Restoration - Update on Surveyor's Compass

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Article taken from "Backsights" Magazine published by Surveyors Historical Society

Theresa Bannock and David St. John - April 1987


Mr. T. R. Oden of New Mexico and SHS member, provided a survey compass for restoration.  The instrument is engraved: "James Prentice, 66 Nassau St., New York."  Evidence exists which places the instrument in the possession of Mr. William Pelham during the early surveys of New Mexico.  Certain facts have come to light about the dating of this instrument as a result of this restoration project.

Lower Portion

The staff adaptor of a surveyor's compass serves the dual purpose of establishing a stable platform at a fixed elevation while its articulating ball joint permits attachment of the compass plate assembly.  Stability is accomplished by loading the ball joint with a friction pad which is compressed sufficiently to permit leveling and turning of the compass assembly.  Staff adaptors are, in general, the same from the period except for the external configuration and, perhaps, the loading method used to secure stability.  In the case of this compass, the staff adaptor conforms to diagram 1.

diag1.JPG (47211 bytes)Disassembly Problem

Mr. Prentice demonstrated excellent threading capability in the construction of his staff adaptor.  Not only did the thread configuration closely match present day standards for 60' thread form, but the face cuts (Area "A"), at the time fabrication were such that when assembled, the unit would have provided little evidence to the naked eye as to how it had been produced.  With the passage of time, normal field use, and resultant surface damage, the mating surfaces became, for all intensive purposes, invisible, even under the microscope.

Benchmark used Flouresence Microscopy in an effort to determine if any parting line existed within the device so that proper techniques could be used for disassembly.  An area approximately 3/8" wide was chemically treated the entire length of the housing to reduce reflectance.  A penetrant formulation of Ethylene Glycol, Glycerin, Ethyl Alcohol and Flourescein was carefully applied and left overnight.  The test area was then viewed under low power with a microscope equipped with both long and short wave ultraviolet illumination.  Indeed, a parting line was found.

 The next step was to modify a 5C soft collect and bond a liner of "rulon", then bore an internal diameter to match the outside of the staff housing to provide a firm, non-marring, high friction clamping force to the assembly.  A prudent application of torque with a strap wrench then released the assembly which had been closed for over a hundred years.

Establishing a Date

Dating an instrument can be difficult even when certain verifiable clues and documentation exist.  In this case, there is sufficient supporting information to make safe an assumption that the instrument was in the possession of William Pelham.  One question arises.  Was this instrument used during early surveys of New Mexico, or, was it acquired by Mr. Pelham at a later date?  The puzzle seems to begin with Mr. Pelham's arrival in Santa Fe during December of 1854 and the signature of Mr. Prentice on the instrument -- and 66 Nassau St., New York -- which was not occupied by Mr. Prentice until sometime in 1859.  This conflict in dates essentially negates the hopeful assumption that the instrument was used during the initial survey of New Mexico.

A Simple Wad of Paper

Restoration can be a complex process.  Rigid guidelines are followed to determine appropriate technique.  From the very beginning, a diagnostic format is used to accumulate as much information as possible before disassembly begins.  In this case, several alternate methods of disassembly could have been used.  Each though, would have contributed in some measure to the loss of historical information.

diag2.JPG (49849 bytes)Referring to diagram 2, tension in this assembly was accomplished by a cork friction pad backed by a number of layers of folded newspaper.  This combination was then compress against a brass disc.  When the initial tension released with wear and time, one had only to deform the disc from behind to regain sufficient tension to maintain a stable platform for leveling.  When this assembly was opened, the wad of paper was seen to hold a legible text of the period.  Fortunately, one layer parted and provided a partial date (t. 11, 1887), and some text.  The remainder of the layers are fast held.

New Problem

newspaper.JPG (109125 bytes)This carefully folded wad of paper contains about 15-18 layers of news print and is approximately 1/8" thick at the center.  This collection of news print has been subjected to pressure, friction, ambient environmental conditions and microbiological activity for over one hundred years.  As the cork slug began to conform to the slope of the ball, so to, did the news print, with attendant distortion.  The objective at this point is to save as much of the text as possible to enable more accurate dating of the instrument.  It is important to determine whether the newspaper was added by Mr. Pelham, or a repairer, sometime after the instrument was in use, or by Mr. Prentice at the time of fabrication.  There is also the possibility that the instrument was imported by Mr. Prentice with his name on it.  The text will perhaps disclose whether the newspaper was printed in New Mexico, New York, or England.  Such information will be important and provide direction for a more accurate date of this compass.

Restoration at best is interesting work, but labor is intensive and often tedious.  As you might surmise, we were visibly excited upon finding the wad of paper and understood its value as well as the importance of selection and careful execution of proper technique.  If we are able to separate the individual pieces of newspaper and salvage the text, the information will be photographed and then mounted and photocopied.  The original papers will be preserved and returned to the owner, Mr. Oden, along with photocopies and photographic prints as part of the restoration project.  

Present Status

We are currently awaiting a consensus opinion from the American Institute for Conservation regarding the proper methodology for saving the newsprint text.  Until then, the materials will be stored in a desiccator chamber with humidity held below the threshold of microbiological activity.

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