The King Mongkut Studies Initiative
His Genius in Science and Technology
Whenever the scientific and technological brilliance of His Majesty King Mongkut is mentioned, one invariably thinks of the total solar eclipse that occurred on August 18, 1868, at Wa Ko village in Prachuap Khiri Khan Province. His Majesty accurately calculated the occurrence of the eclipse two years in advance. Modern astronomers have since verified the precision of his prediction using contemporary methods, including computer simulation and archival analysis. One such astronomer affirmed that the King had performed the calculations entirely by himself and through his own methodology, with greater detail than that of contemporary Western scientists. His work was neither copied nor reliant on foreign scientific data.
He refuted the accusations made by the Jesuit priests and certain groups of Thai people.
His discovery and accurate prediction of the total solar eclipse served as a profound demonstration of the scientific brilliance of a Thai monarch, making manifest to the world His Majesty’s exceptional aptitude in astronomical calculation. By doing so, King Mongkut effectively refuted the long-standing assertion recorded by the Jesuit missionaries—who arrived during the reign of King Narai the Great—which claimed, “The Siamese have some knowledge of eclipses and are able to roughly calculate lunar eclipses, but as for solar eclipses, they possess no knowledge whatsoever.”
At the same time, His Majesty’s accomplishment also dismantled the popular belief held by some Thai people of the era, who maintained that a total solar eclipse was an impossibility in Siam. With scholarly precision and royal foresight, King Mongkut proved to the Thai public that such a celestial event not only could occur, but could be predicted with accuracy.
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Then spoke the Sovereign of sacred grace,
Hearing Indrajit’s words with puzzled face—
“Is she some thing lost in forest wide,
Whom someone found and dared not hide?
Never before have I seen such fate,
Or did one steal her, then hesitate—
Fearing the demon king as spouse,
He flung her down and fled the house?
Yet if that be so, it makes no sense,
The tale still reeks of false pretense.
If she had fallen midst wild terrain,
No words could soothe or ease the strain.”
He Adopted a Scientific Approach
His Majesty King Mongkut of Siam exemplified the spirit of scientific inquiry. Deeply curious and committed to reason, he sought truth through personal investigation and hands-on experimentation—values aligned with Buddhist teachings that discourage blind faith. Even during his monkhood, he mastered Pali to explore the Tripiṭaka, and later studied English, Latin, and modern sciences from Western missionaries and scholars.
Upon learning that solar eclipses could be predicted, the King immersed himself in astronomy and mathematics, eventually mastering the use of scientific instruments. His most renowned achievement was the accurate prediction of the total solar eclipse on August 18, 1868—two years in advance. This not only earned global acclaim but refuted claims by Jesuit missionaries that Siamese lacked such astronomical knowledge.
King Mongkut used his scientific understanding to educate his people, dispel superstitions—such as fear of comets—and encourage rational thought. He even brought scientific tools on provincial journeys to measure celestial bodies and map his location.
The praise he received as a brilliant astronomer and mathematician was well-deserved. His reign marked the dawn of scientific modernity in Siam, blending Eastern wisdom with Western science in a uniquely visionary way.
Calculated by His Majesty Himself
In the reign of King Mongkut (Rama IV), the use of computers was yet unknown. Thus, calculating a total solar eclipse—a task requiring advanced trigonometric methods, particularly spherical trigonometry involving logarithmic functions—was an extremely complex endeavor. Nevertheless, His Majesty demonstrated exceptional intellectual brilliance by personally undertaking and completing these calculations by hand.
Associate Professor Dr. Khaw Mueanwong, a renowned and respected Thai astronomer, later verified the accuracy of King Mongkut’s predictions. Using modern computational tools and historical documentation, Dr. Khaw concluded that the King must have calculated the eclipse entirely on his own, from start to finish. No foreign nautical almanacs or external ephemerides provided the raw data necessary for such computation, nor did such documents include the crucial variables required. Moreover, the precision and early timing of the King’s prediction—made two full years in advance—confirmed that he could not have relied on external sources. His Majesty’s calculations even exceeded the scope of contemporary Western efforts, marking him as an extraordinary scientific mind of his era.
