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so much greater in the antarctic than in the arctic regions. One of the most important practical results attending the publication of Rikatcheft's memoir is the stimulus that it bas given, and probably will give, to the application of Rühlmann's methods for the determination of altitudes by means of the barometer. According to this author, we should, if possible, employ only monthly or annual means for determining altitudes barometrically, and should (especially when only a few observations are available) employ the readings of the barometers at two or more known stations in order to deduce therefrom the temperature of the air without relying on thermometric observations. From the isobaric charts given by Rikatcheff we can find the average normal height of the barometer for any month whatever in Eastern Russia within less than one twenty-fifth of an inch, and in Western Russia within one fiftieth of an inch, and the average annual mean pressure of any point in Western Russia within one onehundredth of an inch.— Wild's “Repertorium,” IV., art. 6.
ON THE TIDES IN THE ROADSTEAD OF FIUME. In a recent prize essay by Professor Stahlberger on the tides in the roadstead of Fiume, the author, from a study of observations extending over thirty-seven lunations made by means of a self-recording tide-gauge, shows that with a rising barometer there occurs a diminished height of water, and, conversely, with a diminished pressure an increased height of water. In connection with the barometric pressure, the northerly and southerly winds exert their influence to respectively increase and diminish the water level. With the southern winds, the curves showing the height of the water are comparatively smooth and regular. With the northerly winds, however, they vary according to the strength of the wind, showing greater or less irregularities. The periodic movements of the ocean level are subject to two principal oscillations, depending on the moon, and two other principal ones depending on the sun. The regularity of this phenomenon is complicated very much by the fact that the tidal waves that reach Fiume come from the Mediterranean. The reason why the twenty-four-hour oscillation is comparatively large, while the twelve-hour is weak, depends, according to Stahlberger, upon the configuration of the Adriatic Guit:
It is probably thus that we explain the fact that the ratio between the mean influence of the sun and the moon is, for Fiume, 1.86, instead of its theoretical value, 2.55, as was to be expected. The known effects of the tides at Trieste are similar to those at Fiume. “Mittheilungen” Austrian Hy. drographic Office, 1874, 723.
THE DIURNAL AND ANNUAL PERIODICITY OF THE MOISTURE
IN RUSSIA. Professor Wild, of St. Petersburg, has communicated an extended investigation into the atmospheric humidity as recorded at the Russian meteorological stations, a study which may be looked upon as a continuation of his previous memoir on tbe distribution of cloudiness in Russia. He finds that the diurnal changes in relative humidity are intimately connected with diurnal changes in temperature, so that a maximum of temperature coincides with a maximum relative humidity, and vice versa. Furthermore, the amplitude of the daily oscillation in humidity has direct relation to the changes in temperature. The diurnal changes in absolute humidity have, however, a much less decided connection with the temperature. The annual changes in both absolute and relative humidity are given by monthly means for forty-one stations. The annual changes in absolute humidity may be directly connected with the temperature. The causes of the various annual changes in bumidity in different portions of Russia are explained by Wild in connection with the seasonal distribution and changes of atmospheric pressure and winds.--Oesterreich, Zeitschrift Meteorologie, X., 258.
ON THE ACCURACY OF ANEMOMETERS. One of the most important and, at the same time, popularly interesting matters relating to meteorology, or rather to the mechanics of gases, is the relation between the pressure and the velocity of winds; which subject, notwithstanding the elaborate researches, both experimental and theoretical, that have been made since the days of Lambert, is still far from being satisfactorily resolved. The numerous experiments secm uniformly to show that the measured pressures of Auids against the surfaces opposed to them differs from
those predicted by theory. The principal source of discordance is probably to be found in the fact that the computations take account only of the pressures against the front surface of the solid, while the reaction that takes place on the binder surface is partly or even totally neglected. In the case of the anemometers employed for the purpose of measuring the velocity of the wind, probably without a single exception, their indications must be interpreted by means of approximate empirical formulæ; and no other method has, as yet, been devised by which the indications given by pressure gauges can be compared with those given by velocity meters. Of these latter instruments, the best are those known as Robinson's anemometer and the Casella anemometer. Of the pressure gauges, those most commonly in use are the Ossler anemometer and Wild's anemometer. Dr. Dobrandt has recently undertaken, at the instigation of Dr. Wild, of St. Petersburg, an elaborate investigation, both theoretical and experimental, into the sources of error peculiar to these instruments; and the memoir embracing his results, which was announced a year ago by Professor Wild, seems to be the most valuable contribution to anemometry that we have had occasion to regard since the appearance, in 1873, of Cavallero's investigations, which were noticed by us at the time. (See Annual Record, 1874, p. 104.) Unfortunately, Dr. Dohrandt was interrupted in his labors by a call, on the part of the Russian Geographical Society, to superintend the establishment of meteorological stations in Asia; but Professor Wild assures us that his researches will be continued by the Physical Observatory, until definite conclusions can be considered as established. Among the means adopted for comparing the actual velocity of the wind with the readings of the anemometer, Dr. Dohrandt experimented first with the method adopted thirty years ago by Duchemin, and less thoroughly by others, and which consists in carrying an anemometer attached to a locomotive, the velocity of whose movement is well ascertained. The railroad from St. Petersburg to Tsarskoe Selo offered a good opportunity for the experiment which was first made on July 1, 1871, in which the average velocity of the railroad train seems to have been from twenty-one to forty-eight kilometers per hour. During the experiment the average velocity of the wind itself, in
the direction of the path of the locomotive, was two and eight-tenths kilometers per hour; and the velocities observed by timing the train as it passed each mile - post agreed with the velocities recorded by the anemometer to within two per cent.
