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Great Pyramid 5-inch standard scale

Imperial powers used colonial spaces to test new scientific programmes. Egypt provides a dramatic example: the Great Pyramid of Giza was a site of study and disagreement amongst European scholars in the 18th and 19th Centuries.

In the 1860s, the Astronomer Royal for Scotland, Charles Piazzi Smyth, boldly claimed this ancient monument as fundamentally British. The Great Pyramid, he argued, embodied complex, precise knowledge of astronomy and metrology—the science of measurement. This made it a “Metrological Monument” built by the ancient Israelites using God-given measures that were the direct antecedents of the British inch.

A basalt standard

Great Pyramid 5-inch standard scale, by Charles Piazzi Smyth
Image 1: Great Pyramid 5-inch standard scale, by Charles Piazzi Smyth, Giza, Egypt, 1865 (Wh.1155).

Charles Piazzi Smyth travelled to Giza in 1864 to measure the Great Pyramid. He had read and admired theories linking the Pyramid with revelations in the Old Testament concerning a ‘sacred cubit’ used by Noah.

This unit, it was argued, was 1/20,000,000th of the earth’s axis of rotation (distance pole to pole), and had been recorded in the shape of the pyramid as a material trace deliberately left by its ancient-Israelite builders. Piazzi Smyth sought to verify these theories, and link them to British imperial units of measurement.

Upon arriving in Egypt, Piazzi Smyth found that his instruments were poorly made and his measuring rods warped in the dry heat.

Needing a reliable standard against which to calibrate his measuring tools, he improvised by plundering a lump of basalt from the Pyramid’s pavement. The stone was ground smooth by “Alee, the day-guard”, and then marked by Piazzi Smyth with a 5-inch scale using his wife’s diamond ring (Image 1).

Piazzi Smyth described the process in his official report of the expedition:

“Alee … was burning with anxiety to turn an extra penny in any honest manner, and could use his hands well, though not his feet. … So at once the poor worthy man began with his tedious grinding, circulating the upper stone as regularly as if his arms had been part of a speculum-grinding machine … with such untiring perseverance, from another sunrise to another sunset … a surface was at length obtained on which fine engraved lines could be creditably placed.”(1)

After use as a reference standard in Egypt, the scale was then taken back to Edinburgh and precisely measured, and all Piazzi Smyth’s data adjusted accordingly.

Instruments and orientalism

Clinometer, by Troughton & Simms
Image 2: Clinometer, by Troughton & Simms, London, c. 1850 (Wh.2554).

As well as using simple wooden rods, Piazzi Smyth also employed fine instruments such as a clinometer (Image 2) to measure the exact lengths and angles of the Pyramid’s various passages and chambers.

Piazzi Smyth worked with the veteran excavator Ali Gabri and a team of local assistants. His accounts record regular interruptions from tourist parties, as well as his views on those he worked with, which, as we can see in this quote, are strikingly orientalist:

“[Of] all the true scientific instruments they had previously seen produced one after another … [Ibraheem] and all the other Arabs … looked on them as of no practical use whatever, and held them rather as signs of weakness in those employing them; proofs, unhappily, in their minds, that a European cannot get on at any occupation without some queer and troublesome contrivance to peep through,—when an Arab has only to look straight at a thing with his simple eyes, and perceive its whole bearings at once.”(2)

Egyptian people and tools are characterised as inherently different, and provide an Other against which Western methods can themselves be defined.

The pyramid inch

“5 Great Pyramid Inches” rule
Image 3: “5 Great Pyramid Inches” rule, by Bryson, Edinburgh, 1881 (Wh1155).

The centrepiece of Piazzi Smyth’s argument came from a striking correlation: the ‘sacred cubit’ he claimed to have recovered in his measurements of the Great Pyramid was very close to being 25-inches long. This was proof, he argued, that the Anglo-Saxons had inherited their imperial measures from God via the ancient Israelites—a powerful defence of the imperial system, then facing serious attack from the French metric system.

Britain had only recently redefined the standard yard, and Piazzi Smyth boldly argued that it was in error and should be re-established using his ‘pyramid inch’, which equalled 1.001 standard British inches (Image 3).

Piazzi Smyth’s project failed. Sceptics reviewed his measurements and questioned his selective use of data.

More tellingly, the Egyptologist Flinders Petrie soon found that new dimensions taken of the Great Pyramid in 1880 were most easily explained using the Egyptians’ own measure of length, the Egyptian cubit.


1.     Charles Piazzi Smyth, Life and Work at the Great Pyramid, Vol. 1 (Edinburgh: Edmonston and Douglas, 1867), pp.293–94.

2.     Charles Piazzi Smyth, Life and Work at the Great Pyramid, Vol. 1 (Edinburgh: Edmonston and Douglas, 1867), p.299.


Joshua Nall

Joshua Nall, ‘Charles Piazzi Smyth and His Imperial Measures’, Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge, 2020.

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