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Bezold, who is led to the conclusion that the phenomena of thunder-storms show, in general, during the summer months in the northern hemisphere, two maxima. These maxima approach each other in proportion as we go away from tropical regions. They are scarcely distinguishable in Germany, but are recognized by taking advantage of the observations in Barnaul and St. Petersburg. Of all the stations examined, only one, Katherineburg, shows a single maximum, and the climate of this station is certainly, on many accounts, to be considered as influenced less by the meteorological conditions of the tropical zones than almost any other point in Europe. It is considered therefore that we shall not go far wrong if in the two maxima of electric phenomena, which is so plainly seen in Europe, we recognize an echo of the two summers, or the two maxima of temperature experienced in the tropical zones. - Sitzb. K.-B. Akad. der Wissens., Munich, 1875, 220.

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CONSTITUTION OF THE ATMOSPHERE OVER THE LIBYAN

DESERT. Pettenkofer has examined the air brought back from the Libyan Desert by Dr. Zittel, the companion of Dr. Rohlfs, with respect to the quantity of carbonic-acid gas contained therein. He finds that the atmosphere in the desert has precisely the same chemical constitution as in Germany, where the quantity of carbonic-acid gas varies between two and a half and five ten-thousandths. He has also examined the air contained in the water of springs, and finds the same agreement. - Sitzb. K.-B. Akad. der Wissens., Munich, 1874, IV., 339.

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EFFECT OF TIDES ON THE ROTATION OF THE EARTH. Mr. Tylor, in some remarks on a new theory of tides and waves, advocates the view that the level of the ocean is nearly represented by high-water mark on coasts and bays where there is free access of the tide, or in a channel without a constant flow. He states that he entirely disbelieves in tidal action having the smallest effect on the rotation of the earth, and that the assumption of a great heap of water traveling in one direction is a gross error. He also suggests that some geological difficulties, such as the evidence that tides

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during the quaternary periods were three or four times as large as at present, may be explained by periodic changes of position of part of the interior of the earth, rather than by supposing great changes in the distance of the moon from the earth.-7 A, XLVIII., 204.

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THE DIMINUTION OF WATER IN SPRINGS, RIVERS, AND WELLS.

The report of Wex on the diminution of water in wells, etc., presented to the Austrian government in 1873, was followed by the appointment, at his request, of a commission of engineers, to whom was intrusted the duty of carefully investigating the points raised by the author in his learned menoir. So important did the matter seem, on account of the long-matured views presented by Wex, that the commission decided to fully investigate the matter. The rivers Danube, Rhine, and Elbe were respectively assigned to certain engineers, while others made measurements in relation to the Alpine streams and the glaciers, and others again undertook a special study of the meteorological questions involved.

During the past two years the committee has accumulated a great mass of valuable material, and has presented a very elaborate report on the subject, which was published in a recent number of the Journal of the Austrian Engineers and Architects' Association. The many details given in the report of the committee may perhaps be summed up as follows: First, an increase is proved in the frequency and the heights of floods in the rivers, as well as a diminution in the altitude of the mean of low waters in most of the rivers and streams of cultivated lands; and all the evil consequences depicted by Wex follow thereon; second, the cause of the injurious changes in the regimen of the rivers, in the drainage of swamps and morasses, in the sinking of lakes and dikes, is principally to be found in the destruction of the forests. These two points having been abundantly established by a large corps of able engineers, the conclusions and the recommendations of the Austrian committee become of the greatest interest to other nationalities, since it is evident that the same causes are at work elsewhere, and especially so in America, to bring about the same disastrous results. The committee recommend that on the one hand exact measures be made of all that relates to the hydrography of the

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land, implying, of course, the establishment of a permanent hydrographic commission; second, that the most stringent laws be enacted to prevent the willful unnecessary destruction of forests; and, third, that every thing be done that is possible to encourage the planting and cultivation of forests; and, finally, that the streams and rivers, as they at present exist, be connected into a system by means of which the height of the water may be regulated, and the traffic therein facilitated as much as possible.—Zeitschrift des Ingen.- und Architekten-Vereins, p. 137.

