'OBERT H. SCOTT, M.A. F.R.S.
PROF. CHARLES A. KOFOID AND
MRS. PRUDENCE W. KOFOID
Weather Charts &. Storm Warnings .
CHART SHEWING THE POSITION OF THE TELEGRAPHIC REPORTING STATIONS.
ROBERT H. SCOTT, M.A., F.R.S.
SECRETARY TO THE METEOROLOGICAL COUNCIL
WITH NUMEROUS ILLUSTRATIONS
THIRD EDITION, REVISED AND ENLARGED
LONGMANS, GREEN AND CO.
AND NEW YORK: 15 EAST i6 th STREET
All rights reserved
PREFACE TO THE THIRD EDITION.
THE second edition of this book having been long out
of print, I have been requested by several friends to
prepare a new edition.
The entire text has been revised, and some new
chapters have been added, mainly relating to changes
and improvements in the Office weather work since the
The subjects of the new chapters are, the Distribution
and Periodicity of Gales, Weather Forecasting, the
Weekly Weather Report, and lastly, Cirrus Cloud Obser-
vations. The subject of ' Suggestions for Improve-
ment,' formerly included under 'Storm Warnings,' has
been made a separate chapter. The chapter on the
Weekly Weather Report contains an account of the
iv Preface to the Third Edition.
method of calculating ' Accumulated Temperature/ in
use in the preparation of that Report.
Chapter XI1L, ' On Cirrus Cloud Observations,' is of
the nature of an Appendix to the book, but it has
seemed best to constitute it a separate chapter.
ROBERT H. SCOTT.
METEOROLOGICAL OFFICE :
July 25. 1887.
PREFACE TO THE FIRST EDITION.
Tills little work has been put together in the endeavour
to supply a want which has been expressed in many
quarters : that of an explanation of the weather charts
which appear in the newspapers, and of the remarks
which are appended to them.
The conceptions and principles on which the science
of weather study is based are apparently quite new to
the majority of ordinary readers, who still hold to the
belief that the barometer rises or falls in direct relation
to the weather, without any attempt to consider how or
ic/iy it does so.
It is hoped that the following pages may convey
some idea, however imperfect, of the present state of
Weather Knowledge, as distinguished from the science
of Meteorology itself, of which this book makes no claim
to be called a manual.
With a very few exceptions, theories of the causes of
storms have been left unnoticed, as the object has been
vi Preface to tJie First Edition.
to explain to the reader what he can learn from a careful
study of the information published in the newspapers
or in the Daily Weather Reports, and which is therefore
accessible to all.
In treating of a science now in process of rapid
development, it can only be expected that every year
will add to our knowledge, and that many of the prin-
ciples stated in. these pages will be extended or modified
by the results of subsequent experience. All that it
is here attempted to give to the public is an account of
the actual state of our knowledge at present.
I must express my sincere thanks to several friends
who have aided me with their advice during the prepa-
ration of the book, and most notably to Mr. Frederic
Caster, of this Office.
The illustrations which are contained in the text
have all been executed by the Patent Type Founding
Company, by the same process as they employ for the
production of charts for newspapers.
ROBERT H. SCOTT.
METEOROLOGICAL OFFICE :
June 10, 1876.
I. THE MATERIALS AVAILABLE FOR WEATHER STUDY . i
II. THE WIND 23
III. THE BAROMETER 32
IV. GRADIENTS 44
V. CYCLONES AND ANTICYCLONES 57
VI. THE MOTION OF STORMS AND THE AGENCIES WHICH
APPEAR TO AFFECT IT 87
VII. THE USE OF WEATHER CHARTS 109
VIII. THE DISTRIBUTION AND PERIODICITY OF GALES . . 126
IX. STORM WARNINGS 137
X. FORECASTING ' 162
XI. SUGGESTIONS FOR IMPROVEMENT 178
XII. THE WEEKLY WEATHER REPORT 193
XIII. ON CIRRUS CLOUD OBSERVATIONS 207
\. WEATHER REPORT. NOVEMBER 29, 1874 .... 218
?,. READINGS OF AUTOMATIC INSTRUMENTS. VALENCIA,
MARCH 26, 27, 1874 221
C. READINGS OF AUTOMATIC INSTRUMENTS. ABERDEEN,
OCTOBER 20, 21, 1874 222
D. READINGS OF AUTOMATIC INSTRUMENTS. FALMOUTH,
FEBRUARY i, 2, 1873 223
P LA TE S.
I. CHART SHOWING THE POSITION OF THE TELE-
GRAPHIC REPORTING STATIONS, JANUARY 1876 . to face Title
II. CLOUDS AND WEATHER IN A CYCLONIC SYSTEM,
ACCORDING TO CLEMENT LEY .... to face p. 65
III. WEATHER CHARTS, NOVEMBER 29, 1874, 8 A.M.
(REDUCED FROM THE DAILY WEATHER REPORT) . to face p. 220
WEATHER CHARTS AND
* CHAPTER I.
</ P. 46, diagram, insert " .02" before "c."
J line 6 ab infra, for " 5 " read " 10."
J P. 194, at head of table insert ''Figures for week ending
April 25, 1887."
The observations taken at these stations refer to
Atmospherical Pressure, Temperature, Humidity (or the
Dampness of the Air), Wind, Rain, Weather, and, at sea-
coast stations, Sea Disturbance.
The drawing of weather charts depends on the com-
PL A TE S.
I. CHART SHOWING THE POSITION OF THE TELE-
WEATHER CHARTS AND
* CHAPTER I.
THE MATERIALS AVAILABLE FOR WEATHER STUDY.
BEFORE proceeding to describe the charts themselves,
or to give an account of their utility in aiding us to form
a judgment as to probable weather, it will be well to
explain the character of the observations and the nature
of the service on which they are based, confining our-
selves exclusively to the instruments employed and
observations taken at our own telegraphic reporting
stations (the outfit of which is necessarily less complete
than that of a fully furnished meteorological observatory),
and omitting technical descriptions of the instruments
The observations taken at these stations refer to
Atmospherical Pressure, Temperature, Humidity (or the
Dampness of the Air), Wind, Rain, Weather, and, at sea-
coast stations, Sea Disturbance.
The drawing of weather charts depends on the com-
2 Weather Charts and Storm Warnings.
parison of various observations taken at the same time,
at several different stations. It is therefore indispens-
able, that all the observations to be compared should
be freed, as far as possible, from incidental inaccuracies
and discrepancies, by reducing the conditions at each
place to common standards of comparison, and this is
done by applying the several instrumental and other
Atmospherical pressure is measured by the
barometer, and by this is meant the mercurial baro-
meter ; for the aneroid, however convenient it may be
for ordinary use as a weather glass, cannot be recog-
nised as an independent instrument, its indications
depending entirely on the delicacy of the mechanical
appliances employed in its construction.
The barometer has a thermometer attached to it, in
order to show the temperature of the instrument itself,
and this must be read whenever an observation of the
height of the mercurial column is taken.
The readings of the barometer are always said to be
'corrected and reduced to 32 and to sea-level,' and it
is necessary to explain these expressions.
' Corrected,' means that corrections have been applied,
a, for the error of the scale of the instrument, which
has been ascertained by sending it for verification to some
recognised establishment, such as Kew Observatory.
b, for what is called ' capillarity/ which depends on
the bore of the tube, and
c, for what is called 'capacity,' which depends on
The Materials available for Weather Study. 3
the proportion which the bore of the tube bears to the
sectional area of the cistern.
4 Reduced to 32,' means corrected according to the
reading of the attached thermometer. The column of
mercury in the barometer tube behaves like almost all
other bodies, being lengthened by heat, and shortened
by cold. It is therefore obvious that unless two similar
barometers be precisely at the same temperature, they
cannot possibly read alike, and hence is apparent the
absolute necessity of reducing all readings to one
common temperature ; for this the temperature of
melting ice, 32 R, has been unanimously adopted as
The temperature of the column being indicated by
the reading of the attached thermometer, we can
discover, by means of printed tables, how much, for each
reading of that thermometer, the column is longer, or
shorter, than it would be at 32, and consequently what
correction is required for the barometer reading.
' Reduced to sea-level,' is a phrase which requires
rather more explanation than the foregoing. The
barometer, as its name implies, measures the weight of
the air, and that weight, of course, depends mainly on
the quantity of air which is above the instrument
pressing upon the cistern, and keeping up the column
of mercury in the tube. If, therefore, two similar
barometers be placed one directly under the other, say,
one in the attic, and the other on the ground-floor, it is
evident that there will be a less quantity of air above
4 Weather Charts and Storm Warnings.
the former than above the latter instrument, and,
consequently, the barometer in the attic will read lower
than that on the ground-floor.
Precisely the same reasoning will apply if we are
considering two barometers at different heights on the
side of a mountain, or one at an inland station, and the
other at the level of the sea ; in every instance the
barometer at the higher station will read lower than
that at the lower.
Hence we find that all readings must be reduced to-
their equivalent readings at a standard elevation, as well
as at a standard temperature. This standard elevation is
the Mean Level of the Sea, and the reduction is carried
out by means of tables.
A slight consideration of the foregoing remarks, and
of the last-named principle in particular, will show how
it comes about that the reading given in a Daily
Weather Report for an inland station, like Oxford, or
Nottingham, can never agree with a casual reading taken
by an observer at either of those stations at the same
time, unless the latter reading be corrected and reduced
to 3 2, and to sea-level. It must, however, be remem-
bered that the problem of the reduction to sea-level is
not so very simple. Its correctness depends on the
accuracy of the knowledge we possess of the temperature
of the supposed column of air extending from the level
of the upper station to that of the lower. Now if the
height of this column be considerable, our knowledge of
this temperature cannot be complete, and therefore for
The Materials available for Weather Study. 5
elevations above one thousand feet, the reduction by the
tables is not quite exact. Accordingly, for such stations
as that on Ben Nevis, at the height of 4000 feet, the
reduction of the readings to sea-level by tables is not
very generally accepted.
Temperature. This does not require much expla-
nation. In addition to the actual readings of the ther-
mometers, ' in the shade ' (i.e., suspended in a properly
constructed louvre-boarded screen at a height of four feet
above the ground), which are taken at certain definite
hours, the Daily Weather Reports give also two columns,
showing, respectively, the maximum and minimum read-
ings taken during the twenty-four hours, ending at 8
o'clock each morning, by thermometers so constructed
as to register, one the highest, and the other the lowest,
temperature reached during the interval which has
elapsed since the last setting.
The last-named readings may also be turned to very
useful purpose. The mean temperature of the day is
often mentioned in connection with sanitary statistics,
as for instance in the Registrar- General's Reports.
This mean temperature is theoretically the average of
twenty-four thermometer readings taken at hourly
intervals during the day. There are well-known rules
for determining this mean temperature out of various
combinations of hours of observation. The simplest
method, and, for practical purposes, nearly the most
exact, is to take the average of the maximum and
minimum readings given in the Daily Weather Report^
6 Weather Charts and Storm Warnings.
on any day, and put that down as the mean temperature
of the preceding day.
Humidity. The amount of moisture in the air is
measured by the indication of a thermometer with its
bulb encased in muslin, and kept damp (a wet bulb),
compared with that of an ordinary (dry bulb) thermo-
meter, without any such mounting, observed at. the
same moment. Tables exist from which the amount of
moisture for each observed difference in readings between
the two thermometers can be ascertained.
This is not the place to enter into the theory of these
observations. Suffice it to say, the greater the differ-
ence between the readings of the two thermometers the
drier is the air, and that when the two thermometers
read alike, the atmosphere is exceedingly damp. The
difference between the two thermometers ranges in
this country from o to 10 or even 15, and sometimes
a difference of upwards of 20 has been noticed.
The chance of rain depends to a great extent on the
degree of humidity of the air from time to time, and if
we are dealing with reports from an extensive tract of
country, as North America, or the Continent of Europe,
the distribution of the moisture is an interesting subject
of study. As regards these islands, the fact that most
of the telegraphic stations are on the sea-coast detracts
from the value of the reports of humidity, inasmuch as
the amount of moisture in the air is seriously affected
by proximity to the sea ; and so in weather study we
are unable to use reports of vapour tension as much as
The Materials available for Weather Study. 7
Rain is measured by means of a rain-gauge. The
values given represent the depth of water which would
have accumulated on a level piece of ground, if none of
the rain which fell had escaped by drainage, &c. Too
much faith must not be placed on the rain returns in
the daily reports, for two reasons. Firstly, the gauges
are often necessarily placed in towns, where a good
exposure is not to be had, so that the amount measured
is not the same as might be yielded by a gauge in a
more open situation ; and secondly, the telegraphic
stations are so sparsely distributed over the kingdom
that it is impossible that they can give a precise
account of the rainfall in every county. What they
do show is whether or not the rain is general and
Wind. As a general rule, for the purposes of the
Daily Weather Report, wind is not measured by an
instrument, but is simply estimated according to the
Beaufort scale, which is so named after the late
Admiral Sir Francis Beaufort, who devised it for his
own use, when in command of H.M.S. Woolwich in
1805, The following is the scale, 1 with the approxi-
1 Since Admiral Beaufort's time there has been a great change in the
rig of ships by the introduction of double topsail yards. It seems
therefore advisable to add to Beaufort's scale the amount of sail which his
ship would have been able to carry, had she been rigged with double
topsail yards, but under all other circumstances the same. The change
would only affect forces 6 to 10.
6. Topgallant sails.
7. Topsails, jib, c.
8. Reefed upper topsails and courses.
9. Lower topsails and courses.
10. Lower maintop-sail and reefed foresail.
8 Weather Charts and Storm Warnings.
mate equivalent velocity of the wind in miles per hour,
for each grade as determined in the Meteorological
0. Calm -3
1. Light air . Or, just sufficient to give steerage way ... 8
I Or, that in which a well-\
conditioned man-of-war, i to 2 knots . . . 13
with all sail set, and 1 3 to 4 knots . . . 18
' clean full, ' would go in ! 5 to 6 knots . . 23
smooth water from . J
5. Fresh breeze .
6. Strong breeze
7. Moderate gale
/Royals, &c. . . . 28
and topgallant sails . 34
Or, that to which she Double-reefed topsails,
could just carry in chase, ( jib, &c. . . .40
Fresh gale . ' full and by ' . . i Triple-reefed topsails,
I &c 48
9. Strong gale .1 .... Close - reefed topsails
/ v and courses . .56
10. Whole gale . Or, that with which she could scarcely bear close-
reefed maintop-sail and reefed foresail . . -65
i r. Storm . . Or, that which would reduce her to storm-staysails . 75
12. Hurricane . Or, that which no canvas could withstand . . 90
It is obvious that as this scale refers to the rate of
sailing of, or to the amount of sail carried by, a ship, it
is at first sight not well suited for use at land stations ;
but experience has shown that the reporters, guided by
the descriptions in the second column, are never very
far from the truth in their estimates, when once they
have gained some practice in observing. There are
objections to supplying instruments for the measure-
ment of wind to telegraphic stations, owing to the great
difficulties which would be experienced in erecting them
in suitable positions. Anemometrical indications taken
in the middle of a town are almost worthless, as the
The Materials available for Weather Study. 9
buildings produce such eddies that the true movement
of the air cannot be ascertained from the instrument.
As regards the numbers of the Beaufort scale, it is
those from 6 upwards which present the most interest.
6 is the lowest number which is taken in the Meteoro-
logical Office to justify the issue of a warning to the
coast, and 9 is the lowest figure which by the regulations
of the Board of Trade can be pleaded by a captain
as ' stress of weather,' in case of casualty to his craft.
These velocities are not uniform, like that of an express
train. The statement of 56 miles an hour, means
56 miles in the hour, but during that hour the wind
may have been gusty, and at times have had a velocity
of nearly 100 miles an hour, while at other times its
hourly speed may have scarcely reached 30 or 40
It may be remarked that if we employed the pres-
sure, instead of the velocity of the wind, to measure the
violence of a gale, we should be able to obtain a record
of individual gusts, and in the opinion of many persons,
such as engineers, &c., such information would be more
practically useful to the public, than statements as to
velocity. The reason that pressure anemometers are
not generally adopted is, that as yet it has not been
found possible to reason with sufficient confidence as to
the pressure of the wind on a structure, such as a
factory chimney, from the indications shown by a
pressure plate of, say, one square foot in area. Till the
influence of the size of the pressure plate on its indica-
i o Weather Charts and Storm Warnings.
tions, in a wind of given strength, has been thoroughly
determined, it seems premature to recommend the em-
ployment of pressure anemometers.
Weather. The various observations which are
comprehended under this general term are those which
do not admit of instrumental record, such as the fact of
the occurrence of thunder, &c. These are reported
according to the subjoined notation, which, like the
wind scale, is due to Sir F. Beaufort.
b Blue sky, whether with clear or
c Cloudy, but detached opening
d Drizzling rain. r Kain ^inued
/ Foggy. s Snow '
Dark gloomy weather.
h HaiK of the weather.
m Misty hazy atmosphere,
o Overcast, the whole sky being
covered with an impervious
p Passing temporary showers.
u ' Ugly,' threatening appearance
Visibility,' whether the sky be
cloudy or not.
The only thing to be remarked about the use of
these letters in the Daily Weather Reports is that,
when two or three are entered to the same place on
the same day, it implies that the observations have
been taken in the order in which they are printed.
Thus b.c.p.r. would mean that, during the interval which
had elapsed since the previous report, the sky was at
first ' quite clear/ then ' detached clouds ' came over it
* passing showers ' ensued, at last turning to persistent
' rain ' which ' continued ' at the time of sending off the
The Materials available for Weather Study, n
Sea Disturbance. Lastly, the table contains a
column for the Sea Disturbance, of which there are
nine grades, depending on estimation, like the scale for
0. Dead calm.
1. Very smooth.
5. Kather rough.
7 . High.
8. Very high.
The height of the waves not unfrequently gives valu-
able information as to the force of the wind in the
offing, but we must not place too much dependence on
this particular indication, for many of our most serious
storms have come on without any previous disturbance
of the sea on our coast. This is due to the fact that
the sea disturbance is caused by the wind outside, and
if that wind is not blowing in the direction of a coast,
it will not impel waves towards that coast. It will
presently appear how a wind may advance to a coast
without blowing towards it, but for the present it may
be said, that the fact of a wind blowing in the direction
of these islands, and driving a heavy sea on to parts of
our coasts, is no positive proof that the wind itself will
ever be felt on our shores. In fact, some of the
heaviest seas reported on our western coasts are proved
to have been caused by Westerly gales blowing far
out in the Atlantic, which never reached Europe
There are yet other remarks to be made as to the
sea disturbance column, which is, after all, a portion of
1 2 Weather Charts and Storm Warnings.
our table often consulted anxiously by such landsmen
and landswomen as may have to cross the Channel.
In the first instance, the sea close in shore, at a place
like Dover, is often much calmer than it is outside, as
that harbour is sheltered from several winds, especially
Northerly ones. Secondly, the roughness of the sea
depends in great measure on the direction in which the
tide is running at the time of observation. 'Wind
against tide ' knocks up a sea at once, and frequently
the delay of a few hours may make all the difference
between the miseries of sea-sickness, and the enjoy-
ment of perfect comfort, if the tide has changed in the
These, then, are the materials with which we have to
deal in drawing charts, discussing weather, preparing
forecasts, and in sending warnings to the coast, and it
is self-evident that they are far from complete.
