History of The Fusee Movement by Craig Duling

The Fusee – A Temporal Adventure

“Punctuality gets marked as a morally elevated thing.”
Robert V. Levine, social psychologist and author of A Geography of Time (June 1997)

For primitive humans, the passage of time was understood as a series of transitions — darkness yielded to light; the phases of the moon altered the brightness of the night sky; and seasonal cycles foretold of shifts in climate, foliage, and the length of the day.  Advancements in civilization eventually necessitated more precise methods of time tracking, leading to the invention of the sundial, which worked by apportioning the day into roughly equal segments based on changes in shadow lengths as the sun moved from east to west.  The first sundials, called obelisks, were built by the Egyptians in 3500 BC; followed in 1500 BC by the Babylonian shadow clocks.  In 325 BC, the Greeks introduced the water clock, or clepsydra, which measured time by monitoring the steady flow of water from one vessel to another.  Incremental markings on the receiving vessel corresponded to time of day as the water level reached them.  Between 100 BC and 500 AD, increasingly complex designs for water clocks were introduced by Greek and Roman horologists.  During this period, sundials remained in regular use; and changes to their design were aesthetic rather than functional.

To be called a clock, an instrument must possess two fundamental properties: (1) a regular, constant, or repetitive action that allows marking of equal time increments; and (2) the means to keep track of these equal time increments and display the result.  A mechanical clock carries out its essential clock functions using an escapement, defined as a mechanism that delivers a rhythmic force, transfers energy to a timekeeping element, and allows the number of its oscillations to be counted.

The earliest mechanical timepieces were powered by the verge and foliot escapement, which consisted of a horizontal bar with weights at each end (the foliot), attached to the top of a vertical rod (the verge).  Energy produced by the rhythmic movement of the weights was transferred to the verge, which then engaged a gear that advanced in equal jumps. Verge and foliot escapements appeared in clocks, and later pocket watches, from the 14th century through the early 19th century.

The first mechanical clocks, built in England in about 1300 AD, were driven by the verge and foliot. It is speculated that the initial “portable” watch prototype also incorporated the verge and foliot, and that it was intended to be worn around the neck as a medallion.

By the early-to-mid-14th century, verge and foliot tower clocks had been constructed in several European cities; however, since they were less reliable than sundials or water clocks; they could not fully replace them.  Sundials and water clocks remained prevalent during this period.

Over the next 300 years, the verge and foliot escapement underwent numerous variations, yet the same challenges persisted:  the period of oscillation relied heavily on the amount of driving force; and the degree of friction encountered as the impulse was delivered impeded its accuracy. Introducing the fusee to the verge and foliot escapement helped regulate the driving force while also reducing friction.

The term fusee originated from the French fusée and Latin fusata, meaning “spindle full of thread.” The fusee was an ingenious, yet marvelously straightforward, technological discovery. While the fusee is famous primarily for its contribution to horology, its initial inspiration was not related to timekeeping.  As early as 1405, the fusee had appeared in drawings of medieval military machinery.  Not until 1490 did Leonardo daVinci introduce the fusee into designs for an improved verge and foliot escapement, which he later called the verge fusee.

The fusee was a cone shaped pulley with an attached line that wound around a cylindrical barrel. In the earliest fusee-based pocket watches, this line was a handmade chain or a sinew of cat gut; while in later, more sophisticated fusee-based timepieces, the line was a tightly coiled steel mainspring.

Helical in shape, the fusee was inscribed with a single, long groove that encircled the cone, becoming successively smaller in diameter.  One end of the line was attached to the barrel and wrapped around it, while the other end was attached to the widest part of the fusee. Guided by the continuous groove, the line connected the fusee to the barrel.  As the watch was wound, the line slowly moved from the barrel onto the fusee following the groove as it simultaneously pulled against increasing tension from the barrel.  Once the watch was fully wound, the entire length of the line had been wrapped tightly around the fusee. The resulting tension on the line by the barrel was powerful enough to rotate the fusee back again, which caused the hands of the timepiece to advance.

The purpose of the fusee was to equalize the overall torque on the escapement as the line unwound. When the line was fully wound around the barrel, the torque applied to the escapement was at its lowest; because the diameter of the barrel was larger than that of the fusee coil.  Then, as the line unwound, moving from the barrel onto progressively larger spirals of the fusee, the torque applied to the escapement gradually increased as the fusee diameter became larger relative to that of the barrel. The net result was to regulate the output of torque and prevent the clock from losing time. When the timepiece was wound, either by key or stem, the fusee turned and subsequently moved the chain from the barrel onto the fusee, causing the barrel to rotate. Due to inherent design limitations, fusee-driven pocket watches would stop running during winding, since winding required that the fusee be rotated in the direction opposite its normal “running” rotation. (Some later fusee movements used a maintaining power mechanism — usually a gear situated in the base of the fusee cone — which allowed the watch to remain running during winding.  Such a fusee movement was called a going fusee.)

