GLOSSARY

A short description of technical names or terms used in, or associated with, this website.

1. Alchemy: Think of a bearded old man, crouched in his medieval den and surrounded by his apparatus, trying yet again to turn base metal into gold…without success. But many believed in the art, from early times, including kings, princes and noblemen, up to the late Renaissance. We have a good selection of early apparatus that can make an authentic-looking set.

2. Aneroid Barometer: A smaller, more compact and easily portable version of the older Mercury Barometer, “Aneroid” comes from the Greek, “without liquid.” It depends on a small partially-evacuated and sealed capsule: the top moves in or out slightly according to changes in the atmospheric pressure. Linkage transmits the movement to turn a hand across a circular dial reading in inches or centimetres (i.e. of mercury). Earlier versions often had an outer scale that read in hundreds and thousands of feet, for mountaineers and balloonists. First produced in France from 1865, they soon enabled the Barograph to be made.

3. Astrology: A false and inexact “science”, purporting to tell a person’s future by the stars, but still believed in by many followers today. Do not confuse with Astronomy, next. See also Zodiac.

4. Astronomy: The exact science of the study of the heavens – the stars, planets and everything else out there. Until the invention of the telescope in 1608 all observations were by the naked eye. The first planet to be identified by telescope was Uranus, in 1781.

5. Armillary Sphere: A spherical instrument composed of interlocking rings or circles, normally brass but sometimes paste-board (as in 18^th or early 19^th century French examples), representing the celestial sphere. They usually have the Sun and (known) planets inside, and were often sold in pairs – one Ptolemaic, or Earth centred, the other Copernican, or the correct system, for comparison. Very decorative. See Globe Section, Items 74, 151, 300 and 379.

6. Astrolabe: A complicated flat circular brass instrument, invented by the early Persian astronomers Before Christ, and introduced into Europe following the Moorish invasion of Spain from AD700. An essential tool of astronomers, Court astrologers and gentlemen scientists until the end of the Renaissance, and a revered one to own. Among other things, they could tell the time, provided you knew your latitude and could see the stars, or, conversely, if you knew the time and could still see the stars, you could work out your latitude. See Navigation Section, Items 80 and 81. See also Mariner’s Astrolabe.

7. Barograph: A barometer – but also produces a record of recent changes in the atmospheric pressure as a trace round a drum of graph paper, marked in days and hours. Thus, you can tell at a glance what the weather has been doing, and might do in a few hours time. See Aneroid Barometer. Interesting-looking things, in glass and polished wood cases, introduced in the late 19^th century. They are still produced today, to the same design. See the Weather Section, Item No. 286.

8. Backstaff: An essential tool for mariners at sea, to measure the angle of the sun to the horizon and thus calculate longitude: beautifully made, of rosewood with boxwood scales. Used in the 17^th and 18^th centuries, after the Cross-staff, and until the introduction of the Octant in 1748. See Navigation Section.

9. Bearing: A straight line between two points on a map, chart or on land, given in degrees and minutes.

10. Binnacle: The housing for a Mariner’s compass, which, by means of two interlocking rings keeps the instrument level and steady even during the most violent weather at sea. See also Gimbals.

11. Celestial Sphere (or Globe): A map of the heavens, as if seen with the observer standing in the middle of it. Some have just the star positions and the outline of the constellations indicated by a dotted line, but the more beautiful and decorative ones have the constellations shown pictorially – animals, humans, birds, fishes and objects. (First depicted by the engraver Albrecht Durer, 1471-1528.) See Globe Section, Items 62 and 69.

12. Chronometer: A highly accurate clock, used for determining Latitude, by mariners at sea or explorers on land. First developed in the 18^th century by John Harrison and then refined by John Arnold and Thomas Earnshaw. Redundant from 1972 with the introduction of SATNAV and now GPS.

13. Co-ordinates: Two values which fix your position: locally, on land, as compass bearings, or both at sea or on land, (think explorers) as Latitude and Longitude.

14. Cross-staff: An instrument used for measuring the height (in degrees) of the sun or a star above the horizon. An essential tool for mariners at sea for calculating Latitude, used in the 16^th and 17^th centuries, coming between the Mariners Astrolabe and the Backstaff. See Navigation Section, item 218.

15. Dead-reckoning: Navigation by bearing and distance, without reference to the stars or the sun.

16. Degree: The 360^th part of a circle, sub-divided into 60 Minutes.

17. Electrostatic Generating Machines: Or, spark machines, developed during the early investigations into the nature of electricity. They produced a miniature bolt of lightning – entertaining, but of no real practical application. Until recently many school or college physics labs had a version called a Wimshurst Machine. Various types were popular throughout the 18^th and 19^th centuries, (see Section of Physics Apparatus and Spark Machines, No’s 409, 410 and 411) - but Michael Faraday showed that what was needed was Alternating Current, not DC, which these items only produced. See also Van de Graaff Generator.