It is obvious that the amount of information as to
the appearance of the weather at each station which
can be conveyed by the three or four letters which, at
most, are given in the proper column, is quite insuffi-
cient to convey to our minds any clear idea of what an
experienced person would have gathered as to the
general character and prospects of the weather at that
station ; and yet the general appearance of the
weather was all that our fishermen and pilots had to
guide them for generations, nay, for centuries, before
the barometer was invented. Right well did they then,
The Materials available for Weather Stiidy. 1 3
and do their successors now, know how to profit by
such signs !
In the first place, the code is necessarily so con-
densed that it cannot give information as to the form of
clouds, whether these be the highest ' mare's tail ' or the
lowest rain cloud, or whether there be more than one
stratum. The value of such particulars for the purposes
of weather study need hardly be mentioned. The cha-
racter of the clouds, their changes, and their amount,
afford to the practised eyed most valuable information
as to the condition of the atmosphere above us.
Moreover, the code does not tell us anything about the
motion of the clouds, so often the truthful indication
of coming wind, though we do endeavour to obtain, by
means of words added to the telegrams, information
on this motion, when there is anything remarkable
By the researches mainly of the Rev. W. Clement
Ley in this country, and of Professor Hildebrandsson
in Sweden, certain principles for the interpretation of
cloud motion have been established. A brief resume
of these will be given in Chapter XIII.
In these and all such particulars, the Weather Tele-
grams, no matter how correct they may be, are only a
poor substitute for actual personal observation. Any
one trying to form a correct judgment of the look of the
sky from these alone is like a physician trying to deal
with a case without a chance of a personal interview
with his patient. What can a resident in an inland
1 4 Weather Charts and Storm Warnings.
town like London know of the appearance of the
weather on the sea-coast on any clay from any tele-
gram, no matter how detailed ?
The reports are therefore incomplete as to quality
and quantity, but in many respects they arc capable of
material improvement, especially if it should ever be ren-
dered possible to devote more money to the service.
As to quality, the instruments should be automatic,
so that by looking at the record traced mechanically, we
should be able to notice all that had passed since the
last observation. Of late years automatic aneroids
have been introduced at some of the most important
stations, and have been found to be of considerable
service. The reporters should be experienced observers,
with outdoor occupations, so as to be constantly on the
look-out for any change of weather which may take
place, and therefore they should be selected from such
a class of men as signalmen on the coast. It is obvious
that such a weather report as can be given by a clerk
who simply runs out to look at the sky just before filling
up his despatch, cannot be of as much value as that of
a man who has been in the open air watching the
weather for an hour or so, or even for the better part
of the day. As to quantity also, the reports are
not sufficiently complete, both as regards time and
As regards time, they are not nearly frequent enough.
The Signal Office at Washington receives three reports
every day from each of its stations ; but, as is well
The Materials available for Weather Study. 1 5
known, that office is most liberally supplied with funds
by Congress. Our own Meteorological Office, however,
can only afford one at 8 A.M. from most of our stations,
and at best we only get additional reports at 2 P.M.
and at 6 P.M. from a limited number of places. As
regards Sunday mornings, the service is necessarily
much hurried, for the telegraph offices are, as a rule,
only open from 8 to 10 A.M., and there is no service
at 2 P.M. at all. On Sunday evenings, however, the
service is the same as on week-days.
Lastly, as to space, the area over which our own net-
work and our international exchange extends, is far too
limited for us to gain a general idea of the conditions
which are prevailing all around us, and it is on these
that our weather in great measure depends. This
might, to a certain extent, be remedied by an extension
of our Continental communications, but, as will be
pointed out later on, the information obtainable from
Europe is comparatively unimportant when contrasted
with what we can supply to our Continental neighbours.
What we really want, to give us a better insight into
our chances of weather from time to time, is unfor-
tunately unattainable, and that is a system of reports
from stations in the Atlantic, say, at a distance of 600
miles from our coasts, for most of our storms advance
on us from the Atlantic. It is a problem as yet
unsolved, to moor a vessel in 1000 fathoms water,
and to connect her with the shore by a telegraphic
cable. The experiment of a floating telegraphic station,
1 6 Weather Charts and Storm Warnings.
which was tried in I 869 at the entrance of the Channel,
in much shallower water than I ooo fathoms, was not
encouraging, as will be explained later (p. 181). It
has, however, been recently proved by the Telegraph
Construction and Maintenance Co. to be possible to
maintain telegraphic communication with a light-
Nevertheless, in spite of all the geographical defects
of our insular position, and the difficulties which are un-
avoidable in the early stages of any branch of knowledge,
satisfactory progress has been made in the science of
Weather Telegraphy in these islands. When so much
has been accomplished in the short space of a quarter
of a century, since the service was first organised by
Admiral FitzRoy in 1861, it may be hoped that with
perseverance, and continued efforts to improve our
methods, we shall one day arrive at some clearer know-
ledge of the laws of our storms and our weather.
The following is a specimen of the Daily Weather
Report, as issued in January 1887. A chart showing
the stations will be found as the Frontispiece.
The matter is exhibited on four lithographed pages.
The contents of three of these are reproduced here.
The fourth appears as Plate III., but the actual charts
given there do not refer to January i, 1887.
The Remarks on the General Situation at 8 A.M., and
on the Weather over Europe during the past twenty-
four hours, explain themselves.
The Forecasts will be explained in Chapter X.
The Materials available for Weather Study. 17
It will be seen that in addition to the absent obser-
vations, which are marked with an asterisk, as is ex-
plained at foot of the table, various spaces are marked
with dots (...), indicating that the' report had not
arrived for that day ; and others with notes of interro-
gation, indicating that for some reason or other the
report appeared to be doubtful, in which case it is
sometimes inserted and queried, and at others omitted
Weather Charts and Storm Warnings.
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Materials available for Weather Study. 19
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2o Weather Charts and Storm Warnings.
YESTERDAY'S 2 P.M. REPORTS.
Sumburgh Head .
EXPLANATION OF COLUMNS GIVEN ON p. 18.
WEATHER. Beaufort scale is given on p. 10.
* An asterisk is inserted in all places for which information is not
\ The evening observations are taken at 6 P.M. in France and our
Islands, with the exception of Oxford, where they are taken at 8 P.M. In
Sweden and Denmark, the observations are taken at 8 p. M. (Christiania
GENERAL SITUATION AT 8 A.M.
/Highest, 30.5 inches and upwards over the South of
J Lowest, 29.9 inches and less over the Gulf of Genoa,
but relatively low, 30.0 inches and less, to the North-
(^ westward of our Islands and the Westward of Norway.
(Highest, 48 at Valencia, 47 at Belmullet, 46 at
Roche's Point, and 45 at Stornoway and Mullagh-
Lowest, 6 at Stockholm, 12 at Ilernosand, 14 at
, Cambridge, 15 at Oxford, and 20 at Munich.
Hard frost prevailed last night over Central England,
the lowest readings being 13 at Cambridge, 17 at
\ Loughborough, and 22 in London.
The Materials available for Weather Study. 21
/ Light or moderate from NE. over Germany, France,
the Netherlands, and the English Channel.
(Southerly elsewhere, strong in force on the West
coasts of Ireland and Scotland.
Dull on our Western and Northern coasts, with driz-
zling rain at Stornoway.
Fair in most other localities, but densely foggy over
Central England and the Netherlands.
(Rough at Stornoway and Valencia, but moderate to
\ smooth elsewhere.
PROBABLE CHANGES IN SYSTEM NOW PREVALENT.
The anticyclone noticed over England and the North Sea yesterday
appears to be still moving Eastwards, and the barometer is falling generally.
The depressions which are travelling along our Western coasts appear
likely to advance closer to our shores, and a further increase of wind is
probable over Ireland and Scotland.
No important change is likely at present over England beyond a gradual
rise of temperature.
FOR THE TWENTY-FOUR HOURS ENDING AT NOON ON
2ND JANUARY 1887.
Southerly and South-westerly winds, increasing
in force ; cloudy, some rain.
Do. Do. Do.
Southerly winds, moderate, fair generally.
Same as No. 5.
Same as No. 5.
Easterly and South-easterly winds, light;
foggy to fair.
South-easterly and Southerly winds, freshen-
ing ; cloudy, some rain.
Do. Do. Do-
Do. Do. Do.
Southerly winds, strong, perhaps a gate,
cloudy, some rain.
*io. IRELAND, SOUTH . | Do. Do. Do.
WARNINGS. The South cone was hoisted last evening in districts o, 6,
9, 10, and part of I. An asterisk is inserted against those districts
in which signals are now flying.
*o. SCOTLAND, NORTH
*i. SCOTLAND, EAST .
2. ENGLAND, NE.
3. ENGLAND, EAST .
4. MIDLAND COUNTIES
5. ENGLAND, SOUTH .
*6. SCOTLAND, WEST .
7. ENGLAND, NW.
8. ENGLAND, SW.
*9. IRELAND, NORTH .
2 2 Weather Charts and Storm Warnings.
GENERAL REMARKS ON THE WEATHER OVER EUROPE
DURING THE PAST TWENTY-FOUR HOURS.
THE reports for yesterday showed that a large anticyclonic system had
spread over the whole of Northern and North-western Europe, its centre
being over the Eastern parts of the British Isles and the North Sea, where
the barometer at 8 A.M. stood at a little above 30.5 inches. In the West
and North-west of our Islands, however, the mercury had begun to fall
steadily, while to the South-eastward of the high-pressure area readings
decreased to 29.5 inches over the Adriatic. Thus, while South-westerly
winds had set in over Ireland and Scotland, calms and variable airs were
felt over England and the North Sea, and North-easterly to Northerly
winds over the South of France and Northern Italy. The weather in the
NW. and N. was dry, cold, and very foggy, while at the more Southern
stations it was somewhat cloudy, with showers locally. Temperature was
below the freezing-point at all but the most Western and Southern stations ;
over the Western and Southern parts of the Mediterranean it was still above
50. The highest individual readings were 53 at Algiers, 52 at Malta,
51 at Brindisi, and 50 at Constantinople ; the lowest, 5 F. at Hernosand,
Stockholm, and St. Petersburg, 9 at Archangel, 14 at Helsingfors, 20 at
Loughborough, 23 at Oxford, 26 at Cracow, 27 at Lemberg.
During the day the South-westerly winds in the West and North-west
continued to blow steadily, but did not spread much over England, where
dense fogs prevailed locally, and the night became very cold.
The Wind. 23
HAVING thus discussed the observations themselves, we
come to the results and conclusions to be drawn from
them, and, in order to make these intelligible, we must
indulge in a little theorising, and refer to some things
which, though not yet recognised as absolutely proved,
appear at least probable, as regards the behaviour of
Every one knows that the East is very different in
its character from the West wind, the former being
reputed to be 'good neither for man nor beast.' Any
one with a touch of bronchitis or rheumatism can (or
at least thinks he can) tell you, without looking at a
weather-cock, whether or not there is Easting in the
wind. This contrast arises from the fact that as a rule
the temperature and dampness of the air in Western
Europe are both lowest when the wind is about North-
east, and highest when it is about South-west. This
is, however, a local phenomenon peculiar to certain
parts of the globe, for if we travel from Western
Europe, along the same parallel of latitude as our own,
24 Weather Charts and Storm Warnings.
either eastwards to the Sea of Ochotsk or westwards to
Labrador, we shall find that in these districts the
coldest wind is near North-west, and the warmest about
South-east In each case the coldest and driest point
of the compass lies towards the region, in the neigh-
bourhood of the point of observation, where the mean
temperature is the lowest. In these islands, in winter,
this region is northern Russia, in Labrador it is the
Barren Grounds of the Hudson Bay Territory, and at
the mouth of the Amur it is the district of Yakutsk.
These two latter cold regions lie to the north-west of
the respective coast districts to which reference has
The wind, then, is cold and dry when it comes from a
cold region, warm and moist when it comes from a
warm district, such as, in these latitudes, the sea surface
in winter. In summer there is not so strong a contrast
between the temperature of different parts of the earth's
surface and between land and water as in winter, and
so the different winds do not differ so much in their
In former years it was the fashion to say, that all
cold winds flowed from the Poles to the Equator,
forming the so-called Polar Currents, and becoming the
Trade Winds when they approached the Tropics, while
the warm winds flowed from the Equator to the Pole,
forming the Equatorial Currents, or Anti-trades.
There can be no doubt that these statements were
right in principle, as the original disturbing action
The Wind. 25.
which produces motion in the atmosphere is the heat
of the sun ; and this acts most strongly in the Torrid
zone, which ought, accordingly, to be the region
towards which all the cold air flowed, were it not for
the irregular arrangement of land and water on the
globe. Recent investigations have, however, shown
that a body of air cannot be proved to have made its
way direct from the Equator to either Pole, inasmuch
as it will probably have been caught up on its way by
some of the eddies and local circulations at all times
existing on the earth's surface. The motions of the
atmosphere are found to be regulated by the distribu-
tion of barometrical pressure over the globe, the
particles moving from the regions where pressure is in
excess the barometer is high, to those where pressure
is in defect the barometer is low, and being modified
in the direction of their motion by various causes,
among which the earth's form, and its rotation on its
axis, are the most influential.
We have said that a body of air cannot be proved
to flow the whole way from the Equator to the Poles
or back again, but nevertheless it is the fact that over
extensive areas of the earth's surface the wind does
maintain a constant direction for a considerable period
of time. To prove this it is only necessary to cite the
well-known phenomena of the Trade Winds and the
Monsoons, where the wind blows persistently from the
same direction, in one case for the whole year, and in
the other for months at a time. In our own latitudes-
26 Weather Charts and Storm Warnings.
the phenomena of the winds are not so regular, but yet
it is found that over large tracts of Europe and the
North Atlantic, the wind at times blows for weeks
together in a definite direction, either Easterly or West-
erly (speaking in general terms), and that these tracts,
or the channels of these great currents, lie the one
alongside the other. Occasionally very intense cold is
experienced in winter over Central and Southern
Europe, while these islands enjoy mild weather. It
will be found that in such cases the winds are all
Easterly where the weather is cold, and all Westerly
where the weather is warm.
It will be explained subsequently how the motion of
the air, both in direction and velocity, is regulated by
the distribution of atmospherical pressure at the surface
of the earth, which is shown by the distribution of the
readings of the barometer in weather charts ; but as
this relation lies at the very foundation of the whole
structure of modern weather knowledge, it will be
.useful, at the very outset, to explain it.
This principle, which, for convenience, is known as
Buys Ballot's Law, from the name of the Dutch
Professor who first stated it definitely, is contained in
-the following statement.
Stand with your back to the wind, and the
rbarometer will be lower on your left hand than
,on your right.
These words hold good, except close to the Equator,
The Wind. 27
for the Northern hemisphere ; in the Southern we must
interchange left and right. If this principle be once
thoroughly recognised, the broad features of wind
motion will be at once understood.
The Force of the wind, as distinguished from its
Direction, is related to the amount of difference of
barometrical pressure over a given distance, and this is
defined as the ' gradient,' a term which will be explained
in Chapter IV. (p. 44). This force therefore in no way
depends on the absolute height of the barometer at any
one station, as the words printed on the scales of many
old-fashioned barometers would seem to indicate. In
fact, as an illustration of this statement we may anti-
cipate the future explanation by stating that at
Liverpool, during a severe storm on January 24, 1876,
from 2 till 3 A.M., the velocity of the wind from SW.
was sixty-two miles within the hour, while the barometer
was 30.10 inches, nearly at 'Set Fair.' Conversely, at
6 P.M. on March 9, 1876, the barometer at Wick read
27.94 inches, far below 'Stormy/ and the force of the
wind was only 3 (a 'gentle breeze') from NW. In
the one case, therefore, we had a heavy gale with a
high barometer ; in the other, a gentle breeze with a
very low barometer. The reason of these discrepancies
between old theories and actual facts will appear when
we treat of gradients.
Storms were formerly divided into two great classes
circular storms (hurricanes and typhoons) and straight-
line storms. The former are almost the only class of
28 Weather Charts and Storm Warnings.
storms which occur within the tropics, and are known-
under the general name of cyclones. The latter class
were formerly supposed to be the most usual type of
storms in these latitudes, inasmuch as it is a common
observation here that the wind will blow hard from the
same point, and for a considerable length of time, over
a large district. The study of observations taken at
the same hour over an extensive tract of the earth's
surface has, however, shown that the storms of the
Temperate zone are without exception cyclonic, or
partially so, in their character, although not so perfectly
developed as those within the tropics. All cases of
so-called straight-line storms are to be explained either
by the persistence of the same characteristics for several
days over the same region, or else simply by the fact
that they are mere local phenomena, due to the contour
of the country, like the exceptionally strong breezes
often met with on rounding prominent bluff headlands,
or, to use a more familiar illustration, at street corners.
By this statement it is not meant to imply that strong
winds from a definite point are not met with for days
together in the region of the Trade Winds and Mon-
soons ; but, firstly, these forces seldom reach those of an
actual ' strong gale/ and, secondly, the conditions which
cause them are of the same nature as those which cause
our own storms, and it is the persistence of the con-
ditions which determines the constancy in the force
of the wind.
In speaking of the general character of storms, it
should be mentioned that in most cases the vertical
depth of the stratum of the atmosphere which is in the
condition of storm is very small in comparison with the
superficial extent of the area over which the storm is
felt. Every one knows that it is a common occurrence
to see clouds at a moderate elevation either moving
rapidly while calm prevails below, or else at rest, or
nearly so, while we are feeling a strong wind. On one
occasion, August 18, 1875, when a whirlwind passed
over a village in Sweden called Hallsberg, in the
province of Nerike, it was expressly noticed that, while
the branches of trees and fragments of the wreck of
buildings were carried by the wind for miles, the clouds
did not indicate the slightest sign of disturbance.
We have already spoken of great currents of air
extending over vast tracts of the earth's surface, and
the best idea which we can gain, for practical purposes,
of the winds which affect us in these islands is that the
air over the North Atlantic Ocean, north of Lati-
tude 40, is constantly flowing from west to east, like a
gigantic river. If such a river be flowing rapidly, we
often see on its surface small waves, each with its own
eddies and circulations, which are carried on with the
stream. If we could imagine it possible to look at the
upper surface of the atmosphere, supposing it to be
homogeneous and of equal density throughout, we should
see much the same sort of conditions, except that
what corresponds to the hollow of the wave would
be a patch of defective pressure, while that which
3O Weather Charts and Storm Warnings.
corresponds to the crest of the wave would be an area
of excessive pressure. We shall shortly learn how
these areas influence the motion of the air and the
There remains one general principle which was
formerly brought forward as almost indisputable, and
that is the principle known under the name of the * Law
of Gyration,' propounded by Professor Dove, of Berlin,
some fifty years ago. This principle is, that the wind
changes more frequently * with the hands of a watch,'
that is, from East, through South, to West, in the
Northern hemisphere, than it does in the other direc-
tion, and that this is true all round the compass. The
enunciation of this doctrine as an universal law has
arisen from the fact of meteorology having been first
studied in Western Europe, where the truth of the
principle is undeniable. When, however, we look to-
the evidence cited by Professor Dove himself for Arctic
stations, we find that the statements from those regions
are not nearly so positive in favour of the law as the
experience gained in lower latitudes, and the evidence
from the German Arctic Expedition shows that on the
east coast of Greenland the direction of change of
wind was more frequently against watch hands than
Moreover, when we come to consider the motion of
wind in the systems of high and low pressure, of which
we have just been speaking, and the motion of these
systems themselves over the earth's surface, we shall
The Wind. 31
find that the question of the shifting of the wind in
accordance with the law ('veering'), or it's shifting in
opposition to the law ('backing'), simply depends on the
motion of the systems of circulation to which the
winds in question belong. For instance, in the Northern
hemisphere a wind ' veers/ or shifts, ' with watch hands '
at any station when an area of low pressure passes from
west to east to the northward of that station, and it
'backs' when the area of low pressure passes in the
same direction to the southward of the station. See
fig. 14 (p. 79).
