"We will have it in less than two hours," said the scientist. "It is a good thing that all afternoon I have had the men and women on the place nailing the shutters tight and fastening everything that can be fastened. We may only get the edge of the hurricane, we may get the center. There is no telling. An island is not like a ship, which can direct its course so as to escape the terrible vortex of the center.

We've got to stay and take it."

"But has every hurricane a center?" queried the boy, a little relieved by the thought that the storm would not come for two hours. In that time, he foolishly thought, it might have spent its force. He did not know that hurricanes possess a life of their own which endures not less than a week, and in one or two cases, as long as a month.

"You wouldn't ask whether every hurricane has a center," the scientist replied, "if you knew a little more about them. As there is nothing for us to do but wait, and as it is foolish to go to the hurricane wing until the time of danger, I might as well explain to you what a hurricane really is. Then, if you live through it----" Stuart jumped at the sudden idea of the imminent danger--"you'll be able to write to your paper about it, intelligently."

"I'd really like to know," declared Stuart, leaning forward eagerly.

"Well," said his informant, "I'll make it as simple as I can, though, I warn you, a hurricane isn't a subject that can be explained in a sentence or two.

"You know that summer and winter weather are different. You ought to be able to see that summer and winter winds are different. The difference in seasons is caused by the respective positions of the northern and southern hemispheres to the sun. The greater the heat, the greater the atmospheric changes. Hurricanes are great whirls caused by violent changes of the air. Therefore hurricanes come only in the summer."

"That's clear and easy!" declared the boy, delighted that he was able to follow the explanation.

"Now, as to why hurricanes strike here and nowhere else. I'll try and explain that, too. There is a belt of ocean, just north of and on the equator, known as the 'doldrums,' where it is nearly always calm, and very hot. There is also a belt of air running from Southern Europe to the West Indies where the north-east trade winds blow all the year round. Between this perpetual calm of the doldrums and the perpetual wind of the trades is a region of atmospheric instability.

"Now, consider conditions to the west of us. The Caribbean Sea and the Gulf of Mexico, together, form what is almost a great inland sea with the West Indian Islands as its eastern sh.o.r.e. The trade winds do not reach it. The Pacific winds do not reach it, for they are diverted by the high ranges of Central America. The winds from North America do not reach it, because these always turn northwards on reaching the Mississippi Valley and leave the United States by the St. Lawrence Valley.

"So, Stuart, you can see that the Caribbean Sea and the Gulf of Mexico have over them, in summer, a region of air, little disturbed by wind, not far from the Equator and which, therefore, becomes steadily heated and steadily saturated by the evaporation from the body of water below."

"Yes," agreed the boy, "I can see that."

"Very good. Now, such a steady heating of one section of air is bound to disturb the balance of the atmosphere. This disturbance, moreover, must be acted upon by the rotation of the earth. Just as all the weather in the United States comes from the west and travels eastwards, so the track of hurricane origins travels eastwards during the course of a summer.

"For this reason, West Indian hurricanes in June generally have their origin west of Jamaica, July hurricanes east of Jamaica, August hurricanes in the eastern Caribbean, September hurricanes in the Atlantic east and south of the West Indies, and October hurricanes far out to sea, perhaps even as far as half-way to the Cape Verde Islands on the sh.o.r.es of Africa. This hurricane which is approaching, is from the direction of East-South-East, judging from the barometer and other conditions, and probably had its cradle a thousand or more miles away."

"And it hasn't blown itself out?"

"Far from it. It is only gathering strength and violence. Not until it twists off on its track will it begin to diminish. For hurricanes follow a regular track, an invisible trail marked out for them in the sky."

"They do!"

"Yes, all of them. This track is shaped like a rounded cone, or, more often, like a boomerang, with a short arm running north-westwards to its place of turning and a long arm running northeastwards until its force is spent. The point of turning is always in the West Indies zone.

As the storm is at its worst at the point of turning, it is always in the West Indies that the hurricane is most destructive.