18. Fusee: Part of an early clock or watch, a brass cone cut with a spiral groove, with a chain wound round it connected to the spring: it exerted a constant “pull” on the movement, no matter whether the mainspring was fully wound or nearly unwound.

19. Gimbals: Two inter-locking brass rings that hold a compass level and steady at sea: the word comes from the old Norman French, gemels = twins. See also Binnacle and Marine Barometer.

20. Gnomon: The part of a sundial which casts the sun’s shadow onto the hour-scale, and thus tells the time (only when, of course, the sun is out). “I am a sundial, and I make a botch/ Of what is done far better by a watch”. (Hilaire Belloc.) Many early English Church towers often had, and still have, a clock-face plus a vertical sundial on the South side: if the clock stopped or went wrong, the locals always knew that the sundial would be true.

21. Gregorian telescope: See Reflecting Telescope, Navigation Section, Item 66
.

22. Hydrometer: A small instrument for measuring the specific gravity of alcohol. Initially used by the Excise Men in the 18^th century, to calculate the amount of duty to be paid on imported wines and spirits, according to their strength, but now mostly used by home-brewers. Do not confuse with -

23. Hygrometer: A small instrument for showing the amount of humidity, especially in a laboratory, but anywhere else, ie garden or greenhouse. First introduced in Switzerland from 1783, early scientists soon realised that they needed it to replicate conditions in their own laboratory to verify experiments performed elsewhere.

24. Knot: A unit of ship’s speed, expressed as nautical miles per hour. (One nautical mile = 1.15 normal mile)

25. Latitude: The angular distance, in degrees and minutes, North or South of the Equator. Normally used in conjunction with Longitude (next).

26. Longitude: The distance, in degrees and minutes, East or West of the Greenwich Meridian (or Zero) Line, which runs from Pole to Pole. Always a problem for Mariners until the introduction of the accurate Chronometer in the late 18^th century.

27. Log: Either a book, a daily record of ship-board events, including changes in the weather or the ship’s position: or a device for measuring the ship’s speed through the water.

28. Marine barometer: an ordinary slim mercury barometer but adapted for ship-board use by mounting it in Gimbals, on the end of a short arm, to counter the movement of the ship. The glass tube had a narrow waist just above the cistern to prevent the mercury bouncing up and down in rough weather. Early versions had mahogany cases, later ones slim brass tubes. See also Mountain Barometer. Superseded by the introduction of the smaller, less fragile Aneroid Barometer from the late19^th century.

29. Mariner’s Astrolabe: A simplified version of the Astrolabe, used at sea between the 14^th and 16^th centuries to determine the height of the sun and so calculate Latitude. Superseded first by the Cross-staff, then the Backstaff, and then Octants and Sextants. See Navigation Section, Items 80 and 81.

30. Mercury Barometer: First produced by Evangelista Torricelli (1608-1647), Galileo’s last assistant, he realised that the pressure of the atmosphere would support a column of mercury: the top of the mercury, inside a slim glass tube, would go up or down slightly according to changes in the weather. Later, the French scientist Blaise Pascal added a short scale at the top, divided into centimetres, with additional comments: “Wind/Rain”, “Variable”, “Fair”, “Good Weather” etc. See also Mountain Barometer, next.

31. Mountain Barometer: Essentially a version of the mercury type (previous), Alpine mountaineers had long known that air pressure decreases with height. By the late 18^th century expeditions carried one to measure their ascent, or the heights of peaks scaled. These instruments had a much thinner tube, with a narrow “waist” just above the cistern, to prevent the mercury, during an awkward climb, from slamming up to the top of the tube and bursting it. See also Marine Barometer.

32. Newtonian telescope: See Reflecting telescope.

33. Newton’s Cradle: Isaac Newton’s simple but elegant apparatus to demonstrate kinetic energy, or work done by a moving body impacting on a stationary one. (Think billiard balls.) We have a nice example in the Physics Section.

34. Nocturnal: A small hand-held instrument, usually of boxwood but sometimes brass, for telling the time at night by star positions. Mostly used at sea, many mariners preferred to mark the passing of the night hours by turning the half-hour glass, rather than fiddling with this more complex instrument – that is, even if the stars were visible. 16^th-18^th century. Redundant after the invention of the Chronometer.

35. Octant: A navigation instrument, introduced from the 1750’s and the fore-runner of the Sextant. See also Quadrant. All were used for measuring the angle at sea from the horizon to the sun, and thus to calculate Latitude. See Navigation Section, Item 77.

