On Time: The Quest for Precision

An exhibition of books from the Linda Hall Library of Science, Engineering & Technology
By Bruce Bradley, History of Science Librarian Emeritus, Linda Hall Library

From sundials to atomic clocks, the fascinating story of increasing accuracy in timekeeping, as documented in rare books and journals, will be on view at an exhibition in New York City at the Grolier Club (14 Sept to 19 Nov 2016). From the fifteenth century to the present, the tale unfolds in books from the comprehensive collections of the Linda Hall Library in Kansas City, Missouri, an independent research library that specializes in science, engineering, and technology. As a supplement to the books, the exhibition will include a small selection of historical clocks and timepieces from the collection of Grolier Club member Fortunat Mueller-Maerki.
Two of the books featured in the exhibition are the first and second editions of a work that describes a collection of mathematical and mechanical curiosities that were created by Nicolas Grollier de Servières, a cousin of the Grolier Club’s namesake. The book was first published as Recueil d’ouvrages curieux de mathématique et de mécanique, (Lyon, 1719) with over 80 engraved plates of machines and designs, including several curious clocks powered by the weight of the clock itself descending on an inclined plane, or by an Archimedean screw with a hidden source of power.

Precision and accuracy in clocks such as these may have been less important than the artistic, decorative, and symbolic features. Such was surely the case with the sunflower clock described and illustrated by Athanasius Kircher in his book, Magnes siue De arte magnetica opus tripartitum (Rome, 1641). A detailed, full-page engraving shows the sunflower clock floating on a piece of cork with its roots in the water. Vegetable magnetism supposedly caused the flower to follow the sun, so that a pointer fixed in the center would indicate the hour on a clock dial.

From Sebastian Münster. Horologiographia. Basel, 1533.

A variety of different sundials, horizontal, vertical, and inclined. From Sebastian Münster. Horologiographia. Basel, 1533. Image courtesy of the Linda Hall Library of Science, Engineering & Technology.

Books on more traditional types of sundials are featured in another section of the exhibition, beginning with Sebastian Münster’s Horologiographia (Basel, 1533). This comprehensive treatise was first issued as Compositio horologiorum in 1531, but it was popular enough to warrant this second enlarged edition just two years later. Both editions illustrate all manner and variety of sundials with beautiful woodcuts, some of which are attributed to Hans Holbein the Younger.

Early mechanical clocks offered several advantages over sundials, such as portability and the ability to show the time during cloudy weather and at night. They lacked precision, however, and had to be readjusted periodically to synchronize them with local solar time. And even after the appearance of mechanical clocks, books about sundials and how to make them remained popular. Demand for them continued throughout the sixteenth century and into the seventeenth.

The first practical book on sundials written in French was a seventeenth-century treatise by Salomon de Caus, a French engineer and scientist who developed a strong interest in mechanical devices. He dedicated his La pratique et demonstration des horloges solaires (Paris, 1624) to Cardinal de Richelieu, explaining to the Cardinal that his book would be easier to understand than earlier treatises on sundials, such as those by Christoph Clavius. In addition, this book would be even more accessible than others due to its pop-up models of sundials made of thick paper.

Even though the first mechanical clocks in the thirteenth century were crude, imprecise, unreliable instruments, a mechanical means of generating and counting a repeating beat marked a revolution in timekeeping. Their oscillating motion, which divided time into countable beats and was first illustrated in an encyclopedic-like book by Robert Fludd in 1617, was the basis for all subsequent improvements in precision timekeeping.

Fludd’s book, Utriusque cosmi maioris scilicet et minoris metaphysica, physica atque technica historia (Oppenheim, 1617‑1618), is famous for its many elaborate engravings that portray an interconnected universe. It also illustrates the key invention that made all mechanical clocks possible: a crown wheel, driven by a weight or spring, that is allowed to “escape” as two pallets on a vertical shaft alternately catch and release it—the famous escapement.

But this was not the first printed illustration of a mechanical clock. That honor goes to a woodcut in a book by Girolamo Cardano, his De rerum varietate libri XVII (Basel, 1557). The clock mechanism appeared in this folio encyclopedia as part of Cardano’s discussion of motion. The clock uses a spring to drive the mechanism and compensates for the diminishing power of the unwinding spring with a conical fusee. The fusee was a standard part of many later spring-driven clocks and watches that gave the spring a nearly constant driving force. An octavo edition appeared the same year and used the same woodcut.

One of the earliest illustrations of a weight-driven clock appeared in another encyclopedic book by Cardano, but only in the French translation published as Les livres … intitulez De la subtilité, & subtiles inventions. (Paris, 1566). Curiously, the space for the woodcut was left blank in the original Latin edition published by Johann Petreius in 1550. The French translation added a small woodcut that shows little of the mechanism other than the weights, dial hand, and a bell to sound the hour. The text describes the falling weight as a type of force. Later in the book, spring-driven clocks are discussed as a new invention, but are not illustrated.

In a book that described and illustrated some of the best astronomical instruments of the sixteenth century, Astronomiae instauratae mechanica (Nuremberg, 1602), Tycho Brahe mentioned that there were four clocks in his observatory. The largest of them must have been huge—one of its three wheels boasted 1,200 teeth and a diameter of two cubits (or about three feet) and was cast from solid brass. That clock is not illustrated, but two smaller clocks are shown in the plate of the famous mural quadrant that Tycho used for making observations of star positions. He used two clocks, Tycho explained, to reduce errors in recording the exact moment of observation.

