By Rear-Admiral FITZ-ROY, F.R.S.

KNOWING these circumstances, and having accurate statistical observations of these various currents, at selected outlying stations, showing pressure (or tension), temperature, and relative dryness, with the direction and estimated horizontal force of wind at each place simultaneously, the consequences are already measurable approximately.

The facts now weighed and measured mentally—in what may be correctly called " forecasting " weather—are—the direction and force of each air-current or wind, reported telegraphically to the central station in London from many distant stations; their respective tension and temperature, moisture or dryness, and their changes since former recent observations.

These show whether any, or either movement or change is on the increase, or decrease; whether a polar current is moving laterally off, passing from our stations towards Europe, or approaching us from the Atlantic; whether moving direct towards the southwestward with great velocity or with slow progress.

If moving fast, in the direction of its length, it will approach England more from the east, its speed direct being twenty to fifty, or eighty miles an hour, while its constant lateral or easterly tendency (like a ship's leeway in a current) being only five miles an hour, is then insensible to us (though clearly deducible from other facts ascertained), and is that much in alteration * Continued from page 124 of the July Number of this Journal.

of actual direction as well as of what would otherwise be the velocity of the polar current.

With the opposite principal current-—the equatorial or south-westerly, more briefly and correctly tropical—similar but opposite results occur; the direct motion from a south-westerly quarter is accelerated, sensibly t our perception, by part of the eastward constant (about five miles hourly), and therefore a body of air approaches us sooner (other things being equal) from the westward than it does from the eastward.

To seamen accustomed to navigate in ships making leeway, while in currents setting variously over the ground, such movements, complicated as they may appear, are familiar.

There are the ship's headway, leeway, and drift, to be considered in combination with the motion or current rate of the buoyant water, and that perhaps an upper current, differing from one beneath, while each is passing across the bottom or bed beneath all.

But the circulating movements of motes in a beam of light across dusty air, in a draft, may perhaps show what is meant by such combined and varying motions of fluid, elastic, and mobile air, as are here mentioned.

One notable consideration is the disposal or progress of bodies of air united, or mixed, or contiguous to each other after their meeting—either directly opposed or at an angle—on the earth's (or ocean's) surface.

They do not vanish; they cannot go directly upwards, against gravitation ; westward they cannot generally go when there is collision or meeting, because the momentum, elasticity, and extent of the tropical " antitrade"* usually overpowers any direct polar current, or rises over it, and more or * Sir John Herschel's excellent term.

less affects the subordinate below by the friction of its eastward pressure.

Downward there is no exit; eastwardly (towards the east) the, accumulating air must go; and this pendency continued causes the varieties of wind from the westward, being more or less mixed, more or less purely polar or tropical as either one prevails in combination.

After a body of air has passed, and gone to some distance southward or northward, it may be stopped by an advancing and move powerful mass of atmosphere which is moving in a direction contrary to or diagonally across its line of force.

If their appulse be gradual and gentle, only a check occurs, and the weaker body is pushed back until its special qualities, respecting temperature and moisture, are so masked by those of its opponent as to be almost obliterated.

But if these currents meet with energy, at very different temperatures and tension, rapid changes are noticed as the wind shifts, and circuitous eddies, storms, or cyclones occur.

Otherwise, when their meeting is, as first mentioned, gradual, there is the return of a portion of either current (which previously prevailed) either direct or deflected—deflected even through more than one quadrant of a circle —by its advancing opponent, and retaining for some considerable time its own previous characteristics.

Thus we have, for short times, cold dry winds from the south-west instead of the usual warm and moist ones, or winds of this latter kind from the north instead of cold ones.

The circuitous tendency of air in motion, and the numerous impediments to its horizontal progress, such as land, ranges of mountains, hills, or even cliffs, induce many a deviation from normal directions extremely puzzling to the student of this subject; but so retentive is air of its tension and temperature, for a time, that, like currents in the ocean, each may be traced by its characteristics as long as within our island web of stations.

When the polar current is driven back by a tropical advancing from a southerly direction gradually, their action united becomes south-easterly (from the south-eastward), and as the one or other prevails, the wind blows more from one side of east or from the other.

Time is required to produce motion in the air, horizontally, and time is indispensable for its gradual cessation from movement.

Statical effects are noticed, at observatories, or by careful observers anywhere, hours or days before dynamical consequences occur.

