We have seen that, though it was probably brought from the southern hemisphere, the Egyptians adopted the year of the Pleiades, and celebrated the new-year's festival of the dead; but they were also advanced astronomers, and would soon find out the change that took place in the seasons when regulated by the stars. And to such persons the date at which the two periods coincided, or at least were exactly half a year apart, would be one of great importance and interest, and there seems to be evidence that they did commemorate it in a very remarkable manner. The evidence, however, is all circumstantial, and the conclusion therefore can only claim probability. The evidence is as follows:--The most remarkable buildings of Egypt are the pyramids. These are of various sizes and importance, but are built very much after the same plan. They seem, however, to be all copies from one, the largest, namely, the Pyramid of Gizeh, and to be of subsequent date to this. Their object has long been a puzzle, and the best conclusion has been supposed to be that they were for sepulchral purposes, as in some of them coffins have been found. The large one, however, shows far more than the rest of the structure, and cannot have been meant for a funeral pile alone. Its peculiarities come out on a careful examination and measurement such as it has been subjected to at the devoted hands of Piazzi Smyth, the Astronomer Royal for Scotland. He has shown that it is not built at random, as a tomb might be, but it is adjusted with exquisite design, and with surprising accuracy. In the first place it lies due north, south, east, and west, and the careful ascertainment of the meridian of the place, by modern astronomical instruments, could not suggest any improvement in its position in this respect. The outside of it is now, so to speak, pealed, that is to say, there was originally, covering the whole, another layer of stones which have been taken away. These stones, which were of a different material, were beautifully polished, as some of the remaining ones, now covered and concealed, can testify. The angle at which they are cut, and which of course gives the angle and elevation of the whole pyramid, is such that the height of it is in the same proportion to its circumference or perimeter, as the radius of a circle is to its circumference approximately. The height, in fact, is proved by measurement and observation to be 486 ft., and the four sides together to be 3,056 ft., or about 6-2/7 times the height. It does not seem improbable that, considering their advancement, the Egyptians might have calculated approximately how much larger the circumference of the circle is than its diameter, and it is a curious coincidence that the pyramid expresses it. Professor Piazzi Smyth goes much further and believes that they knew, or were divinely taught, the shape and size of the earth, and by a little manipulation of the length of their unit, or as he expresses