A more definite method of investigation, however, is that of Combes, which consists in attaching the anemometer to a long arm, which latter is made to revolve in a circle at a known rate, in a space where strong currents of air do not occur. Velocities up to forty kilometers per hour were attained in this way by Dohrandt; and from the investigation of six different Robinson's anemom. eters, and of two of Casella’s instruments, and of a number of electric recording anemometers, it was concluded that the arithmetical mean of the indications of an anemometer, when the arm which carried it revolved in both a positive and a negative direction, might be adopted as the result that would be given if the instrument had simply moved in a straight line. The determination of the effect of the moving anemometer upon the air surrounding it-an effect which it is known consists essentially in carrying the air with it, and thereby diminishing the relative velocity of the air and the instrument—was first made by placing a Casella and a Woltman's anemometer on the same level with the rotating anemometer, but fixed in their positions, and so near to the circle described by the latter that they could feel the influence of the wind dragged along by the Combes' apparatus, and be thereby set in motion. As the result of this portion of his investigation, Dohrandt finds that the wind due to the dragging influence of the moving anemometer is very approximately proportional to the velocity of the latter itself. As a final result in reference to the velocity of the anemometers, Dohrandt gives a formula applicable to each one individually, by means of which the true velocity may be computed from the indications of the dials of the instruments. Having thus some half-dozen well-investigated instruments as standards, it becomes easy to compare numerous others with these. The result of such comparison showed that the errors determined in this secondary manner were of the same nature and expressed by the same formula as those determined by the original investigations. In general, in relation to the velocity of the anemometers, Dohrandt finds that the
centre of the revolving caps of the Robinson instrument, instead of describing exactly one third of the path of the wind, as they should do according to the theoretical researches of that astronomer, differ from this to such an extent that the indications of their dials must be multiplied by numbers varying from 2.1 to 2.9 in order to deduce the true velocity of the wind. The result most to be desired in relation to this branch of anemometry is the determination of the relation between these varying factors and the actual dimensions of the respective instruments. But Dr. Dohrandt finds, as had Cavallero and Stowe before him, that no such relation can be discovered ; only so much is easily seen, that the magnitude of the factor is in more direct connection with the diameter of the hemispherical caps than with the length of the arms of the anemometer. In respect to the pressure
of the wind, Dohrandt experimented with six different specimens of Wild's wind-pressure anemometer, which consists simply of a very thin plane piece of iron or wood, or thin cardboard, hanging by a very thin arm from a pivot, and which is by the force of the wind pushed aside from its vertical into an inclined position. The angular extent of the deflection is measured in degrees by an appropriate divided arc. In connection with this, he calls attention to the fact that the indications of this, and of all pressure instruments, are decidedly affected by the density of the atinosphere, as indicated by the barometer. The comparisons of the indications of this pressure gauge with the velocity deduced from the standard anemometers seems to show that the simple instrument of Dr. Wild suffices, by means of the table given by Dohrandt, to determine the velocity of the wind within less than about one half a meter per second. On account, therefore, of its simplicity and inexpensiveness, it is probable that this instrument will be widely used throughout the world, especially as it has now been introduced at all the Russian meteorological stations, and at many of those in southern Europe.- Wild's "Repertorium," IV., art. 5.
THE SELF-REGISTERING BAROMETER OF REDIER. Among the many contrivances brought forward during the past few years for the self-registration of meteorological instruments, that of Redier seems both economical and ap