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Bernhard huBer The Engineer of Precision Time: Pendulum Clocks by Sigmund Riefler In 2012, Sigmund Riefler was designated by technical drawing material. He profited from the American horologists as the most important growing demand for measuring and drawing clockmaker of all time1. This is a good reason to instruments accompanying rising industrializa- take stock of Sigmund Riefler and his achieve- tion in the nineteenth century. Clemens Riefler ments in the following essay. invented the “Zirkelkopfgriff”, a knob at the top of the drafting compass with which it could be The Early Years. easily held, and it was universally copied, making Sigmund Riefler (1847-1912) was born in a small the firm of Riefler respected world-wide. After village in the Allgäu region. His auspicious fam- his father’s death, Sigmund Riefler devised an- ily background was the basis for his later suc- other system of drawing instruments patented cess. His father, Clemens Riefler, completed a in 1877 which also gained world-wide renown four-year clockmaking apprenticeship and made and was produced unchanged for a hundred a longcase clock himself. As early as 1841, he years. The superior construction and remarkable founded the firm of Clemens Riefler together accuracy of the drawing instruments, for which with three workmen and began at once to make Riefler received many awards, were the basis for Frontispiece: Patent document 50739 for Fig. 1: Clemens Riefler’s awards a double wheel escapement for chronome- ca. 1885 (DGC archive) ters from 1889 (Photo: Dieter Riefler) 262 BERNHARD HUBER – HÖCHSTADT the firm’s economic success and international cision clock, had a great influence. In the engi- reputation. neer’s rigorous way of thinking and as an excel- Sigmund Riefler attended the trade school in lent mathematician, Sigmund Riefler engrossed Kaufbeuren in the Allgäu and, in 1865 near the himself in the problem. end of his apprenticeship as a mechanic in his father’s firm, he crafted a framed wall clock with Riefler was not a trained clockmaker, but he had recoil escapement. Subsequently, at the age of 18, become engaged at an early age with the sub- he attended the polytechnic institute in Munich ject of timekeeping. Initially he focused upon a to study mathematics, geodesy, physics, electrical movement with a balance and balance spring. engineering and astronomy. From 1870 until 1876 After completing his apprenticeship as a me- he worked as a land surveyor in Schleswig-Hol- chanic in 1865, he had the idea of an escapement stein and developed new measuring equipment in which “the energy from the wheel train is at the same time. After the death of his father, the transferred to the balance through the balance three brothers took over the family firm. In order spring”. At the age of 22 in 1869, he constructed to get into closer contact with the institutes of a first model while home in the family business. science, and above all the observatory, Sigmund But neither this model “nor quite a number of Riefler moved to Munich in 1878. His two broth- other constructions which I completed through- ers Adolf and Theodor stayed in the Allgäu and out the years” proved satisfactory. managed the prospering firm making technical Not before “the beginning of the year (1889) drawing instruments. did I manage to construct this escapement de- The thriving finances of the enterprise enabled scribed below, which in theory is perfect and Sigmund Riefler to purchase a high-class resi- at the same time is astoundingly simple. Apart dence in Munich’s Lehnbach Square No. 1. This from that it can be also applied to pendulum became his home, research center and laboratory. clocks with an entirely free swinging pendu- lum”2. Sigmund Riefler was granted patent DRP Sigmund Riefler’s Inventions and 50739 (see fig. frontispiece). In the German Publications clockmakers journal (Deutsche Uhrmacher-Zei- tung) of March, 1890, he described his new in- The Escapements made by Sigmund Riefler. vention, the free-spring impulse escapement as In his laboratory, Riefler devoted himself mainly “an escapement for chronometers and other por- to accurate timekeeping. The head of the univer- table time-keepers with an entirely free vibrating sity observatory in Munich-Bogenhausen, Hugo balance and for longcase/wall clocks with an en- von Seeliger who had expressed a wish for a pre- tirely free swinging pendulum”.3 Fig. 2: The company ca. 1900 with Adolf (left), Sigmund (center) and Theodor Riefler (right) (DGC archive) 264 BERNHARD HUBER – HÖCHSTADT Reading this publication is worthwhile as it sign is shown in fig. 4. In the same way as the bal- impressively demonstrates Riefler’s analytical ance spring is used to impart an impulse to the way of thinking. His revolutionary idea was balance, the suspension spring is used to impart to exclude as imperfect the principle of direct energy to the pendulum on a knife-edge