Mechanical and Technical Processes. Materials 151 rectangular. In the case of a Great Pyramid we cannot suppose that when all was complete the whole was scaffolded before the dressing was carried out. The absence of traces of 'putlogs' in the masonry in places such as the top casing of the Second Pyramid makes this almost certain. The only explanation for the method of dressing large buildings is that it was done while the embankment which, as we have seen, must have covered the whole building, was being removed, to measured lines or other indications left when the building was being erected. From a close study of this point I believe that the top outside edge of each course was dressed in to the eventual surface—a kind of bevel, as it were. If the above sketch is not sufficient to illustrate the vast difference between Egyptian masonry and that with which we are familiar I can cite one other. In some of the less carefully constructed buildings, one course is not quite parallel with those above and below it. This, and other considerations, particularly the Egyptian habit, at times, of building with blocks of irregular height, lead me to believe that the top of the course was dressed after the blocks had been laid. Their only method of levelling was by running a watercourse, the water being banked up with Nile mud, along and about the surface to be levelled, and then measuring down from the surface at many points simultaneously, thus establishing datum points to which the complete surface would be eventually reduced. One instance can be cited to show the likelihood of some such method having been adopted. The platform which runs partly under the Great Pyramid was examined very carefully by the Survey of Egypt, who found that, although the exposed parts lie on an almost perfect plane, the whole slopes up about 6 inches from, the north-east to the south-west corner. If, when the points were being simultaneously checked, a north-east wind had been blowing, such a result might occur; indeed no other explana- tion seems possible.