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the prospect before us of a night's lodging was so discouraging that had it not then been getting quite dark, and being told that we should have to travel several miles before coming to another house, we should have sought for other shelter. The small hut was as usual filled with men, women, and children. Two of the women were lying ill, and one seemed to be dying. There was no room for us in the hut if we had been willing to enter it. We slung our hammocks under a small opensided shed near by and passed a miserable night. A strong cold wind was blowing, and the swinging of the hammocks caused by it kept a number of dogs continually barking and snapping at our hammocks and boots. We rose cold and cramped at daylight, and without waiting to make ready any coffee, saddled our beasts and rode away.

A little maize was grown about this place, and the people told us that sugar thrived, but the plantations of it were small and ill-kept, and everything had a look of poverty and decadence. They said that twenty years ago there was no bush growing around their house. The country was then open grassed savannahs, and there was less fever. Now the bush grows up to their very doors, and they will not take the trouble to cut it down even to save themselves from the attacks of fever. Here, as everywhere throughout the central provinces, deep ingrained indolence paralyses all industry or enterprise, and with the means of plenty and comfort on every side, the people live in squalid poverty.

For four leagues we rode over high ranges with very fine valleys separating them, containing many thatched houses and fields of maize, sugar, and beans. Where

Ch. XVI.] TIGER-BEETLES AND BUTTERFLIES.

299

not now cultivated the sides of the ranges were covered with weedy-looking shrubs and low trees, proving that all the land had at one time been cropped, and this was further shown by the old lines of pinuela fences and ditches that were seen here and there amongst the brushwood. As we got further south the alluvial flats in the valleys increased in size and fertility, and the cultivated fields were enclosed with permanent fences. On some of the ranges we crossed, the rocks were amygdaloidal, containing nests of a white zeolite, the fractured planes of which glittered like gems on the pathway.

Eight leagues from Matagalpa we reached the small town of Tierrabona, where, as the name implies, the land is very good. Every house had an enclosure around it, planted with maize and beans: and though it was evident that the land was cropped year after year, it still seemed to bear well. We stopped at a small brook just outside the town, and ate some provisions we had brought from Matagalpa. Some speckled tiger-beetles ran about the dusty road, and on wet muddy places near the stream groups of butterflies collected to suck the moisture. Amongst them were some fine swallow-tails (Papilio), quivering their wings as they drank, and lovely blue hair-streaks (Theclce). The latter, when they alight, rub their wings together, moving their curious tail-like appendages up and down. Great dragon-flies hawked after flies; while on the surface of still pools “whirligigs(Gyrinidae) wheeled about in mazy gyrations, just as they are seen to do at home.

Savannahs, sparingly timbered, were next crossed ; then we reached one of those level plains, with black soil and blocks of porous trachyte lying on the surface, which are swamps in the rainy season, and have for vegetation sedgy grasses and scattered jicara trees, cactuses and thorny acacias. Up to the time we passed, there had been no rain in these parts, and the plain was dry and bare, with great cracks in the black soil. The grass had not sprung up, not a breath of air was stirring, and the heated air quivered over the parched ground, forming in the distance an imperfect mirage.

Directly overhead the noonday sun hung hot in the hazy sky. As we moodily toiled over the plain, my attention was arrested by a dust whirlwind that suddenly sprang up about fifty yards to our left. The few dry leaves on the ground began to whirl round and round, and to ascend. In a minute a spiral column was formed, reaching, perhaps, to the height of fifty feet, consisting of dust and dry dead leaves, all whirling round with the greatest rapidity. The column was only a few yards in diameter. It moved slowly along, nearly parallel with our course, but only lasting a few minutes. Before I could point it out to Velasquez, who had ridden on ahead, it had dissolved away. I had been very familiar with these air eddies in Australia, and had hoped to carry on some investigations concerning them, begun there, in Central America ; but, though common on the plains of Mexico and of South America, this was the only one I witnessed in Central America.

The interest with which I regarded these miniature storms was due to the assistance that their study was likely to give in the discussion of the cause of all circular movements of the atmosphere, including the dreaded typhoon and cyclone. The chief meteorologists who have discussed this difficult question have Ch. XVI.]

WHIRLWINDS AND CYCLONES.

301

approached it from the side of the larger hurricanes. There is a complete gradation from the little dust eddies up through larger whirlwinds and tornadoes to the awful typhoons and cyclones of China and the West Indies; and it has long been my opinion that if meteorologists devoted their attention to the smaller eddies that can be looked at from the outside, and their commencement, continuance, and completion watched and chronicled, they could not fail to obtain a large amount of information to guide them in the study of cyclonic movements of the atmosphere.

Unless the smaller whirlwinds are quite distinct from the larger ones in their origin, the theories advanced by meteorologists to account for the latter are certainly untenable. According to the celebrated M. Dove, cyclones owe their origin to the intrusion of the upper counter trade-wind into the lower trade-wind current.* More lately, Prof. T. B. Maury has stated that "the origin of cyclones is found in the tendency of the southeast trade-winds to invade the territory of the north-east trades by sweeping over the equator into our hemisphere, the lateral conflict of the currents giving an initial impulse to bodies of air by which they begin to rotate.” Cyclones having thus originated, Prof. Maury considers that they are continued and intensified by the vapour condensed in their vortex forming a vacuum.†

Humboldt had long ago ascribed whirlwinds to the meeting of opposing currents of air. There is this dynamical objection to the theory. The movements of the air in whirlwinds are much more rapid than in any known straight current, such as the trade winds; and it is impossible that two opposing currents should generate between them one of much greater force and rapidity than either. If force A joins with force B, surely force C, the product, must have the power of both A and B. But even if this fundamental objection to the theory could be set aside, the small whirlwinds could not thus arise, as they are most frequent when the air is nearly or quite motionless.

* “Law of Storms,” p. 246. + Quarterly Journal of Science, 1872, p. 418. I "Aspects of Nature,” vol. i. p. 17.

Then, again, when we turn to Prof. Maury's theory that the cyclones, having been initiated by the conflict of contrary currents, are continued and intensified by the condensation of vapour in their vortex forming a vacuum, we find it negatived by the fact that in the smaller whirlwinds the air is dry, and there is consequently no condensation of vapour; yet, in comparison with their size, they are of as great violence as the fiercest typhoon. Tylor describes the numerous dust whirlwinds he saw on the plains of Mexico,* Clarke those on the steppes of Russia, and Bruce those on the deserts of Africa, and nowhere is there mention made of any condensation of vapour. I have seen scores of whirlwinds in Australia, many rising to a height of over one hundred feet; yet there was never any perceptible condensation of vapour, though some of them were of sufficient force to tear off limbs of trees, and carry up the tents of gold-diggers into the air. Franklin describes a whirlwind of greater violence than any of these. It commenced in Maryland by taking up the dust over a road in the form of an inverted sugar-loaf, and

* "Anahuac,” by E. B. Tylor, p. 21.

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