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Leeuwenhoek as Surveyor
In 1669, at age 37, Leeuwenhoek passed an oral examination by mathematician Genesis Baen in the "art of Geometry". Record of this certification is found in 12de Haarlemse Memoriaalboek (memorandum book) of February 4, 1669.
Alsoo Antony Leeuwenhoeck burger ende inwoonder der stad Delft, den hove van Hollant bij requeste te kennen heeft gegeven, dat hij hem in de konste van Geometria, eenigen tijt herwaerts sulcx geoeffent ende soo verre geavanceert heeft, dat hij sich vertrouwt capabel te wesen over 't ampt van lantmeter voortaan ten dienste en de gerieve van eenen ijegelijcken te bedienen, waarvoor hij onderdanig versochte, dat 't hoff gelieven wilde hem nae voorgaende examinatie en de preuve sijner bequaemheijt tot de exercitie van het ampt van lantmeter te admitteeren. Soo ist, dat 't voors. Hoff gehoort het rapport van den commissaris in desen geordonneert in wiens presentie den suppliant door den mathematicus Genesius Baen op sijn bequaemheyt totte bedieninge vant lantmeters-ampt vooren gementioneert, geexamineert, ende daertoe bequaem bevonden is geweest, den suppliant geadmitteert heeft en admitteert hem met desen omme 't selve lantmetersampt ten dienste ende gerieve van een ijgelijck, binnen de jurisdictie van desen hove te mogen excerceeren, ende heeft omme hem wel ende getrouwelijck daerinne te quijten den eedt daertoe staende gedaen aen handen van den heere PIETER OCKERS raet in den hove. als commissaris daer toe gecommitteert.
Gedaen in den Rade den 1111 February XVI honderd negen en sestich.
As Antony Leeuwenhoeck, citizen and resident of the city of Delft, has made a petition to the Court of Holland, that he has for some time now practised the art of Geometry and advanced so far that he deems himself capable of serving from now on in the office of surveyor, and serving to the benefit of everyone, he humbly requests that the Court be pleased to permit him to exercise the office of surveyor, after an examination and trial of his competence: Accordingly, the said Court, having heard the report of the designated commissioner, in whose presence the applicant was examined by the mathematician Genesius Baen as to his competence for performing the previously mentioned office of surveyor, and to that end he was found competent, has admitted the petitioner and hereby authorizes him to perform the office to the benefit of everyone, within the jurisdiction of the Court; and has administered unto him the statutory oath, that he acquit himself well and faithfully therein, at the hand of Mr. Pieter Ockers, councillor of the Court, and commissioner appointed for that purpose.
Done in Council the 4th of February 1669
We do not have any evidence that Leeuwenhoek ever earned money as a surveyor, but its mathematics was a common precursor for those who became a wine gauger (wijnroeier). Because they both measured things, especially things that didn't always have straight lines like real estate and barrels, it was common for a landmeter or surveyor to also be a wijnroeier. However, they further developed his interest in counting and measuring the sizes of things. In his letters, Leeuwenhoek used these spatial mathematics skills to confidently calculate sizes, volumes, heights, and numbers.
In a letter of March 14, 1713, to Jan Meerman, Delft's mayor, Leeuwenhoek wrote about the eye of a whale found at great depth in the ocean. He added a postscript:
De hoogte van onse Nieuwe Kerks-Tooren is over veel Jaren door My, ende Wylen den Lant-meter Spoors, yder met syn quadrant afgesien, en bevonden hoog te syn 299. voeten: zoo is dan de diepte, daar de Walvis op de gront lag, meer dan 26. maal dieper, als de Tooren hoog is.
The height of our Nieuwe Kerk's tower was measured over many years ago by me and the late surveyor Spoors, each with his quadrant, and we found the height to be 299 feet: so then the depth, where the whale lay on the bottom, is more than 26 times deeper than the tower is high.
Jacob Spoors died in 1677 as he was completing the survey of all of the streets and buildings in Delft to deliver to Jan Verkolje, who would paint in the buildings and facades for the Kaart Figuratief. Spoors was in his late seventies, so he may well have directed a team of younger surveyors laying the chains and recording the numbers. Perhaps that is why he and Leeuwenhoek, newly admitted as a surveyor in 1669, were measuring the height of the tower. Given the viewpoint intended for the Kaart Figuratief, to what extent would it obscure the buildings behind it?
In a letter of August 26, 1701, he wrote of a design for a new surveying tool. In a letter of April 8, 1701 (acc to Schierbeek, but no such letter; check date), he wrote about a coal measure for Delft and Rotterdam.