July 24, 1884] 



NA TURE 



305 



being less than two miles an hour, and cairns constitute about 

 one-third of the observations. Also it is shown, by the baro- 

 metric registers of the Himalayan hill-stations, that that 

 distribution of pressure which, on the plains, causes the north-east 

 monsoon, does not exist and is even slightly reversed at an 

 elevation of 7000 feet. 



Hence, in Northern India, the state of things which pro- 

 duces the winter monsoon is restricted to a small height, and is 

 then only an average and not a permanent condition ; and that 

 which chiefly characterises the atmosphere is its stillness, a con- 

 dition in which any local action, small and feeble as it may be 

 at first, may eventually set up a disturbance such as to revolu- 

 tionise the existing conditions. 



The cold weather rainfall is always the result of a local fall of 

 the barometer, the formation of a barometric depression, which 

 generally appears first in the Punjab or Western Rajputana, and 

 then moves eastwards. Towards and around this depression the 

 winds blow cyclonically (i.e. against the direction of the clock- 

 hands), and the winds from the south, coming up charged with 

 vapour which they have collected from the warmer land surface 

 of the peninsula and sometimes from the sea, discharge this as 

 rain chiefly to the east and north of the barometric minimum, 

 where they form an ascending current. 



Thus in the cold weather, rain generally begins in the Punjab 

 and later on extends to the North-Western Provinces, Behar, 

 and sometimes to Bengal. As the disturbance travels eastwards, 

 it is followed up by a wave of high barometric pressure, and cool 

 north-west winds, which usually last for a few days after the rain 

 has cleared off. 



The crucial point of the problem of the cold weather rains is, 

 then, how to account for the formation of these occasional baro- 

 metric depressions in a region where the barometer is generally 

 high at this season. It has been suggested by one writer that 

 they travel to us from the west across Afghanistan. This, 

 however, can be only a guess in the dark, for, at the time it was 

 made, there were no observatories to the west of India nearer 

 than Bushire, at the top of the Persian Gulf There is one now 

 at Quetta, and I have examined the registers of this observatory 

 to see if they give any support to the idea, and find that, with 

 the exception of two doubtful instances, they do not. I con- 

 clude therefore that in most cases, if not in all, these disturb- 

 ances originate in India, and their cause is to be sought for in 

 the meteorological conditions of Northern India itself. In some 

 instances they make their first appearance in Rajputana or 

 Central India, and there can then be no questionwhatever of their 

 purely local origin. 



Now the region over which the winter rains are more or less 

 regularly recurrent coincides with that in which the relative 

 humidity of the air at this season, instead of diminishing towards 

 the interior of the country, increases with the increasing distance 

 from the coast. In any month between March and December, 

 as we proceed from the coast of Bengal towards the Upper Pro- 

 vinces, the air becomes drier and drier, not only as containing 

 an absolutely smaller quantity of water vapour, but also, inmost 

 months, in -virtue of its increased capacity for taking up vapour, 

 owing to its higher temperature. But from December to March 

 the dryness increases inland only as far as Behar. Beyond this, 

 although the quantity of vapour in the air remains very nearly 

 the same or even undergoes a slight diminution, in virtue of the 

 increasing cold there is an approach to that temperature at which 

 this small quantity of vapour would begin to condense, forming 

 cloud or fog ; and it is in the Punjab that, in this sense, the air 

 is most damp. The result is that which our registers show to 

 be the case, viz. that from December to March it is also the 

 most cloudy province. This seems to depend very much on the 

 stillness of the air. The vapour that is always being given off 

 from the earth's surface diffuses gradually upwards in the still 

 atmosphere, and soon reaches such an elevation that it begins to 

 condense as cloud. When once a moderately thick bank of 

 cloud is thus formed, the equilibrium of the atmosphere is 

 speedily disturbed. It is well known as a fact from Glaisher's 

 balloon observations, and is also a consequence of the dynamic 

 theory of heat, that the vertical decrease of temperature in a 

 cloud-laden atmosphere is much slower (about one-third) than 

 that in a clear atmosphere. This initial disturbance will suffice 

 then to cause an indraught of air from around, an ascending 

 current is set up, the barometer falls ; warm, vapour-laden winds 

 pour in from the south, and we have all the conditions of the 

 winter rains. 



If this view be just, the stillness of the atmosphere combined 



with the presence of a moderate evaporation must be accepted 

 as the condition which primarily determines the formation of 

 barometric minima and the winter rains of Northern India. 

 And this stillness is obviously due to the existence of the lofty 

 mountain ranges which surround Northern India, leaving free 

 access to the plains open only to the south. 