The reason that veering, especially from SE. or S.
through SW. to W. or NW., is so common in these
islands is that the most usual path of cyclonic systems
of air is from SW. to NE., the track of the centres of
the storms passing to the northward of most stations
in this country.
We have learnt, therefore, in this chapter, that wind
is always connected with some disturbance of the
pressure of the atmosphere, and it will be at once
understood that its existence is due to the tendency of
an elastic fluid, like the air, to regain the condition of
equilibrium from which it has by any means been
disturbed, while the motion of wind is regulated by
certain fixed laws to which we have alluded, and which
will be more fully stated presently.
3 2 Weather Charts and Storm Wa rnings.
WE have next to consider what is the real nature
of these disturbances of which we have been speaking.
They are connected with irregularities in the distribution
of atmospherical pressure. We only say ' connected
-with/ and do not say ' traceable to/ or use any more
positive expression of opinion, for it is not proposed in
this book to discuss the question of what the original
.causes of the disturbances are. Various theories have
been propounded to account for storms, and some will
be mentioned in Chapter VII., but none of them have
met with general acceptance as yet We must there-
fore only take things as we find them, and endeavour to
make the best of them.
But it is necessary, at the outset, to explain the
meaning of some of the terms which will recur most
frequently in the following pages.
The first of these is the word 'isobar/ which is
.derived from two Greek words signifying ' equal weight.'
An isobar, or isobaric line, is a line passing through
those places where the barometrical pressure is cqiial.
The Barometer. 33
If we look at the chart (fig. i, p. 34) containing the
readings from a report for a day, we see that the
readings, all of which are shown on the chart, varied
from 29.88 at Nice to 30.54 at Stockholm and
Christiania. We find several lines drawn across the
chart : all these lines are isobars, and the values of
each are given.
The courses of these isobars are determined with
reference to the stations on each side of them where
actual observations exist, the probable position of the
line in each case being ascertained by dividing the
distances between the stations in proportion to the
difference in readings between them. Similarly, points
are found for isobars crossing the North Sea by
dividing the distance between the stations on each side
of that sea in proportion to the difference in read-
ings between them. In this manner the courses of
isobars drawn over the sea, and in regions whence no
observations are obtainable, are inferred from the read-
ings taken at the nearest stations whence observations
have been received. As a general rule isobars drawn
on comparatively insufficient information are dotted
instead of being drawn in full.
The isobar of 30.5 forms a closed curve, passing
through Stockholm and enclosing the southern part of
Sweden as well as Christiania and the Scaw, that of
30.4 ins. starts from the Gulf of Bothnia, north of
Hernosand, passes close to Skudesnaes (30.39), York
(30.41), and Prawle Point (30.41), through Cape
34 Weather Charts and Storm Warnings.
Gris Nez (30.40), and is carried out over Northern
The lines of 30.3 and 30.2 run across Norway and
FIG. I. January I, 1887 ; 8 A.M. Barometrical Readings
the North Sea, on a course nearly parallel to that of 30.4,
which has just been described. That of 30.3 passes
The Barometer. 35
very close to Roche's Point and Rochefort (both 30.31)
and to Berlin (30.32). It is dotted across the Bay of
Biscay from want of information, as also is that for
30.2 ins. This latter passes very close to Valencia,
Corunna, and Biarritz (30.21, 30.22, and 30.19
respectively) ; the line for 30.1 just skirts the coast of
Norway, passing thence between Sumburgh Head
(30.09) and Wick (30.11), and outside the coast of
Ireland, to reappear over Southern and Central France.
The reading of 29.95 at Bodo necessitates the
drawing of a line for 30.0 ins. in the extreme north of
the map, white that of 29.85 at Nice calls for two other
lines, for 30.0 and 29.9 respectively, over that part of
From what has been said, it will be understood that,
as these lines pass between stations where the observa-
tions show higher or lower pressures respectively than
the values assigned to the isobars themselves, it is pre-
sumable that the reading at any other station exactly
on any line would have precisely the value shown by
These isobaric lines are drawn on all weather charts,
and a knowledge of their respective values in baro-
metrical readings, and of their courses, lies at the very
foundation of all that we know about weather.
It will already have been seen from fig. i that the
readings are not the same at all stations simultaneously,
and, if we look at any chart representing the conditions
of barometrical pressure over an extensive region for
3 6 Weather Charts and Storm Warnings.
any epoch of time, we shall find that this pressure is
not equal at all stations, being greater in some places
than in others. If we then proceed to draw the isobars,,
we shall find that several of these lines, like that for 30.5
ins. on fig. I (p. 34), form closed curves round certain
spots where the barometrical readings are either lower
or higher than they are over the neighbouring districts.
These two contrasting states of affairs are known by
different names. The districts of low pressure, or of
depression, are termed 'cyclonic,' and those of high
pressure ' anticyclonic/ the names being derived from
the Greek word /cu/cAow, to whirl round in a circle,
and conveying the fact that the wind in each class of
area has a tendency to circulate round the centre of the
system of disturbance, but in opposite directions in the
There is a very marked difference between the areas
in which the barometer is lower, and those in which it
is higher, respectively, than in the surrounding districts,
for the temperature and the weather, as well as the
circulation of the wind, differ most materially under
the respective conditions.
In both cases there is a calm at the centre, or over
the region enclosed by the innermost isobar, and, as a
general rule, in cyclonic systems the extent of this calm
centre is less, and the isobars surrounding it lie closer
together, than in anticyclones. We shall shortly learn
that this indicates a material difference as regards the
force of the wind.
The Barometer. 37
In order to illustrate this it will be necessary to give
some charts as instances respectively of cyclonic and
anticyclonic disturbances, which have existed over the
region embraced by our telegraphic reporting system.
It is, however, comparatively seldom that the whole of
a system of either kind will be found developed over
our limited district. More frequently we only find
curves trending one way or the other, which enable us
to conclude, from the general distribution of pressure,
in what direction the central area of high or of low
pressure, as the case may be, is situated.
Fig. 2 (p. 39) gives a good example of an area of
low pressure, or a ' depression,' or a cyclonic disturbance,
for the terms are used almost indiscriminately, developed
as fully as it is usual to find them in Western Europe.
Since the mode of drawing isobars has already been ex-
plained, it has not been thought necessary to repro-
duce the actual barometrical readings at the different
It will be noticed that the chart contains other
indications, besides those afforded by the isobars, which
require some explanation.
The direction and force of the wind are given by
arrows : a circle indicates a calm, as the wind has
neither direction nor force.
The direction is shown by the direction in which the
arrow is flying.
The force is indicated by differences in the symbols
employed, which are as follows :
38 Weather Charts and Storm Warnings.
Forces o-i (Beaufort scale, p. 8)
above 10 -s >
Thus it will be seen that there is a very heavy gale at
Rochefort from WNW., a heavy gale at Scarborough
from SE., a fresh breeze at Aberdeen from E., a light
breeze at Brussels from SSE., and a calm at Toulon.
(See Appendix A., p. 218.)
The lowest reading (28.55 inches) is at Holyhead ;
the highest (30.00 inches) at Corunna.
The innermost isobar (28.6) embraces almost the
whole of Wales. That for 28.8 is oval in shape, and
covers nearly all England, and the east and north of
Ireland. That for 29.0 takes in a little of France and
Belgium, and the greater part of Scotland. The isobar
of 29.2 envelops the whole of Scotland, but is not
carried out over the Atlantic beyond the Orkneys
on one side and the coast of Brittany on the other,
and it is only dotted in, as being merely inferred,
in the absence of observations, over the Bay of
The other isobars are only partly shown ; in fact, the
position of a portion of that for 30 inches is only indi-
cated by the single observation of 30.00 at the station
The chief feature noticeable in the northern part of
the chart is that the isobars of 29.4 and 29.6 trend
away to the northward, and so the curves spread out in
a fan shape between the Shetlands and the coast of
If \ve now turn to the wind arrows, we shall find
FIG. 2. November 29, 1874 ; 8 A.M. Isobars and Wind, Cyclonic
that they show a circulation round the centre of
depression. They are :
4Q Weather Charts and Storm Warnings.
Westerly at Scilly and in France . . .on its southern side.
Northerly at Valencia ) .,
vr ii i -i-x i i r . on its western side.
North-north-east at Donaghadee J
East at Ardrossan ...... on its northern side.
South-east along the whole east coast of Great \
Britain north of Hull 1- on its eastern side.
South at Yarmouth and in the Straits of Dover)
In fact, the wind sweeps round the central area of
depression, against watch hands, and this is the invari-
able law in all cases of cyclonic disturbances in the
Northern Hemisphere. The wind moves in a direction
opposite to that of the hands of a watch, and its course
is nearly parallel to the isobars ; but to this subject, as
well as to the relation of the force of the wind to the
distribution of pressure, we shall return later on.
Let us now take the converse case, an instance of an
area of high pressure, or an anticyclone, and for this we
have an excellent example in February 4, 1874 (fig. 3).
On this day at 8 A.M. the absolute highest reading is
30.67 at Nottingham, and the only English reports
which give readings below 30.6 are Dover, Plymouth,
and Scilly, the isobar of 30.6 enveloping almost the
whole of England and Wales. That of 30.5 stretches
to Holstein near Fano (30.49), passes south of Paris
(30.52), being shown by dots, owing to deficient infor-
mation, between these points, sweeps close to Valencia
(30.49), is again dotted over the sea outside the coast
of Ireland, and finally reaches Aberdeen (30.49).
In the north and south readings decrease rapidly ; on
the south side, the curve for 30.40 passes half-way
The Barometer. 41
between Rochefort and Biarritz, and 30.30 skirts the
coast of Spain and the Pyrenees, readings being 30.28
at Corunna, and 30.24 at Toulon. In the north 30.4
FIG. 3. February 4, 1874; 8 A.M. Isobars and Wind, Anticyclonic
passes below Stornoway (30.39), runs between Wick
and Thurso and across to Jutland, where the reading
42 Weather Charts and Storm Warnings.
at the Scaw is 30.34. Passing further north, 30.30
runs close to Sumburgh Head and across to the
neighbourhood of Bergen in Norway, while above it
still we find that of 30.20, the reading at Christiansund
When we look at the winds in this case we find that
their circulation is exactly opposite to that which is
shown in fig. 2 ; it is with watch hands, being :
North . . . .in Germany, on its eastern side.
East . . . .in France, on its southern side.
South . . . .in Ireland, on its western side.
South-west to West . in Scotland, on its northern side.
North-west . . .in Denmark, on its north-eastern side.
The arrows also appear to draw out from the
centre instead of drawing in towards it as in cyclonic
The isobars are further apart than in the former
case, and in consequence the force of the winds is much
less. The reason of this will shortly be explained.
We have therefore learnt in this chapter (i), that the
distribution of atmospherical pressure on a weather
map is made clear by the isobars ; (2), that there are
two grand types of disturbance of the equilibrium of
pressure, called respectively, a, cyclonic and, b, anti-
cyclonic, according as the pressure in a given locality
is either in defect or excess of its mean value over the
surrounding region ; (3), that these two types are
characterised by strong contrasts to each other, among
The Barometer. 4$
which the most striking are the differences in the
direction of motion of the wind.
Cyclonic and anticyclonic are, however, merely relative
terms ; the reading may be above 30 inches at the
centre of a cyclonic area, and below 29.5 inches at the
centre of an anticyclonic region. If at any place, or
over any district, the barometrical reading is lower than
at the places all round it, that place or district is the
centre of a cyclonic area ; if, on the contrary, the
reading at the place or district is higher than at the
places all round it, that place or district is the centre
of an anticyclonic area.
44 Weather Charts and Storm Warnings.
LET us now proceed to examine still more closely into
the principles in regard to the motion of the wind,
which have only been faintly hinted at before. The
direction of motion of the wind, in relation to the dis-
tribution of atmospherical pressure, may be easily
perceived to be such that if you stand with your back
to the wind the barometer will be lower on your left
hand than on your right. This is the principle already
cited, and generally known, as Buys Ballot's Law. It
is simply the extension, to all cases of wind motion, of
the Law of Storms first announced by Redfield and
Reid for the Hurricanes of the West Indies as well as
for the Typhoons of the China seas. The Hurricanes
of the Southern Indian Ocean obey a similar law. The
direction of rotation is opposite in the two hemi-
spheres. The law as above stated refers to the
Northern Hemisphere. The law therefore gives the
direction of the wind, but it also enables us to judge of
its force, for it is found that this latter depends mainly
on the amount of difference of pressure between adja-
Air, being a gas, is even more mobile than water,
and as the least difference in level between two
portions of a free surface of the latter generates motion,
tending to produce equality of level ; so in the former
case the slightest difference of pressure causes motion
in the atmosphere, in the endeavour to restore equi-
librium of pressure.
It is evident that the greater the difference of
pressure over a given distance, the greater will be the
effort, and consequently the more violent and rapid
will be the motion required to regain equilibrium.
There is therefore a convenience in fixing a standard
of comparison by which to measure the disturbance of
pressure, and here meteorologists borrow an idea from
engineers, who measure the inclination of a road or
railroad by what is termed the 'gradient/ implying,
when they speak of a gradient of one in sixty, that the
slope rises one foot vertically for every sixty feet of
Meteorologists speak of gradients also, but, instead
of applying the same unit of measurement, as of feet, to
the vertical and horizontal scales, they give the vertical
scale in units of barometrical measurement, and the
horizontal scale in miles of distance. These gradients
therefore are expressed in differences of barometrical
pressure over a given distance. The first person to
introduce the term gradient into meteorology was the
late Mr. Thomas Stevenson, C.E.
The gradients adopted by the Meteorological Office
46 Weather Charts and Storm Warnings.
are expressed in hundredths of an Inch of mercury per
fifteen nautical miles. 1
In the accompanying figure (fig. 4), the horizontal
distance between the two stations A and B is supposed
to be fifteen nautical miles. The divisions on the
vertical line B D are hundredths of an inch, and they
correspond to the differences between the barometrical
readings taken at the same hour at the two stations.
The gradients are the ratios between the intercepts
FIG. 4. Gradients.
B C, B D, &c., and the line A B which is supposed to
be = i. The gradients are given as 2 for the angle
B A C, % for the angle BAD, corresponding to the
several observed differences. These lines A C, A D,
&c., are imagined to be drawn every morning between
the most important stations given in the Daily
Weather Report, and from their inclinations conclusions
as to the probable direction and force of the wind for
1 On the Continent gradients are measured as millimetres per one degree
of sixty nautical miles. These gradients are therefore almost identical with
ours, for one millimetre is nearly 0.04 inch.
the day are drawn. It is found, for instance, that the
force of the wind will not exceed the figure 5 or 6, a
' fresh breeze ' on Beaufort's scale, unless the gradient
be higher than 2 (A c on the diagram).
To reduce this statement to a practical form, we
may put it in these words. The distance from
Penzance to Brest is 1 1 3 nautical miles. A gradient
of 2 between these stations represents a total difference
in barometrical readings of o. 1 5 inch, so that, in
accordance with what has just been said, whenever a
Westerly gale is blowing at the entrance of the Chan-
nel we may expect that the barometer at Penzance
will be at least o. 1 5 inch lower than that at Brest ;
vice versa, the readings at Brest will be proportionably
lower than those at Penzance whenever an Easterly
gale is felt in the district in question.
An instance in point for the former state of affairs is
the gale of January 8, 1870, during which the read-
ing at Brest at 8 A.M. was 29.38, and that at Penzance
at the same hour was 29.19. The difference between
these readings is 0.19, and the resulting gradient 2.5.
A very severe Westerly storm was that morning
reported from the Channel.
The converse conditions accompanying an Easterly
gale were observed on May 14, 1869, when the read-
ing at Penzance was 29.92, and that at Brest 29.68.
The resulting gradient is 3.2, and accordingly heavy
Easterly gales were felt on our Channel coast.
To apply the same principle to the winds of the
48 Weather Charts and Storm Warnings.
British Islands generally, it may safely be asserted that
no storm of any serious extent is ever felt over tire
United Kingdom unless there be an absolute difference
in barometrical readings exceeding half an inch of
mercury between two of our stations. 1
The difference in readings between Rochefort and
Aberdeen on February i, 1868, when a tremendous
Westerly gale was raging, was as much as 1.76 inch,
the reading at Rochefort being 30.16, and that at
Aberdeen 28.40 inches. These figures give a gradient
of 4 over the entire distance of 673 miles, and we find
that gales were reported from seventeen stations that
No very precise relation has as yet been established
between the amount of the gradient and the force of
the wind, but as a convenient figure to be remembered
it may be repeated that a gradient of 0.02 inch per I 5
miles indicates the probability of as much wind as an
ordinary yachtsman likes to meet with.
We are now in a position to see more clearly how
entirely this idea of gradients does away with the old
notion that the actual height of the barometer at one
station gives a certain indication of the probable direc-
tion or force of the wind or of the character of the
weather at that station, a notion which has found ex-
pression in the worcls 'Very Dry,' ' Fair/ 'Change/
1 Local storms, which occasionally do great damage, may be felt when
the barometrical disturbance is itself only local, and when the actual
amount of difference between the extreme readings is less than half an
inch, although the gradients for a short distance may be high.
' Rain,' ' Stormy/ &c. &c., which have been for so many
years placed on barometer scales.
The small trace of truth which the scale lettering in
question contains is accounted for in the following
way. On the average of a great many readings of
the barometer, taken under various circumstances as
regards the direction of the wind, it is found that in
these islands the reading is highest when the wind is
North-easterly, and, as has already been stated, this is
when the air is coldest and driest. Consequently we
have ' Very Dry ' put down at the top of the scale, and
according as the mercurial level rises from ' Change,'
29.5 inches, to its maximum height, we have 'Fair' or
' Set Fair ' entered. Conversely, when the air is warm
and moist and the wind South-westerly, the barometer
is low, and so we have then the descending scale of
' Rain,' ' Much Rain,' and ' Stormy.' It is, however,
quite a mistake to imagine that on any given day there
is any certainty of the weather according with the
description of it given by the word corresponding to
the barometer height for that day.
There are yet other points of view from which the
inutility, and in fact the absolute error, of these words
may be indicated.
Let us take for example the word ' Change ; ' this
is placed opposite the reading 29.5 inches, which read-
ing is naturally supposed to be taken at sea-level. If
the barometer be removed to a station situated, say,
500 feet above that level, the corresponding reading
5 o Weather Charts and Storm Warnings.
will be about 29 inches, so that the whole scale will
be half an inch out, and the error will be the greater
the more considerable is the height of the station.
The lettering is therefore wrong for another reason,
because it does not take account of the necessary
reduction of the reading to sea-level.
Once more, the range of the barometer is far greater
in winter than in summer, so that the reading which
corresponds to ' Fair ' should be much nearer to
' Change ' in summer than in winter. The lettering
is therefore still further in fault, as taking no account
of this difference. The words are in fact little less
than utter nonsense.
It is undeniable that there is more chance of strong
wind when the barometer is low than when it is high,
but this arises, not from the actual height of the
barometer, but from the circumstance that cyclonic
areas are usually much smaller than anticyclonic, so
that when the barometer is low there is a greater proba-
bility of a steep gradient, from adjacent higher readings,
existing in the neighbourhood, and causing high winds,
than is the case when the barometer is high.