When a body of atmosphere is moving from or towards the pole, its impelling force may cease, while the mass itself has a certain impetus, inertia, or momentum.

Diminishing tension results at the place of checked energy, and the upper current (always there) descends.

At the same time, also, there is an alteration of tension at the further extreme, which is then- meeting and mingling with, if not resisted, checked, and deflected by its advancing opponent. Consequent on this, an extent of air, reaching perhaps across some hundred miles, becomes, as it were, isolated.

Detached from its original source and maintenance, whether polar or tropical, and then quite surrounded by air of a different character, it is impelled in new and varying directions, still retaining, for a time, more or less of its characteristics until altevert entirely and totally incorporated with its conqueror. Hence we sometimes have cold tropical wind with electrical and other polar characteristics, for a limited time only, before the tropical current predominates; or, on the other hand, a warm polar air-current with other tropical peculiarities.

Moreover, in addition to these causes of apparent inconsistency or irregularity, there are the results of circling currents—streams of air retaining their features although changed (it may be even totally) in direction along the earth's surface, besides a variety of merely local alterations, such as are effected by high lands, or valleys, or coast lines.

All these, and many other minor considerations, ought to be familiar, to a forecaster of weather who would judge according to observed facts and ascertained laws.

Lunarists and astrometeorologists support theories which, if in accordance with facts, would affect our whole atmosphere, or a hemisphere, or at least an entire zone, in a similar way, on account of the supposed influencing causes acting over all the rotating earth, and not only over Europe or its adjacent islands.

At the Board of Trade from thirty to forty weather telegrams are received daily (except Sundays), and the present daily forecasts, or premonitions of weather are drawn up on the following arrangement.

Districts are thus assumed:— 1. Scotland, generally, along the coast.

2. Ireland, generally, around the coasts.

3. West central (Wales to the Solway) coastwise.

4. South-west England.

5. South-east England.

6. East coast.

As newspaper space is very limited, and as some words are used in different senses by various persons, extreme care is taken in selecting those for such brief, general, and yet sufficiently definite sentences as will suit the purpose.

Such words as are commonly found on published scales of force, or nature of wind and weather, are generally understood, and therefore are used in preference to others however expressive.

In saying, on any day, what the probable character of the weather will be to-morrow or the day after, at the foot of a table showing its observed nature that very morning, a limited degree of information is offered for about two days in advance, which is as far as may be yet trusted generally, on an average, though at times a longer premonition might be given with sufficient accuracy to be of occasional use.

Minute or special details, such as showers at particular places or mere local squalls, are avoided ; but the general or average characteristics, those expected to be principally prevalent (with but few exceptions) the following day, and the next after it, including the nights—not those of the weather actually present—are cautiously expressed after careful consideration.

Ordinary variations of cloudiness, or clear sky, or rain, of a local or only temporary character, are not noticed usually.

A broad general average, or prevalence, is kept in view, referring to a day or more in advance, and to a district rather than only to one time or place, should be remembered.

The great practical difficulty is in separating the effect, on the mind, of present states of air, weather, and clouds, from abstract considerations of what may be expected on the morrow or next following day.

As meteorological instruments usually foretel important changes by at least a day, or much longer, we have to consider what wind and weather may be expected from the morning observations, compared with those of the day immediately previous, as indicative of the morrow's weather, and of the day after, at each place, to take an average of those expectations, for each district collectively in groups, and then to estimate the dynamical effects which may be anticipated as the legitimate consequences of relative tensions, temperatures, and dryness occasioning more or less irregularity in the atmospheric equilibrium, and thus causing greater or less horizontal motions of aircurrents or winds.

Comparisons of the moist and dry thermometers are very useful, if well observed, in telling the hygrometric condition of the air, and thence, with other effects, showing how either current prevails, or has relative influence, a point of much importance in forecasting a change either way, as well as a probability of rainy or dry weather.

Those who are most concerned about approaching changes, who are going to sea, or on a journey, or a mere excursion; those who have gardening, agricultural, or other out-door pursuits in view, may often derive useful cautionary notices from these published expectations of weather, although (from the nature of such subjects) they can be but scanty and imperfect under present circumstances.

