"In studying about the trade-winds and the monsoons, I find that they do not blow directly north or directly south, as we might suppose they would if they came in to fill up the vacancy caused by the rising of the heated air. North of the equator the trade-winds blow from the north-east, and south of it they are from the south-east. The inclination to the east is caused by the rotary motion of the earth from east to west. The earth slips from under the wind while turning on its axis, and it is really the earth that makes the slope of the wind, and not the wind itself. Something like it may be seen when a boat crosses a river. The boatman may try to pull straight across, but if he does so the current carries him down, and he is unable to land opposite his starting-point. The only way he can do so is by going obliquely against the stream. "The monsoons get their direction in the same way as the trade-winds get theirs; with this difference, that the south-west monsoon starts near the equator, and not in the southern hemisphere, like the south-east trade-wind. The rotary motion of the earth is greater at the equator than it is in the northern latitudes, and so the wind gets a westerly inclination instead of an easterly one, as in the case of the trade-wind. Some of the scientific men say that the north-east monsoon is not a monsoon at all, but only the north-east trade-wind taking its regular course, which has been disturbed by the more powerful wind from the south-west." "Very good," remarked the Doctor, when Frank read what he had written. "I am a little fearful, however, that it will not be understood by everybody, and so we will drop the dry subject and think of something easier." The boys admitted that the topic was a dry one, but nevertheless it was interesting; and they thought they would not be doing their duty in their journey if they failed to comprehend the great winds that so materially help or hinder the movements of ships in Asiatic waters. On their third day from Hong-kong the boys heard with delight that land was visible. At first it was like a dark cloud on the horizon; but, as they approached it, the scene changed, and the cloud was resolved into a tropical shore, backed by a line of hills in the distance. The steamer headed for a little promontory, and by-and-by a light-house was revealed that marked the entrance of the river which they were to ascend. A boat came out from the mouth of the river, and a pilot boarded the steamer. He was a weather-beaten Frenchman, who had lived more than twenty years in Cochin China, and was thoroughly familiar with the channel of the river, or rather of its various channels. The Mekong empties into the China Sea, very much as the Mississippi discharges into the Gulf of Mexico; it has several mouths, and the whole lower part of its course is divided into canals and bayous, that are very convenient for the natives in the matter of local navigation.