It, however, sometimes happens that the barometer
in these islands will remain for a day or two below
29 inches, that is, below ' Stormy,' without any gale,
because the area of low pressure is extensive and the
gradients slight. An instance of these conditions has
already been cited at p. 27 as having occurred March 9,
The question is often asked why gradients can be
said to be for certain winds ? The answer to this is
very simple. Let us recur to fig. 2 (p. 39), and add
to the curves and arrows already shown a number of
FIG. 5. November 29, 1874; 8 A.M. Isobars and wind, with
straight lines joining Holyhead to Valencia, Aberdeen,
Skudesnaes, the H elder, and Brest. These lines (fig. 5)
represent the direction of the gradients, and a glance
5 2 Weather Charts and Storm Warnings.
at the chart will show that the winds, as regards their
direction and force, bear a definite relation to these
gradients in accordance with Buys Ballot's Law.
It will, however, be seen that as the form of the
central isobar is oval, not circular, and as the lowest
reading, that at Holyhead, is at some distance from
the centre of the oval, the accordance of the winds
with the gradients is not so exact as would be evinced
in the case of a more perfectly circular storm. This is
particularly the case as regards the relation of the
winds at Scilly and Pembroke to the gradients between
Brest and Holyhead. The centre of the disturbance
really lies not far from Shrewsbury, and a gradient
from Brest to Shrewsbury would be steeper than that
from Brest to Holyhead, and the winds would be more
nearly perpendicular to it than is the case in the chart
In fact, this relation of the winds to the gradients may
be exhibited by the following table :
Valencia to Holyhead
NW. S at Roche's Point
Aberdeen to ,,
E. by S.
f E. 7 at Aberdeen
|SE. 7 at Leith
Skudesnaes to ,,
SE., at Scarboro' and Shields
The Helder to
(S. 5 at Yarmouth
| S. 7 at Cape Gris Nez
Brest to ,,
]WNW. IO at Scilly
|W. 9 at Brest
It is needless to multiply examples. The chart
shows a complete cyclonic circulation, and the gradients
Gradients. 5 3
are taken on various sides of the centre. The entire
condition furnishes a clear ocular proof of the state-
ment that the wind is nearly perpendicular to the gra-
dients, and therefore nearly parallel to the isobars.
From the way in which the direction of the gradient
is described, we gather the direction of the wind indi-
cated. When we speak of a gradient from Valencia to
Holyhead being for North-westerly winds, we imply that
the reading at Valencia is the higher of the two readings,
the station luith the higher reading being ahvays placed
first, and so a man standing midway between the two
stations, with the lower barometer on his left-hand side,
would face SSE. and have his back to the NNW. ; the
wind would therefore be North-North-westerly, which
brings us back again to Buys Ballot's Law.
We have now learnt how the idea that the reading
of the barometer at any time gives an indication of
probable weather is controverted by the more correct
conception of the value of gradients, but there is another
idea which, though not absolutely misleading, is yet an
unsafe mode of interpretation of barometrical readings.
This is the idea that the motion of the mercury in the
barometer is an infallible indication of coming weather.
It is often asserted that if the barometer falls, say, at
the rate of one-tenth of an inch per hour, a storm is
certain to ensue at the place.
Depressions with slight gradients, moving quickly,
will, however, cause the barometer to fall, at stations
5 4 Weather Charts and Storm Warnings.
over which they pass, as rapidly as depressions with
steep gradients which move slowly.
It is of course true that if an area of depression
passes over us the barometer will fall till the centre has
gone by, and then will rise, and that the rates of such
fall and rise, for a given rate of motion, will bear a close
relation to the amounts of the gradients along the path
of the centre ; but it is not by any means certain that
because a barometer falls rapidly there must be a gale
at the place where this fall is observed. A very telling
instance of the fallacy of this opinion is to be found in
the following case, when the barometer fell with extra-
ordinary rapidity over an extensive region, and yet
hardly at a single station within that region was there
any gale felt.
November 22, 1869, a very remarkable barometrical
depression was manifested over Western Europe. The
actual fall of the mercury, since 8 A.M. on the 2ist, had
exceeded 0.9 inch over the entire district extending
from Dover to Valencia and from Lorient to Shields.
This area is bounded by the meridians of i E. and
11 W. and by the parallels of 48 and 55 N., and
its superficial extent is about 200,000 nautical square
On this occasion, although there was such an enormous
disturbance of equilibrium, there were absolutely no
strong winds reported on our coasts during the day r
excepting slight gales from North-west at Cape Clear
and from South-east at Yarmouth.
Gradients. 5 5
Outside our west coasts, however, on the edge of
the disturbance, gradients were very steep, and there
gales were felt between the 2ist and 23rd, not only
by the Atlantic steamers Scotia and City of Brooklyn,
which were near the Irish coast, but also by the Inver-
ness and Foam, which were further south. In fact, the
last-named vessel, in the latitude of Cape Finisterre,
was driven to the southward, out of her course, and
suffered severely. At Corunna, however, and on the
coast of Portugal, the gale was not felt seriously at all.
In this case, therefore, a fall of the barometer of an inch
at several stations was not followed by a gale at those
March 9, 1876, the instance already quoted (p. 27),
affords quite as striking an illustration. That morning,
at 8 A.M., the fall in the barometer within twenty-four
hours had amounted to i.i inch at Wick, had exceeded
an inch over the entire north and east of Scotland, and
had been more than 0.8 inch over the rest of Great
Britain, most of Ireland, and the north of France, yet
the only wind of a force above 7, ' a moderate gale,'
was at Rochefort, where a heavy Westerly gale was
reported, and near the very centre of the disturbance,
where the barometrical fall ivas the greatest, the force of
the wind was the slightest, because the gradients were
This entire depression, like that mentioned just above,
passed off without causing any gale worth notice in the
5 6 Weather Charts and Storm Warnings.
We have learnt in this chapter that the distribution
of pressure, as defined by the gradient, is the best
guide, by the use of the barometer alone, towards a
knowledge of the laws of wind motion and, as we shall
subsequently learn, of coming weather ; but it must
be stated that it appears that the force of the wind is
not regulated solely by the gradients, though meteor-
ologists have not yet determined what are the other
agencies which influence it.
It is therefore evident that any attempt to foretell
weather by the indications of the barometer at any one
station, unsupported by observations of wind, clouds,
weather, &c., must necessarily be imperfect. The
direction and force of the wind in no way depend on
the actual barometer reading at the time.
We have, moreover, seen the meaning of the phrase
'gradients for such and such winds,' which are nothing
more than the expression in a practical form of the
laws of wind motion.
Cyclones and Anticyclones. 5 7
CYCLONES AND ANTICYCLONES.
THE consideration of gradients, and of the effects of
the distribution of pressure, brings us to contrast the
two classes of atmospheric systems, anticyclonic and
cyclonic, and the weather they bring with them.
Anticyclonic systems are marked by a very slow
circulation of the air, or, in other words, by light winds,
by low temperature in winter, great dryness of the air,
at least at the centre, and consequent absence of rain,
although fog is frequently very prevalent. These cir-
cumstances are accounted for by the fact that the air,
in an anticyclone, flows out from the centre, and there-
fore must be supplied from the upper regions of the
atmosphere by a descending current, which cannot
possibly contain much moisture, owing to the very low
temperature of the regions from whence it is drawn,
and which is actually rendered drier by the fact of its
1 Air ascending is expanded, it falls in temperature in the process, and
the moisture it contains is consequently liable to be condensed and to
form clouds, and ultimately fall as rain. Conversely, air descending is
compressed, it rises in temperature in the process, and consequently its
capacity for containing moisture is increased, and it feels dry.
5 8 Weather Charts and Storm Warnings.
Cyclonic systems, on the contrary, are distinguished
by the exact converse of the above conditions. The
air circulates more rapidly, causing strong winds, and
flows in towards the centre, so that it must naturally
be supplied from below and ascend in the centre.
Cyclones in these latitudes bring with them, at least
over a considerable proportion of the area they cover, a
comparatively high temperature, much moisture, and
consequently heavy rain. We say, over a considerable
proportion of the circumference, because, in certain
parts of a cyclonic system, the wind which is felt is
often very dry. This is in the rear of the disturbance-
In the Tropics, there is not such a contrast between
the different parts of a cyclone, as regards dryness.
These statements refer to the winter ; in summer the
conditions are exactly reversed, at least as regards the
temperature which accompanies the respective systems
Anticyclonic systems in summer, produce our hottest
weather, inasmuch as the air is so dry that no heavy
clouds can be formed, so that the sun has full oppor-
tunity for exerting his heating power, while there
is hardly any motion in the air to produce a cooling
Cyclonic systems in summer, on the contrary, bring
cloudy weather, rain, and a reduction of temperature,
the latter being mainly due to the density of the cloud
covering which intercepts the direct rays of the sun.
It is easy to illustrate these statements by examples*
Cyclones and Anticyclones.
Let us take the instance of an anticyclone first, in fact
the very day which we have already cited, February 4,
FIG. 6. February 4, 1874 ; 8 A.M. Isobars and temperature, showing
changes in previous twenty-four hours. 1 Anticyclone.
1 The changes of temperature in figs. 6 and 7 are shown by small figures
placed after the thermometrical readings. When these figures are above
the readings, as at Wick (in fig. 6), they indicate a rise of temperature ;
when they are belong as at Scarborough, they indicate a_/a//.
o Weather Charts and Storm Warnings.
1874 (fig. 3, p. 41), which wilt serve as a very good
illustration of a winter anticyclone. Fig. 6 (p. 59)
exhibits the isobars as before, but the figures on the
chart refer to temperature.
It will be perceived that over the central area,
embraced by the isobar of 30.6 inches (see p. 41), the
temperature is lower than it is anywhere else in these
islands, and that there is a fall in temperature noticed
at every station, varying from i at Plymouth and
Yarmouth to more than 10 in the north of England,
and even 16 at Scarborough. In fact, the cooling in-
fluence of the anticyclone is noticeable over almost the
whole map, except in Ireland and Scotland. In the
north of the latter country, however, the rise in tem-
perature is very marked, amounting to 8 at Aberdeen
and 7 at Wick and Sumburgh Head. This change of
thermal conditions locally arose from the fact that, on
the previous day, the north of Scotland had been the
region of an independent anticyclonic system, as will
be gathered from the examination of fig. 24 (p. 93), but
the barometer had fallen during the night, and the
wind, though still light on our coasts, had shifted from
N. to SW. both in Caithness and in the Lews. In
fact, this rise of temperature was connected with a
cyclonic disturbance further northward, which is shown
in fig. 26 (p. 94).
As regards the force of the winds, a glance at fig. 3
(p. 41) is sufficient to show that they are very light ; in
fact, the only British or Irish station where they exceed
Cyclones and Anticyclones. 6 1
the force of 5 of the Beaufort scale, a ' fresh breeze/
The general dryness of the air is sufficiently evinced
by the fact that rain was not recorded for this morning
from more than five stations out of the fifty-one men-
tioned in the Reports, at three of them the amount
being only o.oi inch ; the greatest quantity was at
Scilly, and that was only 0.06 inch ; nevertheless, the
actual difference between the dry and wet bulbs was
but slight, showing that the atmosphere was near its
point of saturation for the temperature. This circum-
stance is partly owing to the fact that the observations
were taken at 8 A.M., so that the influence of the sun's
heat had hardly made itself felt. In fact, what
moisture there was, was present in the form of cloud or
fog. The reader may be interested to learn that owing
to this latter condition the only region where the sky
was clear was the north of Scotland, and that a
traveller coming south would have met with an entirely
overcast sky at Leith, while fog and mist were reported
all along the east coast of England, as being either
prevalent at 8 A.M. or as having been so during the
preceding twenty-four hours.
Frequently, though this was not the case in this
particular instance, these fogs only last during the
early part of the day and clear off about noon, as the
diurnal range of temperature during the existence of
anticyclones is often very great.
These conditions are more or less characteristic of
62 Weather Charts and Storm Warnings.
the entire class of areas of high pressure, and, as we
shall shortly proceed to show, the most striking feature
of the weather which accompanies them is its per-
manency, i.e., the slowness with which changes succeed
Let us now take the case of a cyclonic area
(November 29, 1874), fig. 2. the very instance which
has been already cited (p. 39), and examine into the
features which characterised the weather which this
system brought with it. This storm was so typical
that the Weather Report and Charts for the day have
been reproduced in Appendix A. (p. 2 1 8).
In the first instance we see (fig. 7) that over almost
the whole of the map the rise of temperature from the
previous day (indicated by figures above the readings,
as before) has been very striking, especially at the
south-eastern stations, where the increase has exceeded
10, amounting even to 23 at Cape Gris Nez, near
Boulogne. This region lies in front of the advancing
disturbance, and is the district of the Southerly and
South-east winds. The motion of this particular storm
will be traced subsequently (figs. 19-22, pp. 90-92).
In the rear of the storm, i.e., in Ireland and Cornwall,
where the wind has shifted to North-west, we find that
a fall (indicated by figures below the readings) is re-
ported at all the Irish stations, as well as at those in the
extreme north of Scotland. That this is due to the
direction of the wind is sufficiently clear from the fact
that, at almost all the places where the cooling effect is
Cyclones and Anticyclones. 63
observable, the direction of the wind is from some point
to the Northward of West, being NE. at Donaghadee,
N. at Valencia, NW. at Roche's Point, and WNW. in
FIG. 7. November 29, 1874; 8 A.M. Isobars and temperature, showing
changes in previous twenty-four hours. Cyclone.
the south of England, where, although no fall of tem-
perature from the reading at 8 A.M. on the previous day
64 Weather Charts and Storm Warnings.
is reported, the rise at Stilly and Plymouth is only i f
as compared with 10 at Dover and 14 in London.
As regards clouds and rain, the facts are still more
striking. Out of the entire list of stations, only thirty-
seven give the amount of cloud in their reports : of
these, twenty-three stated the sky to be * entirely over-
cast,' thirteen others reported various proportions
ranging from the above quantity down to that of six-
tenths of the sky being covered, while at one solitary
place, Hurst Castle, with a WNW. wind, the sky was
' half clear.'
The rainfall is equally clearly marked. During the
twenty-four hours preceding the epoch for which the
chart is drawn, rain fell at every station in these islands
and France whence we have reports, except at Nairn,
and, as to its amount, at four stations this exceeded an
inch, and at ten others it was more than 0.7 inch.
It may therefore be said that areas of low pressure
are accompanied by a high temperature, especially in
the front of the storm, a large amount of moisture in the
air, and consequent prevalence of cloud and rainfall.
The instance which has been given, however, although it
illustrates very well many of the features of a cyclonic
disturbance, does not exhibit all the circumstances
which may be observed in a given storm, as to the
march of the different phenomena within the system
As regards the distribution of clouds and weather in
such a system, the Rev. W. Clement Ley exhibited, at
Weather Charts & Storm Warnings.
DISTRIBUTION OF CLOUDS AND WEATHER IN A
TYPICAL CYCLONIC DISTURBANCE
According to the Rev .W.Clement Ley.
Cyclones and Anticyclones. 65
a lecture which he delivered before the Meteorological
Society in 1878, a diagram of which Plate II. is a
reproduction ; the original appears in ' Modern Meteor-
ology ' (London : Stanford, 1879.)
In this the long arrow represents the direction in
which the system is advancing, and the curved arrows
indicate the motion of the wind. It will be seen that
the cloud gradually becomes denser as the centre
approaches a station, and that as the centre passes
there is, on the right-hand side of its track, a sudden
clearing up, the clouds, with the NW. wind in the rear
of the system, being broken and giving rise to showers,
not to continued rain.
On the left-hand side of its track there is no such
sudden clearing up, as the cloud remains dense until the
vane shifts beyond North, and the subsequent clearing
One of the most striking characteristics of a cyclonic
storm is the sudden shift of wind which takes place
between SW. and NW., accompanied frequently by a
heavy squall and a shower, together with an almost
instantaneous fall of temperature, and this is entirely
absent in the case of the storm shown on fig. 7, as will
be explained on p. 92. To take a very remarkable
instance of this squall, we find that on February 12,
1869, a cyclonic storm passed up the English Channel;
the lowest barometrical reading being recorded at Fal-
mouth at noon, when the wind flew from SW. to
WNW., and the temperature fell 6.2 in a few minutes.
66 Weather Charts and Storm Warnings.
At Kew similar changes took place at 4.30 P.M., but in
a very aggravated form : the shift of wind having been
from WSW. to ENE., and the fall of the thermometer
1 1.6 in about five minutes.
The storm of Sunday, March 12, 1876, was very
severe in the south of England. In this, the shift of
wind at Kew was from SW. to N., and the fall of
temperature 8. 5 in thirty minutes, accompanied by
a heavy snow shower. It is also a remarkable fact
that, at the moment of this sudden change of tempera-
ture, the condition of atmospheric electricity changed
from negative to positive. Further researches on this
subject are very desirable.
I have already said that one great distinction between
cyclones and anticyclones, is that the former move, and
the latter are usually nearly stationary, and as the
usual motion of a cyclonic system is from west to east
across these islands, it will be interesting to see what
we can learn, from the continuous records at our self-
recording observatories, of the actual changes which
will occur at a station during the passage of a storm
moving in that direction.
This will naturally differ according as the station
lies to the north or the south of the centre of the
storm, and, as it very rarely happens that the storms
are truly circular, it is obvious that the shifts of wind and
changes of weather will not always be perfectly regular.
In fact, the extraordinary changes of February 12,
1869, just cited, afford a very good proof of the
Cyclones and Anticyclones. 67
unequal distribution of the gradients in such a system
Let us first take the most common case in these
islands, that of a station lying on the southern side of
the path of the centre of a depression which is moving
from west to east across central England, and that
we are situated in London. We shall experience
first the phenomena belonging to the front of the
system : the appearance of cirrus clouds, ' mare's tails,'
in the sky, then the South-easterly winds, the great
rise of the thermometer and excessive dampness, the
sky becoming gradually overcast and the setting in of
mist and rain, the barometer falling persistently, while
scud begins to drift from the Southward. As the
system advances the barometer continues to fall, the
wind veering through S. to SW., and rain falling
steadily. As soon as the wind passes the SW. point
and draws to W. or NW., the barometer begins to rise,
often with a sudden jump, and the temperature falls,
with a very heavy shower of rain, possibly turning to
hail with a thunderstorm, after which the air becomes
much drier, and the sky clears with a N W. wind, which
as a rule soon dies down. After such a disturbance as
this we have frequently a smart frost at night, inasmuch
as the great dryness of the air has allowed of great
radiation of heat from the ground.
It is not easy to find an instance which exhibits the
entire course of changes just described, but the table,
Appendix B. (p. 221), will illustrate several of the points.
68 Weather Charts and Storm Warnings.
The table represents the hourly readings of the
barometer, thermometer (dry and wet), anemometer
(direction and velocity), rain-
gauge, and the vapour ten-
sion from the continuous
records at Valencia on March
26 and 27, 1874, when the
centre of a cyclonic storm
passed to the northward of
that observatory. At 2 P.M.,
March 27 (fig. 8), the centre
of the storm lay off the
north-west coast of Scotland,
outside the Hebrides. The
diagram (fig. 9) exhibits the
course of the curves. 1
The barometer fell steadily
for twenty-three hours, until
FIG. 8. March 27, 1874; 2 P.M.
Storm passing north of Valencia.
