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return it is preferable to sail from Australia eastward past Cape Horn.-Bulletin Hebdomadaire, XVI., 28.

ON THE THEORY OF TORNADOES AND WATERSPOUTS. In a general investigation into the phenomena of the cyclonic movements of the atmosphere, Cousté states that, starting from the general principle that there exists at the centre of the cyclone a column of ascending gyrating air, he deduces logically the following conclusions: First, the whole columu must rotate about its geometrical axis, in the opposite direction to the gyration. Secondly, there must be a vertical oscillating movement by which the column alternately rises above and descends to the ground, carrying devastation before it. Thirdly, there must be a movement of translation, which is accomplished, as shown by observation, with a rapidity varying between twenty and seventy miles per hour. These three movements are derived from the centripetal forces developed by the gyration which give rise to lateral streams of air, which he calls radiating filaments, in opposition to those interior filaments which gyrate within the helix, and which he calls helicoidal filaments. These radiating filaments of air form a nappe which incloses the whole convex surface of the tornado, and they constitute the wall of the column, which wall, for a given state of dynamic equilibrium, is as solid as if it were a solid matter of sheet iron, for example, yet is permeable and indefinitely extensible according to the conditions of its dynamical equilibrium. These filaments are directed from below upward, following the tangent to the helix farthest from the axis, producing reactions similar to those in turbine wheels. Cousté has also determined the character of the movement along the surface of the earth; this is, in general, of a spiral nature, at least for waterspouts properly so called, which appear as truncated columns, suspended from a cloud. But for those tornadoes whose trajectory is nearly rectilinear, and for the cyclones and hurricanes whose birth takes place upon the ocean the trajectory takes the form of a parabola, whose summit is always near the side of some large continent. These remarkable peculiarities he explains by the following principles, which he has deduced from his theory: First, if the angular velocity of gyration increases or diminishes—that is to say,

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if the energy of the meteor increases or diminishes—the curvature of the trajectory will rapidly increase or diminish. Second, the energy of the meteor is greater in proportion as the air which it draws in is dryer, or has a low relative humidity.

In reference to the rigidity of the column of the waterspout, Cousté says that the equilibrium between the reacting forces due to the radiating filaments exists even when the various diameters of the waterspout are made unequal by the pressure of the wind. The normal components of the movement of the wind bave the effect substantially of pressing the helicoidal filaments together normally to the surface, thus concurring to maintain the rigidity of the column, to which the gyratory movement contributes. This we can easily comprehend if we compare the column to the gyroscope of Foucault; for the column of the waterspout can be likened to a series of gyroscopes having a common vertical axis, the revolving disks being formed by parallel horizontal sections of the column. In the case of the tornado the disks are gascous, it is true, but the gas is kept in its place by the normal components of the forces; and if they have but little mass, they are, on the other hand, actuated by very rapid velocity of rotation.

Theoretically, a waterspout is a collection of parallel whirling tubular masses; a complete illustration of this is, however, very rare in nature, though such have been figured by Mouchez and others.- Nouv. Meteorologiques, 1875, p. 61, 81.

TREATISE ON METEOROLOGY BY MOHN. An important treatise on meteorology has lately been published by Mohn, the distinguished chief of the Norwegian Weather Bureau. It constitutes an original German edition, with many improvements, of the work published two year's ago in Norwegian, under the auspices of the Society for the Dissemination of Useful Knowledge. As was to be expected, Mohn has especially developed in this work the ideas that he has for some years defended with reference to the influence of moisture in the air upon the movements of storm areas. His whole work, in fact, corresponds to the present condition of meteorology, except, possibly, that the attempt to provide a purely popular explanation of the mechanical

laws controlling the movements of the atmosphere is somewhat unsatisfactory to the professional student.


CALCULATIONS. Mr. Scott, of the Meteorological Office in London, reports that perfect success has attended the adoption of Amsler's planimeter in the calculation of the average daily temperatures. The instrument was applied directly to the photographic sheets of the self-recording instruments, and was also applied to the reduced copies of these sheets, as published in the quarterly weather reports, and the results thus obtained check each other satisfactorily.

