Nederlandse Commissie voor Geodesie 41, Delft, 2004. 102 pagina's.
ISBN-13: 978 90 6132 287 0. ISBN-10: 90 6132 287 1.
In 1612 verscheen van de hand van de landmeter Jan Pietersz. Dou een boekje met de titel: Tractaet vant maken ende Gebruycken eens nieu gheordonneerden Mathematischen Instruments. In dit boekje werd, zoals de titel zegt, een nieuw landmeetkundig instrument beschreven. Dou was daartoe gekomen omdat hij niet tevreden was met het bestaande landmeetkundige instrumentarium en daarom had hij een instrument laten maken "wat anders als naar ghemeene lantmeters stijl ghemaeckt" was.
Dit nieuwe instrument had hij onder meer gebruikt bij de droogmakerij van de Beemster. Het werd gedurende bijna 200 jaar het meest gebruikte instrument van de Nederlandse landmeters. Door zijn vorm onderscheidde het zich duidelijk van andere hoekmeetinstrumenten uit die tijd en is daardoor goed herkenbaar.* Dit instrument is men later Cirkel van Dou of Hollandse Cirkel gaan noemen.
We zullen in deze publicatie nader ingaan op de inhoud van dit traktaat, maar eerst aandacht besteden aan de positie en het werk van de landmeter in het algemeen, het destijds gebruikte instrumentarium en het leven van J.P. Dou en daarbij vooral aandacht besteden aan zijn in druk verschenen publicaties.
In tegenstelling tot wat helaas gebruikelijk is geworden, wordt hierna met het woord Holland niet Nederland, maar alleen het gebied van de huidige provincies Noord- en Zuid-Holland bedoeld. Omdat Dou vooral in het gewest Holland heeft gewerkt zal de aandacht vooral gericht zijn op dit gebied, maar de ontwikkelingen in de andere provincies wijken hier weinig van af.
*. Het ontstaan en de ontwikkeling zijn al eerder beschreven: H.C. Pouls - Winkelkruis - Astrolabium - Hollandse Cirkel. Geodesia 1979, p. 238-246, 294-304. De op p. 296 genoemde plaat is ondertussen gevonden.
- De Hollandse landmeter, ca.1300 - begin 17e eeuw
- De theoretische en praktische kennis van de landmeter, 13e - 16e eeuw 9
- De landmeter Jan Pietersz. Dou
- Het instrumentarium van de landmeter tot ca. 1600
- Het maken van een nieuw "Mathematisch" instrument
- Het aanbrengen van de goniometrische verdelingen en het gebruik daarvan
- De naam "Hollandse Cirkel" en de verdere ontwikkeling van het instrument
- Beschrijving van enige bewaard gebleven Hollandse cirkels
- De twee laatste "Hooftstucken" van het Tractaet
- Bijlage 1. Inhoudsopgave van de landmeetkundeboeken van Sems en Dou
- Bijlage 2. Overzicht van alle 25 in het derde hoofdstuk genoemde "Proposities"
- Verantwoording van de illustraties
- Summary Jan Pietersz Dou and the Holland Circle
In 1612 the Dutch surveyor J.P. Dou published a book in which he described a new 'mathematical' instrument invented by him ("een nieu gheordonneert Mathematisch Instrument"). This instrument was made by the Leyden instrument maker Jan David. In the 17th and 18th centuries this type of measuring instrument became very popular with the Dutch surveyors. This instrument, the "Hollandse Cirkel" (Holland Circle), is the subject of this publication. The origin and development are described as well as some additional information about surveying in the Netherlands and the inventor J.P. Dou.
Jan Pietersz Dou was born in Leiden in the province Holland, one of the seven provinces, which formed together the Republic of the seven united Netherlands ("De Republiek van de zeven verenigde Nederlanden").
In the first two chapters a summary is given of the history of land surveying in the province Holland, which is the western part of the Netherlands. The position of surveyors, their practical and theoretical knowledge during the period 1300 - 1600 are described.
The third chapter gives a summary of Dou's career and his scientific publications. Dou was born in 1573 and obtained his official licence as a surveyor (landmetersadmissie) in 1597. He had a long and varied career as surveyor and died in 1635. Together with a fellow-surveyor, Johan Sems, he wrote and published two books on surveying in 1600: Practijck des Lantmetens (Practise of Surveying) and Van het gebruyck der Geometrijsche instrumenten (The use of Geometrical Instruments). These were the first books in the Dutch language about surveying. In 1606 Dou published a translation in Dutch of the first six books of Euclides. This publication had many reprints, the last one in 1702! In 1612 his book about the Holland Circle followed, it was reprinted in 1620.
