By VICE-ADMIRAL E. Fitz-Roy, F.R.S.

THE Life-Boat Journal having aided practical meteorology, the following memorandum, ' as a general answer to numerous observations and questions, may interest its readers: j and as the public pay for what is effected in our international meteorologic telegraphy, all have a claim to " know the reason why." "FORECASTS OF WEATHER.

" Many persons have asked questions about forecasts of weather and their principles. Some have impugned their accuracy, and a few have demurred to their having any claim to a really scientific basis.

" No doubt that as very different views of atmospheric commotions or changes are taken by able men, such subjects may scarcely seem worth their earnest attention, because as yet they have not been brought to the verification of a rigid mathematical analysis.

"But to metaphysical inquiries, and to other researches or avocations, indispensably useful, one might take objection, and decline their study on similar grounds. Meteorology not only abounds in physical facts, excessively useful as well as interesting, but it demands an extensive range of intellectual and extremely comprehensive considerations.

" One cannot take it into full use without due study; yet who is there without on independent opinion of the weather, and perhaps too little understood barometric indications ? " Having ascertained that the principal atmospheric currents are incessantly in more or less circuitous but mutually opposed progress, sometimes side by side but in contrary directions, sometimes superposed, one or other being nearest the earth's surface, temporarily— and always having lateral as well as direct progression, we have a clue to their dynametry—by observations at distant stations and by telegraphing to a centre, somewhat like that which might be given in a tidal estuary to an observer at a fixed station, by ships swinging in advancing or receding tide-streams. j "By the tension or barometric pressure, the i temperature and other characteristics of the air at i each station—by the approximate knowledge now possessed of the set, turn, or progression of atmospheric currents—of their relative breadth horizontally, and of the circuitous eddies usually, or often, between their edges or boundaries—one may tell what conditions of air exist within some hundred miles around—say a sweep of 500 miles from London (as a centre), and, which is of far more value, what changes or movements are impending.

" The capability of doing this for about two days in advance rests on the proved fact of a general lateral translation toward the east in the Temperate Zone, while northerly, southerly, or other (mixed) currents of air are in very various movement, the practical results on the earth's surface being usually composite motions.

"By thus considering the atmospheric area above, around, and within some hundred miles of us; by statical observations at the same hour, and by summary calculations of a dynamic character, all the principal motions and changes are brought within the grasp of forecast.

" But this applies only to general and principal averages, not to local peculiarities or special disturbances so limited in nature that they do not affect more than a few score miles' expanse of atmosphere.

"It ought to be kept in mind that broad shallow currents are the chief aerial features, below or between or among which there can be no vacancy, unless momentarily, as when a violent blast of wind is caused by a sudden (approximate) vacuum; and that when currents act against each other (gravity restraining upward motion) their tendency is to cause more or less rotation.

" The lamented ESPY said that winds always set from the place of higher barometer toward that of lower, but he also said (which some writers seem to have overlooked) that the meeting of such winds causes a circuitous effect. ESPY'S views accord with those of the authoritative DOVE and our illustrious HERSCHEL.

" The word cyclone has been so associated with storm that few persons attach to it now the simple and ancient sense of circuit or circuitous.

" Without duly following the progress and ultimate destination of material fluid, air having great bulk, infinite elasticity, and more or less vis inertia, or rather momentum, according to mechanical laws, some persons have imagined that air-currents intermix, as if unresistingly, instead of opposing each other for a time, especially if in rapid motion, just like currents of water in a river or in the sea.

" Air-streams in opposition must deflect or turn each other, or go upward (against gravitation).

" Without a general, lateral, or transmeridional movement, or translation of atmosphere—toward the east in the temperate zones, but westward in the intertropical regions—in addition to meridional movements from and toward the poles (of which full explanations are given elsewhere), it would not be possible to forecast the character of wind and weather beyond one day's interval. It is the prescience of dynamic consequences, arising out of statical facts, that enables a really scientific calculation of probabilities to be made. Certainty is not yet attainable; but a fair average probability, for a certain area or district, is already within our reach. Out of these forecasts spring the cautionary notices of impending storms.

"It is by a continuous observation of the changes and indications of change that we are now enabled to decide and direct with confidence.

"Without such a generally-informed state we should often be surprised, as we should derive our warnings solely from distant stations, and should not be able as now frequently to warn even outposts, such as Nairn, Talentia, or Rochefort.

