thumb|upright|A modern replica of Han dynasty polymath scientist Zhang Heng's seismometer of 132 CE 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.de Crespigny, Rafe. (2007). A Biographical Dictionary of Later Han to the Three Kingdoms (23–220 AD). Leiden: Koninklijke Brill, p. 1050. .Morton, W. Scott and Charlton M. Lewis. (2005). China: Its History and Culture. New York: McGraw-Hill, Inc., p. 70. . 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 northwest of Luoyang (in what is now modern Gansu).Minford & Lau (2002), 307; Balchin (2003), 26–27; Needham (1986a), 627; Needham (1986c), 484; Krebs (2003), 31. Zhang called his device the 'instrument for measuring the seasonal winds and the movements of the Earth' (Houfeng didong yi 候风地动仪), so-named because he and others thought that earthquakes were most likely caused by the enormous compression of trapped air.Needham (1986a), 626.
thumb|upright|A modern replica of Han dynasty polymath scientist Zhang Heng's seismometer of 132 CE 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.de Crespigny, Rafe. (2007). A Biographical Dictionary of Later Han to the Three Kingdoms (23–220 AD). Leiden: Koninklijke Brill, p. 1050. .Morton, W. Scott and Charlton M. Lewis. (2005). China: Its History and Culture. New York: McGraw-Hill, Inc., p. 70. . 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 northwest of Luoyang (in what is now modern Gansu).Minford & Lau (2002), 307; Balchin (2003) 26–27; Needham (1986a), 627; Needham (1986c), 484; Krebs (2003), 31. Zhang called his device the 'instrument for measuring the seasonal winds and the movements of the Earth' (Houfeng didong yi 候风地动仪), so-named because he and others thought that earthquakes were most likely caused by the enormous compression of trapped air.Needham (1986a), 626.