results to the study of a few hurricanes. The mathematical formulæ by which he has endeavored to show the relation between the velocity and pressure of the air and the dimensions of the whirlwind are apparently deduced in a not very rigor ous, but sufficiently approximate manner. On applying them to the actual observations taken in connection with the hurricane of 1837 (the so-called Antiguan hurricane), and also to the hurricane of the 21st of August, 1871, he finds that the formula represents the observations with a degree of accura cy probably within the errors to which the observations themselves are likely to be subject. The simple principle according to which he is able to calculate the nature of the final shape of the surface which is shown for instance whenever water is allowed to flow out of a bowl through a central hole, consists in this, viz., that when the rotation is once established in the water, each particle describes a circle about the central axis, whose radius is such that the pressure of the water above the moving particle exactly counterbalances the centrifugal force due to its circular rotation. In the case of the atmosphere we have, instead of a well-defined surface, a series of surfaces of equal pressure, and the centrifugal force due to the circular movement around the centre of the hurricane is counterbalanced by the pressure of the atmosphere at that point. Unfortunately, Mr. Colding seems not to have taken account of the force due to the rotation of the earth on its axis. His equations, therefore, apply to tornadoes and to the central portions of hurricanes better than they do to the exterior portions of large storms.-Zeitsch. für Meteorologie, May, 1875, 133.

THE MONSOON.

In the magnificent volume of magnetic observations at Trevandrum, in Southern India, Mr. Broun gives the following interesting account of the advent of the monsoon. He was stationed at certain times at an auxiliary observatory on the peak known to the natives as Agustia, whose altitude is over 6000 feet, and which from time immemorial had been superstitiously regarded by the Hindoos as the resi dence of Agustia, a savant, physician, philologist, and theologian, whose principles were celebrated for their purity. Mr. Broun states that during his visits to this peak he made

daily notes of the appearance of the clouds and sky, and that there is no place in India where the magnificent phenomena which precede the bursting of the monsoon can be seen and studied with more ease. The peak in question is one conspicuous for its height and its isolation. As seen from Trevandrum, it rises in the form of a sharp-pointed cone. On the west it is a precipitous wall for nearly two thousand feet, and on the east it descends at an angle of about 60° with the horizon. Standing on its summit, for a month or more before the final crash of the tempest, the whole operations of the great atmospheric laboratory are developed at one's feet, while the summit of the mountain itself is rarely visited by the storms which rage over its western flanks. On the occasion of his first ascent, Mr. Broun states that, arriving at the summit, he saw to the west Trevandrum lying on the low lands, the intermediate plains spotted with clouds, shadows, and bright sunshine. A thick stratum of clouds, about on his own level, was, however, coming rapidly toward him, and in five minutes after dashed like a hurricane on the cliff below, burying the summit in a dull, gray light and a wet mist. Within the next two days they had twelve inches of rain, and it was evident that the monsoon had set in. On a subsequent visit, made during the dry season, he had ample occasion to study the gradual approach of the monsoon, and in general states that in the mornings chains of finely formed cumuli seemed to rest over the eastern horizon of Malabar and Coromandel. These clouds were irregularly distributed over the country, their shadows projected vertically at noontime, spotting and checking the plains between the sea and the mountain. Early in the morning the vapors began to rise near the western precipices, the clouds accumulated and sought to escape by the lowest passes into the eastern valleys, but were opposed by a repulsive influence, although no breath of air was felt. At last, after noon, in mighty masses it ascended, crowned with cirrus cloud, which spread eastward like an immense parasol overhead. Then the lightning began to play from cloud to cloud, followed by thunder, and drenching rain in the forests below. After one or more hours, according to the distance from the monsoon, the clouds left the mountains, retreated westward, and then

disappeared, the sun shone out from the western sea, the stars sparkled in all their beauty, and the next morning again brought the chain of clouds on the horizon. As the time for the monsoon drew near the cloud-masses with more and more energy endeavored to pass the mountains eastward. Sometimes two such masses presented themselves, one creeping up the eastern valley and the other entering the valley from the west. Day by day the returning clouds made a little further progress. At length on the decisive day, driven on by a giant force, they rose to the tops of the mountains, and poured over their walls into the eastern hills. like steam from a great caldron. They plunged first downward, and then curling upward disappeared in the hotter eastern air. The storm with deluges of rain swept across the mountain, and the monsoon reigned over the low lands of Malabar.-Trevandrum Observations, I., 517.

ORIGIN OF COLD WAVES OF AIR.

