The bizarre object to the right was found in the tomb of an ancient Egyptian architect. For over 100 years, it has languished while archaeologists debated its function.
Now, a physicist has thrown her hat into the ring, arguing that it is the world鈥檚 first known protractor. The intriguing suggestion 鈥� which has drawn scepticism from archaeologists 鈥� is based on the numbers encoded within the carvings on its surface.
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The architect Kha helped to build pharaohs鈥� tombs during the 18th dynasty, around 1400聽BC. His own tomb was discovered intact in 1906 by archaeologist Ernesto Schiaparelli in Deir-al-Medina, near the Valley of the Kings. Among Kha鈥檚 belongings were measuring instruments including cubit rods, a levelling device that resembles a modern set square, and what appeared to be an oddly shaped empty wooden case with a hinged lid.
Schiaparelli thought this last object had held another levelling instrument. The museum in Turin, Italy, where the items are now exhibited identifies it as the case of a balancing scale.
But Amelia Sparavigna, a physicist at Turin Polytechnic, suggests that it was a different architectural tool 鈥� a protractor. The key, she says, lies in the numbers encoded in the object鈥檚 ornate decoration, which resembles a compass rose with 16 evenly spaced petals surrounded by a circular zigzag with 36 corners.
Sparavigna says that if the straight bar part of the object were laid on a slope, a plumb line would revealed its inclination on the circular dial (as illustrated in this graphic).
Significant numbers
The fraction of one-sixteenth features in a calculus system the Egyptians used, says Sparavigna, and they also identified 36 star groups called the decans, which later formed the basis of a star clock. She suggests the object was 鈥渁 protractor instrument with two scales, one based on Egyptian fractions, the other based on decans鈥�.
But Kate Spence, an archaeologist at the University of Cambridge who specialises in ancient Egyptian architecture, is not convinced and maintains the object is simply a decorative case. She says that unlike those on known measuring instruments, the markings in question are not particularly accurate: 鈥淲hen the Egyptians want to be precise, they are.鈥� She says the Egyptians tended to define angles by measuring the two sides of a rectangle, and that no similar instrument is known.
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