Sidereal clock, no. 22


Sidereal clock, no. 22


Measuring instruments


Wood, metal, glass

Wooden mahogany case, there was a spare wooden case, height 59.25 cm, width 44 cm, depth 20 cm. The clock is now in the collection of the Adler Planetarium in Chicago

"The Riefler clock has two interesting characteristics. The first consists in the peculiarly simple and effective compensating pendulum, and the second in the mode of suspending the pendulum.

“As is well known, any good compensating pendulum should have as few parts as possible, should take up changes of atmospheric temperature with equal rapidity in all its parts, should have its compensating material extending as nearly throughout the length of the pendulum as possible, and finally should be heavy and have an appropriate form. How nearly Riefler's pendulum satisfies these conditions can be inferred from the following description:

“Its consists of a hollow steel tube 4 ft. 2 in. long, 0.65 of an inch inside diameter, with its wall 0.04 an inch thick. The tube is filled with mercury to a height of about two-thirds of its length. At the lower end is attached, by a screw with a milled head, a heavy lens-shaped mass of brass whose form permits it to cut its way through the air with almost no resistance. Below the lens are smaller disk-shaped masses whose number and position may be varied for somewhat finer regulation of the rate than can be effected with the milled head. These disks are also used for regulating either to sidereal or mean solar time. At about two-thirds of the height of the pendulum is a light brass cup for the reception of small weights that may be put on or taken off for the most delicate alterations or rate, without disturbing the vibrations of the pendulum.

“The second special feature is the peculiar mode of suspending the pendulum. Its weight is carried by a frame resting by knife edges on agate surfaces. By means of a pair of thin steel springs the two parts into which the pendulum tube is divided near its point of suspension are connected at a distance about one-half inch apart. Through these springs the oscillations of the pendulum communicate a rocking motion to the frame and also to an arm extending downward, terminating in a fork either prong of which carries an agate pin. These pins engage alternately into the tooth wheel of the escapement. The rest of the mechanism of the escapement offers no features especially different from the ordinary form. By means of a pair of screws at the extreme top of the pendulum, the relative lengths of to and fro vibrations may be regulated. The clock is also provided with break circuit attachments and chronographic connections."


Clemens Riefler of Munich, Germany


Myers, George W. "The Astronomical Observatory of the University of Illinois." Popular Astronomy. 6 (1898) 319-321.

Special catalogue of the joint exhibition of German mechanicians and opticians. (1900). Berlin: Reichsbruckerei.


Adler Planetarium, Chicago, Adler: Accession number A-189




graphic image from catalog




physical object


University of Illinois Observatory, Urbana, Illinois





Clemens Riefler of Munich, Germany , “Sidereal clock, no. 22,” University of Illinois Observatory Collection, accessed September 30, 2020,