9 A.M. on the 27th, and then rose in twelve hours
nearly to the same height as it had held before. Tern-
1 These diagrams require explanation. They are copied from the plates
in the Quarterly Weather Report, and exhibit the continuous records of:
1. The barogram or barometer curve, marked bar. The scale for this is
given in the lower left-hand corner. It is in inches, and the readings,
though corrected for temperature, are not reduced to sea-level, and range
over li inch.
2. The thermograms, marked respectively dry and wet. The scale for
these is in the lower right-hand corner, and ranges over 30.
3. The curve of tension of vapour, marked vap. ten., calculated from the
two thermograms, dry and wet.
4. The rain in hourly amounts of fall. These are measured upwards
from the base line of the scale which serves for vapour tension and rain,
Cyclones and Anticyclones. 69
perature and vapour tension remained singularly steady
during the afternoon of the 26th, rising very slowly
during the night, and reaching a maximum at 8 A.M.
nearly simultaneously with the epoch of the lowest
Noon 6 P.M. Midnt. 6 A.M. Noon 6 P.M. Midnt.
FIG. 9. March 26 and 27, 1874. Automatic records at Valencia.
barometer readings. The thermometers then began to
fall briskly, and by 9 P.M. the dry bulb had sunk 5.;.
It will be observed that, owing to the influence of the
and is on the left-hand side, above the barometer scale ; it is in tenths of
an inch, and extends over half an inch.
5. The wind direction, marked direc. This is on a special scale shown
at the left-hand side, which represents a paper wrapped round a cylinder,
and then laid flat. N is at the top, then come successively w, s, E, and N
6. The wind velocity, marked velocity, in hourly amounts, measured by
the scale of miles, up to seventy, shown on the right-hand side.
The time scale is shown at top and bottom.
7o Weather Charts and Storm Warnings.
storm, the temperature was higher during the early
morning hours of the 27th than it was during the after-
noon of either the 26th or 2/th, and yet 2 P.M. 'is
usually about the warmest part of the day. While it
lasted, therefore, the storm entirely disturbed the regular
diurnal march of temperature. The secret of this dis-
turbance of temperature lies in the direction of the
During the whole time that the barometer was falling
the wind remained nearly constant between SSE. and
S., blowing a stiff gale, and a little rain fell. When the
centre of the storm was approaching, the rain set in
again at about 4 A.M., and became heaviest just at
8 A.M., when the barometer was nearly at its lowest level
and the wind was about veering towards SW. At the
hour of the lowest barometer reading we find the first
trace of Westing in the direction of the wind, and at
the same hour the velocity shows a sudden increase, the
rain still continuing. The sky then cleared, the baro-
meter rose briskly, and the wind increased till noon,
when it blew a heavy gale from SW.byS. It sub-
sequently veered pretty quickly to WNW. with a slight
shower of rain at 3 r.M., and fell very light afterwards
at 7 P.M.
The courses of the wet bulb thermometer curve, and
of the curve of vapour tension, illustrate very clearly the
contrast between the Southerly and North-westerly
winds as regards the humidity of the air. As long as
the wind remained to the Eastward of South the curves
Cyclones and Anticyclones. 71
of the two thermometers remained close to each other,
and the vapour tension trace rose steadily, but very
slowly. At the hour of the minimum barometer
reading, we notice the thermometer curves going apart,
and for the remainder of the period they pursued
courses diverging more and more from each other,
indicating, what is also shown by the descent of the
vapour tension trace, that the air was becoming drier
and drier according as the wind became more and more
Owing to this extreme dryness of the air of the
North-west wind, in the rear of a storm, it is believed
by some meteorologists that this wind is a downrush
of air from the upper regions of the atmosphere, which
is necessarily very dry, as explained at the beginning
of the chapter.
The case just cited, though it exhibits some of the
phenomena with great distinctness, is not one which can
be made clear to the reader as an instance of a storm
passing to the northward of a station, inasmuch as the
system to which the gale belonged was so extensive
that the limited area of our charts would not exhibit the
conditions in a convincing manner. Fig. 10 (p. 72),
however, is an indisputable case of a storm passing on the
northern side of Aberdeen, and close to it, October
20-21, 1874, and the course of the curves at that
observatory is shown on fig. II (p. 73). The actual
hourly readings will be found in Appendix C. (p. 222).
The fall of the barometer was slow at first, but then
72 Weather Charts and Storm Warnings.
increased in rapidity, and in twelve hours the mercury
sank to the extent of 1.14 inch. It then rose in the
next twelve hours as much as 0.8 inch, and for a portion
of the time the rate of rise was more rapid than that of
the previous fall had been. It will be noticed that the
epoch of the maximum rise of the barometer was also
that of the shift of wind through three points to the
I r ; T i/ > n i
FIG. io. October 21, 1874; 8 A.M. Storm passing north of Aberdeen.
Northward, as well as of the strongest wind and the
heaviest rain. This is the heavy shower of rain,
coincident with the shift of wind to the North-west, of
which mention has previously been made, p. 65. Tem-
perature (dry and wet bulb) and humidity do not follow
a similar course respectively as they did in fig. 9, as all
Cyclones and Anticyclones.
the curves are far less steady in their course than on
the former occasion. We see, however, that the diurnal
march of temperature is again entirely disarranged, the
thermometers remaining pretty nearly at the same tem-
perature throughout the night of the 2Oth, and the
sudden fall of both temperature and vapour tension
taking place nearly simultaneously with the shift of
Noon 6 P.M. Midnt. 6 A.M. Noon 6 P.M. Midnt.
FIG. ii. October 20 and 21, 1874. Automatic records at Aberdeen.
wind above noticed, and at the time when the natural
rise of day temperature ought to be briskest, viz., about
10 or ii A.M.
The wind commenced at about SSW., and blew
pretty steadily from that quarter for twenty hours, its
velocity being at first slight, and increasing to that of a
stiff breeze at midnight. When the barometer was at
74 Weather Charts and Storm Warnings.
its lowest and beginning to rise, the direction of the
wind rapidly shifted to WNW., and in three hours its
velocity more than doubled itself, rising from 24 to 55
miles an hour. The velocity of a strong gale, however,
only lasted for four hours, from 9 A.M. to I P.M. The
absence of rain is very noticeable during the early period
of the gale ; the reason for this absence can be seen
from the circumstance of the great distance between
the wet and dry thermograms ; in fact, no rain of any
consequence fell excepting just at the period of the
lowest barometer, already noticed.
FIG. 12. February 2, 1873; 8 A.M. Storm passing south ofFalmouth.
It will be seen from figs. 51 and 52 (p. 157) that
this storm, which was a very severe one in other parts
Cyclones and Anticyclones.
of the country, passed just to the northward of
Taking now the second case, that of a cyclonic
system passing on the southern side of a station, we
have a very good instance of the course of the phe-
nomena in the records of Falmouth for February I
and 2, 1873. The hourly values, as before, are given in
Noon 6 P.M. Midnt. 6 A.M. Noon 6 r.M. Mid"t.
29.5 - s
FIG. 13. February I and 2, 1873. Automatic records at Falmouth.
Appendix D. (p. 223), and the instrumental records
are shown on fig. I 3, while the conditions of pressure
at 8 A.M. on the 2nd are shown on fig. 12.
Here, too, as in the previous case, we have a great
dip in the barometrical curve, which falls very regularly
for twenty-four hours until noon on the 2nd. It then
rises more rapidly than it had fallen before, and at
76 Weather Charts and Storm Warnings.
midnight on the 2nd attains to within a quarter of an
inch of its previous height.
Temperature shows very remarkable changes during
the night of the ist and 2nd, rising 10 between 10 P.M.
and 4 A.M. It then continues high until 2 P.M. on
the 2nd, when it falls 6 in a few minutes, a change
nearly as sudden as that at the same observatory on
February 12, 1869, already noticed (p. 65).
As before, we find the explanation of these changes
in the direction of the wind. Up to midnight on the
1st this was steady at ESE. It then veered slightly to
-SE., and even a couple of points further. The highest
temperature, already noticed, coincided with the direc-
tion S.byE. As the centre drew nearer, the vane
shifted smartly to E.byS., E.byN., and NE., and
the sudden fall of temperature marked a shift from
NE.byN., to N.byE. The change of direction went
on further, and the period closed with the wind about
The extreme force of the wind did not precisely
coincide with the period of the lowest barometer
reading, as it was far greater a little before midnight on
the 1st than at any other time. This affords a further
proof, if such is needed, that the violence of a gale does
not depend on the actual height of the barometer at
Vapour tension shows a steady curve, following that
of temperature, until the appearance of the Northerly
and North-westerly winds, when it sank in a marked
Cyclones and Anticyclones. 77
way, thus again corroborating our former statement as
to the dryness of winds from that quarter.
The rainfall was very remarkable ; it continued
almost without intermission from noon on the ist till
5 P.M. on the 2nd, being heaviest shortly before the
period of the strongest wind. The total amount which
was collected during the twenty-four hours, ending with
noon February 2, was no less than 1.275 inch, and it
will be noticed that the rain gradually lessened as the
wind shifted through N., and ceased entirely when the
direction was NNW.
This persistence of rain with the Easterly and North-
east winds in the front of a cyclonic depression is a
very striking characteristic of these disturbances. It is
an unmistakable proof that North-east winds are not
always dry, and the only reason that this fact is not
more frequently observed is, as will shortly be shown,
that the occurrence of these winds in the front of
cyclonic disturbances is a comparatively rare pheno-
menon in the British Isles, for the storms usually pass
by us on the northern side, and at first give us South-
easterly, not North-easterly winds.
These instances are amply sufficient to show the way
in which we are to interpret a couplet, well known to
sailors, which expresses Dove's Law of Gyration, referred
to at p. 30 :
When the wind shifts against the sun,
Trust it not, for back it will run.
Under certain conditions a shift of the wind against
78 Weather Charts and Storm Warnings.
watch hands is quite en regie, and is simply an indica-
tion that a cyclonic disturbance is passing on the
southern side of the observer. The actual motion of
the disturbance of February i and 2, 1873, was along
the north coast of Brittany, and therefore to the south
The rule as regards the shifting of the wind in
connection with atmospherical disturbances may be
If the observer supposes himself at the centre of a
cyclonic system in the Northern Hemisphere and facing
in the direction in which it is advancing, the wind at
all stations which he passes will shift with watch hands
if the station be on his right-hand side, and will shift
against watch hands if the station be on his left-hand
This is made clear by the following diagrams (fig. i 5,
a, b, c, d), in which I. II. III. indicate the successive
positions of a cyclonic system, and the large arrows
represent different directions of its motion. A is always
on the right-hand side of the centre, B on its left-hand
side. The successive directions of wind experienced at
each station are shown by the figures i, 2, 3, and i', 2',
3'. In every case it will be seen that the shift from I
to 3 is with watch hands, and from i' to 3' is against
watch hands, whatever the first direction of the wind
may have been.
The reason that a shift of wind against watch hands
is considered dangerous is, that when the wind shifts
Cyclones and Anticyclones.
So Weather Charts and Storm Warnings.
from NW. towards SW., S. and SE. at a station A in
fig. 14, it indicates that the SE. wind of the north-
eastern side of another area of low pressure is approach-
ing the station which has been experiencing the NW.
wind of the south-western side of the previous area of
low pressure, and which is passing away to the eastward,
so that the wind merely backs until the station is fairly
under the influence of the new disturbance, when it
begins to veer again, if the centre of the depression
passes to the northward of the station, as is usually the
case in these islands.
There is one point in connection with cyclonic dis-
turbances which is gradually attracting more and more
attention, and that is the appearance of secondary
eddies in connection with the larger areas of baro-
metrical depression. These smaller systems are usually
less perfectly developed than the larger ones, and they
manifest themselves in general on the southern sides of
the latter. Accordingly, while they cannot exhibit any
Easterly winds of much force (owing to the fact that
pressure is lower on their northern than on their south-
ern edge), they intensify the Westerly winds on the
extreme southern edge of the original disturbance by
increasing the gradients in that part of the system.
It is probably owing to these circumstances that
Easterly winds are so rare in our storms. Investiga-
tions into the distribution of pressure over the earth's
surface have shown that there is an almost constant
deficiency of pressure in the neighbourhood of Iceland,
Cyclones and Anticyclones.
and so probably most of the depressions which cause
our storms are simply secondary to a vastly more
extensive permanent area of depression over the North
FIG. 15. January 3, 1874 ; 8 A.M. Secondary depression.
It will be interesting to give a few instances of these
'satellite' depressions (as the French call them), to
82 Weather Charts and Storm Warnings.
illustrate what we have been saying, and fig. 15 (p. 81),
for January 3, 1874, shows us on a small scale the
conditions to which allusion has just been made as
characterising many of our gales. We see that there is
a small cyclonic disturbance with its centre near Holy-
head, and that the circulation round it is very imperfectly
developed, inasmuch as it exhibits no Easterly winds at
all. The reason of this deficiency is at once visible
when we look at the northern part of the chart. The
reading of 29.23 inches at Holyhead, which is at the
centre of the secondary depression, almost reappears
over Caithness, in the isobar of 29.2, and to the
northward of this we see that of 29.0 inches, so that
evidently readings would be still lower if we went
further north. As the reading both at Holyhead and
at Wick is about 29.2, and as the highest reading
between these points is 29.3 inches, it is impossible
that there can be a gradient of any magnitude for
Easterly winds over the intervening region, and so those
winds do not appear. On the other hand, the circulation
round the west, south, and east sides of the secondary
depression is clearly shown.
It is not often, however, that we find the secondary
depressions so clearly marked as in fig. 15. The chart
for October 7, 1874, gives us their more common
character (fig. 1 6). They manifest themselves simply
by a loop in some of the isobars, and their effect is, as
already described, to reduce the gradients on the side
turned towards their primary, and to increase them on
Cyclones and Anticyclones.
the opposite side. We could hardly have a better
example of this than that given in fig. 1 6. The strong
NW. wind at Stornovvay, and the SW. gales in the
Skagerrack and in Denmark, show that the conditions
for strong winds prevail generally, but over southern
Scotland and central England nothing but light
16. October 7, 1874 ; 8 A.M.
FlG. 17. October 22, 1874 ; 6 P.M.
Westerly airs are reported. On the other hand, in the
Channel and in France the isobars are crowded
together, and heavy gales are the result.
Another instance is represented on fig. 17, for
October 22, 1874, but here it is the North-westerly
winds of the primary system that are reduced in force,
on account of the fact of the secondary manifesting
84 Weather Charts and Storm Warnings.
itself on the south-west side of its principal. Owing to
the apparent equality of pressure over the Bay of
Biscay there are no gradients of consequence there,
io 5 5 I0
FIG. 18. January 24, 1872; 8 A.M. Co-existing depressions.
and therefore no gales in connection with the smaller
system, but, so far as direction is concerned, the circu-
Cyclones and Anticyclones. 8 5 .
lation round the smaller depression is very clearly
At times it is hard to say which of the depressions is
the primary and which the secondary, as there is appa-
rently not much difference in size between them. This
was the case on January 24, 1872 (fig. 18), when we
see one depression, with central readings as low as 28.3
inches, near Scarborough, while another shows itself off
Valencia. The result of the interference of these two
systems is to produce a comparative calm between them,
the winds being very light over St. George's Channel,
while strong gales are blowing wherever this inter-
ference does not exist.
In treating of the interpretation of weather charts
and of storm warnings, we shall show the use which
can sometimes be made of these secondary cyclonic
In this chapter we have considered the contrast
between cyclonic and anticyclonic systems, or areas, as
they are indiscriminately termed, and the character of
the weather which accompanies each respectively.
We have learnt that, while anticyclonic areas move
slowly, cyclonic areas travel more or less rapidly over
the country, and moreover that their passage past a
station presents marked features of difference in the
weather experienced, according as the station lies on
the right or left side of the path of the centre.
86 Weather Charts and Storm Warnings.
Lastly, we have found that cyclonic systems are not
always isolated, but occasionally have what may be
called secondary systems in connection with them,
which exert a material influence on the gradients, and
consequently on the winds belonging to the original
The Motion of Storms. 87
THE MOTION OF STORMS AND THE AGENCIES WHICH
APPEAR TO AFFECT IT.
BEFORE we treat of the motion of storms it must be
admitted, as will appear in the next chapter, that me-
teorologists are not at all agreed as to what the real
causes of that motion are. It has not been satis-
factorily determined to what extent the storm moves
forward as a whole, or to what extent the advance
observed is only due to the continued reproduction of
the same phenomena at successive points, as is the case
in wave motion.
The fact that storms advance over the earth's surface,
with a motion of translation in addition to their own
rotatory motion, has, however, long been known. The
earliest notice of it which we can discover is an entry
on a map of Virginia, published in 1/47 by Lewis
Evans, to the effect that ' all our great storms begin to
leeward.' Franklin, in 1760, followed in the same
strain, but it appears that his attention had been caught
at an earlier period, in 1743, by the fact of his being
prevented at Philadelphia, by the clouds brought by a
88 Weather Charts and Storm Warnings.
hurricane, from observing a lunar eclipse, while the
eclipse was seen at Boston, which lies further to the
north-eastward, before the storm came on. The reader
hardly needs to be reminded that hurricanes and
cyclonic disturbances in general are accompanied by an
abundance of cloud. Along the eastern coast of the
United States, therefore, the advance of storms from
south-west towards north-east has long been a recog-
The direction of the motion is different in different
parts of the earth. Of storm tracks which are well
made out, those of the West India hurricanes, in the
earlier part of their course, are, speaking in general
terms, from east-south-east to west-north-west : in the
Indian Ocean, the Mauritius hurricanes advance at
first from east-north-east to west-south-west, but both
of these classes of storms generally recurve subsequently
at a sharp angle, and advance towards the eastward.
The typhoons of the China seas also at first move
towards the coast from the eastward and subsequently
Over these islands, however, the motion of storms is
not nearly so constant in direction as in the instances
which have been cited, and, although as a general rule
it may be said that our storms travel from the west-
ward, there are many exceptions to this rule, and
in fact storms can, and do, move from every point of
the compass, but a motion from an easterly point is
The Motion of Storms. 89
It will be best to consider the usual directions of
motion in connection with the causes which appear to
govern them, and we shall also offer some remarks on
the motion of anticyclones, and show what a contrast
in this respect they present to the behaviour of cyclonic
As regards the rate of motion, it may be premised
that this varies very greatly, some storms travelling
very slowly or even remaining apparently steady, while
others are propagated with great rapidity. The rate
of motion of the West India hurricanes ranges from ten
to fifteen or twenty miles an hour in their early stages,
but becomes accelerated in the latter portion of their
path, while in these islands the motion has attained
the prodigious speed, of fifty miles an hour, February 1 2,
1869, an instance already cited, p. 65, and even
seventy miles an hour, December 16, 1869, a velocity
nearly equalled on the night of November 10 II, 1875,
as well as on March 12, 1876.
It must be clearly understood that the rate of trans-
lation of the storm has no direct relation to the velocity of
the ivind in that storm, for the West India hurricanes
exhibit almost the strongest winds of which we have
any knowledge, and they travel slowly, while the
rapidly moving storms just cited were not very excep-
tional as regards their violence. In Europe, however,
it has been found, as a general rule, that the most
violent storms do advance the most rapidly.
However, one of the greatest difficulties which meets
90 Weather Charts and Storm Warnings.
us, in the issue of Storm Warnings in these islands, is
our almost total ignorance of the rate at which any
given storm is travelling, until it has already moved
over a considerable tract of country.
It is easy to cite instances of the motion of storms,
and we shall select the two cases which have already
been employed as illustrations of cyclonic and anti-
cyclonic disturbances respectively, and trace their
progress across the area of our weather maps, paying
attention mainly to the
isobars and the wind.
