The result was interesting, since it shews the great importance of unsuspected details in this kind of undertaking.
In the model, I did not use a tunnel, but allowed the sand to escape at any desired rate through an aperture in the stand on which the model was placed. Since the model was not fixed to the stand, the position of the aperture with regard to the bottom of the funnel could be varied.
I found that, if the aperture was on the side away from the embankment, there was a decided tendency for the obelisk to jam against the opposite wall of the funnel. If, on the other hand, the sand ran out from the near side, the obelisk came down resting against the embankment wall, with its edge where the slot should be. It seems most likely that the sand was removed, not from the tunnel shewn on plate [VIII], but from one on the opposite side, leading out from under the embankment. The tunnel shewn in the plate seems necessary for the proper cleaning of the pedestal before the obelisk was pulled upright.
In a subsequent model, in which the side of the funnel was vertical and made of glass, I was enabled to examine the base of the obelisk and the levels of the sand during the descent. The results shewed no reason for modifying the diagram on plate [VIII] except in the manner mentioned above.
It is possible that the sand was removed from above until the obelisk was low enough for there to be no fear of a jam; after that point had been passed, it would not matter from which side of the pedestal the sand was removed.
I realise that if the model were enlarged up to full-size, the grains of sand would be at least one centimetre in diameter. It seems to me that, using ordinary sand with a full sized obelisk, the flow would be better than is the case in the model, as there would be less skin-friction with the sides of the funnel. On the other hand, there may well be factors, unforeseen by me, which might render the behaviour of the full-sized obelisk different from that of the model, so I give these results without insisting that they are a proof that such a method is possible for erecting obelisks.
Another point arises in connection with the funnel; this is the possibility of the side walls of the funnel having been constructed vertically, the width of the funnel being only slightly greater than the width of the base of the obelisk. The advantage of this modification would be that if sand were piled on to the obelisk in the initial stages of its descent, the weight of the sand would be a great help in forcing the base down the funnel past the point where it might be likely to jam. It would, however, make the examination of the obelisk during its descent a difficult matter owing to lack of space.
Mr. Somers Clarke points out that, if the obelisk came down on to its pedestal supported on one edge, that the strain would crush the granite. It seems that the slot in the pedestal served a double purpose, one to keep the obelisk from twisting, and the other to ensure that the weight {41} is taken on the edge of the slot and not on the edge of the obelisk (see fig. [8]). Let us assume that the edge of the slot crushes until there is 2 inches of supporting surface; then since the obelisk is about 165 inches along its base, the bearing surface will be 330 square inches and the resulting crushing stress about 3 ½ tons per square inch, which is not so very excessive. By putting moderately soft wood in the slot, the weight could be borne both by the edge of the obelisk and the edge of the slot, thus further reducing the stress set up. In the case of the standing obelisk of
atshepsôwet, it has come down without engaging in the slot, with the result that the corners have crushed considerably.