The Sun.
London, England, 1863-12-03 00:00:00

FORECASTS OP 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
com motions 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 duo study; yet
who is there without an independent opinion of the wea-
ther, and perhaps too little understood barometric indica-
-Veils P

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 eart4'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 by ships swinging in
advancing or receding tide streams to an observer at a fixed
station. •

By the tension or barometric pressure, the temperature
and other characteristics of the air at 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
a sweep of 500 miles from London (as a centre),
ar
and,around—say, n ywhich
a is
of far more value, what changes or move-
rcents are impending.
The capability of doing this for about two days in
advance rests on the proved fact of a general lateral transla-
tion towards the east in the Temperate Zone, while north-
erly, southerly, or other (mixed) currents of air are in very
various movement, the practical results on earth's surface
being usually composite motions.
By thus estimating the atmospheric area above, around,
and within some hundred miles of us; by statical observa-
tions 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 cur-
rents are the chief aerial features, below or between or
among which there can be vacancy, unless momentarily,
as when a violent blast of wind is caused by a sudden (ap-
proximate) vacuum; and that when currents act against
each other (gravity restraining upward motion) their ten-
dency is to cause more or less rotation.

The lamented Espy said that winds always set from the
place of higher barometer towards 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
own 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 and circuitous.

Without duly following the progress and ultimate desti-
nation of material fluid air having great bulk, infinite elas-
ticity, and more or less vis inettio, 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 the currents of water in a river or in the sea.

Air streams in opposition must deflect or turn each other,
or go upwards (against gravitation).
Without a general, lateral, or tranameridinal movement,
or translation of atmosphere towards the east in the tempe-
rate zones, but westward in the intertropical regions, in ad.
dition to meridianal movements from and towards 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. Cer-
tainly it 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 im-
pending storms.

It is by a continuous observation of the changes and in-
dications 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 nit be able as now fre-
quently to warn even outposts such as Nairn, Valencia, or
Rochefort.

That errors have occurred, that we have been too slow,
or have given warning where it seemed to have been un-
necessary, 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 cautouary signal, has somewhat discou-
raged such speedy action as might otherwise have been
taken in signalling, but a record of their inutility should be
complied, 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. Tho new sub-
ject 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 Roche-
fort 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 air currents and
their literal translation, I would suggest a reference to
published works, except in one recent and very remarkable
instance.

Daring 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, Notting-
ham, and other places, that to meteorologists even they
seemed unaccountable; but, if we contemplate parallel cur-
rents, side by side, moving rapidlyinupnpeeodsitdeiffderireencttliyonsby,
and having also a lateral movement to the eastward, such
sudden and meridional changes may become as easy to cora.
prehend as those so well described by aeronauts who passed
i 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 influenced
the other.
Tbis momentary effect was accompanied by a rushing
sound, like that of a torrent of water. These currents had
different temperatures, electric characters, degrees of dry-
ness or moisture, and horizontal motions. The sound, caused
by pressure and friction, is suggestive of various ideas in
connexion with heat and electric considerations, inadmis-
sible here.
In this case, of course, the representative of an observa-
tory 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 hori-
zontally.
At the present time our meteorological communications
are utilised, and highly appreciated on the Continent.
At about 10 o'clock in the morning (as soon as in Lon-
don) Paris receives notices of wind and weather, from our
most distant stations, and distributes them,
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 re-
sponsibility.

established in 1855, with a
" What does it cost ?" is, of course, a frequent question.
theThAe
Aml
deirtaelotryololigkiecwali-soeffi, cweaosf the Board of Trade, and for
yearly estimate of £4,200.
This was for many duties, exclusive of those now super-
added, not then contemplated.
To include and provide for all—with these additional
subjects and their contingent expenses. I now ask to have
£5,800, being only £l,OOO wore than 105-8, when motooro-