« ForrigeFortsett »
circumstanced for carrying out effectually the system of stormwarnings.
23. On the contrary, Great Britain, France, and the rest of Western Europe, are unfavourably situated to allow of timely warning being given of coming storms. If no warning is sent till the storm has made its appearance, it is too late for the western seaports. In Europe, however, stormy weather is accompanied by a diminution in the atmospheric pressure, the centre of which, after traversing more or less of the Atlantic, arrives on the coast of Europe. The existence of this diminished pressure is made known by the barometer when the maximum depression is still at a considerable distance out in the ocean ; and collateral information pointing to an advancing storm is to be obtained from the direction of the wind and the cirrus cloud. Here, then, we have the materials for foretelling the approach of storms on the west coast of Europe. For though we have not the same advantages towards arriving at the degree of certainty of the American predictions, and so of telegraphing to ports on the west coast that a storm is actually seen advancing on them, yet from the premonitions afforded by the barometer, the wind, and the cirrus cloud, we can warn them to prepare for a storm likely to visit them. The giving effect to this idea constitutes the splendid contribution to practical meteorology made by Admiral Fitzroy in February 1861, by the system of storm-warnings which has since been adopted by almost every country in Europe—a service which has made his name a household word, and entitled him to be considered as a public benefactor.
24. Considering the practical application of the knowledge of storms towards the saving of life and property, it is a duty incumbent on European meteorologists (being the most important practical problem they have to solve) to examine, analyse, and carefully study in detail the storms which have traversed Europe during the last few years,— when, from the growing popularity of the science, meteorological stations have largely increased—with the view
of ascertaining the course storms usually follow, and the causes by which that course is determined, so as to deduce, from meteorological phenomena observed, not only the certain approach of a storm, but also the particular course it will take in its passage over Europe. In carrying out this extensive investigation, the “ Bulletin International' of Le Verrier, published daily, if supplemented by additional observations from places in the British Islands, and in Northern, Eastern, and South-Eastern Europe, will furnish the required materials. This admirable publication, which must be regarded as the latest important step taken in the progress of meteorology, shows graphically the atmospheric pressure, and the direction and force of the winds, each morning over Europe, together with tables of temperature, rainfall, cloud, and sea disturbance.
25. The next important step to be taken in the development of the capabilities of the science to promote the interests of humanity, will, we trust, be the giving practical effect to a suggestion made by a writer in the 'Athenæum' of the 28th September 1867, to the effect that Mr Reuter should add to his telegraphic messages a line, which need not consist of more than six letters and as many figures, announcing the state of the weather from all points of his world-wide correspondence. Thus, B. 30.15, T. 51, N. E., with R., S., F., would indicate that the barometer was 30.15 inches, the temperature 51°, the wind from the N. E., and R., S., and F., rain, snow, or fair, as the case may be. The benefit of such a practice would, it is justly added, be incalculable, for ere long all who are interested in the weather would be better prepared to take advantage of the warnings of storms on all occasions, particularly during the seasons of the year when gales most frequently occur. Much might also be contributed to the meteorology of the globe by missionaries sent out to the islands of the Pacific, and other parts of the world remote from civilised society. If possessed of the principal meteorological instruments, and of a moderate knowledge of the science, the missionary could not fail to benefit his fellow-men, and legitimately increase his influence over them, by often warning them of approaching storms and other changes of the weather. This can be done more easily and with great certainty in tropical and subtropical countries, where a fall of the barometer slightly greater than usual, and a change of the wind from its ordinary direction, indicate the presence of a storm at no great distance. By closely watching the wind and the barometer, the course the storm is taking can be readily known.
26. In the schools of the United States of America, Meteorological Observations, and the keeping of Meteorological Registers, form a part of the common education of the people. Also in the higher schools of France, and some other European countries, systematic instruction is communicated on this subject. But in this country few even of the liberally educated classes are able to read from a vernier; they are ignorant of the use of the movable cistern of a barometer; they have not the elementary knowledge to give an intelligible interpretation to the fluctuations of the barometer as indicative of coming changes of the weather; and when required to send their barometers to a distance for repair, so ignorant are they of their construction, that they forward them by rail as ordinary parcels, thus almost to a certainty securing their destruction. This state of things is the necessary consequence of the general neglect which meteorology receives in our educational system. There are, however, a few noteworthy exceptions. Meteorology has been taught for upwards of thirty years in the Dollar Institution, which has long been distinguished for the lead it has taken in incorporating science into its curriculum of study. This example has recently been followed by the Roman Catholic College at Stonyhurst, the Grammar School of Aberdeen, the High School of Inverness, Lerwick Educational Institute, Elgin Institution, Larchfield Academy, and other schools in the country. But the objects of meteorology can never hold that place in the public mind to which they are entitled, till the science becomes, as in America, a recognised branch of education. As contributing towards this desired result, the name of Mr Thomas H. Core, now of the International College, London, deserves special mention, in respect of his having, while mathematical master in the Church of Scotland's Normal School, Edinburgh, systematically trained the students to regular habits of meteorological observation. When the law of storms begins to be generally understood, and, as a consequence, the value of observations of the barometer, of the direction of the wind, and of the appearances of the clouds, comes to be appreciated as heralding changes of the weather, we cannot doubt that this very practical age will take steps to provide for the instruction of the people in the elementary facts of meteorology, and in the use of the different meteorological instruments.
THE WEIGHT OR PRESSURE OF THE ATMOSPHERE.
27. THE Barometer is the instrument employed to measure the height of a column of mercury supported by the pressure of the atmosphere. From this height the weight of the atmosphere is ascertained. The fundamental principle of the barometer cannot be better illustrated than by Torricelli's experiment. Take a glass tube (fig. 1), 33 inches in length, open at one end; fill it with mercury, and, closing the open end with the finger, invert it, and plunge the open end into a bowl (c) also containing mercury. The column will fall in the tube to about 30 inches above the surface of the mercury in the bowl, if the experiment be made near the level of the sea. The fluid is upheld in the tube by the air outside of it pressing on the mercury in the bowl ; and since the one thus balances the other, it is evident that the mercurial column will serve as an accurate indicator of the varying pressure of air. The space a b in the tube above the mercury is one of the nearest approaches to a vacuum that can be made. It is called the Torricellian vacuum.
28. The heights of the columns of two fluids in equilibrium are inversely as their specific gravities; and as air is 10,784 times lighter than mercury, the height of the atmosphere