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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. VIII. SYNCHRONOUS WEATHER-CHART OF THE WEST INDIES, FOR 1ST OCTO

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

ME TE OROL O G Y.

CHAPTER I.

HISTORY AND SCOPE OF METEOROLOGY.

1. METEOROLOGY is the science of the weather. The term was originally applied to the consideration of all appearances in the sky, astronomical as well as atmospherical; but it is now restricted to that department of natural philosophy which treats of the multifarious phenomena of the atmosphere that relate to weather and climate, their relations to each other, and the laws to which they are subject.

2. The objects which astronomy takes cognisance of being few in number, and the laws by which their motions are regulated being also few, it is comparatively easy to account for the phenomena, and, from a few data, to assign to the heavenly bodies their past, present, and future positions. But it is quite different with meteorology. Owing to the complexity and intricacy of the phenomena, and the manifold influences by which they are modified and determined, it would be a task, even supposing the data before us, beyond the compass of the human intellect to give a rational and perfectly satisfactory explanation of them. Viewed in this light, meteorology is the most difficult and involved of the sciences; hence the only procedure admissible in the first place is long and patient observation, and a faithful recording of the facts observed.

3. From the nature of the subjects which make up the science of meteorology, we may infer that they occupied men's minds from a remote antiquity. The splendid and evervarying panorama of the sky and the variations of temperature through the days and the seasons, together with the other atmospheric changes constituting the weather which affect in so powerful a manner the necessities and comfort of man, are of a nature well fitted to arrest his attention. From the time spent in the open air during the early ages, and from the imperfect protection then enjoyed against the inclemency of the seasons, the appearances which were found by experience to precede changes of weather were eagerly recorded and handed down in the sententious form of weather proverbs. In this way many valuable facts were ascertained and passed current from hand to hand, so that there is perhaps no science of which more of the leading facts and inferences have been so long incorporated into popular language.

4. Aristotle was the first who collected, in his work 'On Meteors,' the popular prognostics of the weather. A number of these were derived from the Egyptians, who had long studied the science as a branch of astronomy, while a large number were the fruit of his own observation, and bear the mark of his singularly acute and reflective mind. Theophrastus, one of Aristotle's pupils, next took up the subject, classifying the commonly received opinions of the weather under four heads—viz., the prognostics of rain, wind, storms, and fine weather. He contented himself with discussing the subject purely in its popular and practical bearings, making no attempt to explain phenomena the occurrence of which appeared so irregular and capricious. Cicero, Virgil, and a few other writers, also wrote on the weather, but made no substantial additions to our knowledge ; indeed, the treatise of Theophrastus contains nearly all that was known down to comparatively recent times. Partial explanations were at

tempted by Aristotle and Lucretius, but as they had not the elements necessary for such an inquiry, owing to the general ignorance which prevailed on matters of physical research, their explanations were necessarily vague, and abounded with references to superstitious beliefs, often ridiculous and absurd.

5. Meteorology remained in this dormant condition for ages, and no progress was made till proper instruments were invented for making real observations with regard to the pressure, the temperature, the humidity, and the electricity of the atmosphere.

INVENTION OF METEOROLOGICAL INSTRUMENTS.

6. The Barometer.—The invention of the barometer by Torricelli in 1643, and the experimental proof of the weight of the atmosphere by means of it, a few years after, by Pascal, was undoubtedly the first step in the progress of meteorology toward the rank of a science. This memorable discovery, in disclosing, by the elevations and depressions of the barometric column, what was passing in the more elevated regions of the atmosphere, largely extended our knowledge of this element. It should be further remarked that the value of the barometer as an indicator of the weather gave an additional impetus to the study of the science.

7. The Thermometer.—The invention of the air-thermometer, by Sanctorio of Padua, in 1590, laid the foundation of a salutary revolution in the science, since it pointed to an exact determination of the temperature of the air, which is by far the most important element of the weather in its relation to our welfare and interests. Improvements were made on the instrument by an Italian artist about 1655, who used wider tubes, terminating in bulbs, and filled with alcohol ; and by Römer, who used mercury, and, starting from the melting-point of ice, divided the tube into degrees, each intended to represent the 100,000th part of the bulb.

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