variants, nearly 10,000 B-25s were made. These included a few limited models, such as the United States Marine Corps' PBJ-1 patrol bomber, as well as the F-10 reconnaissance aircraft and the AT-24 trainers used by the United States Army Air Forces.
The bee-eaters are a group of near passerine birds in the family Meropidae, containing three genera and twenty-seven species. Most species are found in Africa and Asia, with a few in southern Europe, Australia and New Guinea. They are characterised by richly coloured plumage, slender bodies and usually elongated central tail feathers. All have long down-turned bills and medium to long wings, which may be pointed or round. Male and female plumages are usually similar. As their name suggests, bee-eaters predominantly eat flying insects, especially bees and wasps, which are caught in the air by flights from an open perch. The stinger is removed by repeatedly hitting and rubbing the insect on a hard surface. During this process, pressure is applied to the insect, thereby extracting most of the venom.
Uppsala Cathedral is a cathedral in central Uppsala, belonging to the Church of Sweden, the Lutheran national church. It is the seat of the Archbishop of Uppsala, the primate of Sweden, currently Antje Jackelén. The cathedral dates to the late 13th century and was designed in the French Gothic style. With a height of 118.7 metres (389 ft), it is the tallest church in the Nordic countries. Originally built under Roman Catholicism, it was used for the coronations of Swedish monarchs for a lengthy period following the Protestant Reformation. Some of its chapels were converted to house the tombs of monarchs, including Gustav Vasa and John III. Carl Linnaeus, Olaus Rudbeck, Emanuel Swedenborg and several archbishops are also buried there.
Mr and Mrs Andrews is an oil-on-canvas painting by English artist Thomas Gainsborough, painted around 1750. It is a conversation piece, a genre of art in which a group of subjects are shown with other elements and activities. The subjects of the picture are Robert Andrews, a member of the landed gentry from the town of Bulmer in Essex, depicted in a loose hunting coat, as well as his wife, Frances Andrews (née Carter), a woman from the same parish, depicted in an informal summer suit with a straw hat. The couple are shown in a landscape near their estate, Auberies, in Bulmer Tye.
The work is unusual for an outdoor conversation piece, in that the background setting is agricultural, rather than the gardens of the subjects' own houses. This may have been motivated by Gainsborough's love of landscape painting, as well as the couple's desire to make a more prominent display than was normal in a portrait of the country estate that had formed part of Mrs Andrews's dowry. The painting remained in the Andrews family until 1960 and was very little known before it appeared in an exhibition in Ipswich in 1927, after which it was regularly requested for other exhibitions in Britain and abroad, while also praised by critics for its charm and freshness. It now hangs in the National Gallery in London.Painting credit: Thomas Gainsborough
An aerial view of the Field of Mars, a large park in central Saint Petersburg, Russia, pictured in 2016. It is named after Mars, the Roman god of war. The park's history goes back to the 18th century, when it was converted from bogland and named the Grand Meadow. Later, it was the setting for celebrations to mark Russia's victory over Sweden in the Great Northern War. Its next name, the Tsaritsyn Meadow, appears after the royal family commissioned Francesco Bartolomeo Rastrelli to build the Summer Palace for Empress Elizabeth. It became the Field of Mars during the reign of Paul I. Towards the end of the 18th century, the park became a military drill ground, where they erected monuments commemorating the victories of the Russian Army and where parades and military exercises took place regularly. After the February Revolution in 1917, the Field of Mars became a memorial area for the revolution's honoured dead. In the summer of 1942, as the city was besieged by the German army in the Siege of Leningrad, the park was covered with vegetable gardens to supply food. An eternal flame was lit in the centre of the park in 1957, in memory of the victims of various wars and revolutions.Photograph credit: Andrew Shiva
George Washington Carver (1860s–1943) was an American agricultural scientist and inventor. Born into slavery in Diamond, Missouri, he was raised by his master Moses Carver after being emancipated, having been separated from his parents as an infant during a kidnapping incident. After college, Carver became a professor at Tuskegee Institute, where he developed techniques to improve soils depleted by repeated plantings of cotton. He wanted poor farmers to grow alternative crops, such as peanuts and sweet potatoes, as a source of their own food and to improve their quality of life. Carver spent years developing and promoting products made from peanuts, although none became commercially successful. Apart from his work to improve the lives of farmers, he was also a leader in promoting environmentalism. Carver received numerous honors for his work, including the NAACP's Spingarn Medal. In an era of very high racial polarization, his fame reached beyond the black community; he was widely recognized and praised in the white community for his many achievements and talents. In 1941, Time magazine dubbed Carver a "black Leonardo".
This picture of Carver was taken around 1910 and is in the collection of the Tuskegee University archives.Photograph credit: Unknown; restored by Adam Cuerden
The Allegory of Prudence is an oil-on-canvas painting attributed to the Italian painter Titian and his assistants, dated around 1565 to 1570. It depicts three human heads, representing youth, maturity, and old age, above three animal heads. Both sets of heads face in different directions, which reflects the concepts of past, present and future. Scholars believe that the first of the three human heads is an elderly Titian, while the other two are his son Orazio Vecellio and his young nephew Marco Vecellio, both of whom lived and worked with him. A barely visible inscription across the top of the painting, from which the work acquired its present name, reads Ex praeterito praesens prudenter agit, ni futura actione deturpet (Latin for 'From the experience of the past, the present acts prudently, lest it spoil future actions'). The painting is now in the collection of the National Gallery in London.Painting credit: Titian