EXTRACTION OF OBELISK FROM QUARRY.
(21) Having examined, as far as possible, the methods by which the
obelisk was separated from the surrounding rock, we will consider
by what means the obelisk was detached from its bed and got into a
position in which it could be handled and transported.
It might be remarked that this particular obelisk has _not_ been
transported; there is no doubt, however, that the man responsible for
the work had quite definite ideas as to how he was going to perform
the feat. Although it is the largest obelisk known (_pace_ the phantom
108 cubit obelisk of Ḥatshepsôwet), the old engineers have actually
moved even heavier and more unmanageable blocks: the colossus of the
Ramesseum and the colossi of Amenophis III at Thebes. If we can solve
the ancient method of dealing with this particular obelisk, we can the
more easily understand how the others were dealt with.
There seem to be two methods by which the obelisk could be detached
from its bed; the snapping off of such an obelisk in the manner
mentioned in section 19 being out of the question.
(1) By undercutting the obelisk from both sides to a certain extent,
say a quarter of the breadth from each side, and either detaching
it by a series of very large wedge-slots (as was done all over the
quarries for medium-sized blocks), _or_, if the Egyptians used wooden
wedges, expanded by the action of water, by one long wedge channel on
each side of the obelisk. These could be wetted by flooding the trench
with water, but before this could be done, the trench would have to
be divided into compartments by, say, mud-brick walls to prevent the
water running down to the deep end, leaving the pyramidion end dry. In
this case a large allowance would have to be made in case the granite
did not break evenly across between the wedge-channels. The great
objection to this method is the risk of the obelisk breaking across
owing to uneven strains set up by the wedges; it will be seen, in
section 43, that the obelisk can only just support its own weight when
in a horizontal position. If this method were employed, before the
obelisk could be moved, it had to be raised off its bed to pass ropes
round it. This could be effected by levering from both sides of the
obelisk—using the outer trench wall as fulcra—and gradually rocking the
obelisk higher by packing below it at each tilt. Assuming that only
half a metre was undercut from both sides, it would require 30 12‐inch
tree-trunks going down three feet into the trench (properly packed),
and projecting 18 feet above the trench, being used vertically, with 70
men pulling on ropes attached to the top of each lever. The strain set
up would be about 1000 pounds per square inch, which is well within
the {24} powers of ordinary coniferous wood as cypress. (I assume that
a man pulls 100 pounds.) The more undercutting performed, the less
force would be required to rock the obelisk. Since the obelisk would
have to be tilted from both sides, a good deal of rock would have to be
removed from the south side of it before the levers could be used.
(22) (2) By completely undercutting the obelisk. In spite of the
slowness of the work I am convinced that the obelisk was completely
undercut, most likely by hand pounding, since the expenditure of copper
chisels would be terrific, and the idea, in this kind of work, seems
to be to economise as much as possible on copper. It would be packed
by wooden blocks or stone as near the centre as is consistent with
stability, and in as few places as possible. Ropes would then be passed
round the obelisk, each going several times round and being brought
forward from below to anchorages in front. It is here that the details
of this method assume such great importance; it must be remembered
that, if the obelisk weighs 1170 tons (allowing a margin for the
roughness of the undercutting below), and lies on its side on a hard
bed, then the horizontal pull by ropes necessary to turn it over on to
a new face will be half the weight of the obelisk, _i. e._ 585 tons.
This would need 13,000 men, if a man pulls 100 pounds. I do not see how
such a number could possibly be put on to this work. Figure 6 shews the
obelisk supported on its packing, the section here being at the centre
of gravity, and the outer edge of the packing being 1 metre from the
centre of the obelisk on each side. To pull it over by horizontal ropes
would need 8000 men, which still seems more than is practicable. It
is possible to reduce the number of men required to turn the obelisk
over by means of levers working off the north wall of the north trench,
which seems to have been deliberately left for that purpose (cf.
section 5).
[Illustration: Fig. 6.]
(23) By using, say, 30 21‐foot levers with a mechanical advantage of
six to one, as described in the last section, the obelisk can be made
to turn slightly about N (see fig. 6) so that the packing P can be
removed and perhaps replaced by sand.
About N the moment of the force at the bottom of the lever is to that
of the weight of the obelisk acting at its centre as 7 : 2 (by scaling
off the figure), so that the moment at the top of the lever to that of
the weight will be 42 : 2, or 21 : 1. Let the number of men per lever
be _n_. {25}
Then 30 × 21 × 100 × _n_ = 1170 × 2240, which gives the number of men
as 42, or 1260 men in all[9].
