Anonymous Dutch instruments
#6 Brass rule ca. 1700.
Dutch brass scale rule 159x25.5mm.
There are 3 transversal scales on the front face;
'1. Rhijnl: geom: duijm' (Rhineland geometric inch) =37.67mm,
'1. Rhijnl: werk duijm' (Rhineland werk inch) =26.16mm,
'1. Frans: Kon: duijm' (French Royal inch) =27.07mm.
The reverse face has mapping scales related to the French Royal inch.
B: 1/12th scale
C: 1/16th scale
D: 1/24th scale
E: 1/32nd scale
The Rhineland geometric inch is not a tenth part of a foot as one might think, but the equivalent of 1/100th of a Rhineland roede (3.767 meters). The idea of dividing measures into decimal fractions came from Flemish mathematician Simon Stevin in his work De Thiende (the art of tenths) first published in Dutch in 1585. The first Dutch surveying textbook by Jan Pieterszoon Dou and Johan Sems 'Practijck des Lantmetens' published in 1600, helped popularise the use of decimal fractions in the Netherlands surveying community.
The term 'geometric' as in geometric inch is probably derived from Geometricus, an old term for land surveyor.
Right: Measuring by fingers, hands, feet and pacing. Here the surveyor's pace Passus Geometricus equals 5 feet. [Gemma Frisius/Peter Apian: Cosmographie…, Antwerpen, 1561]
#3 brass protractor 1750-1800.
Anonymous brass protractor, measuring 96.5mm at the base and 74.5mm from the base to the apex. Total length of the transversal scale is 86.5mm.
We find a very similar brass protractor at the Boerhaave Museum in Leiden, but with a different diagonal scale, that the museum dates to 1750-1800.
#4 brass protractor 1750-1800.
#5 brass protractor 1750-1800.
Another anonymous brass Dutch protractor, the third in this series, measuring 103.5mm at the base and 78mm from the base to the apex. The transversal scale is graduated into 400 units. Unknown unit of length.