Late 18th century Pseudo Holland Circle
I found this instrument in 2010 while scouring the internet for antiques dealers. The instrument is a simplified form of the Holland Circle (Hollandse cirkel), invented by the Dutch land surveyor Jan Pietersz. Dou after 1608 and first described by him in 1612 in his work Tractaet vant maken ende Gebruycken eens nieu gheordonneerden Mathematischen Instruments (Treatise on the construction and use of a newly invented Mathematical Instrument).1 Compared to the Holland Circle this instrument lacks a compass, the suspension ring for vertical measurements, and it has been engraved in degrees only. Holland Circles also had trigonometrical scales (sine, tangent and secant) and sometimes a Polygon scale similar to the one on the surveyor's cross in my collection.2 Due to its simplified form the instrument is sometimes referred to as a Pseudo Holland Circle.3
In development the instrument is the link between an equerre and a theodolite, while in an even more simplified form it became known as a graphometer.4 The period name for this instrument would have been Cercle Entier (French, lit.: full cricle) or Geheele Cirkel (Dutch, lit.: full circle). At times Winckelkruis (Dutch, lit: square-cross) is used as well, even though those would normally not have an alidade, but only consist of a cross with four visors. The alidade of the surveyor's cross in my collection can be fixated at 90 degrees, while this instrument has four fixed vanes on the outer circle and another two on the alidade, which can be clamped at any given angle. Similar to the graphometer it has a scale running from 0 to 180 degrees, and an additional one running backwards from 180 to 0 degrees.
Use and diffusion
Clearly the instrument was used in land surveying and would have been supported by a staff (see figure 2), most probably with a brass slotted head (to receive the screw) and a steel point.5 For this the handle is hollow and slightly tapered (17.5mm at the opening, 15mm at the bottom, 40mm deep) as was usual on period instruments. There is however no ball joint as on most similar surveying instruments like the graphometer. Joint-less sockets were however not uncommon in the preceding centuries on these full circle instruments and at times the staff itself would be equipped with a joint.
The instrument would have been placed on the staff and firmly stabbed into the ground. The fixed visors were used to set out right angles and to align the instrument with a reference, while observations were done using the alidade, which could be clamped for the purpose. The alidade has two verniers (see figure 1) on opposite ends allowing the instrument to be read diametrically, reducing eccentricity errors.
In France and the Netherlands full circles were used in cadastral surveys. Although the reign of Napoleon over Holland ended in 1813, the cadastral methods described in Recueil méthodique des Lois, Décrets, Réglemens, Instructions et Decisions sur le Cadastre de la France (Paris, 1811) would remain in use until 1 October 1832, the day the Dutch Kadaster was officially established.6 Article 111 on page 44 states that "Le cercle entier est l'instrument le plus avantageux pour les triangulations de quelque étendue" (the full circle is the most advantageous instrument for extended triangulations). We can be sure that the "full circle" indicated was the instrument described on this web page as in Collection des Lois, Décrets, Instructions, Circulaires et Décisions Relatifs au Cadastre de la France (Paris, 1806) article 24 on page 32 states that "...par la triangulation ... les instrumens (sic) qu'il [le géomètre] a dû y employer sont le graphomètre ou le cercle entier..." (...in triangulation ... the instruments he [the land surveyor] had to employ are the graphometer or full circle...). So while in 1806 the graphometer and full circle were regarded of the same quality (and thus similar in construction), by 1811 the full circle was the preferred instrument.
Dating the instrument
Dating the instrument is far from easy. On the scale two differently shaped zero's can be found; the round ones for every ten degrees that were mainly used up to the 18th century and one oval one indicating zero degrees, which would not have been used in that same period (see figure 3). This indicates that the instrument could have been made in or shortly after the 18th century. In navigational instruments the vernier had largely replaced diagonal scales by 1740, which would indicate a date most probably after this year.7 The combination of round and oval zero's can also be found on navigational instruments from the last quarter of the 18th century.8 If genuine the box might help dating the instrument. Being made of oak and the year rings clearly visible it may be dated using dendrochronology.
The oak box (see figure 13) is without any lining (see figure 5), pine insets to support the instrument were used instead (see figure 6). Through time one of the hooks that were used to close the box has disappeared and so has the key, while the lock seems to be a period replacement.
The 180mm diameter limb (see figure 1) is divided in two halves, both divided in whole degrees. One half is running clockwise, while the other runs counter clockwise. Both are marked from 0 to 180 degrees at ten degrees intervals, which were stamped in (see figure 3).
The alidade is 160mm in overall length (140mm between the hairs of the visors) and can be clamped at any given angle by fastening the central knob (see figure 4). It is equipped with two verniers that allow to read the instrument in a diametrical way like a modern theodolite. The verniers can be read down to five arc minutes, while an estimate to roughly 2 arc minutes is possible (see figure 12). As the limb is divided clockwise and counter clockwise both verniers are divided in the same way, with the zero in the middle of them (see figure 12).
Similar to most Holland Circles the instrument has six visors in total; four around the limb and two on the alidade (see figure 1). The visors have a slit and wire above each other (see figure 9). In this period the wire would have been made of horse hair, but on this instrument they have been made of thread and are possibly later replacements. Other later replacements are three of the screws and the winged fastening screw (compare it to this original), as can be seen from the difference in colour between them, the original ones and the main body (see figure 8).
The instrument lacks a compass, which was typical for Holland Circles and would be attached to the frame. Other instruments contemporary to this Pseudo Holland Circle (e.g. graphometer) were at times as well produced without compass, while contemporary Circles like those by Kleman & Zoon would have their compass mounted on the alidade.4
I am looking for further information of this instrument:
: Pouls, De landmeter Jan Pietersz. Dou..., p.39.
: Pouls, De landmeter Jan Pietersz. Dou..., p.75.
: It has to be noted that theodolites already existed in the 16th century, well before the invention of the Holland Circle. In the Netherlands (and France) however the Holland Circle would become the most used angle measuring device for land surveyors for some 200 years. See Pouls, De landmeter Jan Pietersz. Dou..., p.41.
: See Jordan W., Handbuch der vermessungskunde, Erster Band. Methoden der Kleinsten Quadrate und Niedere Geodäsie, (Stuttgart, 1877), p.140.
: The Recueil Méthodique appeared in a bilangual (French/Dutch) edition in 1812 and between 1825 and 1831 had no less than 111 circulars with instructions, additions and further details or corrections. See Tresoar: Minuutplans – hun ontstaansgeschiedenis.
: P. Ifland, Taking the Stars, Celestial Navigation from Argonauts to Astronauts, (Malabar, 1998), p.56.
: See picture at Ifland, Taking the Stars..., p.57.
If you have any questions and/or remarks please let me know.
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