GENERAL LIBRA University MIONIGA B. TERRESTRIAL PHYSICS AND METEOROLOGY. recommended by Lamont. It consists principally of a rectangular tube buried permanently in the earth, within which five rectangular prisms of wood are placed, one above the other, at different depths in the ground, and which, by a simple arrangement, can be easily and quickly drawn up. Each of these tubes contains a thermometer, and there is a hole in the side of the main tube, opposite to the bulb of the thermometer, where the wood-work is cut away, and the opening closed by a plate of thin sheet copper, whose temperature may be presumed to be the same as that of the adjacent ground. The depths at which the thermometers' bulbs remain are 4, 8, 12, 16, and 20 feet. Schenzl, as the result of observations made during eight years, finds that the time required for heat to penetrate to a depth of one meter is, on the average, 21 days. THE INTENSITY OF TWILIGHT. Mr. Williams, a student of the Massachusetts Institute of Technology, has made some observations to determine the quantity of light reflected during the hours of twilight, when the sun is at different distances below the horizon. The photometer employed was a slight modification of the Bunsen photometer. The illuminated disk was exposed on one side to the light from a standard candle, and on the other side to the light admitted from the sky.-Proceedings Am. Acad. Arts and Sciences, 1875, 421. ON THE QUANTITY OF LIGHT REFLECTED BY THE SKY IN THE DAYTIME. The quantity of light reflected by the sky at any given distance from the sun has long been a subject of meteorological observation, the first rude attempt at its measurement being made by the use of Saussure's cyanometer. Some elaborate investigations have been pursued for a long time at the Mont-souris Observatory. An interesting investigation of the question by a simple photometric apparatus has recently been published by Crosby as a student under Professor Pickering of the Institute of Technology at Boston. His objects were to determine, first, the absolute amount of light received from the sky at different distances from the sun, and second, to ascertain the law of diminution of light with in The extreme severity of the storm seems to have been felt on the coast of Texas. In its subsequent course it extended over a larger area, and seems to have produced heavy gales on the Jersey coast, and to have had some connection with the violent storms which prevailed on the North Atlantic Ocean to the north of Great Britain from the 26th to the 29th of September. The heavy rains that accompanied the storm during its prevalence over the Gulf of Mexico contributed to the large excess of precipitation which prevailed in the Gulf States for the month of September.-Monthly Weath er Review for September, 1875. THE DIRECTION OF CIRRUS CLOUDS. The movement of the cirrus clouds has been the subject of study by Hildebrandsson, of Upsala, who hopes thereby to deduce some results relative to the ascending and descending movements of the atmosphere above the regions of high and low barometer. The observations of Clement Ley show that the cirrus clouds move from areas of minimum toward areas of maximum pressure, and Hildebrandsson has endeavored to extend this interesting generalization over a wider field. He states, in fact, that a general study of the clouds over the whole of Europe shows him that while the air on the earth's surface moves in spiral curves, inward, toward low barometer, the air at a high altitude simultaneously moves outward. The upper winds, therefore, constantly make an angle toward the right with the lower winds. This demonstration was in 1871 also made by Abbe for the United States, and may probably now be considered as a general rule, applicable throughout the world. It is important to notice that the same conclusion was arrived at deductively by Ferrel in 1857, and is fairly stated in his great work on the motions of bodies on the earth's surface. THE TEMPERATURE OF THE EARTH. The interest which attaches to careful observations of the temperature of the earth suggests that the apparatus which is used in Germany should be better known in this country, in order that, when practicable, it may be introduced here. The following is a description of it as used by observers in Hungary. In its general outlines it does not differ from that NERAL LIBRA University MIORIGAN B. TERRESTRIAL PHYSICS AND METEOROLOGY. recommended by Lamont. It consists principally of a rectangular tube buried permanently in the earth, within which five rectangular prisms of wood are placed, one above the other, at different depths in the ground, and which, by a simple arrangement, can be easily and quickly drawn up. Each of these tubes contains a thermometer, and there is a hole in the side of the main tube, opposite to the bulb of the thermometer, where the wood-work is cut away, and the opening closed by a plate of thin sheet copper, whose temperature may be presumed to be the same as that of the adjacent ground. The depths at which the thermometers' bulbs remain are 4, 8, 12, 16, and 20 feet. Schenzl, as the result of observations made during eight years, finds that the time required for heat to penetrate to a depth of one meter is, on the average, 21 days. THE INTENSITY OF TWILIGHT. Mr. Williams, a student of the Massachusetts Institute of Technology, has made some observations to determine the quantity of light reflected during the hours of twilight, when the sun is at different distances below the horizon. The photometer employed was a slight modification of the Bunsen photometer. The illuminated disk was exposed on one side. to the light from a standard candle, and on the other side to the light admitted from the sky.