"No matter where they start, West Indian hurricanes always sweep north-westward until they have crossed the line of the West Indies and then wheel around sharply to the north-east, skirting the United States coast. Some strike Florida. A good many run along the coast and hit Hatteras. Some never actually touch the continent at all, and only a few ever strike inland. But some part of the West Indies is. .h.i.t by every one of them."

"Are they so frequent?"

"There's never a year without one or more. There have been years with five or six. Of course, some hurricanes are much more violent than others. Their destructive character depends a good deal, too, on the place where their center pa.s.ses. Thus if, at the moment of its greatest fury, the full ferocity of the whirl is expended on the ocean, not much harm is done. But if it should chance to descend upon a busy and thriving city, the loss of life will be appalling.

"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 ma.s.s 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 pa.s.sed. 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?"

The scientist tapped his fingers on the arm of his chair in pleased appreciation.

"Very good," he said, "you are exactly right. And, from now on, the barometer will drop suddenly, for the whirl of the wind will make a partial vacuum in the very center of the hurricane."

"But I don't see what makes it whirl," protested the boy. "If it goes up in the middle, flows over at the top and comes down at the outside and then flows into the middle again, why could it not keep on doing that all the time, until the balance was put straight again?"

"It would," the scientist agreed, "but for one thing you have forgotten."

"And what's that?"

"The rotation of the earth."

A single drop of rain fell, then another, making a splash as large as a twenty-five cent piece.

"Now see it come!" said the scientist.

As though his words had summoned it, a liquid opacity, like a piece of clouded gla.s.s, thrust itself between their eyes and the landscape. So suddenly it came that Stuart actually did not realize that this was falling rain, until, looking at the ground, he saw the earth dissolve into mud before his eyes and saw the garden turn into what seemed like the bed of a shallow river. The wind whistled with a vicious note. The squall lasted scarcely a minute, and was gone.

"That's the first," remarked the boy's informant. "We'd better get under shelter, they'll come fast and furious soon."

Pa.s.sing through a low pa.s.sage connecting the house with the hurricane wing, Stuart noticed that, beside the ma.s.siveness of the structure, it was braced from within.

"In case the house should fall on it," the scientist observed, noting Stuart's glances. "I've no wish to be buried alive. In any case, I keep crowbars in the wing, so that, in case of any unforeseen disaster, a breach could be made in the walls and we could get out that way."

They entered the hurricane wing. It was not as dark as Stuart had expected. The scientist, anxious to observe the storms when they should come, had built into the wall two double dead-eye windows, such as are used in the lower decks of liners and which can resist the impact of the heaviest waves.

The crimson light had gone. The vivid sunset reflections, now thrown back from the black arch, yet gave a reddish smokiness to the livid and sickly green which showed, from time to time, beneath the underhanging ma.s.ses of inky black. The sky to the north and to the south had a tortured appearance, as though some demon of a size beyond imagining were twisting the furies of the tempest in his clutch.

"You asked," said the scientist, speaking in the hurricane wing, as quietly as he had on the verandah, and paying absolutely no heed to the moaning and praying of the negroes huddled in the darkest corner, "what makes a hurricane whirl. Yet, in the heavens, you can see the skies a-twist!"

A second rain-squall struck. Thick as were the walls, they could not keep out the wailing shriek of the wind, nor the hissing of the rain, which flashed like a continuous cutting blade of steel past the windows.

The hurricane wing could not rock, it was too low and solidly planted for that, but it trembled in the impact.

After a couple of minutes came a lull, and Stuart's ears were filled with the cries and howling of the frightened negroes, not a sound of which had been audible during the squall. The scientist continued his talk in an even voice, as peacefully as though he were in his study.

"You asked what could set the skies a-twist. I told you, the earth's rotation. For, Stuart, you must remember that a hurricane is not a small thing. This heated region of the air of which we have been speaking, with its outer belt of cooler air, and the descending warm air beyond, is a region certainly not less than five hundred miles in diameter and may be a great deal more.