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MAGNETIC PARTICLES IN ATMOSPHERIC DUST, The atmospheric dust examined by Tissandier was collected in several different ways, and in every case was found to contain minute magnetic ferruginous particles. Part of the dust was collected upon sheets of paper exposed to the air for many days; in another series of experiments air was passed through pure water, and the latter evaporated over sulphuric acid in vacuo. Other samples were collected from rain and snow water, in one instance, particularly, from snow gathered upon Mont Blanc, 2712 meters above sea level. The ferruginous particles occurring in these various specimens of dust were extracted by means of a magnet and subjected to microscopic examination. In diameter they rarely exceed Tøj of a millimeter, and appear to consist of magnetic oxide, resulting from the combustion of iron, Tissandier believes them to be of cosmical, not terrestrial origin, and regards them as the débris of meteoric masses.—6 D, 1875, Oct. 4.

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ON THE HEIGHT OF THE AURORA BOREALIS.

In discussing observations made by himself upon the aurora during the Swedish expedition of 1868 to the North Pole, Professor Lemström, of Helsingfors, states that although Loomis, and even Bravais, believed that observations which give a very low height to the aurora are erroneous, and the result of some illusion, yet he can not agree with them; and he offers in support of his opinion, among other things, the phenomena observed on the 18th of October, 1868, at the entrance of the Norwegian Archipelago, when the whole horizon was covered with rays which were soon united around the magnetic pole, forming a regular crown.

All the phenomena that he has observed and described in regard to the illuminated edges of clouds show very plainly that in these cases the polar light was produced in the region of the clouds, and even lower. We know by numerous observations that the number of thunder and lightning storms diminishes considerably as we approach the polar regions, so that they no longer occur in the latitude of 70°. Must we then conclude that in these regions the clouds are completely deprived of electricity? Certainly not; but only that the electrical discharges are made in some other way. In these high latitudes, electricity is discharged not only by clouds, but also directly by damp air, as takes place in the winter in the temperate zones. A great many direct observations prove the existence of slow discharges of this nature; and a very remarkable confirmation is given by Angström, who on one occasion proved the presence in the spectrum of the yellow or auroral ray over almost the entire sky. - Smithsonian Rep., 1874, 232.

RELATION OF THE PHASES OF THE MOON TO ATMOSPHERIC

PRESSURE. In a memoir by Ludicke, he shows that the atmospheric pressure diminishes with the waxing and increases with the waning moon. The pressure is less at the perigee than at the apogee, and in general the effect of the moon upon the atmosphere is the inverse of that which it produces upon the ocean. The observations on which his results are based extend over eight years; but the actual effect of the moon upon the barometric pressure, although decided, is yet exceedingly small.

IRON IN ATMOSPHERIC DUST. As the result of an examination of atmospheric dust, the mineral residuum from the melting of snow, etc., with special reference to iron in the atmosphere, Mr. Young remarks that this metal, in appreciable quantity, occurs in the dust accumulated in old buildings during a long period of time, and is usually of a globular form, showing that it has been formed at a high temperature. The iron as found in melted snow is much more irregular in shape, and is more abundant in proportion when the snow is collected at the lower levels. Mr. Young has not been able to establish the occurrence of iodine in snow-water, as claimed by other experimenters. — 6 B, 1876, July 17, 242.

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SCHOTT'S TABLES OF ATMOSPHERIC TEMPERATURE. An important work has recently been issued by the Smithsonian Institution, entitled "Tables of Atmospheric Temperature in the United States," by C. A. Schott. The special result reached by Mr. Schott, in reference to secular variations of temperature, are of such general interest and importance that we quote some of his conclusions: “The character of the secular variation in the mean annual temperature is that of a series of irregular waves representing a succession of warmer and colder periods. These undulations, when computed for a number of stations exposed to similar climatological conditions, are seen to have approached to parallelism over large tracts of country. There is, however, nothing to countenance the idea of any permanent change in climate having taken place, or being about to take place. During the last ninety years the thermometric records of mean temperatures show no indication whatever of a sudden rise or fall.” A similar conclusion has also been reached by Mr. Schott in reference to the rainfall. “If, now, we group together stations properly located, the undulations become well marked, the interval between successive maxima or minima being about twenty-two years on the Atlantic coast and seven years in the Mississippi Valley. Even these undulations, however, are not sufficiently regular to serve as a basis of prediction. A comparison of the temperature with the frequency of the solar spots show, so far as these records go, no traces of any direct connection between these phenomena. On comparing the temperatures and the rainfalls, there seems some ground for concluding that years of high mean temperature have also a large rainfall. And, again, for years of low temperature the winds appear to be northerly, and for high temperature southerly. The connection between the temperature, the rain, and the winds must, however, be ultimately considered as due to variations in solar radiation."

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