When I started to construct a 3D virtual model of the Great Pyramid I looked at two other sources for the individual heights of the core blocks and compared them with Petrie's.

The first was produced by Piazzi Smyth in 1865 and he warns that "I measured in a rough manner the height of every course of stones; and repeated the measure the next morning in descending. The two sets were not always as similar as they should have been, and the second gave 202 courses, while the former gave 201". Petrie also points out errors in Smyth's figures so I think we can safely disregard them.

Much more interesting are the measurements done by the French archaeologists George Goyon in 1978. They appear in BIFAO (Bulletin de'l Institut Francais D'archéologie Orientale) Volume 78 and were subsequently republished in his book on the Great Pyramid. He goes into considerable detail about how he did the measurements and there are diagrams showing the technique he used. He also lists the colleagues who collaborated in the exercise.

So I would expect that his measurements would be fairly accurate. It comes as a surprise therefore to discover that there is a considerable difference from Petrie's figures. Sometimes as much as 6 inches on individual layers. Considering that Petrie is measuring to a tenth of an inch this is a really big difference.

Goyon says there are now 200 layers but restores the measurements of two more by using the figures of Jomard from "Description de l'Egypte" from 1822. So that means there were 202 layers in 1822 but 203 when Petrie measured them in 1882!

There's a well known bar chart produced by Petrie that shows the distribution of layer heights as you go up the Pyramid.

Here's my version with Goyon's data overlaid. Petrie's is in green and Goyon's is in red. It shows a general overall agreement but with some fairly obvious difference at an individual level. I know it's small but I think you can get the general idea.



So does it matter? I can't decide. If you add up Goyon's layer heights then you will get different heights for some of Petrie's intersections. For instance the exit points of the two King's Chamber Shafts are located by Petrie at the top of layer 102 and 103 at 3119.1 inches and 3148.4 inches above the pavement. Using Goyon's figures the same shafts would be 3127.2 inches and 3157.1 inches above the pavement which would mean a subtle change in angle.

And there's one final surprise. Goyon's article is heavily notated with references etc and many standard works are referred to but nowhere is there any mention of Petrie or his measurements. Even John Greaves from 1638 gets a mention. But no Petrie, it's as if Goyon was the first to measure the layer heights since the scholars of the "Description de l'Egypte".

As I said I can't make up my mind whether all this is significant or not.

Jon

www.egyptarchive.co.uk