Let us first take the storm
of November 29, 1874.
The earliest unmistakable
signs of its approach
(fig. 19) were at 8 A.M.,
November 28, when a rapid
fall of the barometer at
Valencia, with the Southerly
wind, and the course of
the isobar of 29.3 inches,
showed that there must be
an area of lower readings
at sea, outside the coast.
Over the greater part of
England the direction of the wind was South-easterly ;
a common phenomenon on the approach of a serious
storm, owing apparently to the in- draught of air towards
the region of diminished pressure.
FIG. 19. November 28, 1874 ;
5 A.M. Approaching depression.
The Motion of Storms.
The next chart, for 6 P.M. on the same day (fig. 20),
shows the central isobar (of 29.0 inches) over the south
of Ireland, while the SE. winds over England have
veered to SW., and the isobars, previously running
nearly north and south, show a marked curvature.
Even in Norway pressure has given way, the isobar
FKJ. 20. November 28, 1874;
6 P.M. Depression advancing.
FIG. 21. November 29, 1874
8 A.M. Centre over Wales.
of 29.8 inches having taken the place of that of
29.9 inches on the previous chart.
During the night the storm made rapid progress,
and at 8 A.M. (fig. 21) we have the conditions already
described at p. 39, the centre of the storm lying near
Holyhead, and the influence of the disturbance extend-
ing over the whole of Western Europe.
<)2 Weather Charts and Storm Warnings.
At 6 P.M. on the 2gth (fig. 22) we find the centre
of the storm near Newcastle, with a reading of 28.4
inches, while the general
course of the isobars is that
of an ellipse, with its longer
axis stretching east and
west. The Southerly winds
have nearly entirely dis-
appeared, and the gales are
from East in Scotland, and
from West over England,
without any amount of
Noith-west winds worth
It" we were to pursue
this disturbance further, we
FIG. 22. November 29, 1874; should discover that the
6P.M. Centre near Scarborough. Qyal gh of the isobars
Depression passing off.
was caused by the approach
of a second cyclonic area towards Ireland, which checked
the rise of the mercury and reduced the gradients in
the rear of the former system, and thus hindered the
development of the North-westerly winds a feature
to which allusion has already been made at p. 65. In
fact, the chart for the next morning exhibited two
separate areas of depression, one over Ireland, the other
over the North Sea, while the latter area showed evident
signs of being filled up.
It is not necessary to quote other instances to prove
The Motion of Storms.
the fact of the motion of cyclones, and we shall now
proceed, by way of contrast, to consider the motion, or
rather the comparative absence of motion, in anticyclones,
and shall take the period at the beginning of February
1874. It is not necessary to give more than the daily
FIG. 23. February 2, 1874 ; 8 A.M. FIG. 24. February 3, 1874 ; 8 A.M.
Anticyclone. Anticyclone stationary, but chang-
ing in shape.
charts for 8 A.M., as the changes from day to day are
Fig. 23, for February 2, shows an area of readings
above 30.4 inches over the Channel. In fig. 24 this
has hardly changed its place, but a sudden rise of the
barometer has taken place over the north of Scotland,
so that we have two independent centres of high pressure
94 Weather Charts and Storm Warnings.
over our limited area. In fig. 25, for the 4th, the
secondary anticyclone has vanished, and we have the
conditions already cited at p. 40 as a typical anticyclone,
and at the same time the effects of a cyclone outside
the Shetlands are just felt on the coast of Norway, where
the barometer has begun to give way, accompanied by
a stiff South-west gale at Christiansund.
FIG. 25. February^ 1874 ; 8 A M.
Original shape regained.
FIG. 26. February 5, 1874; 8 A.M.
The last chart of the series, fig. 26, shows us the
central isobar of 30.6 inches over the Eastern Counties,
while all over the North Sea strong Westerly winds
have appeared, owing to the advance over Norway of
the cyclonic disturbance just mentioned.
In this case, therefore, which is a fair sample of the
The Motion of Storms. 95
behaviour of areas of high pressure, it is evident that
the persistence of the conditions of high barometrical
pressure over the south of England was as marked as
the instability of the conditions of low barometrical
readings was proved to be in the preceding instance.
Anticyclones, however, do change their position, but
it is needless to pursue the subject further in this place.
Before treating of the agencies which appear to rule
the motion of cyclones, it may be well to say a word
or two on the influences which appear to modify
that motion, at least in the neighbourhood of these
islands. We find that the storm path is much affected
by the contour of the country. It is well known that
the west coasts of Ireland and Scotland are bold and
rugged. It has sometimes happened that a storm has
advanced from the Atlantic to the coast of Kerry, but
has returned, and, passing out to sea again, has moved
northwards along the coast until it found the opening
of Donegal Bay, and has then crossed Ireland along
the tract of low land stretching from Ballyshannon to
Dundalk, to the Irish Sea, where the centre often appears
to be arrested for a while : or else the disturbance,
clearing Ireland altogether, and crossing Scotland south
of the Grampians, has passed out to the North Sea.
In fact, we have already seen, from the phenomena of
the Hallsberg tornado, p. 29, that the stratum of air
affected by a storm is frequently very thin as compared
with the entire depth of the atmosphere. We can
therefore easily understand that eddies in the stratum
96 Weather Charts and Storm Warnings.
of air which is in immediate contact with the surface of
the ground may be very much affected in their character
and motion by the irregularities of that surface, which
have a tendency to turn them aside.
It need hardly be pointed out that the susceptibility
of storms to such a deflecting influence, exerted by the
contour of the country, bears some resemblance to the
behaviour of smoke-rings, which are deflected from their
course by obstacles placed in their path, although they
may not actually come in contact with the obstacles.
Remembering that the depth of storms is insignificant
compared with their lateral extent, we may to a certain
extent compare cyclonic disturbances to smoke-rings,
although the constitution of the two phenomena is
As regards the actual direction of motion of cyclones,
when we come to examine a series of charts extending
over a wide area, like those of Captain Hoffmeyer and
others, for Europe and the Atlantic, it is found that
the cyclones have a tendency to move round the anti-
cyclones, but it is almost impossible to follow out these
motions fully when we can deal only with the limited
area of our own charts. It is, however, from this
mutual action of the areas of high and low pressure on
each other that we gain some notion of the coasts
which are likely to be visited by a storm, of the direc-
tion which that storm will take, and of the quarter
whence the wind in that storm will blow hardest.
If we find the readings highest over Ireland, the
The Motion of Storms.
depressions will sweep down over Scandinavia or even
over the North Sea, in a direction from the northward
to the southward, giving us Northerly gales along the
east coast of Scotland and England, owing to the fact
that the steepest gradients will be on their western
sides. These areas of low pressure will follow each
FIG. 27. November 17, 1874; 8 A.M. Pressure highest in south-west.
Depression disappearing over Denmark.
other until by some means or other the excess of pres-
sure in the west has been reduced.
Figs. 2730 afford very good examples of the above
conditions. We start on November 17, 1874 (fig. 27),
with readings highest in the south-west, general North-
west winds, and a definite depression existing over
Denmark, marked by the isobar of 29.3 inches. At
98 Weather Charts and Storm Warnings.
the same time a backing wind at Stornoway and the
SSE. wind at Christiansund show that a fresh disturb-
ance is not far off. Fig. 2 8, for next morning, Novem-
ber 1 8, still exhibits the traces of the cyclonic disturb-
ance over Denmark, but the lowest readings there are
about 29.7 inches, showing a rise of half an inch in
FIG. 28. November 18, 1874 ;
8 A.M. New cyclonic disturbance
appearing in north.
FIG. 29. November 19, 1874 ;
8 A.M. Depression over Heligo-
land. A third appearing in the
pressure. All over the chart, except just in the south-
west, the course of the isobars is changed, and the
advancing depression is perfectly visible, and has pro-
duced its effects on the winds, causing them all to
' back ' to W. or SW., and even to SE. in Shetland.
The Motion of Storms.
The morning of the iQth (fig. 29) shows us a great
change j the area of low pressure, which lay off Shet-
land on the previous day, has advanced rapidly south-
wards, and lies over the mouth of the Elbe, while
another similar system has appeared over Shetland.
Each of these independent disturbances has its own
The last chart of the series is fig. 30, for the 2Oth.
In it we see the last-named
depression situated in
nearly the exact locality
of its predecessor, over
northern Germany, while
the disturbance of the winds
at the northern stations
shows that the perturbations
are not yet at an end. The
rise, however, of the baro-
meter over Holland indi-
cates that the general
distribution of pressure is
undergoing a change.
In this case, therefore, FIG. 30. November 20, 1874;
We have a Succession of 8 A ' M - Depression disappearing
cyclonic disturbances chas-
ing each other for several days, along similar paths,
while the region of highest pressure lies in the west.
If the highest readings be over France, the path of
the cyclonic disturbances will run from west to east,
ioo Weather Charts and Storm Warnings.
across the British Isles, and the wind will blow hardest
from the Westward. When the centre of the anti-
cyclone lies over England we find that the storms
hardly affect our stations at all, but pass outside the
north coast of Scotland, producing strong Westerly gales
on the Norwegian coast, above the sixtieth parallel, at
Christiansund, Bodo, and
northwards. It is needless
to cite instances of these
conditions ; they are already
admirably illustrated by
figs. 25 and 26 (p. 94).
When the area of high
pressure is located more to
the east or south-east, over
Denmark or Germany, the
cyclonic systems cannot
make good their footing
over these islands at all, but
pass from south to north
FIG. 31. January 14, 1875 ; 8 A.M. outside the Irish and Scotch
Pressure highest in south-east, coasts, producing gales from
Depression off Hebrides.
the Southward on our
shores. Such storms frequently only appear in the
west of Ireland, and are thence propagated to the
Hebrides, Orkneys, and Shetlands, without extending
to the English coasts.
A very good instance of this type of weather
occurred in the beginning of the year 1875. Fig. 31,
The Motion of Storms.
for January 14, shows us the barometer highest over
Switzerland, and the isobars running NE. and SW.
across these islands, while a depression is just visible
off the NW. coast of Scotland. Fig. 32, for the I5th,
shows but little change of pressure over Central Europe,
but a fresh disturbance has appeared off the west coast
FIG. 32. January 15, 1875 ; 8 A.M.
New disturbance off west coast of
FIG. 33. January 16, 1875 ; 8 A.M.
Pressure highest in south.
Depression off NW. coast of
Scotland, moving eastward.
of Ireland, causing the winds to back to S. and SE.,
and blow with the force of a gale. Fig. 33, for the
1 6th, shows us this second disturbance in the position
of its predecessor of the I4th, but, pressure having
given way over Norway, the conditions are altered, and
IO2 Weather Charts and Storm Warnings.
the region of the highest barometrical readings is
transferred to Spain.
We have hitherto spoken of the cases when pressure is
highest in the west, south, and east respectively, but the
anticyclone must sometimes lie to the northward of us,
and then, if ever, should the disturbances advance from
the eastward. Such a movement is, however, exces-
sively rare in these latitudes, though this is not the case
with the tropical hurricanes or cyclones, all of which
at first move from the eastward. There are, however,
some principles which have not yet been thoroughly
explained, and which are antagonistic to the develop-
ment of such a motion in the storms of our part of the
Temperate Zone. A few words will be said, hereafter,
as to the causes which have been adduced to account
for the motion of storms, but it will suffice, at this
juncture, to remark that the motion of cyclones round
anticyclones will not by any means account for all the
motions which have been noticed in our storms.
The typical cyclone of November 29, 1874, figs.
1922 (pp. 90-92), to which reference has frequently
been made, did not skirt round the region of high
pressure on our charts, but travelled directly towards it.
In this case it is possible that a study of the weather
Over more extensive charts such as those of the
North Atlantic, now being published by our Office
might throw more light on this question of motion.
While discussing the motion of storms, it may be in-
teresting to trace the path of a very erratic disturbance
The Motion of Storms. 103
which visited these islands in April 1872, and the
course of which has been followed out with the aid of
the continuous records at our self-recording observa-
tories. The following seven charts (figs. 34-40,
pp. 104 and 105) show the successive positions of the
central disturbance, and fig. 41 gives its track for the
entire period. It came in over Ireland and retreated
along its own path again. That it did not advance
as far as the Straits of Dover is clearly shown by the
records at Kew, and that it passed first on one side
and then on the other of Falmouth is indicated by
the records at that observatory, which prove by the
direction of the shifts of wind, on the same principles
as are explained in Chapter V., that the path of the
centre lay first on the southern and then on the
northern side of the station.
This storm presents us also with the rare pheno-
menon of an advance from the eastward. As far as we
can at present form an opinion, this latter condition de-
pends on circumstances of pressure far outside the area
of these islands, or even of that embraced by our
weather charts. It is needless to say that such a storm
as that just described afforded a striking instance of
failure of warnings, as will be explained in Chapter
IX. (p. 137).
The storms of which we have been treating have all
exhibited motion more or less rapid, and in various
directions, but it sometimes happens that areas of low
pressure are stationary for two or three days together
FIG. 34. April 20, 1872; 8 A.M. FIG. 35. April 20, 1872; 6 P.M.
Centre of disturbance near Water- Centre of disturbance off south
ford. coast of Ireland.
FIG. 36. April 21, 1872; 8 A.M. FIG. 37. April 21, 1872; 6 P.M.
Centre of disturbance near Havre. Centre of disturbance near Ports-
FIG. 38. April 22, 1872; 8 A.M. FIG. 39. April 23, 1872; 8 A.M.
Centre of disturbance near Pen- Centre of disturbance off south
zance. coast of Ireland.
FIG. 40. April 24, 1872 ; 8 A.M. FIG. 41. April 20-24, 1872.
Disturbance passing off over Ireland. Path of disturbance.
io6 Weather Charts anct Storm Warnings.
nearly to the same extent as the anticyclone already
noticed (figs. 23-26, pp. 93 and 94). It is a remark-
able fact as regards these islands that there are certain
localities which apparently exert an attraction on these
systems, and so retard their motion for a time. This is-
most strikingly the case with the region situated at the
FIG. 42. November 30, 1872 ; FIG. 43. November 30, 1872 ;
8 A.M.. Depression appearing off 6 P.M. Centre of depression near
entrance of the Channel, where at times, especially in
the early autumn, cyclonic disturbances appear to remain
for days together almost immovable.
A very good instance of a stationary depression
occurred at the end of November 1872. Fig. 42, for
November 30, at 8 A.M., shows us the isobar of
The Motion of Storms.
28.5 inches over the south-west of Ireland. There is
nothing else very remarkable, except that readings are
generally very low, and that a secondary depression
appears off the coast of Lincolnshire. Fig. 43, for 6 P.M.
on the same day, exhibits the centre of a storm over
Cork, but conditions otherwise do not show much
FIG. 44. December I, 1872 ; 8 A.M. Centre of depression
nearly in same place, but depression filling up.
change, except that pressure has given way considerably
over France. 1
Fig. 44, however, for 8 A.M. December i, shows us
the centre of the cyclonic area in nearly identically the
same spot as it had occupied fourteen hours previously
1 In 1872 we did not receive 6 P.M. reports from Norway, so that
portion of the chart is blank.
io8 Weather Charts and Storm Warnings.
but the whole system is being filled up, for the lowest
reading, indicated by an isobar, is 28.7 inches, while
28.3 inches was the minimum in fig. 43.
This disturbance subsequently took a course to the
SSE., and passed on to the west of France.
In this chapter, therefore, it has been shown that
atmospherical disturbances advance over the earth's
surface, and that cyclonic systems move more rapidly
than anticyclonic. It has also been remarked that we
know, very little about the rate at which a storm is
moving until it has advanced well within the area of
our telegraphic reporting system. We are also virtually
ignorant of what the real cause of this motion of
storms is whether it is due to the change of position
of the entire mass of disturbed air, or to the continuous
production of a depression in front of the storm while it
is filling up in the rear. We have traced some cases of
motion of cyclones, and have stated that this is modified
by the contour of the country over which they have
to pass, but that it appears to be regulated in great
measure by the position of the anticyclonic areas in the
The Use of Weather Charts. 109
THE USE OF WEATHER CHARTS.
IF we come to consider what is the practical use, to an
ordinary observer, of weather charts, giving, as they do,
a representation of past conditions of weather, it will
be necessary to recapitulate briefly the results to which
we have been led in the several preceding chapters,
and then to enumerate some of the general principles
on which a judgment is formed as to coming weather,
when the observer knows by the study of a chart what
conditions have been prevailing elsewhere. Subse-
quently some of the theories will be mentioned which
have been propounded to account for the origin and
motion of storms, and, lastly, we shall allude to the
ideas which are entertained by some meteorologists as
to a periodicity of rain and of storms, and as to a
connection between disturbances in the gaseous enve-
lope of the sun, and those which take place in our
It will be useful in the first place to summarise
briefly the principles which we hope have been estab-
lished in the preceding chapters.
1 1 o Weather Charts and Storm Warnings.
Chapter I. has been devoted to an account of the
materials, in the way of observations, with which we
have to construct our edifice.
In Chapter II. the wind has been discussed, as the
atmospherical phenomenon which is most directly
related to weather. It has been shown that wind is
always connected with some disturbances of the pres-
sure of the atmosphere ; its existence being due to the
tendency of an elastic body, like the air, to regain the
condition of equilibrium from whence it has, by any
means, been disturbed, while its motion is regulated by
certain fixed laws.
The subject of Chapter III. is the barometer, as
being the instrument by means of which the amount of
atmospherical pressure, and therefore of its disturbances
from time to time, is measured. It is shown how the
distribution of pressure on a weather map is indicated
by the isobars, and how there are two grand types of
disturbance of atmospheric equilibrium, named respec-
tively cyclonic and anticyclonic, according as the
pressure is locally either in defect or in excess of its
average value over the area represented in the special
chart in question. These two types of disturbance are
characterised by different features, among which the
most striking is the contrast in the direction of motion
of the wind.
In Chapter IV. gradients have been explained, and
it has been shown that the distribution of pressure, as
measured by the gradients, is the best guide we have
The Use of Weather Charts. 1 1 1
towards a knowledge of the laws of wind motion, and
therefore, in some degree, towards a knowledge of
coming weather. It has, however, been stated that
there are apparently agencies other than the distri-
bution of pressure which influence the force of the
wind, but that their precise nature has not yet been
ascertained. It has also been pointed out that the
phrases 'gradients for such and such winds,' &c., are
nothing more than the expression of the laws of wind
motion in a practical form.
Chapter V. contains a closer examination into the
principal features of cyclonic and anticyclonic systems
respectively, and into the character of the weather
which accompanies each. It states that, while anti-
cyclonic areas are usually stationary or move slowly,
cyclonic areas travel more or less rapidly over the
country, and shows that their passage past a station
presents marked features of difference according as
that station lies on the right-hand or left-hand side
of the path of the centre. This has been illustrated
by the continuous automatic records of some of
the self-recording observatories in connection with
the Meteorological Office, and it has been shown
how the usual changes of wind are explained by this
It has also been explained that cyclonic systems
are not always isolated, but have occasionally what
may be called secondary systems in connection with
them, which exert a material influence on the gradients,
Weather Charts and Storm Warnings.
and consequently on the winds belonging to the
Finally, Chapter VI. has been devoted to the motion
of atmospherical disturbances, and there it has been
explained, at more length than in the preceding
chapter, that cyclonic systems move more rapidly than
anticyclonic. Some cases of the motion of storms
have been traced, and it has been shown that, while we
know very little of the rate of motion of a storm before
it arrives, we can frequently form a conception of the
probable direction of motion of the storm. This
motion is affected by the contour of the country over
which it passes, and it appears in great measure to be
regulated by the position of the anticyclonic areas in
The least consideration of the principles just enu-
merated will abundantly show that the weather pre-
vailing over any district on a given day is clearly
affected by, if it may not be described as the result of,
the conditions prevailing in the districts round about,
so that, by observing what those conditions have been
for some time back, we are enabled to form some
opinion as to the weather which we are experiencing,
and which is related to those conditions, whether it is
likely to be permanent or transient in its character,
and, if transient, in what way it is likely to change.
