ProtractorsEngineering & 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 brass drawing instrument consists of a narrow 10" arm joined to a base (4-1/8" by 1-1/16") with a thumbscrew. The arm may be placed in two positions: horizontally and at 150° (30° if measuring an angle opening to the right). Since it only measures 30° angles, this device is an isometric protractor. An isometric protractor is used to create three-dimensional drawings by depicting an object from an angle at which the scales on the three axes are equal. The technique was popular in the 19th century for its simplicity and ease of use. In the 20th century, isometric projections were typically created on specialized graph paper marked with triangles. In the 21st century, isometric engineering drawings and the isometric protractors used to prepare them are both created with computers.
- The base of this protractor is engraved with a presentation mark: TO (/) Alexander Leslie C. E. (/) FROM (/) Mortimer Evans. Leslie (1844–1893) was a civil engineer who was especially known for constructing waterworks in Scotland. From 1871, he partnered with his father, James Leslie (1801–1889), in Edinburgh. James was the nephew of the mathematician John Leslie. He trained under the architect William H. Playfair and worked with George and John (Jr.) Rennie early in his career. He was a founding member of the British Institution of Civil Engineers. Alexander was elected to the society in 1869. In 1871, he was elected to the British Association for the Advancement of Science, while Mortimer Evans became a member of that institution in 1876. Little is known of Evans or of when and why he presented this isometric protractor to Leslie. Evans lived in Glasgow in the 1870s and then moved to the Piccadilly area of London, where he patented a precursor of a motion picture camera (with William Friese-Greene) in 1889.
- The protractor is stored in a leather case lined with blue satin and blue velvet. The lid of the case has a protrusion to accommodate the thumbscrew.
- References: William Farish, "On Isometrical Perspective," Transactions of the Cambridge Philosophical Society 1 (1822); William Ford Stanley, Mathematical Drawing and Measuring Instruments, 6th ed. (London, 1888), 268; Catalog of Eugene Dietzgen Co., 12th ed. (Chicago, 1926), 41, 44; Institution of Civil Engineers, "Alexander Leslie," Minutes of the Proceedings 116 (1894): 366–368.
- Currently not on view
- date made
- ca 1870
- Leslie, Alexander
- Evans, Mortimer
- ID Number
- accession number
- catalog number
- Data Source
- National Museum of American History, Kenneth E. Behring Center