I have taken the amount of undercutting in figure 2 as .75 m. at the
centre of gravity; it would increase as far as 1.00 metre at the butt.
As soon as the sand had replaced the packing, the rock AB would be
removed by burning and wedging until it sloped down as much as possible
from the level of the bed of the obelisk. I had not sufficient funds
at my disposal to examine the levels of the rock to the centre of the
valley, so I have to be rather vague as to what distance the obelisk
was rolled out[10]. The obelisk would then, when the sand flowed out or
was removed, take up a position as shewn in the dotted section.
[9] The check the stress in the levers. Referring to figure 6,
(Stress) (Section modulus) = Sum of moments on one side of fulchrum,
_i. e._ (s × .0982 × (25)^3) = (1170 × 2240 × 216)/(30 × 21) = 586
pounds per square inch, which is well within the powers of any wood.
[10] It will be seen that, if the obelisk lies at too low a level
to be rolled _downwards_ to the valley, it can be raised by tilting
backwards and forwards by means of levers acting from the north and
south trenches alternately, as mentioned in section 21. If the butt
were raised even a metre above its present level, it would enormously
reduce the quantity of rock to be removed before the obelisk could be
rolled out.
Then, about Q, the moment of the horizontal force of the ropes round
the obelisk to the moment of the weight will be, from the figure, as 9
to 2, so if _n_ be the total number of men required to pull the obelisk
over, then (_n_ × 100) = (2 × 1170 × 2240)/9 which gives 5824 men as
against the 8000 men which would be required if the levers were not
used. It is an enormous number, but I do not see how they could manage
with less.
A bank of sand just in front of the lower edge of the obelisk would
make the second turn an easy matter, and if from thence the obelisk is
rolled downwards on soft sand, I think that the 5824 men will still be
ample, as the sand can be undercut in front of the edge and so make the
rolling approximate to that of a cylinder.
(24) As to the size of the ropes required for the rolling out of the
obelisk, all we can do is to obtain a very rough idea as to it. If they
spread the men out slightly fanwise, I do not see how they could have
used more than 40 ropes. The strain per rope will be, as we have seen,
(2/9 × 1170/40) = 6.5 tons per rope.
The rope used was probably the very best palm-rope, newly made. The
safe load which can be put on coir rope, which is of about the same
strength, is given by the formula: Load in cwts = (Circumference in
inches)^2 divided by 4 (_Military Engineering_, 1913, Part III A,
p. 49). Substituting, we have (6.5 × 20 × 4) = C^2 which gives a
circumference of 22.8 inches and a diameter of 7 ¼ inches. If such a
rope were used it would require handling loops on it.
(25) Before leaving the work at the quarry, it remains to be seen how
the chiselling of the wedge-slots was done. The apparent impossibility
of cutting granite with a copper chisel has struck every student of
this question. Many suggestions, some of them grotesque, have been
put forward to explain how it might have been performed. Gorringe, in
his _Egyptian Obelisks_, {26} boldly assumes the knowledge of steel.
To my mind, the reasons against this are, _first_: the knowledge of
steel would have soon resulted in its use being widespread for daggers,
swords and, above all, razors; _secondly_, it would have had a special
name, since its properties are so different from iron. Now all the
ancient names for metals have been accounted for, none of which could
be applied to mean steel. If we translate _Benipet_ as ‘steel’, then we
have no word for iron.
Gorringe’s assertion that iron and steel tools would have disappeared
by oxydisation in a few centuries is not borne out by excavations. We
know, from the scanty mentions of iron, that it was not very generally
used, but quite a number of iron tools of late Egyptian date are now
known, and I have myself taken out an iron bill-hook from the filling
of a Roman or Ptolemaic grave which was hardly rusted at all, and in
the Cairo Museum there is an iron fork of Coptic date from a depth of
5 metres in the _sabâkh_ of Tell Edfù which is almost like new. If
the ground is dry and free from certain chemicals, objects such as
iron, wood, linen, papyrus, etc., will keep indefinitely, whereas, in
unsuitable ground, even copper will disappear and leave no traces,
except, perhaps, a blue stain. If steel had been in anything like
common use, we should surely have found examples, either in graves or
in town sites like Kahûn or Tell el-ʿAmarna. PETRIE, in _Tools and
Weapons_, pl. VI, 187, cites a halberd of _iron_ dated to Ramesses III;
had steel been known, we should have expected it to be of that rather
than iron. An examination of such broken iron tools as can be spared
might give us definite information one way or the other, as steel,
though it may lose its temper, will not turn into iron, however long it
is left, and should be easily recognized by a micro-photograph.
