Graphometer

A late 18th century graphometer
Figure 1: A late 18th century graphometer
In my collection since 2005 is this instrument which is the simplified version of the Pseudo Holland Circle, both of which were affordable alternatives to the simple theodolite and transit. The instrument is divided in half degrees with complementairy annotation on the circle (0 - 180 and 180 - 0 degrees) and had quite similar use as the surveyor's cross in my collection.

Invented in 1597 by Frenchman Philippe Danfrie, instruments like these have been used for land surveying since the late 16th century until the late 19th and possibly early 20th century. The alidade has two verniers reading 30 arc minutes. Observations can be read down to one arc minute and estimated down to half an arc minute.

The compass is divided in 360 degrees at whole degrees, with the cardinal points annotated in abbreviated French with N, E, S, O (Nord [north], Est [east], Sud [south] and Ouest [west]). When I obtained it the visors were equipped with copper wires instead of horse hair like in an equerre. Not sure this was original or not, I kept looking for similar grafometers to decide what to do with them.

The instrument has no markings at all, but a similar instrument with signature by Eugène Ducretet (and as Ducretet was the French radio pioneer this could explain the copper wires) can be found on the web site of the French Service d'Histoire de l'Éducation.

This could either mean that Ducretet build both instruments, but never signed the one I own (which I think is quite unlikely), or that Ducretet modified a graphometer (by adding the level) build by the same firm or person as mine and than signed it. The latter means that the instruments were not made by Ducretet at all, but that he signed the one he modified. If anyone knows the answer to this, please let me know.

Then after five years I finally found an exact copy of this graphometer for sale showing horse hair wires instead of copper. This made me decide to remove the copper wires in order to replace them with horse hair. While removing the copper wires from the visors I found small remains of horse hair still around the screws, confirming what I suspected for the last five years (see figure 8). Now the instrument is equipped with horse hair again (see figure 9).

The handle has a conic hole, to make it possible to attach the instrument to a tripod or staff and is equipped with a ball bearing that allows the instrument to be adjusted horizontally.

If you have any questions and/or remarks please let me know.

The instrument as seen from below.
Figure 2: The instrument as seen from below.
 
Detail of the instrument showing the compass.
Figure 3: Detail of the instrument showing the compass.

When I received it the wires were made of insulated copper wire like in use with electromotors.
Figure 4: When I received it the wires were made of insulated copper wire like in use with electromotors.
 
 A similar instrument with signature of Eugène Ducretet made in Paris in 1870.
Figure 5: A similar instrument with signature of Eugène Ducretet made in Paris in 1870.

The graphometer in use on a tripod.
Figure 6: The graphometer in use on a tripod.
 
Here it is on an original tripod.
Figure 7: Here it is on an original tripod.

The copper wires and the remains of the horse hairs that were behind the screws.
Figure 8: The copper wires and the remains of the horse hairs that were behind the screws.
 
Now the instrument is restored to its former glory.
Figure 9: Now the instrument is restored to its former glory.

 This is what you see when you look through the instrument.
Figure 10: This is what you see when you look through the instrument.
 
One of the two verniers on the instrument. It reads to 1/30 of half a degree.
Figure 11: One of the two verniers on the instrument. It reads to 1/30 of half a degree.

Surveyor's crosses Geodetic Sextants Theodolites Total Stations Levels Standards Tools Firms
Equerre 19th century Pantometer? 20th century Pantometer Pantometre à Lunette 17th C. Surveyor's Cross Pseudo Holland Circle Graphometer