My brother Bert¹ recently acquired a curious telescope mount that has a Seth Thomas clock mechanism mounted in its base (Figure 1). The purpose of this device is to provide power to the polar axis of an equatorial mount of a small telescope so that an observed object is kept in the field of view. The mount and a four-inch refracting telescope were made at the California Institute of Technology (CIT) Astrophysical Observatory in the early 1930s. The mount has a nameplate attached (Figure 2).

The clock mechanism is a No. 10 double-spring, 8-day, time-only movement that is illustrated in the Adam Brown Company reprint of the Seth Thomas factory list of clock movements of May 1, 1907 (Figure 3). It is also illustrated in A Treasury of American Clocks² on page 253, photograph 438.

This movement has been modified to remove the original escapement anchor and replace the escape wheel with a combination copper fan-fly governor and eddie-current brake disc. Mounted in the base is a “C”-shaped magnet arranged such that it can be swung over the disc (Figure 4, see next page). The position of the magnet changes the rate of rotation of the disc, and consequently, the rate of the minute arbor (which has been extended to become the drive shaft to a pair of 45 degree helical gears), and then of a worm and worm gear attached to the polar axis.

Brother Bert also acquired the original patterns for the mount castings. He believes that Russell W. Porter  might have used the device as part of the site surveys by the development team in the early 1930s to find the best location for the 200-inch telescope that ended up on Palomar Mountain in southern California. The small size of this telescope and mount and its clockwork drive (eliminating the need for external power) indicate the instrument was designed for use in the field.³ Porter may have also had a hand in the construction of this device since it is known that he made similar instruments.

Based on the following points, I postulate that the whole mechanism was designed around the timepiece itself.

1. The aluminum case is roughly machined to clear the movement’s mainsprings.

2. The case has been end-milled to provide flat surfaces that were then drilled and tapped to accept four mounting screws. The two top mounting tabs and two holes in a bar riveted towards the bottom of the front plate are made of copper rather than brass. I first thought that these were adaptations but they appear to be original, as shown in the photograph of the front plate in Figure 2.

3. The two winding arbors are extended through the mount casing to winding levers with redundant ratchets—the original winding ratchets have been retained on the movement.

4. A peephole is provided in the base, which provides a way to confirm the mechanism is operating and to kick-start it if it is not.

5. The increase in rotation rate changes the original one revolution per hour of the minute arbor into approximately one revolution per day around the mount’s polar axis.

6. The back plate of the movement is slightly modified to give clearance to the case-mounted rate adjustment device. This may not have been the first attempt at rate regulation; one of the plate separation posts has a half-diameter notch cut away for no obvious reason.

7. It is unlikely that CIT intended to go into production on this device—both because of its limited application and because such is not their business. However, being technically inclined, they probably started the design from the ground up.

8. Each casting is hand-marked with a CIT number matching the pattern number.

About the Author

David G. Willard is the third cousin six times removed of clockmaker Simon Willard the elder. He is a retired communications engineer and has dabbled in clock and watch repair since the 1960s. He learned much valuable information over the early years from master collector and NAWCC Fellow Fredrick Mudge Selchow.

1          Berton C. Willard. Past president of the Springfield Amateur Telescope Makers (Stellafane Club) in Springfield, Vermont, and curator of their museum at the Hartness House in Springfield.

2          Brooks Palmer, A Treasury of American Clocks (New York: The Macmillan Company, 1967).

3          Berton C. Willard, Russell W. Porter, Arctic Explorer, Artist and Telescope Maker (The Bond Wheelwright Company, 1976)