The Naturalist in Nicaragua
into the spiral whirl. The movement was similar to that which occurs when a small opening is made at the bottom of a wide shallow vessel of water: all the liquid moves towards it, and assumes a spiral movement as it is drawn off. The conclusion I arrived at, and which has since been confirmed by further study of the question, was, that the particles of air next the surface did not always rise immediately they were heated, but that they often remained and formed a stratum of rarefied air next the surface, which was in a state of unstable equilibrium. This continued until the heated stratum was able, at some point where the ground favoured a comparatively greater accumulation of heat, to break through the overlying strata of air, and force its way upwards. An opening once made, the whole of the heated air moved towards it and was drained off, the heavier layers sinking down and pressing it out. Sir George Airey has suggested to me that the reason of the particles of air not rising as they are heated, when there is no wind blowing, may be due to their viscosity: and this suggestion is correct. That air does not always rise when heated, appears from the hot winds of Australia, which blow from the heated interior towards the cooler south, instead of rising directly upwards. Sultry, close weather, that sometimes lasts for several days, would also be impossible on the assumption that air rises as soon as it is heated. This explanation supplies us with the force that is necessary to drive the air with the great velocity with which it moves in whirlstorms. The upper, colder, and heavier air is pressing upon the heated stratum, and the u
3o6 THE NATURALIST IN NICARAGUA. [Ch. XVI.
greater the area over which the latter extends, the greater will be the weight pressing upon it, and the greater the violence of the whirlwind when an opening is formed for the ascent of the heated air. There is a gradual passage, from the small dust eddies, through larger whirlstorms such as that at Lough Neagh, to tornadoes and the largest cyclone; every step of the gradation might be verified by numerous examples; and if this book were a treatise on meteorology, it might be admissible to give them; but to do this would take up too much of my space, and I shall only now make some observations on the largest form of whirlstorm—the dreaded cyclone. Just as over the little plain at Maryborough, protected by the surrounding forest from the action of the wind, the heated air accumulates over the surface until carried off in eddies, so, though on a vastly larger scale, in that great bight formed by the coasts of North and South America, having for its apex the Gulf of Mexico, there is an immense area in the northern tropics, nearly surrounded by land, forming a vast oceanic plain, shut off from the regular action of the trade-winds by the great islands of Cuba and Hayti, where the elements of the hurricane accumulate, and at last break forth. In this and such like areas, the lower atmosphere is gradually heated from week to week, and, as in Australia the quivering of the air over the hot ground foreshadows the whirlwind, and in Africa the mirage threatens the simoom, so in the West Indies a continuance of close, sultry weather, an oppressive calm, precedes the hurricane. When at last the huge vortex is formed, the heated atmosphere rushes towards it from all sides, and
is drained upwards in a spiral column, just as in the dust-eddy, on a gigantic scale. Unlike the air of the dust-eddy, that of the hurricane coming from the warm surface of the ocean is nearly saturated with vapour, and this, as it is carried up and brought into contact with the colder air on the outside of the ascending column, is condensed and falls in torrents of rain, accompanied by thunder and lightning. I advanced this theory to account for the origin of whirlwinds in a paper read before the Philosophical Institute of Victoria, in 1857. It was afterwards communicated by the Astronomer-Eoyal to the London Fhilosophical Magazine^ where it appeared in January 1859. A suggestion that I at the same time offered, that the opposite rotation of cyclones in the two hemispheres was due to the same causes as the westerly deflection of the trade-winds from a direct meridional course, has been generally adopted by physicists, and I am not without hopes that the main theory may also yet be accepted; but whether or not, I am confident that a study of the smaller eddies of air is the proper way to approach the difficult question of the origin of cyclones.
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CHAPTER XVII.
Cattle-raising— Don Filiberto Trano's new house — Horse-flies and wasps — Tenstepe — Spider imitating ants — Mimetic species —
Animals with special means of defence are conspicuously marked, or in other ways attract attention—Accident to horse—The Mygale —Illness— Conclusion of journey.
After crossing the tracbytic plain, we reached a large cattle hacienda, and beyond, the river Chocoyo, on the banks of which was some good, though stony, pasture land. We saw here some fine cattle, and learnt that a little more care was taken in breeding them than is usual in Nicaragua. The country, with its rolling savannahs, covered with grass, is admirably suited for cattle-raising, and great numbers are exported to the neighbouring country of Costa Rica. Scarcely any attention is, however, paid to the improvement of the breeds. Few stations have reserve potreros of grass. In consequence, whenever an unusually dry season occurs, the cattle die by hundreds, and their bones may be seen lying all over the plains. Both Para and Guinea grass grow, when planted and protected, with the greatest luxuriance and the latter especially forms an excellent reserve, as it grows in dense tufts that cannot be destroyed by the cattle. When not protected by fencing, however, the cattle and mules prefer these grasses so much to the native ones, that they are alwa.ys close- cropped, and
when the natural pasturage fails there is no reserve of the other to fall back on. I planted both the Para and Guinea grasses largely at the mines and at Pital, and we were able to keep our mules always in good condition with them.
