vessel remains vertical, the segment of the image of the horizontal line will continue at a constant height upon the plate. Consequently it would trace upon the plate a horizontal line. Let us suppose now that the ship rolls; at each instant there would be a certain inclination, i, and at this moment a certain zone of the plate will be found behind the opening of the shutter. The image of the horizon will traverse this window at some point of this zone, and it will fall upon the plate at a distance from the reference line equal to f, tang. i. Experiments have been authorized according to this method, which is the invention of Huet, at Brest, and the photograph proofs show the good results that were obtained.

BAROMETRIC OBSERVATIONS ON THE OCEAN.

Dr. Buys Ballot communicates in a preliminary way the results of the great unpublished work undertaken by the Meteorological Institute of the Netherlands, and which consists in the derivation from over three hundred thousand observations on board vessels of the average barometric pressure for each month, and for every five degrees square throughout the navigated portions of the North and South Atlantic Oceans. The average barometric pressure within ten degrees of the equator is 760.04 millimeters. The pressure within ten degrees of the parallel of 30° north is 765 millimeters; and within ten degrees of the parallel of 30° south it is 762.5. Beyond these latter parallels the pressure diminishes steadily toward the poles, and is, apparently, at the limits of Buys Ballot's tables, viz., about 50° of latitude, in the southern hemisphere, 750 millimeters, but in the northern hemisphere 760.-Oesterreich. Zeitschrift für Meteorologie, X., 159.

THE SMALL OSCILLATIONS OF THE BAROMETER.

Hon. Ralph Abercrombie has examined the connection between the wind and the small oscillations of the barometer. He finds, for example, that with an open window looking south and the wind nearly south, in strong gusts the first movement of the barometer is always upward, and about one tenth of an inch, as if the effect of the wind on being resisted by the house was to compress the air in the room. In a corner house, one window open to the south and another to the west, the wind south, in strong gusts, with the west

window open, there were violent oscillations; but the first movement was always downward. Upon opening the south window as well as the west, the oscillations ceased. It is well known by medical men that some acute diseases are aggravated by strong winds; and the author has observed that this distress is associated with those small oscillations of the barometer. He suggests the following practical method of palliation. If windows can not be borne open, try, by closing or by otherwise arranging windows and doors, to diminish the distress. When, as in most cases, windows can not be opened, all doors and windows should be closely shut, as well as the vent of the chimney if there is no fire; and, if possible, the patient should be removed to a room on the lee side of the house.-12 A, XII., 78.

ON THE DISTRIBUTION OF BAROMETRIC PRESSURE IN EUROPEAN RUSSIA.

The well-known work of Buchan, published in 1866 by the Royal Society of Edinburgh, was the first that offered an extensive collection of barometric observations, and gave the first approximate idea of the correct isobaric lines throughout the whole world as drawn for every month in the year, and for the average of the entire year itself. While Buchan in this work sought to obtain greater accuracy by using only the observations made between 1850 and 1860, he was, however, frequently thrown into serious error by the uncertainties of the altitudes above sea-level of the stations in the interior of Europe and America. For the latter country annual barometric means have been of late published by the Army Signal-office; and we have now to record the appearance of an important work by Rikatcheff, on the distribution of barometric pressure in the interior of European Russia. The author states that, as regards Asiatic Russia, we have still too little material to justify the drawing of isobaric lines as Buchan has done. For European Russia he gives many, and in some respects important corrections to the figures employed by Buchan. Having personally inspected many of the Russian stations, Rikatcheff has been able to discriminate between the observations that are reliable and those which should be rejected; he has collected all the valuable barometric observations that have been made in

Russia, and has applied to those stations whose altitudes were correctly known by levelings the barometric reductions (as computed by Rühlmann's formula) necessary in or der to reduce the observed pressures to the theoretical sealevel. The highest station to which he has applied this process is Tiflis, whose altitude is about 1500 feet, and at which altitude he states the reduction to sea-level already becomes quite uncertain. The longest series of observations employed by him is, for the Russian stations, that at Warsaw, embracing thirty-three years. Having reduced the annual pressures to sea-level for these stations, he has, by means of preliminary approximate isobars, determined the mean annual pressure at sea-level for the other stations whose altitudes were not correctly known, and has there computed the altitudes as dependent upon long series of good observations, of five interior stations, with a probable accuracy of less than forty feet, and has determined the altitude of eight other stations with an error of less than ten feet. These secondary stations thus became valuable in the formation of the monthly isobars, although, of course, they can not be used on the annual charts. The final charts thus completed by Rikatcheff present the same phenomena as those given by Buchan, but of not quite so extreme a nature. The change from a very high pressure in the interior of the continent during the winter to a low barometer in the summer time is very decidedly marked (the explanation of this phenomenon given by Rikatcheff is too much at variance with mechanical laws to escape severe criticism). On the other hand, the annual chart shows a well-marked diminution in the average barometric pressure as we proceed northward. Its depression he attributes to the numerous cyclones that occur in this region, although he states very plainly that the average annual temperature, as well as the tension of aqueous vapor, should conspire to annul this effect. It is probable that at the time of composing his memoir he had not yet become acquainted with the writings of Ferrel, Thomson, Peslin, Colding, Everett, and others, by whom the depression of the barometer in the polar regions of the earth is very accurately explained as due to the rotation of the earth on its axis, combined with the general atmospheric currents. Ferrel has even explained, in a very perspicuous manner, the reason why this depression is

so much greater in the antarctic than in the arctic regions. One of the most important practical results attending the publication of Rikatcheff's memoir is the stimulus that it has 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 Gulf.

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 Hydrographic 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 the 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 humidity in different portions of Russia are explained by Wild in connection with the seasonal distribution and changes of atmos pheric 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 seem uniformly to show that the measured pressures of fluids against the surfaces opposed to them differs from