By Rear-Admiral Fitz-Roy, F.R.S.

INFORMATION about the weather, or respecting instruments available for popular use, as indicators of changes in our ever-varying atmosphere, has been extensively diffused daring late years, and especially since the telegraph has extended its electrical intelligence in every frequented direction.

The Board of Trade having arranged telegraphic and frequent communication between widely separated stations, and a central office in London, a means of feeling if not seeing successive simultaneous states of atmosphere over the greater extent of our islands was established, and an insight into its laws has been obtained, to which each passing month has added value.

Extensions of our arrangements to the Continent are contemplated in France, in Hanover, and in Prussia; and it may now be desirable to circulate amongst life-boat men and others a brief description of the basis and nature of the forecasts and occasional warnings which are given by the Meteorological Department.

These forecasts are not prophecies; they are carefully-drawn estimates of average probabilities, obtained by intercomparison of facts, observed, telegraphed, and duly weighed, according to known laws.

To explain the chief grounds on which they are based, and to assist in rendering the published tables or reports of weather more generally available by those whose interests are affected by atmospheric changes, the following passages are offered :— 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, 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 of atmosphere which seem to be more electrical in their characteristics, if not in their origin.

When 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.