Yet the arc lamp was a frightening level of illumination for some humans (and animals) compared with gas-lights, which produced a glow equivalent to 16 candles. Such brightness was unfit for domestic spaces, and barely tolerated in large indoor environments such as theatres. Arc lamps, the manufacturers proposed, were best enjoyed outdoors at a distance, with between four and eight lamps mounted at the top of skeleton towers that could reach upwards of 75 m (250ft). 

Arguments against them included the disruption of sleep, the unflattering colour the lights gave one’s appearance, and an anxiety rooted in the inability to tell night from day. But for their champions, there was the novelty of reading a newspaper or watch-face outdoors in the dark, while the notion of personal moons for every new town across America held a strong poetic appeal. 

Soon, moon towers stood sentry-like over American cities including Austin, San Francisco, Denver and New York. In Minneapolis, an “electric moon” was reported; in Los Angeles, the towers numbered 36. For a time, the city of Detroit implemented moon towers exclusively over anything else. In total, 122 were raised across the city, set at 305–365 m (1,000–1,200ft) intervals in the centre (where they stood 53m, or 175ft, tall). The city rationalised that 100 towers would be cheaper to service than 1,000 lamps, and that they would look spectacular. 

Moon towers were effective in open or low-built areas, where the angle of light from each tower would not throw obstructive shadows as it encountered the buildings below. At this time, however, Detroit was known as the “City of Trees” – a styling that disappeared as many trees were felled in the 20th century – and during spring and summer, especially in residential areas, the light was obscured by the canopy. When foliage was not a problem, mist was – and high-rise architecture was beginning to alter Detroit, like other US cityscapes. 

Within just 10 years of its construction, the Detroit system had been dismantled. What was dazzling in the imagination of city planners was dark and patchy on the ground. What’s more, the incandescent light bulb had developed far enough by this time to be easily, affordably and inoffensively mounted at street level. By the start of the 20th century, any moon tower still standing in America was there as a curiosity.

Yet this doesn’t mean that the moon towers left no residue on the field of street-lighting worldwide. For example, in 2018, the Chinese city of Chengdu announced with great fanfare a plan to launch an artificial moon in 2020 that would illuminate an area 10–80 km (6–50 miles) wide. It was “designed to complement the Moon at night”, but eight times brighter. (The plan has not yet been realised.)

UV-Radiated Artificial Beach, by Maarten Liefooghe 

Of all the defunct building types of the late 19th and early 20th centuries, children’s colonies constructed on the Belgian coast are among the most striking. They were built to prevent tuberculosis for city children through a collective stay at the seaside. 

With few of these complexes remaining, postcards now do a better job of evoking them. Some show the colony buildings in the dunes; others depict the activities that were aimed at “strengthening” children physically and morally: eating in the refectory, sports activities, sunbathing in the dunes, as well as medical treatments. Finally, a stranger genre of postcard portrays shiny modern equipment from industrial kitchens, laundries, bathing facilities and sports halls. 

An “artificial beach” at the De Haan Sea Preventorium, featured on a postcard from the late 1930s, is one such “extinct object”. A group of white children, each wearing protective glasses, play in a sandpit lit by UV lamps. A nurse is supervising. Beach scenes are painted on the walls, but the real coastal landscape remains behind bubbled window glass. What’s shown is the medical practice of heliotherapy and phototherapy for tuberculosis, and there are many photographs of similar artificial beaches in 1930s France.