De landmeter Jan Pietersz. Dou en de Hollandse Cirkel
H.C. Pouls
Nederlandse Commissie voor Geodesie 41, Delft, 2004. 102 pagina's.
ISBN-13: 978 90 6132 287 0. ISBN-10: 90 6132 287 1. € 9,00
Inleiding
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.
Inhoudsopgave
Inleiding
1. De Hollandse landmeter, ca.1300 - begin 17e eeuw
2. De theoretische en praktische kennis van de landmeter, 13e - 16e eeuw 9
3. De landmeter Jan Pietersz. Dou
4. Het instrumentarium van de landmeter tot ca. 1600
5. Het maken van een nieuw "Mathematisch" instrument
6. Het aanbrengen van de goniometrische verdelingen en het gebruik daarvan
7. De naam "Hollandse Cirkel" en de verdere ontwikkeling van het instrument
8. Beschrijving van enige bewaard gebleven Hollandse cirkels
9. De twee laatste "Hooftstucken" van het Tractaet
10. Nabeschouwing
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
Summary
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.