He Calculated It Two Years in Advance
Chaophraya Thipakorn Wong recorded that His Majesty King Mongkut had calculated in the Year of the Tiger, Athasok (corresponding to Chula Sakarat 1228 or B.E. 2409)—two years before the total solar eclipse—that in the Year of the Dragon, Samritthisok, Chula Sakarat 1230, there would occur a total solar eclipse on the first waxing moon of the tenth month. Later, Nongyao Kanchanacharee examined the plausibility of this calculation from existing documents and affirmed that it was indeed possible that the King had performed such a computation two years in advance. This was evidenced by the thorough preparations made for the royal observation of the eclipse: a three-story wooden pavilion and royal encampment were constructed, and foreign guests such as Sir Harry Orde and a French astronomer were invited—arrangements that required lengthy advance notice due to the constraints of 19th-century travel, which relied on maritime routes.
Furthermore, preparations for entertaining the visiting dignitaries included hiring a French chef with assistants, and ordering food, wine, and ice from Singapore. These arrangements, logistically intricate and time-consuming, further affirm the early precision of the King’s astronomical forecast. So unexpected was the level of accommodation amidst the Siamese wilderness that foreign guests expressed astonishment at finding such refined hospitality deep within the forests of Siam.
His Majesty calculated with precise accuracy.
Wako Subdistrict
His Majesty had calculated since the Year of the Tiger, Atthasok (corresponding to Chula Sakarat 1228 or B.E. 2409), that a total solar eclipse would be visible within the Kingdom of Siam—specifically at the locality of Wako, in Prachuap Khiri Khan Province—on Tuesday, the 1st waxing day of the 10th lunar month, in the Year of the Dragon, Samritthisok, Chula Sakarat 1230, which corresponds to the 18th of August, B.E. 2411 (A.D. 1868).
The eclipse, according to His Majesty’s precise calculation, would be fully visible from Pranburi down to Chumphon. The moon was to begin its obscuration of the sun from the northwest direction at 4 mong and 1 baht (10:06 a.m.), and would exit from the southeast direction at 1 mong and 6 baht (1:36 p.m.). The totality would last precisely one baht of the clock—equal to 6 minutes of mechanical time—and the moment of full obscuration, when the sun would be entirely covered, was to occur at 5 mong and 7 baht (11:42 a.m.).
On August 18, 1868 (B.E. 2411), at precisely 10:06 a.m., the sky was overcast with thick clouds. However, by 10:16 a.m., the clouds began to dissipate, revealing the sun already partially eclipsed from the northwestern direction. The daylight dimmed gradually until, at 11:20 a.m., the sky darkened to the extent that stars became visible. Then, at 11:36 a.m. and 10 seconds, the total solar eclipse occurred, lasting for 6 minutes and 45 seconds. The eclipse continued until it passed entirely, with the sun fully unobscured once more by 1:37 p.m. and 45 seconds.
Later, Associate Professor Dr. Khaw Mueanwong confirmed that on August 18, 1868, a total solar eclipse indeed occurred, with the moment of greatest eclipse at 11:42 a.m., which corresponded precisely with the calculations made by King Mongkut (Rama IV)—a testament to His Majesty’s scientific acumen.
He Laid the Foundations of Science
1. He Established a Standard Time System
Associate Professor Dr. Khaw Mueanwong observed that King Mongkut’s successful prediction of the total solar eclipse was the result of a true scientific process. For His Majesty to perform such precise astronomical calculations, Siam must have already possessed a reliable system of standard timekeeping—comparable to that of civilized nations. This standard time system would have been sufficiently accurate and consistent to be used in determining geographical positions on Earth.
The King’s scientific foresight thus extended beyond theory, into the development of practical tools and institutional systems—laying the groundwork for modern astronomy and timekeeping in Thailand.