" That, errors have occurred—that we have been too slow, or have given warning where it seemed to have been unnecessary—may appear to have been unavoidable in such new and tentative experiments.

" But there have been four special causes of occasional failure which ought to be fairly considered.

" 1. A watch having been officially set to report on the results of each cautionary signal, has somewhat discouraged such speedy action as might otherwise have been taken in signalling, lest a record of their inutility should be compiled, rather than the contrary.

" 2. Public offices are not open on Sundays, and only a few principal telegraph stations are then available. Hence there is sometimes unavoidable delay between Saturday and Monday.

" 3. No one or two persons can be always at their station all the year round from morning to night. The new subject of forecasting and warning is hardly yet so familiar to many persons, however zealous, as it may be in due time.

"Lastly, the telegraph offices are not open in general till 8 or 9 in the morning, or after those hours at night; therefore official communications are only practicable, over so wide a range as ours, between those times of the day.

" To communicate between Nairn or Valentia or Rochefort and our office in London usually takes about two hours, in actual practice.

" For proofs of what has been thus stated, perhaps too dogmatically, about the movements of aircurrents and their lateral translation, I would suggest a general reference to various publications, except for one recent and very remarkable instance.

" During the storm of last October 29-30, such remarkably sudden and violent shifts of wind took place about the same time at many places in a nearly meridional direction across England, between or by Oxford, Greenwich, Nottingham, and other places, that even to meteorologists they seemed unaccountable; but if we contemplate parallel currents, side by side, moving rapidly in opposite directions, and having also a lateral movement to the eastward, such sudden and meridional changes may become as easy to comprehend as those so well described by aeronauts, who passed out of one stratum or current of air into another, so closely superposed that while the balloon was tilted (dragged aside as it were) by the one, the car was affected differently by the other.

" This momentary effect was accompanied by a rushing sound like that of a torrent of water.

These currents had different temperatures, electric characters, degrees of dryness or moisture, and horizontal motions. (The sound, caused by pressure and friction, is suggestive of various ideas in connection with heat and electric considerations, inadmissible here.) " In this case, of course, the representative of an observatory moved vertically through horizontal air-currents, at times differing in velocity (referred to earth's surface) from some 30 to 60 miles an hour. In the former instance—that of a land station —the currents were separated vertically, their division passing across any place suddenly, but horizontally.

" At the present time our meteorologic communications are utilized, and highly appreciated on the Continent.

" At about 10 o'clock in the morning (as soon as in London), Paris receives notices of wind and weather from our most distant stations, and distributes them. Near the same time we receive telegrams at this office from three French coast stations—Brest, Lorient, and Rochefort; being all that we can utilize.

" Two hours afterwards the French Government despatches our forecasts, and (if any) cautionary notices to more than 18 stations on the coasts of France.

" This British system has, therefore, incurred a large responsibility.

" What does it cost ? is, of course a frequent question.

" The Meteorologic Office of the Board of Trade, and for the Admiralty likewise, was established in 1855, with a yearly estimate of 4,200/.

" This was for many duties, exclusive of those now superadded, not then contemplated.

" To include and provide for all—with these additional objects, and their contingent expenses—I now ask to have 5,800?., being only 1,600/. more than in 1855-58 when meteorologic investigations had not led to their practical utilization nationally.

" In conclusion, may I be permitted to say that, while admitting many errors of judgment and numerous instances of tardy decision, it has been proved by general opinion of the maritime, if not also of the agricultural, interests that the system of meteorologic information existing now under the Board of Trade is worth its cost to the nation, and is deserving of efficient maintenance.

"R. Fitz-RoY.

Postscript.—Having been asked to send out forecasts, and occasional cautionary notices to the wider Midland districts, I am anxious to say that such detailed definitions seem hardly requisite, as they could not be given for highlands and valleys, exposed districts, and sheltered places alike.

Fair comparisons of the daily weather reports or notices for those coasts which are nearest to any such inland place—especially those to the westward—and due consideration of the reports immediately preceding the time of observation, or expected, as probable to occur during next day, or on that to follow it—may give better information than a special forecast—not duly estimating local peculiarities.

The whole area of the British Islands is so small, comparatively, that changes over them may be better estimated comprehensively, on a wide scale (having especial reference to principal upper, or cloud-bearing currents), rather than to local effects in confined, or very limited districts.

R. F.