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-Royal to the "London Philosophical 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. CHAPTER 17. Cattle-raising. Don Filiberto Trano's new house. Horse-flies and wasps. Teustepe. 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.