A word of explanation is, perhaps, needed on the system of weights and measures used in this volume. It has been the custom of my Department to insist on metric scales in all plans. In the text, however, I enter somewhat deeply into the stresses and strains set up in the granite, and since nearly all the English engineering text-books and tables use the ton-inch units, I have adhered to the English system, reducing the metric linear measures to inches in my calculations. The _tonne_ and the _kilogramme-per-square-centimetre_ still convey little to the average English-speaking engineer, who has to have recourse to his slide-rule before being able to realise the strains set up when they are given in metric units. {3} CHAPTER I. DESCRIPTION OF THE OBELISK. (3) The obelisk is 41.75 metres long, lying with its point 18.5 degrees north of east, and sloping down towards the butt at an angle of 11 degrees, making the base of the pyramidion 7.05 metres above the level of the butt. When complete, the obelisk would have weighed 1168 tons English. It is curious that, during all the years that this obelisk has been known, those who were interested in the ancient methods of quarrying have not taken the trouble to clear it. Nearly every work in which it is mentioned dismisses it in a few sentences. Both Gorringe in his _Egyptian Obelisks_ and Bædeker give its length as 95 feet and the width at the butt as 11 feet 1.5 inches. How they arrived at the latter figure passes my understanding, as it was buried under a chip-heap to a depth of 7 metres. Perhaps the measurements were given by the original writer, whoever he may have been, not as a fact, but as a prophecy. The measurements of the obelisk are: Total length 41.75 metres. Base 4.20 metres. Base of pyramidion 2.50 metres. Height of pyramidion 4.50 metres. Weight when finished 1168 English tons. Round the obelisk, partly separating it from the surrounding rock, is a narrow trench, whose depth averages about 2/3 that required to disengage it to a square section. Plate I is a plan, with sections, of the obelisk to a scale of 1/100, and plate II, nos. 1 and 2, shews the obelisk viewed from the tip and butt respectively; the trench around the obelisk can be seen in plate II and in plate III, no. 1, and is discussed in chapter ii.