Very important and useful for surveyors was his Tractaet van de roeden en landtmaten ... published in 1629. This was a treatise on the relation and conversion of the many different rods and feet used in the Netherlands.
In chapter 4 information is given about the instruments used by Dutch surveyors until 1600. In the beginning the instruments were very simple: a surveyor's cross, measuring rod and measuring cord or rope was all that was needed. In the first half of the 16th century the measuring chain and a common seaman's compass came into use, as well as simple angle-measuring instruments such as the quadrant and the surveyor's astrolabe (plate 12).
In the next two chapters the construction of the Circle of Dou is discussed. The old-Dutch text, used by Dou in his treatise, is analysed and explained. Plate 15 shows the original drawing of Dou. The instrument has a diameter of approximately 30 cm and a small compass in the centre. This is fixed to the bottom plate. The alidade has two sights and turns around the compass. The instrument has large openings leaving a cross within the circle. Two stationary pairs of sights are fixed at right angles at the outside of the cross; consequently it could be used as a surveyor's cross. There is also a suspension ring for vertical angle-measurements and levelling. When used horizontally the instrument was mounted on a staff by means of a swivel joint.
According to Dou the instrument has a circle, which is divided into one tenth of a degree or six minutes. Taking the diameter of the instrument into account this seems almost impossible! Furthermore he proposes some special divisions for sinus, cosinus, tangent and secans. In his book tables are given to enable the instrument maker to mark lines for this purpose on the instrument. The idea behind this is that the surveyor does not have to carry trigonometrical tables with him in the field but that he may read the value of these functions direct on his instrument.
In the seventh chapter the name "Hollandse Cirkel" and the further development of the instrument are discussed. Dou did not give his instrument a new name and as a result various names were used. Most common was the word astrolabe but this name was also used for astronomical and other types of surveying instruments. It seems that the Frenchman A. Laussedat was the first to recognize the typical form of this instrument of Dou, which separates it from other measuring instruments. In a book about instruments, written in 1898, he introduced the name "Cercle Hollandais". Other writers in various countries such as Schmidt, Kiely, Daumas, Holbrook and Engelsberger followed his example and so the names "Holländischer Kreis", "Holland Circle" and "Hollandse Cirkel" came into use **.
During the two centuries after Dou's publication numerous Holland circles were made by several well-known Dutch instrument makers and we also see improvements such as the use of transversals and the nonius. Sometimes a small folding sun dial was fixed on the compass. In the second half of the 18th century one occasionally sees the use of small removable telescopes.
Due to developments in France the first simple theodolites came into use in the Netherlands by the end of the 18th century and slowly the Holland circle was replaced by this new type of measuring instrument (plate 37).
In the past numerous Holland circles have been made but only a small number have survived. This is no wonder because this instrument was a tool used by surveyors. One got rid of it when it was damaged or replaced by newer instruments. At that time it did not have any collectors value. Now the Holland circle is an interesting collector's item and one finds them in several instrument collections in and outside the Netherlands.
In chapter 8 photo's of some instruments are shown and technical descriptions given, including some basic dimensions. The aim was to show the development and changes made during two centuries starting with some instruments made by Jan David or his son Jacob (plate 23, 25 and 26). According to Dou, Jan David was the maker of the first Holland circle.
Applied geometry is the subject of the last two "Hooftstucken" (chapters) of Dou's treatise. Questions related to (simple) field work are asked and solutions given. Any modern surveyor with some field practise recognizes the problems and knows the answers. As an example some of these problems and solutions are discussed in chapter 9. We have more trouble reading the old-Dutch text than understanding the questions and solutions of the problems! There is very little relation with to Holland circle itself. The text is more an addition to the theory given in Dou's first book, the Practijck des Lantmetens.
Why was the Holland circle so popular with the Dutch Surveyors? The simple reason is that Dou invented a new instrument by combining useful parts of existing instruments. It was purely a surveying instrument without any traces of astronomical parts, as with the astrolabe and the quadrant. It was an all-in-one instrument or, to use a modern name, it was the total-station of the 17th century.
In horizontal position it could be used as a surveyor's cross or as an angle-measuring instrument with or without orientation. Observations are made by moving the alidade. As the alidade moves around the compass this means that the compass does not move but stays at its place during the observations. One sees immediately if the instrument as a whole was moved accidentally because in that case the compass needle is in a different position.
In vertical position one could measure elevations or depressions and with the alidade in a horizontal position the instrument could be used for levelling.
Dou proposes several goniometrical graduations but this was not adopted by other surveyors. The only graduations which is frequently found on the circle is a tangent-cotangent or ursa recta - ursa versa division 0-100-0.
**. See notes 3, 4, 5 and 7 of chapter 7.