The boys paid a second visit to the tomb of Keit Bey, and carried along their sketching materials. They found the architecture more difficult to represent than they had supposed, and Frank made two or three attempts at the graceful minaret before he succeeded in satisfying himself. The minaret is one of the finest in Cairo; it rises from a corner of the building, and has three stages or balconies, which diminish as they approach the top. The summit is shaped like a pear, and is usually disfigured with poles, from which flags are hung on days of festivals. The dome bears a marked resemblance to that of the Taj Mahal at Agra, in India, and terminates in a sharp spire instead of the conventional half-moon that generally surmounts a Moslem edifice. While Frank was busy with the structure, Fred made a sketch of several camels that were halted in front of the famous mausoleum, and the work of the two youths was afterward united into a single picture. An early day was devoted to the Museum of Egyptian Antiquities at Boulak, a suburb of Cairo, and practically a part of the city. An excursion was made to Old Cairo, and from there by ferry to the island of Rhoda. On the latter is the famous Nilometer, or instrument for measuring the depth of water in the Nile; it is a square well, connected with the river, so that the water can freely rise and fall within it. In the centre of the well is a stone column, marked like a scale, with the old Arabic measures: the _dra_, or ell, was the unit of measurement, and was 21-1/8 inches in length, divided into 24 _kirat_. The height of the column is 17 ells, or about 30 feet, and the Nile at its lowest point covers about 7 ells of this length. When the water mounts to 15-2/8 ells the river is considered full, and the whole valley of the Lower Nile can be inundated. The embankments that restrain the water are then cut with a great many ceremonies, and the prospect of an abundant harvest causes general rejoicing.