About four o'clock in the afternoon our animals were getting tired, and we ourselves were rather fatigued, having been in the saddle since daylight, with the exception of a few minutes' rest at Tierrabona. We halted at a thatched cottage on some high stony savannah land, and were hospitably received by the peasant proprietor, Don Filiberto Trano. He informed us that we had entered the township of Teustepe, and that the town itself was eight leagues distant. The family consisted of Don Filiberto, his wife, and four or five children. They had just prepared for their own dinner a young fowl, stewed with green beans and other vegetables, and this they placed before us, saying that they would soon cook something else for themselves. We were too hungry to make any scruples, and after the poor, coarse fare we had been used to, the savoury repast seemed the most delicious I ever tasted. I think we only got two meals on the whole journey that we really enjoyed. This was one, the other the supper that the padre's housekeeper at Palacaguina cooked for us, and I have recorded at length the names of the parties to whom we were indebted for them.
Don Filiberto had about twenty cows, all of which that could be found were driven in at dusk, and the calves tied up. As they came in, the fowls were on the look-out for the garrapatos, or ticks; and the cows, accustomed to the process, stood quietly, while they flew up and picked them off their necks and flanks. The calves are
3IO THE NATURALIST IN NICARAGUA. [Ch. XVII.
always turned out with the cows in the morning, after the latter are milked, so that if not found again for some days, as is often the case in this bushy and unenclosed country, the cows are milked by them and do not go dry. They give very little milk, probably due to the entire want of care in breeding them. It is at once made into cheese, which forms a staple article of food amongst the poorer natives.
The small house was divided into three compartments, one being used as a kitchen. It was in rather a dilapidated condition, and Don Filiberto told me that he was busy building a new residence. I was curious to see what progress he was making with it, and he took me outside and showed me four old posts used for tying the cows to, which had evidently been in the ground for many years. " There," he said, " are the corner-posts, and I shall roof it with tiles." He was quite grave, but I could not help smiling at his faith. I have no doubt that, as long as he lives, he will lounge about all day, and in the eveuinsf, when his wife and children are milking the cows, will come out, smoke his cigarette, leaning against the door-post of his patched and propped-up dwelling, aud contemplate the four old posts with a proud feeling of satisfaction that he is building a new house. Such a picture is typical of Nicaragua.
Don Filiberto told us that there was a limestone quarry not far from his house; and as I wished to learn whether it occurred in beds or veins, I proposed next morning to walk over to it, but be said we should need the mules to cross the river. Thinking, from his description, that it was only about a mile distant, I started on mule-back with him; but after riding fully a league, dis-
covered that he actually did not know himself where it was, but was seeking for another man to show him. We at last arrived at the house of this man. He was absent. A boy showed us a small piece of the limestone. It was concretionary, and I learnt from him that it occurred in veins. I was vexed about the time we had lost, and the extra work we had given the poor mules; my only consolation was that as we rode back I picked a fine new longicorn beetle off the leaves of an overhanging tree. When we came to settle up with our host he proposed to charge us twenty-five cents, just one shilling, or fourpence each. They had given us a good dinner and put themselves to much inconvenience to provide me with a bedstead, and this was their modest charge. Nor did they make it with any expectation that we would give more. It is the universal custom amongst the Mestizo peasantry to entertain travellers; to give them the best they have and to charge for the bare value of the provisions, and nothing for the lodging. We could so depend upon the hospitality of the lower classes that every day we travelled on without any settled place to pass the night, convinced that we should be received with welcome at any hut that we might arrive at when our mules got tired or night came on. The only place in the whole journey where we had been received with hesitation was at the Indian house a day's journey beyond Olama. There the people were pure Indians, and other circumstances made me conclude that the Indians were not so hospitable as the Mestizos. We finally started about nine o'clock and rode over dry savannahs, where, although there was little grass, I
was told that cattle did well browsing on the small brushwood with which the hills were covered. All the forenoon we travelled over stony ranges and dry plains and savannahs. At noon we reached the dry bed of a river and crossed it several times, but could find no water to quench our thirst, whilst the sun shone down on us with pitiless heat. About one o'clock we came to some pools where the bed of the river was bare rock with rounded hollows containing water, warm but clean, as the cattle could not walk over the smooth slopes to get at it. Here we halted for an hour and had some tiste and maize cakes, and cut some Guinea srrass that grew amongst the rocks for our mules. Over the heated rocks scampered brown lizards, chasing each other and revelling in the sunshine. Butterflies on lazy wings came and settled on damp spots, and the cicada kept up his shrill continuous monotone, but not so loudly as he would later on when it got cooler. The cicada is supposed by some to pipe only during midday, but both in Central America and Brazil I found them loudest towards sunset, keeping up their shrill music until it was taken up by night-vocal crickets and locusts. We were returning parallel to our course in going to Segovia, but several leagues to the westward, and this made a wonderful difference in the climate. There we were wading through muddy swamps and drenched with continual rains. Here the plains were parched with heat, vegetation was dried up, and there was scarcely any water in the river beds. The north-east trade-wind, before it reaches thus far, gives up its moisture to the forests of the Atlantic slope, and now