Objection has been taken to such forecasts, because they cannot be always correct, for all places in one district. It is, however, considered by most persons that general, comprehensive expressions, in aid of local observers, who can form independent judgments from the tables and their own instruments, respecting their immediate vicinity, though not so well for distant places, may be very useful, as well as interesting; while to an unprovided or- otherwise uninformed person, an idea of the kind of weather thought probable cannot be otherwise than acceptable, provided that he is in no way bound to act in accordance with such views, against his own judgment.

Like the storm - signals, such notices should be merely cautionary, to denote anticipated disturbance somewhere over these islands, without being in the least degree compulsory, or interfering arbitrarily with the movements of vessels or individuals.

Certain it is that although our conclusions may be incorrect, our judgment erroneous, the laws of nature and the signs afforded to man are invariably true. Accurate interpretation is the real deficiency.

Seamen know well the marked teristics of the two great divisions of wind, in all parts of the world, and do not care to calculate the intermediate changes, or combinations, to two or three points. They want to know the quarter whence the gale may be expected, whether northerly or southerly.

Every seaman will admit, that however useful, and therefore desirable, it would be to know exactly the hour of a storm's commencement —as our acquaintance with meteorology does not enable such times to be fixed—the next best thing is to have limits assigned for extra vigilance and due precaution, which limits are clearly stated, in all the printed popular instructions, to be from the time of hoisting the signal until two or three days afterwards.

But, say some, and justly, are ships to remain waiting to avoid a gale that, after all, may not happen? Are fishermen and coasters to wait idle and miss their opportunities ? By no means. All that the cautionary signals imply is, " Look out." "Be on your guard." "Notice your glasses and the signs of the weather." " The atmosphere is much disturbed." Perhaps sufficient thought has not always been given to the consideration of mere loss by wear and tear, risk, accident, delay, and demurrage, caused by a gale at sea, balanced against the results of waiting for a tide or two, perhaps once in two months, when cautioned by a storm signal.

But be this as it may, with coasters, short traders, or even screw colliers, the question is entirely different with ordinary over-sea or foreign-going ships, especially when starting from a southern or from a western port. To such vessels a gale in the Channel, or even during the first day or two after clearing the land, must always be very prejudicial. Officers and men are mutually strange. Things are not in their place, often not secured; and the ship, perhaps, is untried at sea.

Of course, however, these remarks are inapplicable to fine first-class ships, and to powerful, well-managed steamers, independent of wind and weather, which start at fixed hours.

It is scarcely too much to say, even now, that if due attention be paid on the coasts to cautionary signals, and at the central office, to the telegraphed reports, no very dangerous storm need be anticipated, without more or less notice of its approach being generally communicated around the British islands, or to those particular coasts which probably may be most affected by its greatest strength. But this hardly applies to our extreme outposts, such as Jersey, Valencia, and Heligoland especially, because their remoteness, invaluable as that condition is for warning other places nearer the centre, is an obvious reason why they cannot always be forewarned themselves.

In using the daily weather reports, it ought to be kept in mind that only one state of atmosphere in twenty-four hours is there recorded (excepting for rainfall) ; therefore, it is only by comparisons, and due reference to previous reports, that probable consequences can be fairly inferred.

It is advisable, in considering the forecasts, to look at the second, as in some degree part of the first: time of weather continuing not being a certain or reliable notice.

In conclusion, it may be impressed on the reader, that this system is still a tentative experiment. Each month, however, has hitherto added useful facts, and increased our acquaintance with the difficult though not uncertain varieties of the subject.

Nothing, however, could have been well effected in an attempt to apply meteorology to daily practice with confidence, had not a foundation of facts existed in the works of scientific authorities, whose statical records, and invaluable deductions, afforded a sufficiently extensive basis on which to rely while utilising modern powers of communication by telegraph, from any stations, simultaneously.

In the " Station Instructions for Meteorological Telegraphy" are explanatory direc tions which, with the " Barometer Manual," fifth edition,* will suffice, it is hoped, to give enough information, in a few pages, to satisfy the inexperienced in using weatherglasses, and to show the really weatherwise, or scientific reader, that he may give these weather reports, forecasts, and occasional warnings such weight as is justly due to deductions from facts.

Warnings, or cautionary notices of gales of wind, or storms, are given by the following signals at places on the coasts:— » Sold by Potter, 31 Poultry, London, E.G.—Price One Shilling.