mxa fork HaU (^allege of Agriculture At Qlorncll IniwetaitH atljata, SJ. 1- ICxbrarg Library Bureau Cat. No. 1137 Cornell University Library QC 990.I39B6 A practical guide to the climates and we 3 1924 000 030 514 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924000030514 CLIMATES AND WEATHEE OF INDIA A PKACTICAL GUIDE TO THE CLIMATES AND WEATHEE OF INDIA, CEYLON AND BUKMAH AND THE STOEMS OF INDIAN SEAS BASED CHIEFLY ON THE PUBLICATIONS OF THE INDIAN METEOROLOGICAL DEPARTMENT HENEY F. BLANFOED, F.E.S., F.E.Met.S. LATE METEOROLOGICAL REPOBTER TO THE GOVERNMENT OF INDIA HONORARY MEMBER OF THE IMPERIAL AND ROYAL METEOROLOGICAL SOCIETY OF AUSTRIA AND OF THE METEOROLOGICAL SOCIETY OF THE MAURITIUS CORRESPONDING MEMBER OF THE GERMAN METEOROLOGICAL SOCIETY HonOon MACMILLAN AND CO. AND NEW TOEK 1889 Printed by R. & R. CLARK, Edinburgh, TO LIEUT.-GENERAL EIOHABD STRACHEY R.E., C.S.I., F.R.S. :^ PKBSIDENT OF THE KOYAL GEOGBAPHICAL SOCIETY THE ORIGINAL PKOJEOTOE AND PKOMOTEE F OP THE C^ METEOEOLOGIOAL DEPAKTMENT OF THE GOVEENMENT OF INDIA TO WHOSE ADVOCACY ITS ESTABLISHMENT IS MAINLY DTTE THIS. LITTLE BOOK WHICH IS THE OITTCOMB OF THE WOBK OF THAT DEPAETMENT IS COEDIALLY INSOEIBED BY THE AUTHOR ^ ^yy ^ PKEFACE Owing mainly to the systematic work of the Meteorological Department, established by the Government of India in 1875, we now possess a far better knowledge of the weather and climate of India than of those of any other tropical country, and, in some respects, better than of those of many parts of Europe ; thanks to the greater simplicity of the processes concerned, and to the prominence and regular recurrence of the more striking phases of the seasons. But to the great majority of the lay public, of those to whom information of this kind is a matter of daily interest and importance, this knowledge is as a sealed book. It may be found, indeed, embodied in the volumes periodically issued by the meteorological office, or scattered through the journals and transactions of various scientific societies : but all publications of this class are addressed to students and co-workers in the field ; and besides being, in most cases, too technical in form to approve itself to the tastes and requirements of the general public, the literature is too voluminous, and the information it contains too diffuse, to be readily accessible to those who have neither the time nor the opportunity to search through so wide a field. The want of some work that shall afford, in a compen- dious and apprehensible form, such information as is con- stantly in demand by those engaged in administration, in — viii PREFACE agriculture, sanitation, engineering works, and the like, and especially in the navigation of Indian seas, or by those who wish to follow, intelligently, the current reports of the weather issued daily at Simla and Calcutta, has long been obvious, and has been definitely expressed in the anniversary address of the President of the Asiatic Society of Bengal, delivered at the annual meeting of the Society in February 1887, in the following terms. After noticing the errors of the older storm literature, as represented by the works of Eeid and Piddington, he remarks : " It is much to be desired that steps should be taken by some recognised authority, to prepare a simple and popular manual on the subject [of storms], based on the sounder knowledge which modern science has acquired. And indeed such a work is also needed for the meteorology of the land, to enable the lay public to understand and iutelligently appreciate the mass of meteorological literature which the Government Gazettes and the entire press so lavishly place before us. We want something more popular ' than the very valuable Vade Mecum ' of Mr. Blanford, not a scientific investigation of principles, but a brief, clear, and comprehensive explanation of the observations ordinarily made, their objects, uses, and mode of application." It is to meet this want that the present work has been taken in hand. It is not addressed to meteorologists and physicists, although some of the data and facts adduced may be not without interest to those who are principally concerned with meteorology in its scientific aspect ; but more particularly to agriculturists, medical officers, engineers, pilots, and other seafaring men, and to those others of the general public to whom the weather and the climates of India and of its seas are practical and not scientific objects of interest. I have therefore selected from the abundant materials now available, and from the general conclusions from these, PREFACE ix worked out lay Messrs. Eliot, Hill, and other Indian meteor- ologists, such portions as are of practical importance