Two clocks are also shown in an illustration of the observatory of Ole Rømer, in the account of his methods and discoveries by Peder Horrebow, Basis astronomiae. (Copenhagen, 1735). One of the plates shows Rømer working at his meridian telescope, observing star positions. Two clocks were built into the wall for the same reason that Tycho used two clocks. But a Huygens-style pendulum clock supplanted them, as it was undoubtedly more accurate than the two built-in clocks and had been hung by the window where the astronomer could easily read the time of an observation.

Christiaan Huygens designed a pendulum clock in 1656, and contracted with the clockmaker Salomon Coster in The Hague to build one the following year. It was the first successful pendulum clock, but Huygens improved its precision by altering the pendulum’s swing with two curved metal pieces at the top, changing the swing to the arc of a cycloid. The mathematical proof that a cycloid was the perfect curve to produce constant oscillation for a pendulum is what he presented in his book, Horologium oscillatorium (Paris, 1673). The book’s famous woodcut shows the clock, its mechanism, and the “cycloid cheeks” that changed the swing from a circle to a cycloid.

The Clockmaker. From Hartmann Schopper.

The Clockmaker. From Hartmann Schopper. [Panoplia] omnium illiberalium mechanicarum. Frankfurt, 1568. Image courtesy of the Linda Hall Library of Science, Engineering & Technology.

Practical instructions for building a pendulum clock, written for the “vulgar workman,” appeared in The Artificial Clock‑Maker (London, 1696), by William Derham, a clergyman. It was Derham’s first book and in his later book, Astro-Theology, he compared the ordered universe of the Creator to the clockwork machinery of a clockmaker. His The Artificial Clock-Maker includes the only documentation of a claim by Robert Hooke to have invented the anchor escapement, which is usually credited to William Clement.

Improving the design for the escapement mechanism was one way to improve the accuracy of a clock. Another was to improve the design of the pendulum. John Ellicott is remembered for his work on temperature-compensated pendulums, but during his lifetime his superior clock-making skills led to his appointment as Clockmaker to King George III. The “Ellicott pendulum” used iron and brass rods, cleverly connected to keep the overall length constant and compensate for errors otherwise caused by changes in the temperature. His design appeared in 1752 and was published in the Royal Society of London’s Philosophical Transactions with a large folded plate.

Scientific periodicals were exceedingly rare before the late seventeenth century and the Philosophical Transactions, which began in 1665 allowed quick dissemination of new discoveries and results. Details of Huygens’ balance-spring watch appeared in Paris only a few weeks before its announcement and explanation in the Philosophical Transactions in March 1675. The spiral spring keeps the balance wheel rotating back and forth regularly, like a pendulum. The invention was vital in providing portable watches with the same degree of accuracy as pendulum clocks, but it was not without controversy. Robert Hooke immediately claimed that he had invented the balance spring years earlier, without publishing the design.

Experts recognized that the balance spring, a spiral spring attached to an oscillating balance wheel, could be used in a sea-going watch or clock, a potentially great leap forward in solving the thorny problem of longitude. There was a huge gap, however, between the published concept of a balance spring and the design and construction of a watch that would be reliable at sea. When John Harrison finally built one, a chronometer known as H-4, the accurate working model was not enough to win the longitude prize offered by the British government. It also had to be practical, and that meant publishing the design so others could emulate it. Exacting care was taken to print engravings of the mechanism, along with a technical description in The Principles of Mr. Harrison’s Time-Keeper (London, 1767). The Preface is by Nevil Maskelyne, Astronomer Royal, who also wrote the “Notes,” which was based on when Harrison dismantled H-4 in the presence of experts.


Harrison’s Principles is just one of 86 printed books on science and technology in this exhibition that have described techniques of timekeeping, announced new inventions and discoveries, and instructed others in the construction and use of timekeeping instruments since the beginning of printing in the fifteenth century. The long advance toward precision in time leads to the twentieth century when Nature, a scientific journal known for publishing important new advances and original research, published the description of the first atomic clock, designed and built by Louis Essen with Jack Parry at the National Physical Laboratory in Teddington, England.

Because of the precision in timekeeping made possible by atomic clocks, the International Bureau of Weights and Measures redefined the concept of a second in 1967, publishing the result in the proceedings of their scientific meeting. And since atomic clocks are more accurate than the Earth’s rotation, the delegates knew that astronomical timekeeping was doomed. The new definition of a second was in terms of the frequency of light: precisely “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.” And the quest for precision continues.

The Linda Hall Library, established by the wills of Herbert and Linda Hall, opened in 1946. A not-for-profit, privately funded institution, the Library is open to the public free of charge and serves scholars, students, and researchers around the world. The Library remains devoted to its goal of being one of the world’s pre-eminent collections of materials devoted to science, engineering, technology, and their histories.

The Grolier Club of New York is America’s oldest and largest society for bibliophiles and enthusiasts in the graphic arts. Founded in 1884, the club is named for Jean Grolier, the Renaissance collector renowned for sharing his library with friends. The club’s objective is to foster the literary study and promotion of arts pertaining to the production of books.

An illustrated catalogue will accompany the exhibition On Time: The Quest for Precision, which will be on display at the Grolier Club, 47 East 60th Street, New York, NY 10022, from 14 September until 19 November 2016. Hours are Monday–Saturday, 10 am – 5 pm. The exhibition gallery is open to the public free of charge. For more information call the Grolier Club at (212) 838-6690.