WEEKLY EVENING MEETING,

Friday, March 28, 1862.

JOHN PETER GASSIOT, Esq. F.R.S. Vice-President, in the Chair.

REAR-ADMIRAL FITZ-ROY, F.R.S.

An Explanation of the Meteorological Telegraphy, and its Basis, now under trial at the Board of Trade.

THE telegraphic communication of meteorological changes from distant stations to a central position, whence occasional warnings of impending storms might be given, which has been organized and tried by Government, had its origin at a meeting of the British Association in 1859, at Aberdeen, under the presidency of that deeply lamented Prince whose short life was wholly devoted to the most useful objects. It was then resolved by their Council that application should be made to Her Majesty's Government for an organization and trial of a plan by which the approach of storms might be telegraphed to distant localities. two meetings in Buckingham Palace, early the following year (1860), minutes were authorized on this subject, and correspondence ensued which resulted in establishing a telegraphic communication of meteorological facts between twenty home stations, besides foreign ones-and daily with Paris.

The Aberdeen meeting had only just terminated, when public attention was startled by the loss of the Royal Charter.' It so happened that the storm which caused the destruction of that iron ship (notwithstanding power of steam additional to that of sails-and while a sailing ship, managed differently, was bearing its brunt uninjured within a few miles distant *)-that storm, completely cyclonic, passed over the middle of England, and could be more fully investigated than any storm hitherto, because in every direction observers happened to be ready, who recorded ample statical facts, and many valuable dynamical results.

Advancing gradually, the first cautionary or storm-warning signals were made early in 1861, but on that occasion were unhappily disregarded in the Tyne, and on the following days awful losses of life were witnessed on the north-east coasts. From that time to the present similar warnings have been given there and elsewhere, with increasingly advantageous effects, it appears-if one may judge, in the first The Cumming.'

instance, by applications since sent officially from all the principal ports, and from the chief associations of Underwriters, in addition to Admiralty approval, and the co-operation of the Coast-guard.

In August, 1861, the first published "forecasts" of weather were tried; and after another half-year had elapsed for gaining experience by varied tentative arrangements, the present system was established. Twenty reports are now received each morning (except Sundays), and ten each afternoon, besides five from the Continent. Double forecasts (two days in advance) are published, with the full tables (on which they chiefly depend), and are sent to six daily papers, to one weekly,-to Lloyds' to the Admiralty, -and to the Horse Guards, besides the Board of Trade.

These forecasts add almost nothing to the pecuniary expense of the system,—while their usefulness, practically, is said to be more and more recognized.* Warnings of storms arise out of them; and (scarcely enough considered) the satisfaction of knowing that no very bad weather is imminent, may be very great to a person about to cross the sea. Thus their negative evidence may be actually little less valuable than the positive.

Prophecies or predictions they are not:-the term forecast is strictly applicable to such an opinion as is the result of a scientific combination and calculation, liable to be occasionally, though rarely, marred by an unexpected "downrush," † of southerly wind, or by a rapid electrical action not yet sufficiently indicated to our extremely limited sight and feeling. We shall know more and more by degrees. At present it is satisfactory to know that the measures practised daily in these proceedings do not depend solely on one individual. They are the results of facts exactly recorded,-and deductions from their consideration, for which rules have been given. An assistant has been practised and is able to share their responsibility. Others are also advancing in the subject of dynamical meteorology.

Air currents sometimes flow side by side, though in opposite directions, as "parallel streams," for hundreds or even thousands of miles. Sometimes they are more or less superposed-occasionally, indeed frequently, crossing at various angles; sometimes combining, and by the composition of their forces and qualities causing those varieties of weather that are experienced as the wind veers more toward or from the equator or the nearest pole; and sometimes so antagonistic in their angular collision as to cause those large circling eddies or rotatory storms called cyclones (in modern parlance), which are really like the greater storms in all parts of the world, although they do not quite assimilate to those local whirlwinds, dust-storms, and other commotions

At a recent meeting of the shareholders of the Great Western Docks, at Stonehouse, Plymouth, it was stated officially that "the deficiency (in revenue) is to be attributed chiefly to the absence of vessels requiring the use of the graving docks for the purpose of repairing the damages occasioned by storms and casualties at sea."-(Feb. 24, 1862.)

+ Herschel.

of atmosphere which seem to be more electrical in their characteristics, if not in their origin.

Whenever a polar current prevails at any place, or is approaching, the air becomes heavy, and the barometer is high or rises. When the opposite (equatorial or tropical) prevails or approaches, the mercury is low or falls, because the air is, or is becoming, specifically lighter, and these changes take place slowly.

Whenever, from any causes-electrical, chemical, or simply mechanical either current, or any combination of currents, ceases to press onward without being opposed, a gradual lightening of the atmosphere, through a greater or less area of hundreds, or perhaps thousands of miles occurs, not suddenly, but very gradually, and the barometer falls. There is less tension.

To restore equilibrium, the nearest disposable body of air (so to speak) or most moveable, advances first; but an impulse, at the same time, may be given to other and greater masses that-though later in arriving-may be stronger-last longer, and cause greater pressure mechanically as well as by combination. Air, like water, mingles very slowly, either from above or laterally.

Taking, with Dové, north-east and south-west (true) as the "windpoles," all intermediate directions are found to be more or less assimilated to the characteristics of those extremes; while all the variations of pressure, or tension, many of those caused by temperature, and all varieties of winds, may be clearly and directly traced to the operations of two constant principal currents-equatorial or tropical, and polarour north-east and south-west.

Great distinction should be marked between those ever alternate and often conflicting main currents-tropical and polar, and the local effects of their union, or antagonism, namely mixed winds-whether westerly or easterly, with occasional cyclones or circulating eddies, on a large or small scale.

