"What becomes of the north-east trade-wind when it reaches the end of its journey, and where is that end think you, my boy?" asked Captain Frankland. Jerry looked puzzled, and I had not a notion to give forth on the subject. "I will try and explain the matter; but when you can obtain a work, written by Lieutenant Maury, of the American navy, you will comprehend the subject much better," said Captain Frankland. "There are three calm regions or belts surrounding the globe--one under the equator, and one in each hemisphere, under the tropics of Cancer and Capricorn, which you have heard spoken of as the horse latitudes. Between these two belts blow the north-east and south-east trade-winds, meeting at the equatorial belt. Now, when they get there, instead of causing a whirlwind, the excessive heat causes the particles of which they are composed to expand and rise, gradually producing a calm. After rising a certain height, they again commence moving round the globe. Which course they took it was difficult to say, till we find these clouds of red dust carried along in an upper region of the atmosphere from south-west to north-east; for not only are they found here, but up the Mediterranean and across Switzerland. They are raised into the atmosphere probably by whirlwinds which occur during the vernal equinox, which is the dry season, from the valley of the lower Orinoco. Thus, had a label been attached to each particle of which the wind is composed, to show whence it came, the problem could not have been more perfectly solved." While the captain was speaking, Mr McRitchie came on deck, and collected in sheets of paper a quantity of the red dust. "It will be prized by some of my scientific friends at home," he observed; "and even the unscientific may value a substance which has travelled half round the globe high up in the atmosphere." "There is another substance, doctor, which travels farther, and is of much greater use to man; and yet how little he troubles his head to consider where it comes from," remarked the captain. "What do you mean, sir?" asked the doctor, a little puzzled I thought.