suspen- power transmission to the balance, a principle sion. In time with the pendulum oscillations, the used for centuries in every escapement. Instead, suspension spring is impulsed and thus provides Riefler moved the balance spring stud to and the necessary force to to sustain the oscillations. fro with the vibrations of the balance so that the balance itself could oscillate entirely freely. After the patent application in July, 1889, numer- In order to achieve this, he introduced a special ous incremental improvements were made until double-wheeled escapement, an entirely new 1894, and in 1907 a final version emerged. Along concept without precedent. A model of this is with Eduard Saluz4, Jürgen Ermert has authored shown in fig. 3. a multi-volume standard work — ­Precision Pen- In his patent specifications, Sigmund Riefler dulum Clocks in Germany 1730-19405 — and he wrote that his entirely free escapement could also has done intensive research on this which soon be applied to pendulum clocks. The relevant de- will be published6. Fig. 3: Model for new escapement with a completely freely oscillating balance and driven via the balance spring stud (Photo: Dieter Riefler) Fig. 4: Free spring escapement for pendulum clocks, schematic diagram. In red: pendulum block with pallets and knife-edge suspension (gray), suspension spring (blue), pendulum (yellow) THE ENGINEER OF PRECISION TIME: PENDULUM CLOCKS BY SIGMUND RIEFLER 265 In operation, the free spring escapement Apart from that, the mercury was all at the lower proved to be susceptible to shocks and land end of the pendulum and could only compensate tremors which could seriously disturb the clock’s at that position whereas the thermal reaction oc- rate. Therefore, Riefler designed another escape- curred along the entire pendulum length. More- ment which is simpler and superior7. He named over, the shape of the conventional mercury it “a free gravity escapement with the pendulum pendulum was unfavorable because of air drag. oscillating on a knife edge”. In June, 1913, it was Sigmund Riefler overcame these disadvantages granted German patent DRP 272119. The impulse to the pendulum was imparted by two small gravity arms attached to the pendulum block and activated by a double escape wheel like the free spring escapement’s. It was not Riefler’s intention to further perfect his new gravity escapement in place of his free spring escapement. His intention was to create a reasonably priced precision pendulum clock which would be easy to set up. He downplayed optimum performance but the clocks with a gravity escapement actually performed even bet- ter than those with a free spring escapement.8 The New Pendulums made by Sigmund Riefler. Riefler was well aware that he also needed a first- class pendulum along with a new escapement for his precision pendulum clocks. In the intro- duction to his comprehensive paper of 1894 he wrote: “The uniformity of the rate of a pendu- lum clock depends mainly on 2 factors: firstly the thermal compensation of the pendulum, secondly the superiority of the escapement”.9 It is interesting that he referred to the pendulum as first in importance. Consequently. after Siegmund Riefler developed his free spring impulse escapement, he immedi- ately concentrated on improving the pendulum. There were four requirements he set for a pendu- lum in order to achieve optimal thermal compen- sation10. Riefler concluded in his analysis: “For the production of compensation pendulums the best material is without doubt mercury”.11 Since the invention by Graham in 1721, the mercury compensation pendulum, with an iron rod and a container filled with mercury at the lower end, had proven deficient. Rapid temperature changes are quickly absorbed by the thin pendulum rod, but it takes a long time for the large compact Fig. 5: Mercury compensation pendulum by Riefler mass of mercury to reach the new temperature. (Photo: Jürgen Ermert) 266 BERNHARD HUBER – HÖCHSTADT by using a steel tube filled two-thirds with mer- cury. He added a slim steel bob weighing several kilograms. For this he received in March, 1891, German patent DRP 60059. As the extent of thermal compensation was critically dependent upon the individual coefficient of expansion of the steel tubes, Riefler had each of them tested in the Physikalische Reichsanstalt (Imperial In- stitute of Physics) in Berlin. The first use of this pendulum was in Riefler clock No. 1 (fig. 6), with a free spring impulse escapement, at the observatory in Munich in 1891, and it represented a quantum leap forward. The remarkable performance achieved by this clock is registered in the records of the Munich observatory (fig. 7)12, as well in a contemporary examination of the rate of Riefler No. 1 during changes in temperature. Compared to the time- keeping results of pendulum clocks offered by other manufacturers, Riefler’s was superior to all competitors as fig.

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