portion of air which is not equally dense on all sides of the ray, it is deflected toward the side on which the density is greatest, the sharpness of the curvature being proportional to the rates at which the density varies. If the air is strati fied horizontally, it follows that a ray traveling nearly hori zontally will be bent the most, and it is by such rays that we see the images which constitute mirage. In the average state of the atmosphere the curvature of horizontal rays is about one fifth or one sixth of the curvature of the earth's surface, being greater in cold than in warm weather, and greater with high than with low barometer. The curvature, however, depends principally upon the rate at which the temperature changes with the height. The average rate is one degree for 300 feet. If the rate were one degree for fifty-three feet, the horizontal rays of light would be straight lines. A more rapid rate than this will render the air above denser than that below, and cause rays to bend up instead of down. This condition of affairs may exist for a time, although it is a condition of unstable equilibrium, and must eventually be broken up by the inflow from the surrounding regions of cold air. An increase of temperature upward at the rate of about one degree in sixteen feet will make the curvature of horizontal rays equal to that of the earth, so that they may encircle the globe. Any such downward bending of rays of light increases the range of our vision, enabling us to see around the horizon, which otherwise limits the view, thus bringing distant objects in sight, and rendering nearer objects more distinctly visible, but without in any way inverting them.-12 A, XI.,

151.

THE NEW SELF-RECORDING BAROMETER.

A self-recording barometer has recently been made by Mr. Redier, which seems to have many excellent points, and to be enthusiastically received in France. In a communication to the Meteorological Society of Paris, he states that his instrument consists of an ordinary syphon barometer carrying a very light ivory float, upon which is fixed a vertical steel wire terminating in a point. A horizontal needle rests upon this point, its other extremity is in connection with a double series of clock-work, the wheels of which move either forward

or backward, according as the ivory float rises or falls. The movements of the clock-work are followed by a pencil which draws a curve upon a revolving cylinder. In a very similar instrument devised by Professor G. W. Hough, of Albany, and highly prized by American meteorologists, the connection between the horizontal lever and the wheel-work is an electric one, and subject therefore to all the uncertainties of the electrical batteries and connections. In Redier's barometer no electricity is employed, the entire apparatus depending only upon gravity and atmospheric pressure, and its working is evidently perfectly regular and reliable. An aneroid barometer may be made to record its indications in the same manner as the mercurial, and such instruments have, we understand, already been constructed under Mr. Redier's directions. Mr. Silberman has suggested a method by which a similar automatic system of registration could be applied to the indications of the magnetic needle.-Nouvelles Meteorologiques, 1875, p. 16.

CURRENTS OF AIR WITHIN CYCLONES AND WATERSPOUTS.

In a memoir on cyclones and waterspouts, Mouchez publishes some observations made by him while upon the ocean, and which, if correct, are quite important. According to him, at or near the surface of the ground the movement of air in the cyclone is always from below upward, while in whirlwinds the movement is, on the contrary, from above. downward. In the former case the winds are winds of aspiration; in the latter case the wind descends from the cloud in the form of a bag or tube, which terminates in a point. He believes that waterspouts have no relation whatever to cyclones, having an opposite appearance and cause. In this opinion Renou also concurs.-Nouvelles Meteorologiques, 1874.

THE PROGRESSIVE MOVEMENT OF AREAS OF COLD AIR.

Dove has attempted to deduce, from the five-day means of temperature for European stations, some general views as to the progress of days of remarkable cold, and finds that in the months of January and February of the years 1855, 1856, 1870, and 1871, numerous cases occurred to show, almost uniformly, that the "cold terms" move westward over Europe;

a result that may, perhaps, be considered as entirely in agreement with the deductions of Buchan, based upon the barometric charts prepared by him.-Monatsbericht Berlin Acad., Feb., 1874, 118.

A VERY DELICATE BAROMETEL.

An ingenious device has been constructed by Mendelef, which shows the slightest variations of pressure by means of a small U-shaped tube containing petroleum oil. One end of this tube is closed, and contains a certain volume of dry air maintained at a constant temperature, while the other end is open to the air. The instrument being accurately adjusted by means of a mercurial plunger connected with the bottom of the U-shaped tube, so that the petroleum is exactly on a level in the two branches of the tube, it is found to be so extremely sensitive that the slightest variation of atmospheric pressure is shown by the alteration of the level, and the amount of this alteration can be measured with the greatest precision.-12 4, XI., 55.

