The population of Paris today is lower than its historical peak of 2.9 million in 1921. The principal reasons were a significant decline in household size, and a dramatic migration of residents to the suburbs between 1962 and 1975. Factors in the migration included de-industrialisation, high rent, the gentrification of many inner quarters, the transformation of living space into offices, and greater affluence among working families. The city's population loss came to an end in the 21st century; the population estimate of July 2004 showed a population increase for the first time since 1954, and the population reached 2,234,000 by 2009.
What year was the first population increase since 1954?
2004

The alkali metal ions are small and mobile; their presence in glass allows a degree of electrical conductivity, especially in molten state or at high temperature. Their mobility decreases the chemical resistance of the glass, allowing leaching by water and facilitating corrosion. Alkaline earth ions, with their two positive charges and requirement for two non-bridging oxygen ions to compensate for their charge, are much less mobile themselves and also hinder diffusion of other ions, especially the alkalis. The most common commercial glasses contain both alkali and alkaline earth ions (usually sodium and calcium), for easier processing and satisfying corrosion resistance. Corrosion resistance of glass can be achieved by dealkalization, removal of the alkali ions from the glass surface by reaction with e.g. sulfur or fluorine compounds. Presence of alkaline metal ions has also detrimental effect to the loss tangent of the glass, and to its electrical resistance; glasses for electronics (sealing, vacuum tubes, lamps...) have to take this in account.
What types of ions does typical glass have?
alkali and alkaline earth ions

Viking raids from 840 onwards contributed to the decline of Hamwic in the 9th century, and by the 10th century a fortified settlement, which became medieval Southampton, had been established.
What year did the Vikings start attacking Hamwic?
840