Conserving a Colonial Instrument

Colonial instruments specialist and conservator Jeff Lock visited the Historical Society last week to perform treatment on a special piece in our collection.


Our David Rittenhouse surveyor’s level is a telescope with a precision level.  It is an eighteenth-century surveying instrument most likely used in the field by Rittenhouse himself.  A resident of Montgomery County and renowned astronomer, instrument maker, and scientist, David Rittenhouse began making clocks at the age of nineteen.   One of his earliest clocks is in HSMC’s collection (come see it!).  He also made astronomica    l instruments for universities as well as for his own use, like the one in our collection.  In 1769 he was the first person in North America to witness the transit of Venus.  And, with Andrew Ellicott, he finished the survey of the Mason-Dixon Line.

 rittenhouse protrait

The telescope was later used by Alan Corson, county surveyor, in the mid-19th century.  It was his relative, Walter Corson, who donated it to the HSMC in 1900.  Before treatment, the piece had been suffering from a layer of polishing compound residue and a loose gear.  If left in contact with the surface of the piece, the polishing compound residue becomes acidic over time and can actually eat away at the metal.  The loose gear was not only preventing the eyepiece from focusing, but also presented a hazard to the glass lenses.

Copy of Ritt. D. level Loose Gear

Jeff and his associate, Ron Hoppes, came prepared with hand-made screwdrivers, soft brass brushes, and precision measurement instruments.  They carefully removed screws and plates from the tripod base and the telescope, making sure to document the original location of all the pieces.  They then used both nylon and brass brushes with a solution of ethanol and water to gently remove the residue without damaging the existing patina.  The result isn’t shiny, but that’s not what we were looking for!  The piece will now be coated with Renaissance Wax, a petroleum-based conservation wax, which will prevent corrosion in the future.


The experts also extracted the detached gear from inside the telescope and reaffixed the gear to it’s original position.  Now a user can adjust the telescope to focus the eyepiece, as David Rittenhouse intended!  Jeff and Ron completed this treatment in one whirlwind day, and we at HSMC are very grateful for their hard work.

To learn more about Jeff Lock, visit his website at:

And don’t forget to come in to HSMC to see the finished product!



Figure 1, Full telescope: HSMC

Figure 2, Signature: Jeff Lock

Figure 3, David Rittenhouse: HSMC

Figure 4, TPI measurement: HSMC