Dr. Klein, in reference to the use of daily weather reports, states that in Europe as in America, in all cases, the reports of the weather westward of a given station are of the greatest importance, while reports from stations to the east are, on the average, of minor importance in making weather predictions. A southerly wind in the region of Ireland, Scotland, or Norway indicates the approaching side of an area of low barometer. It is therefore a sign of a coming change in the weather. A northerly wind in those regions indicates, for Germany, that the pressure of the air from the ocean is high, and can be considered as a sign of steady pleasant weather. Irregular changes of atmospheric pressure and of the winds are extremely slight in Eastern Asia, and the cold of winter when once commenced continues uninterruptedly in Eastern Siberia with a permanent high barometer. The reason of this is found in the existence of the great mountain chains of Asia. The region of high barometer is generally separated from oceans and from equatorial regions by these lofty chains of mountains. The coldest and densest stratum of air can therefore not flow away toward the sea. Its only escape is found at points like Jakutsk, where it passes over land 3000 feet above the ocean. Thus, throughout the whole interior of Asia, the lower stratum of air remains quite cold and heavy,

until the summer sun, heating the surface of the earth, stirs up the atmosphere, very much as water boils in a vessel over the fire. That which takes place in Asia is repeated in a much less intense degree in America. The area of the greatest cold on this continent is not prevented by any range of mountains from extending southward and eastward, but is only hemmed in on the west by the Rocky Mountains. Thus while the Pacific coast is protected from an overflow of very cold air, the whole eastern portion of America becomes peculiarly subject to it.-7 C, II., 9.

DALTON'S LAW, AND THE CONSTITUTION OF THE ATMOSPHERE. It is well known that the famous law of Dalton, with reference to the diffusion and independent existence of aqueous vapor in the atmosphere has exerted a very strong influence in moulding the views of meteorologists as to the method by which this portion of the atmosphere operates in modifying meteorological phenomena. Of late years, however, very strong suspicions have existed as to the propriety of carrying Dalton's views to the extreme that has been maintained by many. In fact, so early as 1840, Espy distinctly controverted them. Of late, Hildebrandsson, Hann, and especially Stefan, have more correctly explained the limitations within which Dalton's laws may be applied. According to the latter, these obtain in the case of a mixture of gases only under conditions of static equilibrium, and do not hold when these are in relative motion. Since the vapor of water in the air, in consequence of its continual evaporation and condensation, is always in movement, it does not conform to Dalton's laws. The permanent gases of the atmosphere, especially oxygen and nitrogen, which retain in general the same proportions, are in equilibrium, and do form atmospheres independent of each other, according to Dalton's laws. It necessarily follows that the percentage of dense oxygen must be smaller as we ascend in the air; and, in fact, chemical analysis gives this result.-19 C, VIII., 90.

THE TEMPERATURE OF THE AIR.

One of the most difficult problems in all matters relating to the atmosphere consists in the determination of the true temperature of the air; and the errors in these determina

tions affect very sensibly both astronomical, meteorological, and hypsometric labors. Professor Plantamour was among the first to show that observations of the barometer taken simultaneously at two distinct stations ought to enable us by calculation to arrive at the average temperature of the intervening atmosphere. Among those who have lately applied this method is Mr. Schott of the Coast Survey, who has, from observations made about fifty miles northwest of San Francisco, calculated the temperature of the air between two stations occupied by Mr. Davidson. As the results of these studies, it appears that the average temperature of the air between two stations differing 2000 feet in altitude remained sensibly constant throughout the entire day, as though the sun's rays passed through it without apprecia bly heating it; while, on the other hand, the thermometer at the two stations respectively rose to a maximum at 1 P.M., and fell to a minimum in the morning and evening. The daily variations of temperature seem, therefore, to be confined mainly to the layer of air in close proximity to the earth's surface. The corrections to be applied to the observed thermometers, in order to obtain the true temperature of the air, varied regularly throughout the day, and are decidedly larger than those obtained by Professor Plantamour at Geneva. M. Schott, in explanation of this phenomenon, suggests that probably the 20 or 30 per cent. of total solar radiation which is absorbed by the atmosphere is consumed in the processes of expansion and evaporation; and thus gives no sensible heat.-Coast Survey Report, Appendix XI., 1871.

THE UPPER CURRENTS OF THE ATMOSPHERE.

The upper currents have been much neglected by meteorologists until recent times, when the extensive weather-maps published in Europe and America have enabled proper attention to be given to their study. Some of the important laws relating to the movements of the cirrus clouds were apparently suspected by Redfield, and were in a general way predicted by Ferrel; but extended observations and deductions are due principally to Clement Ley (1872), and more recently to Hildebrandsson, the Director of the Meteorological Bureau of Sweden. This gentleman states that