Passing from the temple at Karnak to others in a better state of preservation, we can gather that the part of the axis furthest from the entrance was covered, so that in the _penetralia_ there was only a dim religious light. The entrance is also, as it were, guarded by a massive exterior pylon, as in the more or less modern temple of Edfû. This, again, reduces the light in the interior. It is easy to recognise that these arrangements bear out the idea of an astronomical use of the temple. [Illustration: INNER COURT AND SANCTUARY AT EDFÛ. (_From a Photograph by the Author._)] First of all we know that the temple was directed to the place of the sun's setting; and if the Egyptians wished to lead the narrow shaft of light which was bound to enter the temple, since it was directed to the sunset, they would have contrived the very system of gradually narrowing doors which we have found to be one of the special features of the temple. The doors were considered as very important--and no wonder. In the account given of Thothmes III.'s restoration of the temple of Amen-Rā, we read that after the building had been constructed in a "position corresponding to the four quarters of heaven" the great stone gateways were erected. "The first had doors of real acacia wood covered with plates of gold, fastened with black bronze and iron." Then came a propylon (Bekhen) with three other gates connected with it covered with plates of copper, and the sacrifices were brought through these.[29] This idea is strengthened by considering the construction of the astronomical telescope. Although the Egyptians knew nothing about telescopes, it would seem that they had the same problem before them which we solve by a special arrangement in the modern telescope--they wanted to keep the light pure, and to lead it into their sanctuary as we lead it to the eyepiece. To keep the light that passes into the eyepiece of a modern telescope pure, we have between the object-glass and the eyepiece a series of what are called diaphragms; that is, a series of rings right along the tube, the inner diameters of the rings being greatest close to the object-glass, and smallest close to the eyepiece; these diaphragms must so be made that all the light from the object-glass shall fall upon the eyepiece, without loss or reflection by the tube. These apertures in the pylons and separating walls of Egyptian temples exactly represent the diaphragms in the modern telescope. What then was the real use of these pylons and these diaphragms? It was to keep all stray light out of the carefully roofed and darkened Sanctuary; but why was the Sanctuary to be kept in darkness?