RAINFALL AND SOLAR SPOTS. In the monthly notices of the Meteorological Society of Mauritius, Mr. Meldrum, of that island, concludes that, whether we take the annual rainfall for the largest possible portion of the globe for short periods, or for a small portion of the globe for a longer period, we arrive at the same result: viz., an increase of rain at or near the epochs of maximum sun spots, and a decrease of rain at or near the epochs of minimum sun spots. The exceptions to this law are few and trifling, and disappear from the results as the inquiry is made to cover more extended portions of the earth's surface and a longer interval of time.-12 A, X., 418.

THE DRY SEASON OF BRAZIL. As an illustration of the extreme dryness of the soil during the dry season in Brazil, it is stated that, in June, all vegetation ceases, the seeds being then ripe or nearly so. In July the leaves begin to turn yellow and fall off; in Angust an extent of many thousands of square leagues presents the aspect of a European winter, but without snow, the trees being completely stripped of their leaves; the plants that have grown in abundance in the wilderness drying up, and serving as a kind of hay for the sustenance of numerous heads of cattle. This is the period most favorable for the preparation of the coffee that grows upon the mountains. The beans are picked and laid on the ground, which gives forth no moisture, but on the contrary absorbs it, and being surrounded by an atmosphere possessing the same desiccating properties, the coffee dries rapidly without becoming mouldy.-The Empire of Brazil, p. 23.


The Signal Service observer on the summit of Pike's Peak reports that the local storms there experienced originate over the parks to the westward, on hot afternoons. On one occasion he was favored with an excellent view of the interior structure of the clouds of a tornado, when he observed that while the cloud-bearing currents of air float toward the centre they had a decided downward movement, but that masses of smoke-like vapor rapidly ascended through the interior funnel.

THE FREQUENCY OF STORMS. Köppen has made an investigation of the frequency with which barometric minima occur in Northwestern Russia. He finds that during the years 1872 and 1873 107 cyclones occurred, lasting altogether 393 days, the mean duration of each one of these being about three and seven-tenths days. According to a table given by him, if a barometric depression is just leaving the observer, it is probable that within one or two days a second cyclone will occur. If, on the other hand, many days have elapsed since the passage of a depression, and uniform and high pressure has prevailed, then the probability that a new depression will arrive within twenty-four hours is diminished by one half.—19 C, VIII., 86.

THE PASSAGE OF STORMS TO EUROPE FROM AMERICA. The great storm that passed over the coast of Germany on the 22d of November, 1873, has been investigated by Prestel, who concludes that it was identical with the storm that left the United States on the 18th day of the same month, which was at the time distinguished as a severe disturbance. In his remarks upon this subject, Mr. Prestel possibly goes too far in attempting to show that certain storms recur at certain epochs of the moon, but he is nevertheless probably nearly correct in saying that many attempts to trace lunar and other periods in the changes of the weather have, as yet, had only a negative result, because we have considered only


observations referring to a single place. It may, in fact, be stated that the currents of the atmosphere never follow precisely the same routes, nor have precisely the same effects; consequently individual places on the earth's surface are at one time within, at another time beyond, their influence, and the weather at one point shows nothing of the periodicity that may possibly regulate the movement of the current itself. Under these circumstances, the observed local readings of the barometer, temperature, rainfall, etc., can not be expected to follow any such laws of periodicity as may possibly be followed by the atmosphere as a whole. The periodicity of atmospheric phenomena can, actually, only be properly investigated when we combine the geographical details with the element of time. Following this idea, Prestel feels justified in the conclusion that certain storms which have visited the earth have passed over nearly the same paths at their successive apparitions, which latter always occur when the moon returns to about the same position with reference to the earth. As this can only happen every nineteen years, it follows that the storms of 1873 are to some extent a repetition of those of 1854.-Zeitschrift für Meteorologie, IX., 224.


NORWAY. Professor Karsten, in an address delivered before the Society of German Scientists and Physicians, stated that the comparatively mild temperature which characterizes the west coast of Norway is not, as has been hitherto considered, the effect of the Gulf Stream, but of a warm current of water that leaves the Baltic when the cold weather sets in.—13 A, November 21, 1874, 560.


Messrs. Mitchell and Buchan have made a very thorough study of the influence of the seasons on human mortality, basing their investigations on thirty years of observations at London. The greatest mortality is above the average from November to April; falls to a minimum at the end of May; then rises to a maximum on the third week of July, continuing there until the second week of August, and falling thence to a secondary minimum in October. Deducting the summer

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