Protractors - Engineering & Drafting
By the end of the 18th century, protractors were routinely manufactured by machinery, with the invention of dividing engines, such as Jesse Ramsden's, particularly important for enabling the precise division of a circle into fractions of angles. Makers produced protractors that read minute fractions of angles, particularly when a vernier was added to the instrument.
Mechanics or machinists also used protractors to draw designs for new types of machinery. For instance, there were several forms of limb protractors for draftsmen that both functioned as T-squares and provided angle measurement. Similarly, protractors assisted with the preparation of architectural drawings. The instruments were only displaced by the advent of computer-aided drafting in the late 20th century.
"Protractors - Engineering & Drafting" showing 1 items.
- This metal drawing instrument allows civil engineers to translate their measurements into drawings with a minimum of calculation. It consists of a flat steel base bar 81.5 cm (about 32 inches) long, a semicircular protractor with a flat plate along the diameter that slides along the base bar, a long steel arm clamped to the protractor at its center, a brass set square or sliding square that moves along the arm, and a tri-leaved scale (like an architect’s scale) that moves along the arm or along the set square. There are four metal springs, each with its own screw. The two smaller springs hold the protractor plate to the base bar and the two larger ones hold the tri-leaved scale or the set square to the arm. The entire instrument fits in a wooden case. A sheet of instructions is pasted inside the case.
- The protractor is divided by half-degrees and marked by tens from 0° to 90° to 0° and from 90° to 0° to 90°. An attached vernier permits angle readings to one minute of arc. The ratios on the architect's scales range from 1:10 to 1:60. Each scale is divided into tenths of a unit.
- This is a modified form of the protracting trigonometer patented by Josiah Lyman of Lenox, Mass., in 1858, with reissue of the patent in 1860, and extension in 1872 (for an example of the protracting trigonometer, see MA*328738; for an architect’s rule patented by Lyman, see MA*308914). The instrument was made by Heller & Brightly of Philadelphia. According to a Heller & Brightly circular, the instrument sold with either a tri-leaved scale that was 6 inches long or one that was 12 inches long. This instrument has the 12-inch scale, and would have sold in 1878 for $30.00.
- Hobart Cutler Dickinson (1875–1949), a 1900 graduate of Williams College who obtained a master’s degree there and did further graduate work at Clark University (Ph.D. 1910), owned this object. Dickinson worked at the U.S. National Bureau of Standards from 1903 until his retirement in 1945. Dickinson was the father of Anne D. Ross, one of the donors of the instrument.
- References: "Circular of Lyman’s Trigonometer and Universal Draughting Instrument" (Philadelphia: Heller & Brightly, 1878); P.A. Kidwell, “Josiah Lyman’s Protracting Trigonometer,” Rittenhouse, 3 (November 1988): 11–14; Robert C. Miller, “A Lyman Protracting Trigonometer Made by Heller & Brightly,” Rittenhouse 3 (August 1989): 129–131.
- Currently not on view
- date made
- ca 1880
- Heller & Brightly
- ID Number
- accession number
- catalog number
- Data Source
- National Museum of American History, Kenneth E. Behring Center