The Thacher Cylindrical Slide rule preceded the modern slide rule. In 1881, a patent was granted to Edwin Thacher (1839-1920) to create a slide rule that could fit on a desk. The previous slide rule measured 59 feet, as compared to the Thacher slide rule at 22 inches long. Keuffel & Esser manufactured this “calculating instrument” for Thacher in 1887. With operating instructions affixed, the rule was housed in a wooden case with U.S.G.S. hydrography designation.
This quality engineering instrument, the Thacher Cylindrical Slide rule, facilitated the Gunnison Tunnel construction. With the assurance of a constant water supply for both agriculture and domestic use, the Uncompahgre Project has supported a steady growth in both population and agriculture. With approximately 76,000 irrigated acres of land under cultivation, the Uncompahgre Project supports an agricultural based economy ranking in the top third of Colorado counties. In 1979 the Gunnison Tunnel was listed on the National Register of Historic Places because of its significance in Colorado.
This instrument was used by the United States Geological Survey, to plot the Uncompahgre Project, one of the initial five authorized by the newly created U.S. Bureau of Reclamation in 1902. Mapping a construction route for the Gunnison Tunnel, through rugged mountainous terrain, required a compact but accurate “calculating instrument.” Project computations were confirmed when the headings of the longest irrigation tunnel in the world met within inches beneath the mountain. The quality of the engineering was recognized in 1972 when the Gunnison Tunnel was designated a National Civil Engineering Landmark.
Montrose County Historical Museum
21 N Rio Grande Ave
Montrose, CO 81401