Wednesday, June 20, 2012

A Ruler for a Ruler

I made a claim a couple posts back that the Egyptians were the first to have what modern man would call or recognize as a ruler. The Egyptian ruler is most often called a cubit stick or a cubit rod. Rods of various forms had been found. Wooden rods were most likely those actually used by craftsman in their labor or architects while drawing or building. Stone cubit rods have also been found and it is suggested these were strictly ceremonial. (though some ceremonial cubit rods were also wood.) This makes perfect sense. A heavy stone ruler a foot and a half long would be unwieldy for drafting or carrying around all day. Also, a stone rod would likely break often when dropped or hit wrong against the stone or bricks being measured. However, it is not unusual that Egyptians created a ceremonial replica because this is a common trend both in their spiritual practices and in their death practices.

So, what is a cubit?

A cubit is the standard Egyptian measurement comparable to the modern foot or meter. There are two cubits used. The short cubit which is the distance from the elbow to the tip of the fingers of the pharaoh. The royal cubit is the distance from the elbow to the fingertips plus a palm width. The royal cubit was the standard cubit in use.
Like the foot or meter, cubits were also broken into smaller measurements. These increments were 6 palms for the short (7 palms for the royal), 4 fingers for each palm, a finger was then broken into fractions from halves to 1/16th. 1/16th of a finger seems to be the smallest measure the Egyptians used. 1/16th of a finger is approximately .12 cm (mm) or .05 inches. To give you an idea of how small this is the width of 1/16th of a finger is approximately the width of a standard earring post or an 16-18 gauge piece of piercing jewelry. It is this precision that was likely to allow for such perfection in their buildings as far as fitting stones together.

Two other measurements were common the short span and the great span. Short Span is the distance between the thumb and the pointer finger when they are spread as far as possible. The Great Span is the distance from the thumb to the little finger when they are spread as far as possible.

Great Span
Short span

This leads us to why the Egyptians were the first in history, that we know of, to show up with a standardized ruler. Large scale building and moving of materials. The ruler is a necessary tool when you consider an architect on the Giza Plateau telling some overseer in a stone quarry how big to make the stone blocks. The second reason for a ruler was the obsessive way the Egyptians measured the flooding of the Nile. Priests needed a standard to exist over many generations so that Nile floods and Nile predictions could be made. 

A workman's cubit rod at the Liverpool Museum.

A little more about the cubit rod.

The rods had other markings on them besides the tick marks for measuring. Most of the rods included inscriptions invoking gods related to science and craft. Th inscription from the wooden rod above is:
"A boon which the King gives (to) Amun-Re and (to) Ptah, Lord of the Two Lands, and (to) Thoth, Lord of Divine Words, great god who dwells in Hermopolis, that they may give life, prosperity and health, and a good lifespan, following their Ka's, for the Ka of the Servant in the Place of Truth, Any."

In addtion to the inscription ceremonial cubit rods had lists of the nomes arranged by their order from Lower Egypt to Upper Egypt. These nome inscriptions were usually listed by the image or name of the god of that nome.

Ceremonial cubit rod at the Louvre showing the names of the nomes along the top
as well as the measurement symbols along the edge.
(Remember to read right to left like an Egyptian.) Photo by Jon Bodsworth.

Close up of the Louvre Cubit rod
Notice on the rod that the fractions are very clear. The mouth glyph which indicates that it is a fraction and then the number after. We can also more clearly see the second line from the top which names the sections of the cubit and then the upper most line with the names of the nomes.

Fragment of a stone, ceremonial cubit rod on display
at the Metropolitan Museum of Art

Quick Cubit Conversion Chart:

(Conversions are approximations from measuring a variety of cubit rods)
- 1 Short Cubit = 45cm = 18 inches
- 1 Royal Cubit = 53 cm = 21 inches
- 1 Royal Cubit = 1 Short cubit + 1 palm
- 1 Royal Cubit = 7 Palms
- 1 Palm = 4 Fingers
- 1 Royal Cubit = 28 Fingers
- 1 Great Span = 2 Palms

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