There are several huge collections of antique plumb bobs in the world. Plumb bobs do not age, unless they are broken. It’s funny, but true – these museum pieces would still work just fine today. The metal construction allowed thousands of ancient plumb bobs to survive to this day. Pointy end was critical for the accuracy of measurements and hard metals retain their shape better. This gives the plumb bob the necessary weight, but at the same time keeps its surface hard. However, lead is a relatively soft metal, so antique plumb bobs are often bronze or brass with a lead core. ( Gaius Cornelius, Wikimedia(CC BY-SA 4.0) ![]() A heavy lead plumb bob stops swinging quicker, although in some cases plumb bobs were filled with a liquid – mercury, water or even molasses – to dampen the movement.Īn ancient Roman plumb bob. ![]() Plumb bobs had to be made from a heavy metal so that wind would move the plumb line too much. The name “plumb bob” refers to the material that this tool was made of in the past – the Latin plumbum means lead. Plumb bobs are used not only by builders, interior decorators, electricians, construction engineers and carpenters, but also by well diggers, foresters, astronomers, shipbuilders, artillerymen, mining engineers, scale makers and calibrators, pipeline layers, road builders, etc. The plumb bob is one of the few tools that is (or was) used by people from so many different professions. As a result, plumb bobs were often ornamented, characterised by a beautiful curved shape, and were depicted in art and heraldry. For example, the book of Isaiah says, “I will make justice the measuring line and righteousness the plumb line.” Whether you are a believer or not, this shows the symbolism of the never-failing plumb line in Western culture. ( Andreas Praefcke, Wikimedia(CC BY 3.0)īecause of this objective and eternal accuracy, the plumb bob is mentioned several times in the Bible. Bisecting this angle would always give a true North (nowadays we may look at Polaris as our North Star but at the time of the Egyptians it was not where it is today because the Earth ‘wobbles’ over time - a phenomenon known as Nutation).Old construction tools in art. This process would be repeated to create an angle between where a star rises and where it falls. A second person could move until a Plum Bob suspended from a Merkhet crossed the line of sight and then mark a point on the ground. One person would have stood at an observation point and sighted the falling (or rising) star through a narrow slit in a palm leaf, known as a Bay. Text and illustrations of the time suggest that the Merkhet was used to mark where a particular star would sink below the horizon and then reappear later (in much the same way as our nearest star, the Sun, sets and rises each day - a good candidate for such a star at that time would have been Vega although b-Ursae Minoris and z-Ursae Majoris have also been put forward). They will have observed that, when looking at the night sky to the North, stars appeared to precess in a circle around the North Pole (a consequence of the Earth's rotation). Egyptian architects, surveyors and builders are known to have used two specialised surveying tools: the Merkhet (the 'instrument of knowing', similar uses to an Astrolabe) and the Bay (a sighting tool probably made from the central rib of a palm leaf). They used Sundials (perhaps they noticed that the moving shadows from their ceremonial Obelisks created a kind of Sundial but it is not thought they were used as such until erected by the Romans much later), they constructed Calendars and used their skill with Astronomy to determine dates of religious festivals and the hours of the night.Įgyptian Pyramids were very accurately aligned North, South, East, West and it was their knowledge of Astronomy which made this possible. Measurement of time, especially of the seasons, was extremely important to the Ancient Egypt since they needed to know when to sow their crops and when the Nile would flood each year.
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