36. Orrery: An intriguing mechanical device showing the (known) planets as they revolve outwards from the Sun. First made in the UK for the Earl of Cork and Orrery (hence the name) by John Rowley in 1712, later and cheaper versions were produced until the end of the 19^th century. By mid-Victorian times, many gentlemen amateur-astronomers or scientists had one in their study. They are all highly decorative. (Think of Joseph Wright of Derby’s wonderful painting “A Philosopher Giving a Lecture on the Orrery”.) See Globe Section, Item 72.

37. Pantograph: An instrument used by architects (including naval architects) to reproduce plans or drawings to a larger or smaller scale. When opened out for use it looks like a large inverted W.

38. Pedometer: An instrument the size of a pocket watch, worn by a walker, to record his paces, and thus a distance covered. 18^th/19^th century. A version in 18^th century Germany was made to be worn by a horse.

39. Plane Table: Not an ordinary piece of furniture, but a small table with a folding tripod base, taken out by surveyors: on a map pinned to it they would record the angles measured by the Theodolite. 18^th/19^th century. Early versions had a compass that slotted underneath, and a folding boxwood ruler, divided into 360 degrees, that fitted round the four sides.

40. Quadrant: Normally associated with the Octant and the Sextant, for observations at sea, but much larger versions were made for astronomers, mounted on a wall or a tall stand. (See the mural quadrant at the Old Royal Observatory, Greenwich.) Early versions were small, usually boxwood, sometimes brass, with engraved lines and punch-stamped numbers and letters. See Navigation Section, Items 371 and 372.

41. Reflecting Telescope: These use a system of two polished metal mirrors, an ingenious invention by James Gregory in Scotland 1664, hence the name Gregorian. He never made one, but his plans were seen by Isaac Newton, who did, four years later, and then modified it: hence the other name, Newtonian. (NB: In this case, “Gregorian” has nothing to do with plain-song: that was Saint Gregory of Tours, in the 6^th century AD.) See Navigation Section, Item 66.

42. Refracting Telescope: The more usual type, with glass lenses arranged along a sliding tube. Small and portable, in the olden days they were often called a “spy-glass”, a “ship’s captain’s long-glass”, or a “bring ‘em near”.

43. Sextant: The 19^th century development of the Octant, by now brass, with a silver scale. See Navigation Section.

44. Stadia Rod: Used in land survey, a telescopic pole, marked with graduations, held upright by the Surveyor’s assistant some way from the Theodolite, which focussed on it.

45. Surveyor’s Chain: Sometimes known as Gunter’s chain, after its inventor Prof Edmund Gunter (1581-1626) of Gresham College. Used as measurement, and as the name implies, a chain 66 feet long made up of 100 links, which formed the base-line for the start of a survey. Mid 17^th to early 20^th centuries. Ten square Chains became one acre, an area up to then generally accepted as the amount of land that a man with a team of two horses could plough in one working day. Superseded from 1908 by the more familiar circular steel tape-measure. A Chain is still, traditionally, the length of a cricket pitch, 22 yards.

46. Terrestrial Globe: Equally, as the name implies, a globe of the Earth. On a film set, the known geography of the time must conform to the period of the film – you cannot have a late 19^th century globe in a film about Queen Elizabeth 1^st and the Spanish Armada in 1588. See Globe Section, Items 385 and 424.

47. Theodolite: Mounted on a tripod, a complicated and beautifully-made instrument used for land survey, it measures angles in both the horizontal and vertical planes. The earliest versions used in England followed the Dissolution of the Monasteries under Henry VIII in 1534, when the (considerable) Church lands were seized and divided up between the King and his Court favourites.

48. Traverse Board: A handy but simple wooden device, kept by the Watch on a ship, and then handed over to the incoming Watch. It provided a temporary record of course and wind direction. Introduced during the Renaissance, they were still being used by mariners in the late 19^th century. By then they had a brass face. See Navigation Section, Item 65.

49. Van de Graaff Generator: The ultimate in Electrostatic Generating Machines, capable of producing a massive spark of millions of volts. Invented by Dr Robert J. Van de Graaff at the Massachusetts Institute of Technology in 1926 (yes, as late as that) it was not used for serious scientific research until 1932. It soon became a favourite prop in early Frankenstein-type films. See Physics Apparatus and Spark machines, No.150. A now largely-forgotten rock band in the 1970’s adopted the name.

50. Waywiser: (Sometimes called a Hodometer.) A device for measuring distance, along a road or round the boundary of an estate, consisting of an iron-rimmed wooden wheel connected to a dial, with a handle to push it along: the dial, with two hands, read off in yards, chains, furlongs and miles. 18^th and 19^th century.

51. Wimshurst Machine: See Electrostatic Generating Machines. This version, the most efficient up to then, with two counter-revolving glass plates, was developed by James Wimshurst by 1880.

52. Zodiac: Twelve of the major constellations, shown on Celestial Globes as running round a band, the Ecliptic, at an angle to the celestial equator: in Astrology, associated with people’s birth signs.