A new discovery for finding the longitude

In Short

This technical proposal outlines a method for determining longitude by using a specialized timepiece not to track absolute time, but to record relative mechanical motion. Rather than struggling to build a "perfect" clock that remains unaffected by the environment, the author suggests a system of record-keeping. By measuring how a clock’s performance shifts under different latitudes and temperatures during trial voyages, a navigator can use these recorded deviations to calculate time at a departure point, thereby solving the persistent nautical challenge of determining east-west position.

The Story

In the early 18th century, the determination of longitude remains the great, unsolved puzzle of maritime navigation. While latitude is easily found by the sun or stars, longitude requires knowing the time difference between one's current position and a fixed reference point, such as London. The central obstacle, as the author observes, is the "vicissitude of the air"—the reality that heat, cold, and the motion of a ship inevitably cause any clock to gain or lose time, rendering it inaccurate.

Instead of demanding a perfect, unmoving mechanism, the author proposes a radical shift in perspective: acknowledge that the clock will be inaccurate, and account for that inaccuracy through empirical data. The process begins on land with a "Spring-Movement," a clock or watch of simple construction. Before a voyage, the device is set by a precise meridian line. As the ship travels into different climates, the clock’s performance is recorded. Upon return, the device is brought back to a meridian line to verify how much it has deviated over the course of the journey.

The core of the argument lies in the creation of a "Book." For every movement, the sailor maintains a ledger of "proportional numbers" that correspond to specific latitudes and seasons. If the ship arrives in a certain latitude during autumn, the navigator consults the book for the pre-calculated adjustment factor that accounts for the expected mechanical drift in that climate. Through this system of ratios, the author claims that even a flawed, erratic clock becomes a tool of scientific precision.

The narrative reaches its practical end with a call to action. The author suggests that a fleet of such movements be calibrated through a series of controlled voyages—to Newfoundland, Virginia, and the Caribbean—to map the "laws" of the movement's behavior across the globe. By building this index of behavior, the navigator can "equate" the motion, effectively cancelling out the influence of the environment. The book concludes not with a finished invention, but with an invitation for partners and watchmakers to adopt this method, asserting that the legislative reward for solving the longitude problem is within reach if the maritime community simply agrees to follow his rigorous system of trial, record, and calculation.

How It Unfolds

The theoretical foundation The author posits that longitude is solvable if one can obtain the time at the place of departure and the place of arrival. He argues that even if a clock is imperfect, its drift is a predictable response to environmental variables like temperature and motion.

The mechanism The movement is designed to be simple, potentially of pocket-watch size, featuring two indexes—one fast, one slow—to track time. Rather than attempting to maintain perfect time, the clock is treated as a diagnostic tool that records its own performance against the sun.

The method of calibration Before sailing, the clock must be set by a meridian line and its behavior tracked over a period of weeks or months. This establishes a baseline of "natural" operation before the device is subjected to the stresses of the sea.

The system of proportional numbers Navigation relies on a ledger that contains adjustment values for different latitudes and seasons. The sailor uses these numbers to perform a mathematical proportion, converting the clock's recorded time into the actual time at the departure point.

The empirical validation The author suggests a rigorous series of sea trials to populate the ledger with data. By comparing the clock's behavior in diverse climates—from the equator to the cold north—the navigator creates a comprehensive map of how the machine behaves.

The final proposal The text closes with a plea for collaboration, inviting investors or watchmakers to join the enterprise. He remains confident that by "equating" the natural vicissitudes of the air, this method renders the longitude problem entirely manageable.

The People

The author, William Hobbs, presents himself as a "Philo Mathem"—a lover of mathematics—who is deeply frustrated by the limitations of traditional clockmaking. He is not a builder of perfect instruments, but a man of systems and logic. He views the maritime world as a space where human error and environmental unpredictability can be tamed through the rigid application of arithmetic. He is pragmatic, viewing the sea not as a chaotic void, but as a series of repeatable, measurable conditions.

The intended reader is a member of the Board of Longitude or a fellow scientist/navigator. To these men, Hobbs is a persistent advocate who wants to shift the burden of proof from the clockmaker to the record-keeper. He is clearly addressing a skeptical audience, as his tone is defensive regarding the "vicissitudes of the air." He wants to convince them that the problem is not one of engineering failure, but of a failure to understand how machines react to their surroundings. He is joined in spirit by the "Honourable Persons" of the government, whom he treats as the gatekeepers of both national maritime security and his own potential financial success. He views the ship captain as a diligent clerk, one who must be willing to painstakingly fill out logbooks and perform daily calculations to reach his destination.

In Its Own Voice

Note, The time is Regulated or Conformed to the Motion: Whereas in former Movements, the Motion is Regulated or Conformed to the Time.

In this central passage, the author summarizes the inversion of the traditional clockmaking philosophy that defines his entire approach.

And seeing it was near the Winter Season: If you should add the Autumn and Winter Numbers, and Hours respectively together; and make them the two first Numbers in your Proportion; it would Æquate the Seasons more exactly.

The author provides this instruction to illustrate how the sailor must adjust their calculations based on the time of year to ensure the clock’s drift is accounted for.

What It's Really About

The book is an argument for the superiority of data over hardware. Beneath the technical instructions for building a clock lies a profound question of epistemology: can a human-made object ever be "true" in a changing world, or must we always account for the object's relationship to its environment? Hobbs argues that truth is not something inherent in the machine, but something derived from the relationship between the machine and the observer. He treats the sea as a laboratory where variables—latitude, temperature, and time—can be balanced like an algebraic equation. It is a work that attempts to bring the messy, unpredictable experience of long-distance sailing into the orderly, predictable domain of the ledger book.

Why Read It Today

Reading this work today offers a fascinating glimpse into the "pre-digital" mindset of scientific inquiry. It is a window into the desperation and intellectual ferment that defined the 18th-century race to solve the longitude problem. The reader will encounter a specific, rigid, and ultimately hopeful version of the scientific method that relies entirely on human discipline and manual arithmetic.

However, the book is not an easy read. The prose is densely layered with period syntax, mathematical notation, and a specific, antiquated vocabulary regarding mechanical parts. The reader must be prepared to navigate tables of data and complex, multi-step geometric instructions that do not always translate clearly to a modern audience. There is a distinct, rhythmic quality to the author's voice—earnest, slightly repetitive, and intensely focused on his own logic. You read it not for the plot, but for the experience of watching a mind attempt to organize the chaos of the ocean into a series of predictable, manageable numbers. It leaves you with an appreciation for how much we take for granted in our modern, automated world, where the "vicissitudes of the air" are handled by satellite, not by hand-wound springs and meticulous, ink-stained logbooks.