Sidebilder
PDF
ePub

facts in comparison with the vastness of the weatherchanges they were adduced to explain; but above all, the real difficulty of the subject, owing to the manifold influences in operation. But now that Meteorology has discarded all pretensions and theories, except in so far as the latter are the legitimate result of observation, it has acquired rapid development, and established its claim to be regarded as the youngest of the sciences.

In consequence of this, a great and growing interest on the subject is spreading among all classes, as is evinced by the number of meteorological instruments purchased, by the many zealous and self-denying observers in all parts of the civilised world, and by the still more numerous class who volunteer their services as observers. But since a knowledge of the elementary principles of Meteorology is not yet very generally diffused, much time and labour are often wasted from the use of imperfect instruments and imperfect methods of observation. To meet this want, the author has particularly described the various instruments in use, given directions for placing them in situations and in positions best suited for observation, pointed out how they are liable to get out of order, and explained the methods by which they may be put right when they happen to go wrong. The methods of reducing Meteorological Observations are explained at length, and tables are given for facilitating the work.

DIRECTIONS TO METEOROLOGICAL OBSERVERS IN KEGARD TO THE PUBLICATION OF THEIR STATISTICS.—The height of barometers above the level of the sea, accurately ascertained, is a serious desideratum in not a few published abstracts of Meteorological Observations. The labour which, in preparing this edition, the omission, or rough and incorrect statements, of heights has occasioned, has been excessive. In many cases it was necessary to ascertain the heights, or check those given, by the method of the barometric measurement of heights-viz., by selecting a number of days during which the barometer remained steady over the region in which the place was situated, and then calculating the height from the pressure and temperature at the place as compared with places in the vicinity whose heights were known. When the place was isolated from other stations the annoyance was still greater. Thus, since the height of Santiago de Chile, usually given at 2600 feet, is evidently 500 or 600 feet too high, the observations at this important station had reluctantly to be omitted in the construction of the Isobarometric Charts. Meteorological societies and observers should lose no time in rectifying this flagrant omission.

In publishing monthly or other Abstracts of Barometric Observations, the following information ought to be given :-1. The hour or hours of observation ; 2. The height of the cistern of the barometer above the sea; 3. The latitude and longitude; 4. The barometer reduced to 32° F., and corrected for instrumental errors, but not corrected for daily range ; 5. The mean temperature of the air. A column of the observations reduced to sealevel may be added ; but in such cases the reduction to 32° only should also be given. If these simple directions were observed, much labour and annoyance would be saved, and the value of the observations would be correspondingly enhanced. What meteorologists ask for, are simply the results of actual observations. It would be difficult to name any abstracts which excel, in these respects, those issued by P. Secchi.

Since storms and other important questions of Meteorology can only be discussed by Synchronous Charts which represent the weather at specified hours, it is indispensable, in publishing daily observations, to state the hour or hours at which they were made. When this is not done, much confusion and unsatisfactoriness is the result. Sometimes daily barometric means alone are published ; that is, if three observations are made a-day, none of these three observations, but a mean deduced from them, is published,—a figure which in discussing storms is in all cases of little use, and in cases when the storm is passing the place, absolutely of no use; and it cannot be used in determining the amplitude of the barometer fluctuations accompanying storms and other weather-changes. By this mode of publishing daily observations, a considerable proportion of the observations published in the ‘Annales de l'Observatoire Physique Central de Russie,' the greatest storehouse of meteorological facts in the world, are unfortunately deprived of a great part of their value. Indeed, if instead of daily barometric means, one daily observation at a specified hour had been given at the stations, it might have been possible to prepare synchronous charts of the greater part of the northern hemisphere. The observations published by the Meteorological Institute of Norway may be referred to as models of daily Meteorological Records. Uniformity in the methods of observation practised by Meteorologists is also most desirable. A SECOND BRUSSELS CONFERENCE is perhaps the only means by which the advantages of uniformity of observation and of publication of results may be secured.

June 1868.

LIST OF CHARTS.

PLATE

I. ISOBAROMETRIC LINES SHOWING THE MEAN ATMOSPHERIC PRESSURE

OF THE GLOBE FOR JULY.

II. ISOBAROMETRIC LINES SHOWING THE MEAN ATMOSPHERIC PRESSURE

OF THE GLOBE FOR JANUARY.

III. ISOBAROMETRIC LINES SHOWING THE MEAN ANNUAL ATMOSPHERIC

PRESSURE OF THE GLOBE.

IV. ISOTHERMAL LINES SHOWING THE MEAN TEMPERATURE OF THE

EARTH FOR JULY.

V. ISOTHERMAL LINES SHOWING THE MEAN TEMPERATURE OF THE

EARTH FOR JANUARY. VI. ISOTHERMAL LINES SHOWING THE MEAN ANNUAL TEMPERATURE OF

THE EARTH.

VII. SYNCHRONOUS WEATHER-CHART OF EUROPE, FOR 20 NOVEMBER 1863,

AT 8 A.M., to face page 242. VII. SYNCHRONOUS WEATHER-CHART OF THE WEST INDIES, FOR 1ST OCTO

BER 1866, at 8 P.M., to face page 265.

« ForrigeFortsett »