-Proceedings Am. Acad. Arts and Sciences, 1875, 421. ON THE QUANTITY OF LIGHT REFLECTED BY THE SKY IN THE DAYTIME. The quantity of light reflected by the sky at any given distance from the sun has long been a subject of meteorological observation, the first rude attempt at its measurement being made by the use of Saussure's cyanometer. Some elaborate investigations have been pursued for a long time at the Mont-souris Observatory. An interesting investigation of the question by a simple photometric apparatus has recently been published by Crosby as a student under Professor Pickering of the Institute of Technology at Boston. His objects were to determine, first, the absolute amount of light received from the sky at different distances from the sun, and second, to ascertain the law of diminution of light with in creasing angular distance from the sun. The method pursued was to so adjust the apparatus that an image of the sun would fall upon the Bunsen disk of the photometer, and then to measure the intensity of the light at regular intervals of time, as the sun receded from the portion of the sky whence the light was received. Observations were made on days both hazy and clear; and notwithstanding the great differences in the intensity of the light, it was found that it was proportional to some power of the sun's angular distance. This power was approximately for hazy days 1.04, but for the clearest days 1.21.-Proceedings Am. Acad. Arts and Sciences, 1875, 425. = WIND VELOCITY AND THE BAROMETRIC GRADIENT. The term barometric gradient was introduced into meteorology some years ago by an English engineer to express the rate at which the barometric pressure varies as we pass from one part of the country to another. It has long been adopted by Europeans as a rule in weather forecasts, that rapid changes of the pressure or steep barometric gradients will be followed by strong winds blowing nearly at right angles to the direction of the gradient. The explanation of this well-established generalization was partially given some years ago by Professor Ferrel of the United States Coast Survey; and his views have been adopted of late years by most European meteorologists who have studied dynamic laws. According to Professor Ferrel, whenever, from any cause whatever, an influx of air takes place from the surrounding regions toward a central spot, a gyratory motion must at once be set up, as illustrated in the whirls at the corners of the streets and in the tornadoes and hurricanes of the tropics. A very slight disturbance in the equilibrium of the atmosphere, such as would scarcely be shown by any but an unusually exact barometer, suffices to initiate the inflow of air and to give rise to the gyrations. If the earth were not revolving upon its axis these gyrations would take place in either direction, viz., either with or contrary to the movements of the hands of a watch; but owing to the great power of the immense velocity with which the earth revolves on its axis daily, the direction of all gyratory movements in the northern hemisphere is regulated thereby, being in fact uni formly contrary to the movement of the hands of the watch. It is to the centrifugal force due to this gyratory movement, by reason of which the air may be considered as revolving not only about the centre of the hurricane, but also about the earth's polar axis, that Professor Ferrel attributes the greater part of the depression of the barometer which is observed at the centre of the storm. The amount of this depression can be quite exactly calculated by the formula given by him. Not only does the air revolve about, but it also preserves its tendency to move inward toward the centre of lowest pressure near which it rises, and then the upper region of the atmosphere continues its gyratory movement, but flows outward, gradually descending until it meets the earth again. Professor Ferrel has been successful in explaining satisfactorily, by one single formula, and in grouping together under one common point of view, the phenomena of tornadoes and waterspouts and extensive hurricanes. His formula, after allowing for the density of water, applies also to the movements of the ocean; and by means of it he is able to compute the gradient of sea-level due to the deflecting force of the earth's rotation, showing that, for instance, we obtain about six tenths of a foot as the depression in sea-level due to a change in position of a hundred miles on a parallel of 30°, the sea-level being highest in the middle of the gyration, that is to say, in the central portions of the Atlantic and Pacific Oceans.-4 D, November, 1874. THE MECHANICAL THEORY OF CYCLONES. Among the treatises on the mechanical theory of the movements of air in revolving storms, both hurricanes and tornadoes, but few have such practical value as that of Colding, published in Danish in 1871, translations of which have recently been prepared by Hann, of Vienna, and Abbe, of Washington, by means of which the English-reading public is introduced to a series of novel investigations into the flow of liquids, which forms a very acceptable addition to our knowledge of the subject. According to Colding, the laws governing the movement of water may, with certain restrictions, be applied to the movement of the air; and after having, as an engineer, for many years successfully studied the currents of rivers and oceans, Mr. Colding has applied his |