King Mongkut became king after His Majesty's elder brother King Nang Klao (King Rama III). The Coronation Ceremony was held on May 15, 1851 and He was on the throne for 18 years before he passed away on October 1, 1868 at 64 years of age.
His Mayesty was the founder of basic science in Thailand. He had introduced the standard time in 1852 by establishing the Phuwadol Tassanai Hall as the first standard time clock tower of the country. He also used the standard time in the accurate two-year prediction of a full solar eclipse clearly visible at Wa Kaw in Prachuap Khiri Khan province on August 18, 1868.