On the rocks of the Wady Hammâmât, the following inscription is to
be seen, together with others having the same title (GOLÉNISCHEFF,
_Hammamat_, II, no. 3, and COUYAT et MONTET, _Les inscriptions
hiéroglyphiques et hiératiques du Ouâdi Hammâmât_, in _Mémoires de
l’Institut français du Caire_, vol. XXXIV, p. 54) : ([glyph])
[Illustration: Hieroglyphs, etc.
May Amûn give life (to) the worker of iron tools, _Ptaḥi_, son of the
worker of iron, _Ken_, etc.]
The determinative [glyph], sometimes written [glyph], seems to suggest
iron tools in general, and we are hardly justified in deducing from
this that the chisels for cutting granite were necessarily of iron; it
is very likely, however, that the wedges were of iron.
(26) The suggestion, put forward by Donaldson, that the Egyptians
softened the granite by chemical means before using the chisels on it,
is not worthy of serious notice, as a glance at the tool marks shews
that the granite was quite hard, and behaved in exactly the same way
as it does under modern tools. His other suggestion, that the granite
was first pounded to render it more workable, cannot be accepted as the
explanation, as how did they pound the bottom of the wedge-slots?
A far more reasonable suggestion is that the granite was cut by chisels
of dolerite or similar {27} basic rocks. Mr. Firth tells me that,
except for the grinding of the cutting-edge, they occur naturally in
the Wady Alaqi. A series of trials with such a chisel left me entirely
unconvinced, the more so since many of the old chisel-marks shew that a
narrow-edged tool had been used.
From my own experiments, I can believe that the Egyptians _could_ have
cut granite with a copper chisel, but more time is spent sharpening
the tool than in cutting the stone, and the expenditure of metal would
be appalling in any but the smallest works, but I cannot admit that
copper tools, as we know them, could have ever been used to cut hard
quartzite, which gave the Egyptians no special trouble, if we judge by
the huge chambers which they cut, polished and transported, as in the
case of the burial chamber in the Hawara Pyramid.
It has also been suggested that the copper chisels were fed with emery,
but anyone who has handled a chisel will appreciate the impossibility
of feeding the tool with emery; on the other hand, emery may well have
formed the basis of the polishing process, and have been regularly used
in stone drilling and sawing.
(27) How, then are we to explain this problem? Much as I hate to
admit it, I am driven to the conclusion that the ancient Egyptians
possessed some simple method of tempering copper to the hardness of
modern tool-steel[11]; even now copper with 2 % of alloy may, by heavy
hammering, be brought to the hardness of mild steel. This has been
suggested by many writers, and examples of tools are known—Wilkinson
quotes one in volume II, p. 255—where the malletted end of the chisel
was worn by the blows, but where the point was sharp; of course that
might be explained by the fact that it had just been re-sharpened,
but I have myself seen a chisel where the cutting-edge was chipped in
the same manner as a modern steel tool instead of being burred. I was
unable to purchase this specimen, but I tried the point with a knife,
and was able to scratch it as I could any other piece of copper; the
temper, therefore, must have been temporary (cf. WILKINSON, _Manners
and Customs_, vol. II, p. 255, and PETRIE, _Arts and Crafts_, p. 100).
[11] There has lately been a rumour that a method has been discovered
in America for tempering copper, and that a company is being formed
for its exploitation; if this is true, it will relieve archæologists
considerably, who have been at their wits’ end for a good explanation
for the last 50 years.
If this is the true solution, it is probable that the knowledge died
out when the use of iron and steel became general, as its value in not
producing sparks could hardly have been foreseen. It is not surprising
therefore that the knowledge died out when it was no longer a necessity.
It might be remarked that instead of having a method of greatly
hardening copper, the Egyptians might have been able to temper iron.
The experiments on iron and its properties during the last century
have been innumerable and, had there been a method, apart from the
introduction of carbon, of tempering iron to a very great hardness,
I think that it would certainly have been discovered by now. In our
present state of knowledge, it is best to leave the subject as an open
question.
{29}