Seismology: To better prepare for calamities, Zhang Heng invented a seismometer in 132 CE which provided instant alert to authorities in the capital Luoyang that an earthquake had occurred in a location indicated by a specific cardinal or ordinal direction. Although no tremors could be felt in the capital when Zhang told the court that an earthquake had just occurred in the northwest, a message came soon afterwards that an earthquake had indeed struck 400 km (248 mi) to 500 km (310 mi) northwest of Luoyang (in what is now modern Gansu). Zhang called his device the 'instrument for measuring the seasonal winds and the movements of the Earth' (Houfeng didong yi ), so-named because he and others thought that earthquakes were most likely caused by the enormous compression of trapped air. See Zhang's seismometer for further details.
What did the Chinese caused earthquakes?
enormous compression of trapped air

One-color light is well suited for traffic lights and signals, exit signs, emergency vehicle lighting, ships' navigation lights or lanterns (chromacity and luminance standards being set under the Convention on the International Regulations for Preventing Collisions at Sea 1972, Annex I and the CIE) and LED-based Christmas lights. In cold climates, LED traffic lights may remain snow-covered. Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, e.g. night time animal watching and military field use.
What is another use for one-color light?
exit signs

Encompassing a wide variety of post-Romantic styles composed through the year 2000, 20th century classical music includes late romantic, modern, high-modern, and postmodern styles of composition. Modernism (18901930) marked an era when many composers rejected certain values of the common practice period, such as traditional tonality, melody, instrumentation, and structure. The high-modern era saw the emergence of neo-classical and serial music. A few authorities have claimed high-modernism as the beginning of postmodern music from about 1930. Others have more or less equated postmodern music with the "contemporary music" composed from the late 20th century through to the early 21st century.
When did modernism take place?
18901930