It is hardly necessary to say that the fresher the
information is the better, but, owing to the cost, it is
The Use of Weather Charts. 1 1 3
not possible in this country to follo\v the example of
the United States, and send out by telegraph, in all
directions, the entire mass of figures in the Daily
Weather Reports, in order that it may be published
simultaneously in every large town. Practically, in
these islands the readers of newspapers and the sub-
scribers to the Daily Weather Report cannot see their
charts until several hours, frequently even an entire
day, after date.
Such information, however, can generally be turned
to very good service, if rightly used, and we shall take
the case of an observer resident not far from London,
and see what he can do with it.
It has already been explained that most of our dis-
turbances travel from the westward, and, as they take
a certain time to advance over the distance which
separates the east of England from the west of Ireland,
we can learn, by studying the chart for the previous
day, what conditions were then existing at the western
stations, and consequently can gain some idea of what
is likely to be the result of the changes which we
notice by our own local observations, instrumental and
If, for instance, the barometer at our station is high
and steady, with dry weather and light winds, either in
winter or summer, we may form a general notion that
the type of weather is anticyclonic, and, as this type is
peculiarly permanent, we may feel sure that any change
will give us at least several hours' notice of its coming,
1 1 4 Weather Charts and Storm Warnings.
by alterations in instrumental readings, occurring over
some part of the district covered by the Reports. The
study of the charts in this case is the more important,
because frequently, at such a time, ' cirrus ' or ' mare's
tail ' clouds appear in the sky, which are usually the
precursors of coming wind ; and change of wind in such
a case means change of weather. The charts then will
show whether or not this change of weather had made
its way down to the earth's surface at any place on the
previous day within the district just referred to.
In the case of cyclonic conditions, we have already
learnt that it will not do to trust implicitly to the fact
of storms advancing from the westward, but, on the
other hand, some ideas have been advanced by means
of which we can, at least in some cases, forecast the
probable direction of motion of a storm. At any rate
we are usually able to learn, from a careful study of the
chart, whether we have to deal with disturbances on a
large or a small scale, and, accordingly, whether the
changes in progress indicate lasting, or merely temporary
conditions of weather.
These charts are therefore useful helps to the local
observer, and will be found so by those who study them
regularly, and combine with that study careful and sys-
tematic observations of their own instruments, and of local
weather ; but for the purpose of judging whether a
particular afternoon will be wet or fine, which is all
that the public generally care to know about weather,
it is obvious that charts which are necessarily twenty-
The Use of Weather Charts. 1 1 5
four hours old in many places cannot be of much
service. Moreover, the phenomena which we include
under the general term ( weather ' often depend in great
measure on the nature and conformation of the ground
in the neighbourhood of the observer, so that one place
will be much more liable to rain during disturbed
weather than another, while a second may exhibit a
greater tendency to the formation of fog at a calm
period than an adjacent district. As, therefore, such
exceptional tendency is confined to each special locality,
and does not belong to the phenomena produced at all
stations by the system of circulation prevailing at the
time, it is necessary that the observer who endeavours
to forecast probable weather should seek to ascertain
under what conditions such peculiarities manifest them-
selves, as it would be useless to apply merely general
rules in order to interpret the meaning of phenomena
of a purely local character.
On the whole, it must be said that our insular and
exposed position precludes us, in the present state of
our knowledge, from the possibility of issuing forecasts
of future weather with such confidence as some of our
neighbours on the Continent of Europe, not to speak of
the staff of the Chief Signal Office in Washington,
which has attained a marked proficiency in weather pre-
diction. We shall, however, in Chapter X. state what
is being done in this direction.
Let us now examine in what manner the knowledge
we have gained would enable us to issue storm warnings
1 1 6 Weather Charts and Storju Warnings.
to the coasts. In the first place, we can in many
instances learn from the general conditions of wind, &c.,
in fact, of weather as a whole, what will be the character
of the changes likely to occur, and in what direction they
will propagate themselves.
We then notice the conditions of pressure as shown
by the barometer, what its changes are, and whether
any changes which may manifest themselves at any
spot are traceable at adjacent stations, and in what
degree, so that we can gain some idea of the extent of
the disturbances which are approaching.
We next see in what degree the barometrical changes
are borne out by the wind, both in direction and force ;
in fact, we often get earlier intimation of approaching
change of weather from abnormal features in the direc-
tion of the wind, than from the barometer readings
taken by themselves.
Temperature, too, must be looked to, for as a general
rule, in winter, if the temperature has been very low,
even though the wind has been Southerly, we need not
fear a Southerly gale until the advancing depression has
exerted a marked influence in raising the temperature.
We have then the reports as to weather at the different
stations, and the deficiency of information of this nature
has been amply explained in Chapter I. To this class
of observations belong reports of the character and
motion of clouds, and of the clearness or mistiness of the
air. Each of these latter may be, in its way, a
prognostic of storm ; the former, an unnatural clearness,
The Use of Weather Charts. 1 1 7
being a very bad indication before the storm has
actually reached us and affected our winds, while the
latter, mistiness, is often the immediate forerunner of
coming rain, and sets in when the wind in an advancing
cyclonic system has begun to blow from the South or
South-east, or more especially on th^ ridge of high
pressure or debateable ground, which lies between the
NW. wind of a retreating, and the SE. wind of an
advancing, area of low pressure.
Reports of the Aurora are also very useful as cor-
roborative evidence. The winter of 1875-6 was
remarkably free from Westerly winds, i.e., from cyclonic
disturbances passing to the northward of these islands,
and was also remarkable for the rarity of reports of the
It is, however, obvious that we, in the Meteorological
Office, labour under prodigious disadvantages in at-
tempting to issue warnings for the United Kingdom,
Interest therefore attaches itself to the attempts which
we are making from time to time to draw con-
clusions from the experience of past weather which
may be useful to us in forming opinions on what is
Attention has already been drawn to cyclonic dis-
turbances which follow each other along the same track
as long as the general distribution of pressure remains
unchanged, and it has also been stated at p. 15 that
cyclonic disturbances travel across the Atlantic for long
distances, if not from shore to shore. This is abun-
1 1 8 Weather Charts and Storm Warnings.
dantly proved by the fact that steamers, when outward-
bound to America, often meet a succession of such
cyclonic systems on their way towards Europe, and,
when homeward-bound to England, often run for a cer-
tain time with such systems, so that in the former case
the changes in the instrumental indications, as well as
in winds and weather, are much more rapid than in the
latter, on the simple principle that if walking in a
crowded thoroughfare you meet many more vehicles
than you pass or than overtake you. We shall return
to this subject of the advance of storms from America
at p. 183.
If, then, these disturbances are frequently travelling
in succession over the Atlantic, it is evident that we in
these islands must at times encounter a series which
bears a close resemblance to a series which has pre-
ceded it, as to the general character of the areas of
depression themselves, and as to the intervals which
occur between them. This we have noticed in our
own weather on various occasions, and the parallelism
has been found to hold good for as many as eight
As to the theories which have been of late years
propounded to account for the origin and motion of
storms, no attempt will be made to discuss them, but
the broad features of some of them will be indicated
in a very cursory way.
Professor Mohn, the Rev. W. Clement Ley, and
others attribute the generation and motion of storms
The Use of Weather Charts. 1 1 9
to the condensation of moisture in the form of clouds,
resulting in rain. This condensation takes place prin-
cipally in front of the storm, and, so to speak, draws
Mr. Thomas Belt and Professor Reye account for
the origin of the storm by the existence of a condition
of unstable equilibrium in the atmosphere ; a cold
stratum being situated at some height above the ground,
if the air at the earth's surface becomes heated, it must
eventually force its way through the superincumbent
colder layer, and the upward current thus generated
will be the core of the resulting cyclone. Professor
Reye goes so far as to say that the storms of the
largest dimensions experienced in these latitudes are
substantially analogous to the smallest waterspouts or
dust-whirls we can observe.
In direct contradiction to this view, M. Faye has
long propounded the view that cyclones are vortices
descending from the upper regions of the atmosphere
to the earth's surface, and that their motion is that of
the upper current.
Lastly, Mr. Meldrum and others consider that
cyclones are generated in the space intervening
between two currents, which themselves are tangents
to the nascent cyclone. Thus, in the North Temperate
zone, the conditions which would give rise to the
cyclones are those of Easterly winds on the northern
side of Westerly winds. The reader need hardly be
reminded that every perfectly developed cyclonic
120 Weather Charts and Storm Warnings.
disturbance here must have East winds in the north
and West winds in the south.
It is clear that when 'doctors differ' to the extent
indicated in the above sketches of the different theories,
the world in general must be content to wait patiently
for a complete theory of weather to be developed.
Before we leave the subject altogether, it will per-
haps be interesting to see the extent to which we are
able to forecast the weather for longer periods than a
day or two. Attempts have not unfrequently been
made to predict the seasons for a long period in ad-
vance, but without much success hitherto. One great
cause for failure is that accurate meteorological records
do not extend beyond the beginning of the present
century at more than a few stations, and at these we
are unable altogether to eliminate the local influences.
Thus, it is hardly possible to say what has been the
approximate temperature of these islands for more
than forty years a period far too short for the
definite recognition of a cycle. The shortest of such
cosmical cycles which has been determined is the sun-
spot period of I i T y years, according to Wolf, and there
are indications of far longer periods, such as 33 years,
or even 69^ years, according to Hornstein.
Of late years Mr. Meldrum, of the Mauritius, has
shown that the cyclones, for which that district of the
Indian Ocean enjoys an unenviable notoriety, have
been more frequent in some years than in others, and
that these epochs of maximum frequency occur at
The Use of Weather Charts. 1 2 1
intervals of about eleven years, coinciding with those of
maximum sun-spot frequency.
This agreement is very important, and it appears to
be corroborated by an examination of the rainfall at
several stations which has been conducted by Mr.
Meldrum and others. The results, for the compara-
tively short period to which they refer, are striking,
and are sufficient to show that a periodicity is traceable
in the weather of the Southern Indian Ocean, which is
suggestive of a relationship between the changes which
take place on the sun's surface and the phenomena of
our own atmosphere.
It will at once be asked, Why has not this periodicity,
if it exists, been detected long ago by an examination
of European records, which are far more complete than
any existing for the Indian Ocean ? The answer to
this is twofold.
In the first place, we are pre-eminently in the region
of the variable winds, and our storms are not nearly so
regular in their type as those of the Mauritius, where
almost the sole type of storm is the true tropical
cyclone with its concomitant rainfall. It is next to
impossible in this country to keep a record of all the
storms which pass over us. We have already seen
that the existence of conjugate storms is not unfrequent,
two or even three systems of disturbance being trace-
able at one time within the limited area of the United
Kingdom. Are these one single storm or several ? and
how should they be counted in a catalogue ? Rain
1 2 2 Weather Charts and Storm Warnings.
also cannot be taken as a sign of the frequency of wind
storms in a year; for although we know that warm
winters are invariably wet and stormy, and, moreover,
that cyclonic disturbances are accompanied by rain
at all seasons, yet it cannot be asserted that the almost
constant rain of 1872, and the recurrence of floods
in 1875, were in any way related to storms of wind,
though their connection with the presence of areas
of depression over these islands is indisputable.
There is, however, in the second place, a far deeper
reason for the non-discovery of these cycles in any
chance series of rainfall records. The sun passes
through phases of greater and less activity, and the
terrestrial phenomena corresponding to the epochs of
the former character are excessive evaporation in some
parts of the globe, and consequent excessive precipita-
tion in others. We must therefore ascertain in what
districts we are to look for the one and in what for the
other of these phenomena respectively.
It may be said at present that the precise mode
in which the sun exercises his action on our atmo-
sphere has not yet been explained, and, as far as the
climate of western Europe is concerned, the warmest
adherents of sun-spot influence must admit that obser-
vations of the sun's surface cannot as yet be depended
on as a sound basis for prophecy of coming weather.
That this assertion cannot well be disputed appears
from the figures which follow.
The Use of Weather Charts.
1884-5 4 2 -2
The first column gives the mean temperature of the
entire United Kingdom for the six months October-
March, for the last eleven years, and the second gives
the number of sun-spots observed at Kew during the
No approach to concordance is traceable between
the two columns of figures.
If we go further afield and compare the general
temperature of the globe, at least the closest approxi-
mation to it which is attainable, with the sun-spot curve
for the thirty-five years ending with 1875, as has been
done by Dr. Koppen l fig. 45, p. 124), we see that,
though for some part of the time some of the tempera-
ture curves appear to agree v/ith the curve of sun-spots,
the accordance in one hemisphere is associated with a
striking discordance in the other.
1 Zeitschrift dcr ostcrrcichischen metcorologischcn Ccsdlschaft^ Bd. xvi.
124 Weather Charts and Storm Warnings.
The figures which I have cited therefore support the
statement that the precise nature of the relation be-
tween what we may call solar and terrestrial weather
has not as yet been demonstrated.
As regards the whole question of prediction of the
I 6 5
FIG. 45. Diagram showing for the period of thirty-five years, 1841-75
inclusive, the number of sun-spots and the average temperature of the
Torrid and two Temperate Zones.
seasons, either by sun-spots or by any other means,
the same author, Dr. Koppen, has published several
papers ' On Protracted Periods of Weather,' devoting
The Use of Weather Charts. 1 2 5
his attention especially to severe winters, and he gives
the following summary of his results 1 :
'The main feature of the entire investigation has
been to prove that, for certain intervals, strongly
marked periodical influences make their appearance and
then vanish entirely, at times being replaced by others
of a totally different character. No law has as yet
been discovered for these changes, and so the outcome
of the inquiry is on the whole negative, and indicates
that all forecasting of the seasons is the merest
We may therefore conclude that at the present date
there is no immediate prospect of any one being able
to state what the character of a future season will be,
much less to tell a farmer in spring what crops he
should put in with a prospect of a favourable period
for the harvest.
1 Zeitschrift dcr osterreichischcn meteorologischen Gesellschaft, Bd. xvi.
126 WcatJier CJiarts and Storm Warnings.
THE DISTRIBUTION AND PERIODICITY OF GALES.
BEFORE we treat of storm warnings and the general
prediction of weather, it may be interesting to state
what has been ascertained as to the frequency of gales
on different parts of our coasts, and also as to their
periodicity, that is, the tendency which they exhibit to
recur at distinct seasons.
As regards their local distribution, a table has
recently been prepared in the Meteorological Office
showing for each month, and for each quadrant of the
compass, the total number of gales, and also of severe
gales, for the different parts of the coast. The statis-
tics refer to the fifteen years 1870-85. The coasts are
divided into ten districts, as shown in the subjoined
It is not necessary to give the details of the table in
such a book as this, and accordingly the monthly
percentages of the annual totals, and the totals them-
selves, are all that will be reproduced, without dis-
criminating between the different directions of the
Distribution and Periodicity of Gales. 127
I 9 8
The Irish Sea
The table bears internal evidence that the number
of gales bears a certain proportion to the number of
stations in each district from which reports have been
obtained. The figures have been compiled from the
Returns of the results of Storm Warnings which are
prepared every year. From these Returns the north-
west of Ireland has been excluded, inasmuch as no
storm warnings have ever been sent to any point, except
Galvvay, situated between the Shannon and Malin
Head. Accordingly, the number of reports of storms
which were collected from that region before the
establishment of Belmullet and Malin Head as report-
ing stations was not great. This is the main reason
why in the column of totals the north of Ireland
comes only seventh in point of frequency, instead of
taking a position between Ireland SW. and Scotland
NW., corresponding to its geographical situation.
It will be seen that the entrance of the English
Channel heads the list of frequency. This is mainly
JAN IUR PAY
JUY SEPT. NOV. JAN
En 3 l
( 128 )
owing to the extreme stormi-
ness of Scilly.
The eastern part of the
Channel and the east coast of
England are the least storm-
swept parts of our shores. This
is naturally to be expected, as
the force of the storms is broken
by their passage over the land.
If we now exhibit graphically
the monthly march of storm fre-
quency in the ten districts (fig.
46), we find that in every case
the summer is all but absolutely
free from storms. In almost
every district, also, November is
stormier than December.
The most remarkable portion
of the diagram is that represent-
ing the spring time. It will be
seen that in most of the districts
there is a distinct maximum of
storminess in March, which is
especially prominent in the
north-east of England, while it
is entirely absent in the south-
west of Ireland, and very nearly
so in the Irish Sea and the
south-west of England.
Distribution and Periodicity of Gales. 1 29
All these results require further study to explain
them fully, but as far as they go they are very interest-
ing and of much practical importance.
In the matter of periodicity of storms there is a
belief, which is very widespread, that equinoctial gales
are a phenomenon recurring with almost perfect
regularity. The remark is often made that it would
be well for those proposing to take a voyage to
wait until the equinoctial gales were over. In order
to test the foundation of this general belief, I made
a catalogue of all the serious storms which have been
reported in the British Isles since Easter 1870, and
communicated the results to the Royal Meteorological
Society in i884. 1 I have recently extended the list
up to Easter 1887, so that the figures refer to a period
of seventeen complete years.
The mode of inquiry has been to take fifteen-day
periods (that is, to take seven days on each side of the
equinox), and to divide the year into equal intervals of
this length. Of course, we have twenty-four such
spaces, with a remainder of five days, which have been
omitted at the beginning of July, that being the
calmest part of the year.
The dates of the several storms are given in Table I.
(p. 132), and curves are also given (fig. 47, p. 130)
showing the march of frequency in the fifteen-day
period, both for the crude and the smoothed figures.
1 Quarterly Journal of the Royal Meteorological Society, vol. x. p. 236,
1 30 Weather Charts and Storm Warnings.
These show that the storms are all but exclusively
confined to the winter half-year.
A glance at Table I. (p. 132) will show how for a
certain interval the stream of storm depressions sets
over us and then for a time takes another path, leaving
us at rest. In some years we have as many as four or
five storms in a fifteen-day period, and in others we
FIG. 47. Frequency of Storms in fifteen-day periods, according to
Scott and Prince.
In this diagram (representing Table III., p. 135) the vertical rules correspond approxi-
mately to the middle days of the respective months.
The faint full line corresponds to the original figures }
The dark ,, ,, smoothed J
The faint dotted . ,, ,, original ,,
The dark ,,
have none or only one. This happens even in the
latter half of January, the stormiest period of all.
The diagram shows that there is no strongly marked
maximum of frequency at either equinox, but there are
indications of periodicity which are very interesting. .
Distribiition and Periodicity of Gales. 1 3 1
Leaving the summer alone, as not worth notice, the
frequency remains practically constant from the middle
of August until the autumn equinox is past. The curve
then rises rapidly, the value doubling itself and trebling
itself in the two succeeding intervals. We then find
a falling off at the time of the Martinmas summer in
the first half of November, the latter half of November
is stormy again, but the beginning of December is
quieter. The absolute maximum of frequency is in the
latter half of January, from which period the curve
descends gradually, with one decided check early in
February, to the same value which it had in August,
and which it attains at the end of April.
