In the 18th century, the determination of longitude was an urgent problem to be solved in the field of navigation. On the vast ocean, due to the Earth's rotation, people could determine latitude through celestial observation, yet the lack of a reliable method to measure longitude led to frequent shipwrecks. Ships often fell into desperate situations due to getting lost or straying off course, casting a huge shadow over the maritime industry. To address this, the British government offered a substantial reward for anyone who could solve the longitude problem. This incentive drew numerous scientists, mathematicians, and mechanical experts to devote themselves to the cause, sparking a fierce competition between the "astronomical method" and the "chronometer method". Amid widespread attention, John Harrison, a clockmaker from a rural area in Britain, stood out from the crowd. ### 01 The Legendary Journey of a Rural Clockmaker Details about John Harrison's early life are as vague as a hazy painting. With scarce historical records, biographers can only piece together the full picture from scattered fragments. Born on March 24, 1693, in Yorkshire, he was the eldest child in his family. He grew up on the estate of Nostell Priory before moving to the village of Barrow in Lincolnshire. As a young boy, he learned carpentry from his father and showed remarkable versatility: he was skilled at playing the old six-string fiddle, rang and tuned church bells, and even served as a choir conductor. Around 1712, a visit from a clergyman became a turning point in his life. The clergyman lent Harrison a precious textbook—a handwritten copy of lectures on natural philosophy by Nicholas Saunderson, a mathematician at the University of Cambridge. Harrison cherished this book like a treasure. With his solid reading and writing skills, he carefully copied and annotated the text, studying it repeatedly with the devotion of a pious scholar poring over the Bible. This laid a solid intellectual foundation for his future inventions, and it was at this point that he quietly embarked on his journey to tackle the longitude problem. In 1713, at the age of less than 20, Harrison created his first pendulum clock. Amazingly, this clock was made almost entirely of wood: oak gears, boxwood axles, with only a small amount of brass and iron used for connections and driving mechanisms. The design was ingenious—the wooden teeth of the gears cleverly utilized the grain of the oak, giving them excellent durability. Later, he made two more similar wooden clocks in 1715 and 1717. Though these early works have weathered the test of time, with some parts lost, they still bear the marks of his technical growth, quietly telling the story of the past. ### 02 The Birth of the Marine Chronometer: A Beacon of Innovation Breaking Through Difficulties During Harrison's era, traditional clocks were extremely inaccurate for timekeeping in the harsh maritime environment. Factors such as temperature changes, humidity erosion, and the swaying of the ship acted like the hands of a demon, disrupting the clock's precise operation at will. Nevertheless, Harrison was determined to rise to the challenge, using his wisdom and craftsmanship to dispel the fog of uncertainty. To overcome the challenge of temperature fluctuations, he skillfully leveraged the difference in thermal expansion coefficients between two metals to design a temperature compensation device. It was like equipping the clock with a sensitive "temperature sensor" that could automatically make fine adjustments based on the ambient temperature, ensuring a constant oscillation period and keeping the passage of time unaffected by temperature changes. To tackle the problem of ship sway at sea, he abandoned the pendulum (which was vulnerable to interference) and adopted an innovative "hairspring" escapement mechanism. This was like putting a "stability armor" on the clock, greatly reducing the impact of external movement on the core timekeeping component and allowing it to operate steadily even amid rough waves. Harrison pursued excellence in material selection and craftsmanship. The use of special lubricating oil provided a protective "coat" for the mechanical parts, shielding them from the erosion of maritime moisture and salt. The internal movement parts were meticulously crafted, with every detail reflecting his pursuit of extreme precision—from the mainspring power system to the escapement mechanism, all embodied his ingenuity. Around 1720, Harrison, who had already gained a certain reputation, was invited by Sir Charles Pelham to build a tower clock for Brocklesby Park. This tower clock was not only a superb demonstration of his carpentry skills but also a key step toward the invention of the marine chronometer. It featured a gear mechanism that required no oiling and used special wood, balancing strength and weight. Having operated continuously for over 270 years, it still keeps time faithfully to this day, witnessing the vicissitudes of history. By 1727, driven by the allure of the longitude reward and his dedication to solving technical challenges, Harrison devoted himself fully to the research and development of the marine chronometer. After nearly four years of arduous exploration, he finally conceived a brand-new device. Filled with hope, he embarked on a journey to London, striding forward toward the great goal of solving the longitude problem. ### 03 An Analysis of the Marine Chronometer: The Outstanding Structure of a Precision Instrument The marine chronometer boasted an ingenious exterior design. Most were encased in a copper shell, with a square or circular shape paired with a gimbal. It was like a timekeeper sitting on a stable throne—no matter how violently the ship tossed, the gimbal ensured the movement inside remained perfectly horizontal. Housed in a wooden box, it exuded an air of antique elegance. The hands on the dial had clear functions, indicating hours, minutes, seconds, and the winding status of the mainspring, making all information easily readable at a glance. Its internal structure was a masterpiece of precision engineering. The movement was powered by a strong mainspring, and a power reserve mechanism worked in tandem with a special escapement to ensure a smooth and steady output of power—just like a heart supplying blood to the body in a stable rhythm. The balance wheel, equipped with a bimetallic strip and a spiral hairspring, had a keen sensitivity to temperature changes and could automatically compensate for them, serving as a key guarantee for accurate timekeeping. Some marine chronometers were also fitted with a dual-balance system and a special balance staff linkage structure, which further enhanced their shock resistance and kept them stable as a mountain even in stormy seas. Material selection was the cornerstone of the marine chronometer's outstanding performance. The copper shell, hard and corrosion-resistant, built a solid defense for the precision movement inside. The bimetallic balance wheel skillfully countered the effects of temperature fluctuations, while key components such as the hairspring and mainspring were made of special metal materials. With their excellent elasticity and stability, these materials supported the marine chronometer in keeping accurate time and operating reliably in the complex and ever-changing marine environment. ### 04 The Impact of the Marine Chronometer: A Great Invention That Rewrote History The birth of the marine chronometer was like a beam of bright light piercing through the navigational fog, showing sailors the way. Thanks to its precise timekeeping, the calculation of longitude became accurate and reliable. At the Earth's equator, a 15° difference in longitude corresponds to a 1-hour difference in time. The marine chronometer kept its daily error within a few seconds, allowing sailors to accurately calculate the ship's longitude, plan stable routes, and greatly reduce the risk of getting lost or suffering shipwrecks. This invention had a profound impact on global trade, maritime exploration, and the development of geography. Oceanic trade thrived as maritime safety improved, expanding the map of world trade. Navigators and explorers like Captain Cook successfully embarked on long voyages with the help of marine chronometers, discovering new lands and accelerating the era of geographical discovery. Disciplines such as navigation and astronomy flourished with the support of the marine chronometer, propelling humanity's understanding of the universe and the Earth to new heights. Furthermore, the marine chronometer provided inspiration for many fields in later generations. In the field of time and frequency technology, it offered ideas for the design of ultra-high-precision devices like modern atomic clocks, enabling them to output accurate frequencies stably in complex environments. Industrial manufacturing drew on its reliability design concepts, focusing on material and structural optimization to improve the performance of products under harsh working conditions. From sealing technology and exterior design to the promotion of technological innovation and the concept of resource utilization, the marine chronometer has acted like a beacon illuminating the development path of modern products. It has become an eternal classic, embodying humanity's courage and wisdom in exploring the unknown, and shining brilliantly in the long river of history.