Functional Description: First, place your eye near the eyepiece and look into it. After looking into the eyepiece, align the reticle in the eyepiece with the astronomical body that you are measuring. When the reticle and the body are aligned, this means that the body is at an altitude of 60 degrees. The light that enters the lens is then reflected into the eyepiece using a mirror that is suspended inside the instrument.
The name "pendulum astrolabe" may seem strange at first becasue the device neither looks like a typical astrolabe nor does it appear to have a pendulum located on or in the device. However, an astrolabe is simply a device used to measure the altitudes of astronomical bodies. Also, the mirror located inside the device is suspended in a pendulum-like fashion.
The actual measurement of 60 degrees seems unimportant other than that it is known that the angle is in fact 60 degrees. This can used to determiniation the declination of an astornomical body. If one measures every time that body crosses the 60 degree mark, then they could make a more educated statment about the motion of that body (period of its revolutions, etc.).
Base: 1cm high x 34 cm long x 21.5 cm across
Instrument: 48 cm high (Top of base to top of eyepiece) x 32 cm long (tip of lense to tip of eyepiece) x 21 cm across
Lenses: Large central lense diameter of 7 ½ cm, Smaller side lense diameter of 4 ½ cm
Crate: 54 cm high x 38 cm wide x 27 cm back
Case: Wood, various alloys including brass
PENDULUM ASTROLABE | David White Co. | Milwaukee. Wis., U.S.A. | No 67476 | M-5107 1952 | U.S. Tech I.D. Number
Property of | 38268 Michigan | Technological | University
Paper taped to front of Astrolabe above level below main aperture:
THE OPTICS IN THIS ASTROLABE | ARE COATED TO INCREASE EFFICIENCY. | CAREFUL CLEANING WILL NOT INJURE | THE LENSE SURFACES.
History of the Object
The box that Tech’s astrolabe is stored in is marked with a piece of tape bearing the hand-written label, OLD PRISON SITE | JACKSON MICH, suggesting that Associate Professor H.B. Anderson of the Mathematics Department found and purchased the device second-hand in 1967 when he wrote to the company for more information. Unfortunately, a copy of this letter is not with the device, although the response letter from Edwin A Setzke, Manager of Realist Inc. Customer Services Division and a booklet titled “Supplementary Information for use with the Willis Pendulum Astrolabe” which was sent enclosed with the letter can now both be found with the Astrolabe, along with the owner’s manual which accompanied the device throughout its various ownerships.
A Michigan Tech equipment number is found on the device, and tables and charts accompanying the book are filled in, suggesting that Anderson used the astrolabe in instruction.
The David White Company would continue to make the Astrolabe until 1952, according to the letter from Edwin Setzke. An inscription on the base of the Astrolabe at Tech says that the model was produced in 1952, making it one of the last astrolabes made by the company. The David White Company became Realist Inc sometime between 1952 and 1967. Realist Inc., based out of Menomonee Falls, and continued to make surveying equipment, as well as rifle scopes, projectors, and cameras well into the late eighties. The last word located on Realist Inc. was a brief New York Times article from 1989 stating that the company purchased majority stock of a Swiss company called Ammann Laser Technik AG.