The fusees of the earliest (and most finely crafted) pocket watches were equipped with delicate chains — nearly all of them handmade in Christchurch, New Zealand, by young women, who would sell them to watchmaking factories.  No two watch chains were alike; in fact, some chains were so fine, they could fit through the eye of a needle. Assembling each chain was a painstakingly slow, highly-detailed process, which added considerably to pocket watch production costs.

Perhaps the most significant enhancement to fusee-based clocks was the incorporation of a mainspring into the movement. The mainspring was comprised of a spiral steel ribbon tightly coiled around the barrel.  The mainspring provided a vigorous and portable power source, while eliminating some of the bulk of the verge and foliot.  The first mainspring-powered pocket watches emerged in Europe during the early 15th century, a logical sequel to the use of coiled springs in lock fabrication.  In fact, many of the early watchmakers were also locksmiths.

By the 16th century, spring-powered pocket watches had become prized wardrobe accessories for the wealthiest citizens of Europe.  Watchmakers continued efforts to increase timepiece accuracy; but they also turned their attention toward pocket watch aesthetics. Instead of equipping pocket watches with plain steel cases (as had been the convention), watchmakers began fashioning cases out of silver and gold, rendering them canvasses for intricate, often theme-based, etchings; and transforming each one into an exquisite work of art.

Extremely rare today, these elaborate pocket watches are highly sought after by collectors, not only for their magnificent exteriors, but for the delicacy and precision of their movements. No two pocket watches were identical. Even the components of their movements could not be interchanged.

The 17th and 18th centuries were rich in innovation, bringing about important functional enhancements to spring-driven fusee pocket watches. For instance, instead of needing to be wound every 12 hours, watches could run as long as 40 hours between windings.  Whereas previously, watches featured only an hour hand to display the time, now a minute hand had been introduced. Due to their hardness and ability to absorb heat, jewels (typically rubies) were inserted between the metal parts of the movement, which reduced metal-to-metal friction and increased wear. Finally, the balance wheel replaced the weighted bar of the foliot, which further minimize bulk, as well as improved timepiece accuracy.  Along with implementing these impressive technical developments, watchmakers continued to create ornate pocket watches for those who could afford them, which featured handsomely-etched cases and colorfully embellished hand-painted dials.

Although the fusee was an effective mainspring compensator, it presented numerous drawbacks.  Not only were fusee-powered pocket watches expensive to manufacture; but they were difficult to adjust. Also, since fusees were inherently tall and bulky, so were the pocket watches that contained them. Furthermore, if the mainspring broke — a common occurrence with mechanical watches, brought on by metal fatigue — the force exerted by the suddenly-released spring would damage other delicate components in the movement.

The balance spring conquered many of the fusee’s shortcomings.  Invented in the mid-17thcentury, the balance spring consisted of an extremely fine torsion, either spiral or helical in shape, which attached to the balance wheel and controlled its rate of oscillation.  (The balance spring was also known as the hairspring, since its diameter was literally that of a strand of hair.)  The eventual transition to the balance spring greatly increased the accuracy of portable timepieces, while further diminishing their thickness and weight.  The balance spring was ultimately responsible for transforming early pocket watches from expensive novelties into useful timekeepers.

By the turn of the 19th century, the Industrial Revolution was in full swing.  Railroad networks sprawled across the United States, England, and throughout Europe, facilitating access to raw materials and enabling efficient distribution of goods. Meanwhile, manufacturing processes had been streamlined through mass production, effectively lowering costs across virtually every industry. Watchmaking proved no exception.  Finally, after hundreds of years devoted to achieving timepiece accuracy and isochronism (the ability for a watch to run at the same rate whether fully or only partially wound), the balance spring addressed these challenges. Thus, watchmakers could confidently use mass-produced movements, called ebauches, in the manufacture of pocket watches — a sweeping industry change that significantly lowered production costs; and, in turn, brought down prices.  Pocket watches became affordable for everyone, regardless of social status.  Indeed, by the mid-19th century, the pocket watch had asserted itself as far more than an indispensable tool.  It was the symbol of prosperity.

England continued to manufacture fusee-driven pocket watches until about 1900, although by that time, they were sold only as inexpensive models to the lower classes; and, hence, derisively called “turnips.”  Eventually, all fusee-powered pocket watches were phased out; and the single remaining application for the fusee was in marine chronometers, where high precision was needed and bulk was less of a disadvantage.  Fusees became obsolete in the 1970s.

Since the mid-19th century, improvements in timepiece performance have exclusively been the result of modifications to the balance spring. Most significant was the 1896 innovation of a specialized, low temperature coefficient nickel-steel alloy, called “Invar” or “Elinvar,” trademarks referring to its “invariably” low coefficients of thermal expansion and elasticity.  Balance springs comprised of this alloy retained accuracy and reliability under wide temperature fluctuations.