"Dr. Schweinfurth says that the steps of a man are a more accurate standard of measurement than those of an animal. The camel, when urged to its full speed, does not increase the number of his paces but their length; while those of a man, at whatever rate he walks, are about the same. He suggests that any one may satisfy himself on this point by measuring his own footsteps in moist ground. He will find them varying very little, no matter what the rate of speed. Dr. Schweinfurth says his steps varied, according to the nature of the road, from twenty-four to twenty-eight inches, and we may set this down as the average step of a man of medium height. [Illustration: AN AFRICAN HORIZON.] "In addition to sextants and pedometers, we will have a complete apparatus for taking photographs, with plenty of dry plates, sensitive paper, and the other necessary materials; then we must have a stock of compasses, barometers, and thermometers; and we must not forget an anemometer, an instrument for measuring the force of the wind. One of our compasses must be an azimuth, which resembles the marine compass, but has a more accurate graduation, and is provided with vertical sights, so that the variation of the needle may be detected. This is done by observing the position of a star through the sights, and comparing its azimuth, or point on the horizon, with the direction of the needle. The position of the star being known, the computation is easy." Doctor Bronson explained that the instruments, tents, fire-arms, and personal outfits could not be procured in Egypt, but must be ordered from London or Paris. The bulk of the provisions might be obtained in Cairo or Alexandria, but the character of the supplies could not always be relied upon. Consequently it was decided to make the list as complete as possible and ship everything from the English and French capitals, so that they would not be delayed at Cairo. Of course there would be some deficiencies, and these could be filled from the Cairo market before the date of departure. The plan was carried out without accident. We have seen our friends on their way to Central Africa, and have now landed them safely at Korosko. [Illustration: A VILLAGE IN "THE DARK CONTINENT."] CHAPTER II. LEAVING KOROSKO.--EARLY EXPLORERS OF THE NILE VALLEY. The preparations for leaving Korosko required several days. Camels were to be hired, loads distributed, and drivers and servants engaged. A great many small details consumed the time of our friends, from the hour of their arrival till their departure. Twenty camels were engaged, sixteen for baggage and four for riding purposes, three of the latter being for the Doctor and the boys, and one for the dragoman. The boy Ali was assigned to a place on one of the baggage camels, as he was considered too young to have a saddle animal all to himself.