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Rh which. fully deserves being widely known. All taken, his views so well agree with the facts relative to the movements of the atmosphere, and they give such a sound method for further investigation, that they are sure to become for some years to come the leading theory of meteorology. They already have given a strong impulse to theoretical research, and have created a whole literature in Austria and Germany. Roth has already abandoned the mathematical objections he had raised against Ferrel's theory in the Wochenschrift für Astronomie, 1888. The objections raised by Teisserenc du Bort and Supan against the "density surfaces" have been answered by Prof. Davis in Science, and are not shared by the most prominent meteorologists. And the mathematical analysis of Prof. Waldo, Sprung (the author of the well-known Treatise of Meteorology), M. Möller, and Pemter has further confirmed the accuracy of the theory. So also Hildebrandsson's observations of upper clouds (Annuaire de la Société météorologique de France, xxxix, 338), Teisserenc du Bort's high-level isobar?, and Guaran de Trommelin's researches relative to coast winds. The transport of the Krakatoa dust and Abercromby's observations of clouds having rendered the existence of an upper east current very probable on the equator, Pernter has mathematically deduced from Ferrel's theory-the existence of such a current in a belt 4º 45' wide on both sides of the equator, and he therefore has withdrawn the restrictions he had previously made in a lecture (published in Nature, 1892, xlv, 593) in favor of Siemens's views. It must be added that the idea of three superposed currents blowing in spirals may have been suggested to Ferrel by a communication of James Thomson to the British Association in 1857. Such was, at least, the claim raised and developed at some length by the Glasgow professor before the Royal Society in a Bakerian lecture, now published in the Transactions (A. 1892, pp. 653-685). Though Thomson's paper was never published, and only given in a very short abstract without a diagram (the diagram in the Transactions is now published for the first time), the few lines in which his theory was stated (British Association Reports, Dublin, 1857, pp. 38, 39) contained the idea clearly expressed. It is certainly a matter of great regret that James Thomson has not returned to this subject.

Another theory of the general circulation of the atmosphere which is also awakening a good deal of interest among physical geographers was propounded in 1886 by Werner Siemens, and further developed by him in 1890. Siemens did not consider that air might flow down the density surfaces, as supposed by Ferrel and Helmholtz, and admitted by many meteorologists, and he maintained that the source of the energy required for all disturbances of equilibrium in the atmosphere must be looked for in the unequal heating of its different strata by the sun, and in the unequal loss of heat through radiation in space. From these considerations he inferred the existence of an ascending current in the equatorial belt, an upper warm current, and a cold polar current. As to the eastward and westward directions of these currents, he made the very just remark that the energy of rotation of the whole atmosphere must remain constant and unchanged, even though masses of air move from one latitude to