Felsenthal FAE-19A Artillery Protractor

Description
While many protractors simply measure angles in degrees, others have been adapted for more specialized contexts. For instance, they may be combined with other drawing instruments, such as rulers or templates for flow chart components. Or, they may make measurements in other scales for angles, such as radians. Before computerized and satellite navigation equipment was in wide use, protractors were employed in military applications, including positioning artillery.
Thus, this clear plastic protractor, which is in the shape of a sixth-circle, permitted the user to plot the distance traveled by a projectile from the time that elapsed before the sound of the projectile was heard. The outer edge of the protractor's arc is divided by hundredths and marked by tenths from +3.4 to +0.1 (in black print) and from -0.1 to -3.4 (in red print). The scale is labeled: TIME INTERVAL, SECONDS and MIDPOINTS FOR 4-SECOND SUB-BASE, 1/25000.
A scale marked DEGREES is further inside the arc. It is divided by minutes and marked by fives from 55° to 0°. Finally, a scale for MILS is divided by tens and marked by hundreds from 1000 to 100. 1000 mils is equivalent to 56.25°. A scale for THOUSANDS OF YARDS 1/25000 is along the right edge of the protractor. It is divided by five-hundredths and marked by ones from 14 to 1.
The maker's mark is near the vertex: 4 SOUND SECONDS (/) FELSENTHAL INSTRUMENTS CO. (/) MFR'S PART NO. FAE-19A (/) MFR'S CODE 22040.
The Felsenthal Instruments Company was the leading supplier of mathematical instruments to the U.S. Army Air Force and the U.S. Navy Bureau of Aeronautics, particularly during World War II (when the firm was known as G. Felsenthal & Sons). After the company ceased operations in approximately 1976, it provided a large sample of its products to the Smithsonian.
See also 1977.1141.02, 1977.1141.03, 1977.1141.05, 1977.1141.08, 1977.1141.09, 1977.1141.10, 1977.1141.11, 1977.1141.12, 1977.1141.18, 1977.1141.19, 1977.1141.20, 1977.1141.21, 1977.1141.22, 1977.1141.23, 1977.1141.24, 1977.1141.30, and 1977.1141.39.
Reference: Deborah J. Warner, “Browse by Maker: Felsenthal,” National Museum of American History Physical Sciences Collection: Navigation, http://amhistory.si.edu/navigation/maker.cfm?makerid=173.
Location
Currently not on view
Object Name
protractor
date attributed by donor
1950
date made
1970s
maker
Felsenthal Instrument Co.
Physical Description
plastic (overall material)
Measurements
overall: .2 cm x 54.5 cm x 56 cm; 3/32 in x 21 15/32 in x 22 1/16 in
place made
United States: Illinois, Chicago
ID Number
1977.1141.01
accession number
1977.1141
catalog number
336385
subject
Mathematics
Protractor
Artillery
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Protractors
Data Source
National Museum of American History, Kenneth E. Behring Center

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