to inquirers of this class, and have endeavoured to set them forth in clear and concise language, avoiding, as a rule, all discussion of a technical character, and all technical forms of expression that have not become more or less familiarised to the public through the medium of the weather reports and other literature of a popular character. The explanation of these latter is one of the objects of the work. The work consists of two parts. The first gives a con- cise general description of the kinds of observations made at Government observatories, and the information they directly afford. This constitutes what may be termed the elements of the climate and weather. The second deals with the practical applications of weather knowledge. In the first part, the intensity of the sun's heat in India, the air temperature, humidity, cloud, winds, and rainfall, together with the principal variations they present in differ- ent parts of the Empire, and the changes they undergo in the course of the year, the behaviour of the barometer and the methods of interpreting and utilising its teachings, and the constitution and nature of storms, are briefly described in separate sections. The second and more extensive part is devoted to a detailed notice of the local climates—first, those of the chief hiU stations, and then those of the different provinces of the low country. Then follow the weather characteristics of the three Indian seasons, illus- trated by the information furnished by the daily weather charts published at Simla ; the tracks and seasons of storms on the seas around India, with some practical deductions for the guidance of seamen; and finally, the statistics of rainfall, evaporation, and wind pressure, which are chiefly required by engineers in dealing with questions of water X PREFACE supply, drainage, and the stability of structures. In this section an attempt has been made for the first time to estimate the average rainfall of some of the chief river basins, a datum of great importance to physical geographers, not less than to engineers. In the Appendices are given, in a condensed form, some portions of the statistical data on which the above de- . scriptions are based, much of which have been computed specially for this work. They include the more import- ant climatic elements of 92 places in India, Burmah, and Ceylon, a list of weU-recorded storms in the Bay of Bengal, with their approximate places of origin, tracks, and rates of movement, and tables of the average, maximum, and minimum monthly rainfall at 114 places. Among the friends to whom I am indebted for informa- tion and assistance, I must especially mention Mr. James Forrest, Secretary of the Institution of Civil Engineers, to whose kindness I owe much of the information respecting engineering works and professional observations in India, Africa, and Australia, which will be found quoted in the final section of Part II. Also Captain Henry Toynbee, late of the London Meteorological OfBice, and his successor. Lieutenant C. W. BaiUie, E.N., to whom I am indebted for valuable assistance in preparing the section on Storms in Indian Seas. Folkestone, A-pril 1889. — CONTENTS PART I.—ELEMENTS OF CLIMATE AND WEATHER 1. THE HEAT OF THE SUN IN INDIA— paoe Use of the Sun Thermometer—Insolation Temperatures at Hill Stations and on the Plains—Duration of Sunshine . 1 2. THE TEMPERATURE OF THE AIR— Observation of Temperature—Mean Temperature—Diurnal Varia- tion and Range—Irregular Changes—Annual Range—Hottest and Annual Variation 6 Coolest Months ; .... 3. THE TEACHINGS OF THE BAROMETER— Effect of Elevation—Annual Fluctuation—Diurnal Fluctuation Magnitude of Variations with Weather—Temperature Correction —Barometric Changes with Weather—Distribution of Pressure Barometric Depressions — Reduction to Sea-level — Barometric Charts- and Isobars—Barometric Gradients—Persistent and Tem- porary Differences—Summary ..... 19 4. THE WINDS— Lightness of the Winds in India—Wind Measurement— Beaufort's Diurnal Variation Annual Variation Numbers—Wind Pressure— — ; the Monsoons — Relations of Winds to Barometric Pressure; Cyclonic and Anticyclonic Systems . 30 5. DAMPNESS AND DRYNESS— Relative and Absolute Humidity — Variations of Humidity in India—Diurnal Variations—Relation to the Winds—Geographical Distribution of Humidity—Annual Variation . .46 - — CONTENTS 6. HAZE, FOG, AND CLOUD— page Haziness of the Sky—Dust Haze—Fog—Forms and Nomenclature of Clouds—The Teachings of Clouds—Cloud Proportion—Distri- hution ........ 53 7. THE RAINFALL The Contrasts of Indian Eainfall—Geographical Distribution Seasonal Disti'ihution—Statistics of Monthly Eainfall ; Quantity and Frequency — Average Heaviness—Excessive