Phra Thinang Phutthadon Thatthanai
The Roof of Phra Thinang Phanumat Chamrun within the Aphina Niwet Complex, Photographed from Phra Thinang Phutthadon Thatthanai
This photograph, estimated to have been taken circa 1864 (B.E. 2407), captures the roof of Phra Thinang Phanumat Chamrun
According to historical records, in 1852 (B.E. 2395), King Mongkut (Rama IV) commissioned the construction of a royal residence named Aphina Niwet, which included the notable structure Phra Thinang Phuwadon Thatthanai, a five-story tower. Atop this edifice, a large four-faced clock was installed to announce the kingdom’s standard time to the populace. The King, foreseeing the importance of precise timekeeping for both science and governance, appointed two officers to maintain this system:
Phan Thiwathit was responsible for daytime calibration, verifying time as the sun passed the meridian line of the clock tower.
Phan Phinit Chanthra managed nighttime calibration, verifying time as the moon passed the same meridian.
These two roles represented the first formal scientific appointments in Thailand’s history, focused on astronomical observation and time regulation.
This royal time standard, derived from the longitude of the royal clock tower itself, is believed to have served as the baseline for King Mongkut’s astronomical calculations, including his renowned solar eclipse prediction in 1868. Remarkably, this establishment of a Thai standard meridian predated the British Parliament’s adoption of Greenwich Mean Time by nearly three decades (the UK standardised GMT in 1880 / B.E. 2423), underscoring King Mongkut’s visionary grasp of modern science.
2. His Calculations for the Intercalary Month (Athikamat)
King Mongkut also made significant contributions to calendar science, particularly in the determination of intercalary months (extra lunar months added to synchronize the lunar calendar with the solar year).
Through extensive study, he discerned that between C.S. 1093 (Year of the Pig) and C.S. 1301 (Year of the Rabbit), there occurred a consistent pattern: every 19 years, there would be 7 years with intercalary months. For instance:
From C.S. 1093 (Year of the Pig) to C.S. 1111 (Year of the Snake), there were exactly 7 intercalary months.
Similarly, from C.S. 1112 (Year of the Horse) to C.S. 1130 (Year of the Rat), the same held true.
Based on this observation, the King proclaimed that in any 19-year cycle, intercalary months would occur in the 3rd, 6th, 9th, 11th, 14th, 17th, and 19th years.
To facilitate memorisation, he proposed mnemonic patterns such as “33, 32, 332”, or an arithmetic method: Take the Chula Sakarat year, subtract 8, then divide by 19.
If the remainder is 3, 6, 9, 11, 14, or 17, that year will have an intercalary month (i.e., double eighth lunar month).
All other remainders denote a regular year.
Sextant
Star Chart
He Established a Unit for Measuring Rainfall
Queen Victoria of the United Kingdom gifted King Mongkut a rain gauge calibrated in imperial inches, which was more precise than traditional Thai measurements—it could measure even the lightest rainfall. Therefore, the King introduced a simplified unit system as follows:
1 English inch was divided into 100 parts, each called a satang.
10 satang = 1 thasang
10 thasang = 1 inch
This new system was more refined than the traditional Thai unit where 1 Thai inch = 10 krabiet.
Adoption of Western Technology
Recognizing the scientific and technological advancements of the West, King Mongkut aimed to modernize Siam through the selective adoption of Western innovations—those beneficial and appropriate for Siamese society at the time. He stressed practicality, instructing his envoys abroad to focus on anything that could “make the difficult easier or improve what had not been good.” As a result, he introduced several Western technologies across various sectors:
Transportation: Commissioned the construction of roads, bridges, and canals to facilitate travel and trade.
Medicine: Embraced missionary medicine, introduced Western treatments to the general public, and even wore dentures made of sappanwood.
Finance: Founded the Royal Mint to produce coins replacing traditional bullet money (phot duang) and introduced early forms of banknotes and treasury notes to pay civil servants.
Industry: Adopted machinery to increase productivity and efficiency in rice milling, sawmilling, and sugar manufacturing.
Printing: Ordered printing presses for religious texts, sermons, and official bulletins such as the Royal Gazette.
Geography: Employed experts to map the eastern territories of Siam.
Architecture: Built Western-style palaces, including observatories and modern kitchens.
Public Relations: Commissioned royal portraits to be sent abroad for diplomatic purposes with Western nations.
Military: Purchased firearms to strengthen the defense of the capital.
Commerce: Launched steamship construction to support international trade logistics.
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