Were the Himalayan chain absent and replaced by an un- 

 broken plain stretching up to the Gobi Desert, it is probable 

 that the winter rains of Northern India would cease ; any local 

 evaporation in the Punjab and Gangetic valley would be swept 

 away by strong, dry, north-east winds blowing from the seat of 

 high pressure, which, in the winter months, lies in Central Asia, 

 and instead of the mild weather and gentle breezes which now 

 prevail at that season on the Arabian Sea, it would be the 

 theatre of a boisterous and even stormy monsoon, such as is its 

 local equivalent of the China Seas. 



SCIENTIFIC SERIALS 



Bulletin de V Acadimie des Sciences de St. Pctersbourg, vol. 

 xxix. No. 2. — On a new comet, by O. Struve. Its elements, 

 calculated by Herr Seyboth, are:— T= 1SS4, January 23-225 

 average time of Pulkowa ; x = 92 19' 39" ; SI - 253" 22' 52" ; 

 i - 74° 21' 56" ; ui = 19S 56' 47" ; q = 9-87922. Dr. Struve 

 considers it as identical with the comet of 1812, calculated by 

 Encke, and adds a note, by Herm. Struve, about the sudden 

 increase of its light on September 19 to 22. — A report on M. 

 Backlund's memoir on the motion of the comet of Encke from 

 1871 to 1881, by O. Struve.— On petrified wood from Ryazan, 

 by Prof. Mercklin ; it is like Cupressinoxylon erraticuni. — Ob- 

 servations on some propositions relative to the numerical function 

 E(x), by V. Bouniakovsky (third paper). — Remarks on Gina- 

 kirti's " Kampakakathanakaka," translated by A. Weber, by 

 Otto Bohtlingk. — On the contact of inverse figures with the 

 polar reciprocals of the directing figures, by J. S. and M. N. 

 Vanecek. — Note on wollastonite, by N. Kokscharow. — Tele- 

 phonic phenomena in the heart produced by the irritation of 

 nervus vagus, by N. Wedenski. — On the use of the telephone for 

 the measurement of temperature, by R. Lenz. —On terrestrial cur- 

 rents compared with magnetic variations, by H. Wild. — On the 

 variability of the light of Y Cygni, by Ed. Lindemann. The 

 observations were made in 1S81 to 1883, and the magnitude 

 varied from 6'8 to io'4, showing an annual periodicity. The star 

 changed its colour, as also its shape, becoming sometimes more 

 nebulous, and the changes could scarcely be explained by mere 

 conditions of observations. — Determination of the parallax of a 

 Tauri, by Otto Struve. Its value, deduced from observations 

 made in 1850 to 1857, is o'''5l6, with a probable error of o" '057. 

 — On some arithmetical consequences of the formulae for the 

 theory of elliptical functions, by Ch. Hermite. — Note on the 

 discovery of kalait in Russia, by N. Kokscharow. — Studies on 

 milk (second and third papers), by Heinrich Struve ; being a 

 series of analyses of cows' and human milk, which bring the 

 author to the conclusion that there are two kinds of caseine, 

 the o-caseine and the /3-caseine. — On the atmospheric waves 

 produced by the Krakatoa eruption, by M. Rykatcheff. 



Verhandlungen des Naturhistotischen Vereins der preus- 

 sischen Rlieinlande und Westfalens, fortieth year, 1883. — Contri- 

 butions to the knowledge of the igneous rocks in the Carboni- 

 ferous hills and New Red Conglomerates between the Saar and 

 the Rhine, by H. Laspeyres. — On the trachyte of Hohenburg 

 near Bonn, by the same author. — A study of the Devonian 

 formations between the Roer and Vicht Rivers, by E. Holzappel. 

 — Remarks on the loess of the Lahn Valley, by F. F. von Ducker. 

 — Tertiary shingles of marine origin on the slate hills of Nassau 

 and Ems, by the same author. — An account of some living 

 American reptiles, spiders, and insects found at Uerdingen amongst 

 the dye-woods imported for the Crefeld silk dyeworks, by F. 

 Stollwerck. — Report on the prehistoric remains of the Sieg 

 Valley, by Dr. M. Schenck. — On the development of the mining 

 and smelting industries in the Sieg district, by H. Gerlach. — 

 Remarks on some monstrosities and aberrations in the colour of 

 the mammals of Westphalia, by Dr. H. Landois. — On the 

 greenstone of the Upper Ruhr Valley and its association with 

 the slates of the Lenne district, by A. Schenck, jun. — A descrip- 

 tion of some archaeological remains from the Vlotho district, Weser 

 Valley, by H. D'Oench. — A contribution to the study of the 

 flora of the Rhenish Province, by M. Melsheimer. — A surveyof 

 the geological relations in the French Ardennes, by Prof, von 