Considering that the lower current does not ordinarily extend far upward (only a few thousand yards, or even feet), and that high land, mountains, especially ranges of mountains, alter and impede its progress, a variety of eddy winds, or as it were streams of wind, with local and apparently anomalous effects, must be frequently caused.

Electrical action, condensation of vapour into hail, snow, rain, or fog, causing heat; or its other changes, namely, evaporation, rarefaction, and expansion-absorbing heat, and therefore causing coldimmediately affect currents of air in a degree proportional to such influence; inducing horizontal motion.

The polar current always advances from the polar quarter, while laterally moving eastward (like a ship making lee-way), being pressed towards the east by the tropical flow which advances from the southwestward, usually above and at an angle with the polar stream or current of air, often mixing with it, but at times separately penetrating downward, then sweeping and warming the earth's surface, uncombined with the polar current, even while feeling its approaching

influence and thus, as it were, forcing passages between streams of chilling polar air that at the same time are moving in opposite and nearly parallel directions.

Sometimes their opposition is so equal, and equilibrium is so complete, that a calm is the result, no sensible movement horizontally along the earth's surface being perceptible.

Self-registering barometers show the alterations in tension, or, so to speak, the pulsations, on a large scale, of atmosphere, by hourly marks; and the diagram expresses to a practised observer what the "indicator card" of a steam cylinder shows to a skilful engineer, or a stethoscope to a physician.

Our own Islands have very peculiar facilities for meteorological communication by telegraph, between outlying stations on the sea coast and a central place-all being at nearly the same level, and nearly all comparatively uninfluenced by mountain ranges.

And now, the results are, that, having daily knowledge of weather (including ordinary facts of a meteorological nature), at the extreme limits and centre of our British Islands, we are warned of any great change taking place; the greater atmospherical changes being measured by days-rather than by hours. Only local changes, however violent they may be occasionally (and dangerous in proportion to their suddenness and violence),-only such changes are unfelt at a distance, and do not influence great breadths,—say, hundreds of miles in area,— of atmosphere.

Extensive changes, showing differences of pressure, above or below the normal or mean level, amounting to an inch or thereabouts, are certain to be followed by a marked commotion of the elements in the course of a few days. If the fall has been sudden, or the rise very rapid, swift, but brief, will be the resulting elementary movement; if slow, or gradual,-time will elapse before the change, and the altered state of weather will take place more gradually, but last longer.

Notice may thus be obtained, and given, a few hours, or a day, or even some days, before any important change in the weather actually

occurs.

Having such knowledge, it obviously follows that telegraphic warning may be sent in any direction reached by the wires, and that occasionally, on the occurrence of very ominous signs, barometric and other-including always those of the heavens-such cautions may be given before storms as will tend to diminish the risks and loss of life so frequent on our exposed and tempestuous shores.

It has been proved also, lately, that storms, indeed all the greater circulations of atmosphere between the tropics and polar regions, have an eastward motion, bodily, while circulating around a centrical area. Within the tropics it is otherwise, or westward, till they recurve.

In answer to a question from the Royal Commissioners on Lights, Buoys, and Beacons, Sir John Herschel stated that "the most important meteorological communication which could be telegraphed, VOL. III. (No. 35.)

2 H

would be information just fresh received by telegraph, of a cyclone actually in progress at a great distance, and working its way towards the locality. There is no doubt that the progress of a cyclone may be telegraphed, and might secure many a ship from danger by forewarning."

Successive, or rather, consecutive gyrations, circuits, or cyclones often affect one another, acting as temporary mutual checks, until a combination and joint action occurs; their union causing even greater effects as may be seen even in water currents, as well as in the atmosphere.

Between the tropics and the polar regions, or in temperate zones, the main currents are incessantly active, while more or less antagonistic, from the causes above mentioned: besides which, wherever considerable changes of temperature, development of electricity, heavy rain, or these in combination, cause temporary disturbance of atmospheric equilibrium (or a much altered tension of air) these grand agents of nature, the two great currents, speedily move by the least resisting lines, to restore equilibrium, or fill the comparative void. One current arrives, probably, or acts sooner than the other, but invariably collision occurs, of some kind or degree, usually occasioning a circuit, a cyclonic or ellipsonic gyration; however little noticed when gentle, or moderate in force.

As there must be resistance to moving air (or conflicting currents), to cause gyration, and as there are no such causes, on a large scale, near the equator, there are no storms (except local squalls) in very low latitudes.

It is at some distance, from about five to twenty degrees, from the equator that hurricanes are occasionally felt in their violence.

They originate in or near those hot and densely-clouded spaces, sometimes spoken of as the "cloud-ring," where aggregated aqueous vapour is at times condensed into heavy rain (partly with vivid electrical action) and a comparative vacuum is suddenly caused, towards which air rushes from all sides. That which arrives from a higher latitude has a westwardly, that from a lower an eastwardly tendency, due to the earth's rotation, and to the change of latitude, whence a chief cause of the cyclone's invariable rotation in one direction, as above explained.

The hurricane or cyclone is impelled to the west, in low latitudes, because the tendency of both currents there is to the westward, along the surface although one, the tropical, is much less so, and becomes actually easterly near the tropic, after which its equatorial centrifugal force is more and more evident, while the westwardly tendency of the polar current diminishes; and therefore, at that latitude, hurricane cyclones cease to move westward (re-curve), go then eastwardly, and toward the polar quarter.

Great and important changes of weather and wind are preceded, as well as accompanied, by notable alterations in the state of the atmosphere. Such changes, being indicated at some places sooner than at others around the British Islands, give frequent premonitions; and