A circumferentor, or surveyor’s compass, is used to measure horizontal or magnetic bearings for lines laid out in a survey. It consists of a box containing a magnetic needle, which moves freely over compass rose divided into 360 degrees and a pair of sights located on the North-South axis of the compass. Circumferentors were typically …
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Before we had sextants and octants, celestial navigation was accomplished using the astrolabe. Originating in Greece and perfected by medieval Islamic scholars, this astronomical “multi-tool” and rudimentary analog computer revolutionized navigation, timekeeping, and astronomy before being replaced by the sextant and pendulum clock. Want to have the Regimental Brewmeister at your site or event? You …
The sector is a hinged calculating tool used by navigators, draftsmen, and woodworkers to solve problems using proportions and the rules of similar triangles. It consists of two rulers joined by a hinge. By opening the hinge at different widths, the user can use dividers to solve proportions, scale dimensions up or down, and compute …
In 1730 Thomas Godfrey of Philadelphia invented what was referred to as a double reflecting sextant. At the same time, entirely independent of Godfrey, John Hadley, an English mathematician and astronomer, invented the Hadley’s Quadrant which was also a double reflecting. Both instruments were equipped with half mirrors and sights. Latitude measurements were taken by …
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An alidade is a device that allows one to sight a distant object and use the line of sight to perform a task, like recording a line on a map. These devices are often incorporated into other tools like the surveyor’s compass or circumferentor but can also be used independently on the plane table. The …
Developed by Edmund Gunter in 1620, Gunter’s chain sought to reconcile traditional English land measurements, based on the number 4, with the decimal system. Each chain was composed of 100 links, measuring 66 feet total (each link measures 7.92 inches long). A chain is subdivided into four parts—each made up of 25 links measuring 5 …
A surveyor’s artificial horizon is a device developed by London instrument maker John Elton in 1732, this tool (traditionally a tray of mercury but this can be oil, water, or a specialized mirror) allows “for taking altitudes without a horizon.” With the artificial horizon, precise latitude readings may be taken with a sextant when a …
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The quadrant is an instrument used to simplify astronomical calculations and to make observations. Developed by Isaac Carver, a student of Edmund Gunter, in 1706. The quadrant is used to observe and measure astronomical phenomena, to perform the basic tasks of surveying. Designed to work at specific latitudes (in this case 38-41 N), the quadrant …
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Gunter’s Rule was invented by Edmund Gunter in 1620 to operationalize the work John Napier did with Logarithms. Napier published a table of logarithms in 1614 with which one can replace complex multiplication and division with simpler addition and subtraction of the equivalent logarithms. This is an improvement if you must calculate by hand but …
The larger end of a bird’s egg contains an air cell that forms when the contents cool and contract after the egg is laid. A freshly laid egg has a relatively small air cell, but the size increases with time since the shell is slightly porous. A fresh egg, however, is dense enough that it …
Michael Carver -- Historical Interpreter/Reenactor 