sector with squadra mobile and divider points
Date: late 16th Century
Inventory Number: DW0954
Classification: Sector
Subject:
Maker: Italian
Cultural Region:
Dimensions:
0.3 x 33.6 x 11.6 cm (1/8 x 13 1/4 x 4 9/16 in.)
Description:
This brass instrument is a squadra mobile combined with a sector. The two sector arms terminate in steel divider points.
The squadra mobile is unfinished. The protractor portion is divided by dots every degree and lines every 5 degrees from 0°-180°, although no numerals are present. Light construction lines are inscribed on the shadow square portion and divided each side into four parts. No subdivisions are present. The reverse side of the squadra mobile is has some construction lines, but is less finished than the obverse.
There were three sights on the sector arms--one at the hinge and one at the end of each arm. These are missing.
The sector is engraved with the following scales (all are unlabled):
side a:
line of metals
line of chords
line of solids (?)
line of equal parts
side b:
four more lines (purpose unknown)
The squadra mobile is unfinished. The protractor portion is divided by dots every degree and lines every 5 degrees from 0°-180°, although no numerals are present. Light construction lines are inscribed on the shadow square portion and divided each side into four parts. No subdivisions are present. The reverse side of the squadra mobile is has some construction lines, but is less finished than the obverse.
There were three sights on the sector arms--one at the hinge and one at the end of each arm. These are missing.
The sector is engraved with the following scales (all are unlabled):
side a:
line of metals
line of chords
line of solids (?)
line of equal parts
side b:
four more lines (purpose unknown)
Signedunsigned
FunctionThis is a sighting sector that could be used for angle measuring in surveying as well as for transferring the observed angles to a plot and for making mathematical calculations. (In use for surveying, there would have been a sight at the end of each arm and a third in the center of the hinge. The sights are missing in this example.)
Historical AttributesThe squadra mobile is a surveying instrument devised around 1598 by Ottavio Fabri. It consisted of a shadow square and protractor with hinged arms that carried sights. The user would align the arms with two points and measure the angle between them on the protractor or use the divisions on the shadow square to simplify trigonometric calculations involving the triangle formed by the surveyor and the two points sighted.
The maker of this instrument has added divider points to the squadra mobile. These enable the user to transfer observed measurements directly to his plot or survey map on a plane table. The addition of sector scales let the user also make mathematical calculations in the field.
The maker of this instrument has added divider points to the squadra mobile. These enable the user to transfer observed measurements directly to his plot or survey map on a plane table. The addition of sector scales let the user also make mathematical calculations in the field.
Curatorial RemarksXRF of this instrument show it to be low-zinc brass with a minor amount of tin--an alloy typical of 16th century brass.
Primary SourcesOttavio Fabri, L' uso del la squadra mobile : con la quale per teorica, et pratica si misura geometricamente ogni distanza, altezza, e profondità (Padua: 1615)
see this page for an example of the squadra mobile being used for surveying:
http://echo.mpiwg-berlin.mpg.de/ECHOdocuView/ECHOzogiLib?pn=56&wx=0.2858&wy=0.1428&ww=0.7141&wh=0.7141&mk=0.0919/0.0634,0.4497/0.2693&mode=imagepath&url=/mpiwg/online/permanent/library/4KY9GTGC/pageimg
see this page for an example of the squadra mobile being used for surveying:
http://echo.mpiwg-berlin.mpg.de/ECHOdocuView/ECHOzogiLib?pn=56&wx=0.2858&wy=0.1428&ww=0.7141&wh=0.7141&mk=0.0919/0.0634,0.4497/0.2693&mode=imagepath&url=/mpiwg/online/permanent/library/4KY9GTGC/pageimg
ProvenanceBerne Auction July 2,1958, lot 3559; E. Weil, London, July 2, 1958; David P. Wheatland, Topsfield, MA, July 2, 1958.