THE PENETRATION OF COLD INTO THE EARTH.

From observations on the temperature of the surface of the earth which have been made regularly at the Botanical Gardens at Paris, by the Messrs. Becquerel, by means of the electric thermometer invented by them, some interesting conclusions have been deduced. Their observations have been extended to the depth of one hundred and seventeen feet; but most attention has been paid to that portion of the earth nearer the surface. With reference to the penetration of cold into soils of similar character, but one of which is bare and the other covered with grass, while both are covered with snow, the observations have shown that when the temperature of the air sinks from zero to – 12° Centigrade, the temperature of the earth at the depth of twenty inches never sank to zero under the grass-covered earth, while it sank at the same depth to -5° under the bare surface. From these observations Becquerel makes the practical suggestion that if in a sandy soil we desire to cultivate plants whose roots suffer from frost, we must cover the soil with grass-sod; and, for similar reasons, if we desire to preserve vegetables or other products during the winter under the soil, and secure

them from frost, we should in this case also cover the soil with grass.-19 C, XIV., 135.

AQUEOUS VAPOR IN THE ATMOSPHERE.

The Academy sums up the conclusions of Dr. Hildebrandson, of Upsala, in regard to aqueous vapor in the atmosphere, as follows: 1. The permanent gases in the atmosphere do not form independent atmospheres, but have effected a complete mutual interpenetration; as all experiments show that the constitution of the air is the same at all heights. 2. The incessant evaporation and condensation which are in progress render impossible the existence of an independent vapor atmosphere, or of a homogeneous mixture of the vapor with the permanent gases, and must cause the vapor to diminish rapidly with height. 3. It is not allowable to subtract the vapor pressure from the barometer reading to obtain the pressure of dry air.-13 A, Feb. 6, 1875, 145.

THE NEW ANEMOSCOPE.

Michelle describes an ingenious anemoscope in which three arrows are used, of which the upper one indicates the direction of the wind at each moment. The second indicates the extreme wind on the right, and the third indicates the extreme wind on the left hand. Thus, when one looks at the wind vane, we see not only the wind that now prevails, but the extreme winds on either side that have prevailed since the preceding observation. - Bulletin Hebdomadaire, XVI.,

12.

PERIODICITY OF RAINFALL.

Governor Rawson, of the island of Barbadoes, whose remarkable studies upon the rainfall of that island have been already noticed, states that it is an error to suppose, as Mr. Meldrum does, that the observed rainfall in Barbadoes in any way really supports Mr. Meldrum's theory that there is a sun-spot period in these meteorological phenomena. He, however, very philosophically adds that, if the conclusions. drawn from a wide area and very long periods of observation do support that theory, then the opposite results obtained in Barbadoes, although that island is most favorably situated for these observations, only show that no particular

locality can draw a safe inference as to the manner in which the presence or absence of sun spots is likely to affect it.

But looking more deeply into the matter, Governor Rawson very justly adds that if there has been more rain in certain quarters of the globe in certain years, there must have been in other quarters during those same years greater evap oration, whence it results that the same solar phenomena produce in one portion of the world opposite effects to those produced elsewhere.-12 A, X., 264.

MARITIME CONFERENCE IN LONDON.

At the recent Maritime Conference in London the resolutions adopted by the meeting embraced the following subjects. It was resolved that there should be but one form of meteorological register for naval and merchant services, and that so far as possible a uniformity in methods and hours should be observed. Ocean currents and magnetic variations were recommended for observation. The upper and lower clouds are to be recorded in separate columns. The precise patterns of instruments were not specified, the only requirement being that those used should satisfy certain tests, and that they should be carefully compared with standard instruments. It is considered that the general influence of the Conference was decidedly in favor of united action on the part of the merchant service and the navies of the world. Particular stress was not laid upon the conducting of special investigations by sea-captains, as such can be most econom ically performed at the central meteorological stations and by government naval vessels.-12 A, X., 431.

THE TEMPERATURE OF STORMY WINDS.

Dr. Fritsch, of Vienna, communicates to the Annual of the Vienna Meteorological Institute some observations on the temperature of the storm-winds at Salzburg. He states that, since 1864, he has every summer resided in Salzburg without noticing the high temperatures of the southeast storm-winds; but that since he has resided there constantly during the past few years, this has been forcibly brought to his attention, as also the great dryness which accompanies these winds. From the records made at 7 A.M., and 2 and 9 P.M., from 1863 to 1869, he has selected the stormy winds, and