Slide RulesCircular Slide Rules
Slide rules that are round offer the length of a 10" rectangular slide rule in a pocket-sized (roughly 3.6") format, since the scales are on the circumference of circles. The scales are also continuous, so there is no need to make adjustments, such as folded and inverse scales, for results of calculations that go off the ends of the scales. Furthermore, these instruments are relatively easy to construct: the scales are printed on one or more disks, and the disks or a single disk and cursor are fastened together with a pin at the center. However, this simple construction is also not very durable, and so circular slide rules may get out of position and thus they lack accuracy, compared to linear slide rules with slides that move along carefully grooved channels.
This collection suggests the diverse appearances and functions of circular slide rules that were manufactured between the mid-19th and late 20th centuries. For example, before Mannheim-type linear slide rules became popular in the late 19th century, American inventors patented a variety of circular designs. Some circular slide rules were made to look like pocket watches, while others were intended to promote particular businesses—Whitehead & Hoag and Perrygraf were especially influential American manufacturers of promotional items. Inventors and makers such as Albert Sexton, Louis Ross, Claire Gilson, Norman Albree, and Ross Pickett wanted their circular slide rules to compete with linear instruments in the engineering and education markets. Other circular slide rules were designed specifically for surveying, such as stadia computers, or for navigation, such as Dalton instruments that may also be seen in the Smithsonian's exhibition, Time and Navigation. Even more specialized in purpose were slide rules for grading earthworks, determining the effects of nuclear bomb explosions, writing efficient computer programs, and betting on horse races.
"Slide Rules - Circular Slide Rules" showing 1 items.
- This circular slide rule describes the effects of a nuclear explosion on people. After World War II, scientists at the Los Alamos Scientific Laboratory prepared a report on forms of damage associated with the explosion of atomic bombs. These included physical damage, fire and heat, and nuclear radiation.
- With the development of the more powerful hydrogen bomb, physical chemist Samuel Glasstone and his associates prepared an updated report, and published it under the title The Effects of Nuclear Weapons. This information was distributed for use in planning against possible nuclear attack.
- From 1962 onward, copies of The Effects of Nuclear Weapons had a pocket containing a Nuclear Bomb Effects Computer. Setting the indices on the front of the instrument for the yield of a nuclear bomb in megatons and the distance of its explosion in miles, scales on the front of the instrument describe changes in atmospheric pressure and winds associated with the blast, as well as cratering and the velocity of window glass.
- Charts on the back indicate the initial nuclear radiation and the thermal radiation. Tables indicate the probable medical effects of various doses of radiation, from no illness to severe burns to death. The Nuclear Bomb Effects Computer was developed at the Lovelace Foundation in Albuqueque, New Mexico, for the United States Atomic Energy Commission.
- Currently not on view
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- Lovelace Foundation
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- National Museum of American History, Kenneth E. Behring Center