"Of these disastrous hurricanes, it would be fair to state that at least once in every four years, some part of the West Indies is going to suffer a disaster, and once in every twenty years there is a hurricane of such violence as to be reckoned a world calamity."
The botanist rose, took another look at the barometer, and called one of the older servants.
"Send every one into the hurricane wing," he said. "See that the storm lantern is there, filled and lighted. Tell the cook to pour a pail of water on the kitchen fire before she leaves. See, yourself, that every place is securely fastened. The rain will be here in ten minutes."
The negro, who was gray with fright, flashed a quick look of relief at the orders to seek the hurricane wing, and ran off at full speed.
"The first rain-squalls will not be bad," continued the "Old Doc," "and I like to stay out as long as I can, to watch its coming. It will be nearly dark when this one strikes us, though, and there won't be much to see."
"But what starts them, sir?" queried the boy, who had become intensely interested, since the grim phantasmagoria was unfolding itself on sea and sky before his eyes.
"As I have told you, it is the creation of a super-heated and saturated mass of air, only possible in a calm region, such as the Caribbean west of the West Indies, or the doldrum region southeast of them. Let me show you how it happens.
"A region of air, over a tropical sea, little moved by wind-currents, becomes warmer than the surrounding region of air; the air over this region becomes lighter; the lighter air rises and flows over the colder layers of surrounding air, increasing the pressure on that ring and increasing the inward flow to the warm central area where the air pressure has been diminished by the overflow aloft. The overflowing air reaches a point on the outside of the cold air area, when it again descends, and once more flows inward to the center, making a complete circuit. Do you understand so far?"
Stuart knitted his brows in perplexity.
"I—I think so, but I'm not sure," he said. "Then the barometer rose, yesterday, because we were in the cold air area, which became heavier because there was a layer of warm air on the top of it. The storm has moved westward. The cold air section has passed. The barometer is falling now because we're in the region of warm air, which is steadily rising and is therefore lighter. That shows we're nearer to the center. Is that it?"