Portal:Technology

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A sextant is an instrument generally used to measure the altitude of a celestial object above the horizon. Making this measurement is known as sighting the object, shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at noon to find one's latitude. See celestial navigation for more discussion. Held horizontally, the sextant can be used to measure the angle between any two objects, such as between two lighthouses, which will, similarly, allow for calculation of a line of position on a chart.

The scale of a sextant has a length of ¹⁄₆ of a full circle (60°); hence the sextant's name (sextāns, -antis is the Latin word for "one sixth", "εξάντας" in Greek). An octant is a similar device with a shorter scale (¹⁄₈ of a circle, or 45°), whereas a quintant (¹⁄₅, or 72°) and a quadrant (¹⁄₄, or 90°) have longer scales.

Sir Isaac Newton (1643-1727) invented the principle of the doubly reflecting navigation instrument (a reflecting quadrant - see Octant (instrument)), but never published it. Two men independently developed the octant around 1730: John Hadley (1682-1744), an English mathematician, and Thomas Godfrey (1704-1749), a glazier in Philadelphia. The octant and later the sextant, replaced the Davis quadrant as the main instrument for navigation.

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Credit: Larry McElhiney

The Curta is a small, hand-cranked mechanical calculator introduced in 1948. It has an extremely compact design, a small cylinder that fits in the palm of the hand. It can be used to perform addition, subtraction, multiplication, division, and, with more difficulty, square roots and other operations.

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Did you know...

• ... that both the Mozilla Firefox and Microsoft Internet Explorer web browser design ideas descended from the Mosaic web browser?

• ... that a coherer, hot wire barretter, electrolytic detector, cat's whisker and vacuum tube were all types of radio detectors?

• ... that in 2008 Hewlett-Packard created a prototype of the theoretical fourth and last passive circuit element, the memristor, that may one day revolutionize electronics, although the theory was devised in 1971?

• ... that a mercury arc rectifier converts alternating current to direct current by means of an electric arc through mercury vapor?

• ... that only one of the 266 1076 Class steam locomotives built for the Great Western Railway was named, and the rest had only numbers?

• ... that the six Charles Tayleur locomotives ordered by Isambard Kingdom Brunel for the Great Western Railway were unsuccessful?

• ... that the intensity of a tropical cyclone (pictured) is usually determined by the Dvorak technique using only visible and infrared satellite images?

• ... that the technique of double-balloon enteroscopy allows any position along the gastrointestinal tract to be visualized in real-time?

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