"The monsoon winds are known all over the Eastern seas, from the coast of China to the shores of Arabia. Their periods of blowing are so well understood that the steamship captains know exactly when they may be expected, and their voyages are arranged accordingly. On the printed time-tables of all the steamship companies you will find 'monsoon allowances;' and on the coast of India there are certain ports where the ships cannot touch at all when the monsoon is unfavorable. The Peninsular and Oriental Steam Navigation Company allows four days for its ships between Suez and Shanghai when the monsoon is against them, and one day on the voyage between Hong-kong and Yokohama. The French mail steamers have the same allowances. In August, when the south-west wind is blowing, a steamer goes from Hong-kong to Yokohama in seven days; but in April, when the wind is the other way, she is allowed eight days for the voyage. "The monsoons are caused just like all other winds--by the heated air rising and cold air rushing in to fill its place. In summer, when the sun is over Asia and the ground becomes heated to a high degree, the air rises, and the cooler air from the south comes to fill up the space. This makes the south-west monsoon; and when the seasons change, and it becomes summer in the southern hemisphere and winter in the northern, then the air goes the other way, and the wind blows from the north-east. This is the north-east monsoon. [Illustration: RUNNING BEFORE THE TRADE-WIND.] "The monsoons should not be mistaken for the trade-winds which blow in the Atlantic and Pacific oceans, and also in the southern part of the Indian Ocean. The monsoons change every half year, as I have explained, but the trade-winds blow regularly all the year round in the same direction. They are caused by the warm air rising from the vicinity of the equator, owing to the great heat, and the cool air rushing in from the south and from the north. The trade-winds have been so named because they have been of great assistance to commerce; sailing-ships can calculate their voyages with great accuracy by means of these winds, and I have read and heard of ships in the trade-winds that sailed for twenty or thirty days without moving a rope or altering the position of a sail. They went along ten or twelve miles an hour, and the sailors had nothing to do but lie around the deck or in the forecastle, and amuse themselves in any way they liked." Fred read his production to the Doctor and Frank as they sat on deck, the second day of the voyage from Hong-kong. Frank wanted a copy, but took the precaution to ask the Doctor if it was all correct. The latter said it was entirely, so far as he knew, but it did not tell the whole story. Thereupon Frank set at work to find something additional, and in the course of an hour or so he offered the following post-script to the essay of his cousin: