Protractor and Shadow Square

Description
This brass semicircular protractor is divided by single degrees and marked by fives from 5° to 180°. The letter X is at the 90-degree mark. The upper right side of the protractor contains a shadow square. This is divided on both sides into sets of four units, each approximately 3/8" long and numbered from 1 to 12, for a total of 48 units on each side. The vertical side is marked: OMBRA VERSA. The horizontal side is marked (upside down): OMBRA RETTA.
The scale on the "ombra versa" side measured tangents from 0 to 45°. The scale on the "ombra retta" (or "recta") side measured tangents from 45° to 90°. The lines for degrees and on the shadow square appear to be made by hand, perhaps by placing the instrument next to a pattern. The instrument is decorated with floral and solar motifs. The protractor rests in a brass base that unfolds to form a limb, which is chipped. There are two holes in the limb; the numbers 2 and 1 are scratched next to the holes. There are four holes in the base; the numbers 3 and 1 are scratched next to the outermost holes, which align with the holes on the limb. This instrument is Italian in origin and was likely made before 1800. New York University donated the object in 1963.
Reference: J. A. Bennett, The Divided Circle (Oxford, 1987), 42–43.
Location
Currently not on view
date made
18th century
Physical Description
brass (overall material)
Measurements
overall: 34.8 cm x 13.4 cm x .8 cm; 13 11/16 in x 5 1/4 in x 5/16 in
place made
Italy
Italy
ID Number
MA*326978
catalog number
326978
accession number
1990.0646
subject
Protractors
Science & Mathematics
Mathematics
Protractor
Surveying
See more items in
Medicine and Science: Mathematics
Protractors
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of New York University

Visitor Comments

11/22/2012 6:21:33 PM
Paul Johnston
What is the 20C origins of the now common used Solar protractor to determine the angel and azimuth of the sun in order to measure shading devices.
Add a comment about this object

Submit a comment or ask a question about this object using the form below. Submissions are moderated and may receive a curator response. Please note that we cannot evaluate or appraise your personal artifacts. For other questions or general inquiries please visit our FAQ or contact page.

Personal information will not be shared or result in unsolicited e-mail. See our privacy policy.

Image CAPTCHA
Enter the characters shown in the image.