The frequency at the spring equinox is nearly double
what it is at the corresponding interval in autumn, being
twenty-two instead of twelve (col. i. Tab. III.). In one
point, however, the phenomena agree : the equinoxes are
periods of change in storm frequency. In the autumn
this rises from twelve to twenty-nine as soon as the
equinox is passed ; in the spring it falls from twenty-
nine to twenty-two as the equinox approaches.
Accordingly, persons who wait till the autumn
equinox is over materially increase their chance of
falling in with a storm, but in the spring it would
apparently be wise to wait till April was well advanced
if you wished to have calm weather at sea.
If we look to see what evidence of the recurrence of
storms for particular short periods is discoverable in
our data, we find that the days most frequently so
1 3 2 Weather Charts and Storm Warnings.
!!--; ;^ s ;? 5
' - ' I - " c_"3
? 8 M
; ; : i :
: = ! : i 5
a -c B
g 4- H
Distribution and Periodicity of Gales. 1 3 3
distinguished in Table II. are Jan. I and 19, on both of
which storms occurred six times in the seventeen years.
TABLE II. DIURNAL FREQUENCY.
Seven days Jan. 18 and 26, Feb. 26, March 9,
Nov. 10 and 20, and Dec. 20 show five each, and
twenty-five days show four.
134 Weather Charts and Storm Warnings.
The stormiest period of all is the six days succeeding
Jan. 22, the figures for which are 3, 4, 4, 5, 3, 4.
The date of the Battle of Trafalgar, Oct. 21, is
marked by two fours, but no other storm of historic
fame is specially noticeable.
It is of interest to find that the results above given
for storm periodicity have recently been confirmed in
a very satisfactory manner by the figures for storm
periodicity in Sussex published by Mr. C. L. Prince
in a recent number of the Quarterly Journal of the
Royal Meteorological Society (vol. xiii. p, 79). Mr,
Prince has carried on meteorological observations for
nearly half a century, first at Uckfield, and latterly at
his observatory on Crowborough Beacon, and the paper
to which reference has been made gives the dates of all
storms recorded by him during the forty years 1846 to
As Mr. Prince's data refer to one district only, while
mine refer to the entire United Kingdom, the total
number of gales recorded by him in forty years is only
371, while the larger area for seventeen years yields 459^
The distribution of gales in the two investigations
agrees very closely, as will be seen by comparing the
figures in cols. ii. and iv. of Table III. (p. 135) with
those in cols. i. and iii.
There is one remarkable exception that Mr. Prince
finds a greater frequency of storms in May than my
His results are shown graphically in fig. 47 (p. 130)
by the dotted lines.
Distribution and Periodicity of Gales. 1 3 5
Mr. Prince concludes his paper with the very
confident statement : ' We may now assert that gales
at the period of the equinoxes are more the exception
than the rule.'
TABLE III. FIFTEEN-DAY PERIODS.
April 12 to April 27
April 28 , May 12
May 13 , May 27
May 28 , June n
June 12 , June 26
July 2 , July 16
July 17 , July 31
Aug. i , Aug. 15
Aug. 16 , Aug. 30
Aug. 31 , Sept. 14
Sept. 15 , Sept. 29
Sept. 30 , Oct. 14
Oct. 15 , Oct. 29
Oct. 30 , Nov. 13
Nov. 14 , Nov. 28
Nov. 29 , Dec. 13
Dec. 14 , Dec. 28
Dec. 29 , Jan. 12
Jan. 13 , Jan. 27
Jan. 28 , Feb. 11
Feb. 12 , Feb. 26
Feb. 27 , Mar. 13
Mar. 14 , Mar. 28
Mar. 29 , April 12
i. Numbers according to R. H. Scott,
ii. Ditto C. L. Prince,
iii. The figures in column i. smoothed by the formula
a + 2b -f c
It may be said that this is not the first time that
the notion that equinoctial gales are felt in northern
Europe has been combated. Professor Dove, in the
136 Weather Charts and Storm Warnings.
last edition of his 'Gesetz der Stiirme ' (1873), says
at p. 197, when speaking of storms arising outside
the Trade- Wind Zone :
' In western Europe these storms are rare, and pro-
bably are never experienced in summer ; we must now
examine into the reason of this, and must take care to
remember the changes in atmospherical conditions
which occur in spring and autumn. Lucretius calls
these epochs " the wartime of the year," and in fact an
Italian may well speak of equinoctial storms. Such an
expression, however, sounds strange from the mouth of
a German, for we cannot help thinking that he puts the
equinox at Christmas, and forgets that September is
the most usual month for the occurrence of that
In conclusion, it may be said that in the Annalen der
Hydrographie und Maritimen Meteor ologic for 1884, at
p. 625, a paper appeared which showed that for the
north coast of Germany the periods of the equinoxes
were not remarkably stormy ; and as for the Adriatic,
a paper by Dr. Robert Muller in Mittheilungen aus
dem Gebiete des See^vcsens for 1887, at p. 144, shows
that, though there exists at Pola a slightly marked
maximum of frequency at the time of the spring
equinox, nothing of the kind is traceable at the autumn
Storm Warnings. 137
STORM WARNINGS may be considered as the most
immediate practical application of weather knowledge,
and in fact it was the possibility of issuing such intelli-
gence which gave the first impetus to the development
of Weather Telegraphy. Although this branch of the
subject has not yet been reduced to such strict rules of
procedure as are demanded by the requirements of an
exact science like Astronomy, meteorologists can at all
events lay claim to having established some principles
which are sufficient, in many cases, to throw valuable
light on the conditions which may be expected to result
from existing circumstances, and so to some extent to
lift the veil which shrouds the future from our eyes.
The first suggestion of the electric telegraph as a
method of conveying intelligence of storms from one
place to another is apparently due to Mr. Redfield in
America, who shares with our own countryman, Sir
W. Reid, the honour of having reduced the Law of
Storms to a science. Redfield's paper is in the
American Journal of Science and Art for 1847,
1 3 8 Weather Charts and Storm Warnings.
this was followed in this country, after a brief interval,
by a communication from a man still living amongst
us, Mr. John Ball, F.R.S., as will be seen below.
The subject was taken up in a tentative way in the
United States between the years 1850 and 1860, but
further operations in this direction were brought to a
standstill by the war in 1861.
On this side of the Atlantic the credit of taking the
initiative is due to Leverrier, the famous director of
the Paris Observatory, who, as early as on February 1 7,
1855, received the Emperor's sanction for the creation
of an extensive organisation destined to distribute
intelligence of weather over the countries embraced by
it. The possibility of rendering such an organisation
really useful had been previously shown by the study of
the Balaclava storm of November 14, 1854, which had
wrought immense damage to the allied fleets in the
Black Sea, and by whose effects hardly a country in
southern Europe had been left unscathed. It was evi-
dent, from a mere cursory study of the facts of this
storm, especially of its rate of progress, that timely
notice of its approach might have been issued from the
coasts which were first visited to those which subse-
quently felt its effects.
The plan gradually assumed a definite form, and in
the spring of 1860 M. Leverrier addressed a letter to
Sir George Airy, inviting the co-operation of this
country in his scheme. This letter contains certain
expressions which have such an important bearing on
Storm Warnings. 139
the subsequent history of storm warnings that they are
worth translation and quotation. They are as follows :
' The ultimate result of the organisation which we
are establishing should be to announce a storm as soon
as it appears at any point in Europe, to follow it on its
course by means of the telegraph, and to give timely
notice of it to the coasts which it may reach.'
We shall presently learn to what extent this pro-
gramme has been carried out, and to what extent it
has been possible to go beyond it.
In this country the idea of storm warnings had been
broached before 1860, for at the meeting of the British
Association at Swansea in 1848, Mr. John Ball, F.R.S^
read a paper entitled ' On rendering the Electric
Telegraph subservient to Meteorological Research.'
This communication is so interesting and brief, that we
reproduce it in a note. 1 Eleven years subsequently, at
1 ' What is popularly termed the weather is a general expression for
the physical condition of the atmosphere with reference to heat,
pressure, moisture, and the velocity and direction of its motion. Two
classes of causes determine these conditions at any given point of the
earth's surface. The first class may, for short periods of time, be con-
sidered as constants, depending on the position of the point of observation
on the globe, and the physical conformation of the adjoining district. The
second class, upon which the proverbial uncertainty of the weather
depends, arises from the influence exerted by each portion of the atmo-
sphere upon those surrounding it, by virtue of which a disturbance of
equilibrium at any one point is rapidly propagated in all directions. In
common language, this is expressed by saying that the direction of the
wind is at once the cause and the indication of changes of the weather.
However far we may be from a general solution of the problem of atmo-
spherical disturbances, meteorologists have made considerable progress in
tracing the connection between successive states of the weather, owing to-
the mutual influence of contiguous portions of the atmosphere. The^e
1 4Q Weather Charts and Storm Warnings.
the Aberdeen meeting of the same Association in 1859,
.a formal resolution was adopted in favour of the organ-
isation of such a system. A month after the meeting
the loss of the Royal Charter on the coast of Anglesea
arrested universal attention, and as there seemed, at
first sight, a chance that that ship might possibly have
been warned of her danger, the hasty conclusion was
drawn that no storm could ever come on without giving
timely indication of its own approach. Subsequent
experience soon proved how very unsafe such a gene-
Early in 1861 the first tentative warnings were sent
out, and by the beginning of 1862 Admiral FitzRoy's
cases have been studied d posteriori, comparing the known results with
observations extending over considerable areas. Now that we have the
means of receiving information in an indefinitely short space of time by the
Electric Telegraph, these problems, under favourable circumstances, may
be studied d priori. In London we may receive instantaneous intelligence
of the condition of the atmosphere, as to the five ab.ove-mentioned
elements, from nearly all the extremities of Great Britain. With a delay
of about four hours we can have similar intelligence from the western part
of Ireland, and with a still shorter delay, our communications may extend
to the centre of France, the banks of the Rhine, and even to the frontiers
of Hungary and Poland.
' I do not pretend to say that with such elements for calculation we should
at once be enabled to predict changes in the weather with absolute
certainty. It would require some time to eliminate the action of accidental
and local causes at particular stations ; but there is no reason to doubt that
in a short time the determinations thus arrived at would possess a high
degree of probability. The ordinary rate at which atmospherical disturb-
ances are propagated does not seem to exceed twenty miles per hour;
so that, with a circle of stations extending about five hundred miles in each
direction, we should in almost all cases be enabled to calculate on the state
of the weather for twenty-four hours in advance.' Report British Association,
1848 (' Notices and Abstracts,' p. 12).
Storm Warnings. 141
system was definitely established. The principles on
which our present warning system is based are mainly
the same as the principles of that devised by the
Admiral, but exhibit some contrasts to them.
Admiral FitzRoy, when he issued a signal, intended
by it to imply that the storm of which he gave warning
would be likely to occur within the next seventy-two
hours. He therefore had the signals kept up until the
evening of the day on which they were hoisted, and
then lowered, while by the present system they are not
lowered until all danger of the gale appears to be past
It is evident from this that if, as often happens, threaten-
ing symptoms disappeared without the actual occur-
rence of a gale, Admiral FitzRoy had no means of
announcing to the ports, on the day after the issue of a
warning, the fact of the improvement in the weather
prospects. This arose from the fact that once his
signal had been lowered there was no public indication
that it had even been hoisted at all, and yet the warn-
ing had been intended to cover three whole days. By
the present system the fact that no signal is exhibited
is, to a certain extent, a proof that no danger is appre-
hended at the Office in London.
It is hardly necessary to describe the signals, as their
appearance is familiar to all who have been at seaside
places, but for the sake of those who may not have been
on the coast in winter, at which season the signals are
most frequently visible, the following official explana-
tion of their meaning may be reproduced.
142 Weather Charts and Storm Warnings.
TELEGRAPHIC WEATHER INTELLIGENCE.
The Meteorological Office issues (free of charge) to ports and fishing
stations approved of by the Board of Trade, notices of atmospherical dis-
turbances on or near the coasts of the British Islands.
The fact that such a notice has been received at any station is made
known by hoisting a Cone, which is three feet high and three feet wide
at base, and appears as a triangle when hoisted.
The Cone point downwards means that gales, or strong winds, are
probable, at first from the Southward (from S.E. round by S. to N.W.)
Should it appear likely that a gale beginning from between N. and N.W.
is likely to veer towards N. or N.E., the North Cone is hoisted in preference
to the South Cone.
The Cone point upwards means that gales, or strong winds, are pro-
bable, at first from the Northward (from N.W. round by N. to S.E.)
Should it appear likely that a gale beginning from between E. and S.E.
is likely to veer towards S. or S. W., the South Cone is hoisted in preference
to the North Cone.
Sudden Shifts of Wind.
It must be remembered, that a Southerly wind is much more likely to veer
quickly to a point North of West than a Northerly wind is to veer to a
point South of East, and that a gale from East is more likely to back to the
Northward than to veer to the Southward.
Accordingly, when the South Cone is hoisted and the anchorage of
harbour is exposed to the North- West, it is advisable to bear in mind that
a gale commencing at South- West may shift suddenly to North-West*
S tor in }Varni\
SOUTH CONE. NORTH CONE.
Gale probably Gale probably
from the from the
Night Signals (instead of the above) Lights in triangle.
Three lanterns and one yard, 4 ft. long, will be sufficient.
144 Weather Charts and Storm Warnings.
On Hoisting the Signals.
The signal is to be kept flying until dusk, and then lowered to avoid
unnecessary wear and. tear, but to be hoisted again at daylight next morning ;
and so until the end of 48 hours from the time at which the message was
issued from London, unless orders to lower the signal are received pre-
viously. The time of issue is always marked on the telegram.
At dusk, whenever a signal ought to be flying if it were daylight, a night
signal may be hoisted in place of the Cone, consisting of three lanterns
hung on a triangular frame, point downwards (for South Cone), or point
upwards (for North Cone) as the case may be. They should be kept
burning until late in the evening, say 9 or 10 o'clock, or longer if the loca^
authorities should think it important.
These signals may be made with any lanterns, showing white or any
colour, but the lanterns should be all alike. Red is best. Lamps are
better than candles. The haulyards should be of good rope, and should be
protected from chafing. The lanterns should hang at least three feet apart.
Meaning of Signal.
The hoisting of any of these signals is intended as a sign that in the
neighbourhood (say, within a distance of 50 miles) of the place where the
signal is hoisted, there is an atmospherical disturbance in existence which
will probably cause a gale from the quarter indicated by the signal used,
and the knowledge of which is likely to be of use to ihe sailors and fisher-
men on that part of the coast. Its meaning is simply, "Look out ! It is
probable that bad weather of such and such a character is approaching
Hitherto it has been found that these signals have been justified in four
cases out of five as follows :
(l.) In three cases out of five by Fresh, Strong, or Heavy Gales
(*".<?., Force eight or more).
(2.) In one case out of five by Strong Winds or Moderate Gales
(i.e., Force six or seven).
In every case some of the principal reasons which have led to the hoist-
ing of the signal are briefly explained in the telegram, which should always
be kept posted up for public inspection while the signal is flying.
The simplicity of the idea of using a cone, which
Storm Warnings. 145
must necessarily show the same shape as a triangle, no
matter how it is blown about by the wind, is the great
merit of FitzRoy's plan, as the sailor need not burthen
his memory with a complex code of signals. In fact,
when the Meteorological Office in 1868 made an
attempt to introduce a more complex apparatus, like a
railway semaphore, in order to convey intelligence to
ships in the offing, the experiment fell perfectly flat,
owing to the difficulty of instructing our coasting sea-
men, for whose benefit storm warnings are originally
intended, in the use of a totally novel system.
The question of signals is not an easy one to set
finally at rest. There is no doubt that the information
conveyed by them would be infinitely more valuable if
they could be shown from headlands which shipping
usually make, such as the Lizard, than if they were
simply exhibited in harbours. Here then we see the
necessity for a special signal code. By our present
system we can only give a limited number of possible
signals, so that we cannot convey detailed information
to ships at any distance from the shore ; say, even
riding at anchor in the Downs.
Our system is to hoist the signal as an indication
that some information of a certain kind has been sent
to the signal station, which it is of importance to the
seaman to know : but he must land and read the tele-
gram himself if he wants to learn more precisely what
the facts are. We are as yet a long way off from the
condition which may be described as the acme of
146 Weather Charts and Storm Warnings.
weather-signalling, and which has often been suggested,
that of having a weather signal book containing charts
of different types of weather, much like the illustrations
in these pages, duly numbered, so that by simply hoist-
ing a number on the signal staff, we could tell the
seaman to what page in the book he had to turn, and
what weather he had to expect. Thus, such a chart
as that for November 29, 1874 (fig. 2), might be de-
scribed as No. 371, and so on. It will, however, be
many a long year before our knowledge of weather will
justify our issuing such a collection of typical weather
maps as would be likely to be of service for such a
purpose, but possibly in the future something of this
kind may be done.
If it be asked what the real practice of storm warnings
is at present, the reply is that it is a moderate advance
on Leverrier's anticipations in 1860 (p. 139). It will
appear from the previous pages that we have some sort
of knowledge of the circumstances under which the
various types of storms approach the different parts of
our coasts, but these are not sufficient to tell us in
every case when a storm is imminent.
Some conditions give us more warning than others,
but the cases in which we have definite premonitions
are not of very frequent occurrence, and in general it is
not until the storm is quite close at hand, and the
barometer has begun to fall briskly at the outposts,
that we feel ourselves justified in issuing a definite
warning. The appearance of one of the small secondary
Storm Warnings. 147
depressions, however, not very unfrequently precedes
that of a more serious storm ; accordingly, if we notice
one of these lesser disturbances, we are at once put on
A rapid and unexpected rise of the barometer is
often the precursor of a coming depression, so that
whenever we see a sudden rise we may expect an
equally sudden fall, and must be on the look-out for
the slightest tendency of pressure to give way.
It should, however, be remembered that, as regards
barometrical indications, we are guided not only by the
actual fall of the mercurial column on a certain line of
our own coasts, but also by the behaviour of the baro-
meter at far distant Continental stations. Thus, in the
case of the storm already so often quoted, November 29,
1874, a warning had been issued to the coasts at
3.30 P.M. on the 28th, when the most alarming sign
was not so much the fall of the barometer at our south-
western stations, taken by itself, as the fact that this
was accompanied by a slight rise, of o.oi inch, since
8 A.M. at Rochefort, readings in the south-west of France
being already seven-tenths of an inch higher than in
the south of Ireland. This showed that pressure was
banking up to the southward, and that gradients were
consequently becoming steeper along the Channel. If,
when the barometer falls at our south-western stations,
the fall affects those in the south of France, we know
that we have less to fear from Westerly winds, as the
tendency of such a change is to reduce the gradients
148 Weather Charts and Storm Warnings.
for winds from that point, while a rise of pressure over
France when it is already relatively high there, puts us
at once on our guard for a blow from the Westward.
Similar reasoning will apply to barometrical indica-
tions in other parts, but the changes in direction of the
wind are of almost equal value to them, and in some
respects of even higher importance, as giving earlier
The proverbial danger of a backing wind has already
been alluded to, p. 78 ; this, however, is chiefly true
as concerns the * backing ' of the wind from NW. to
SW. and S., which indicates the approach of a fresh
disturbance, for it has been explained that if one
cyclonic system is following another in quick
succession, as the wind on the southern side of each
runs gradually from SE. through S. and W. to NW.,
the approach of the second depression must cause the
vane to shift back from NW. towards SE. This back-
ing is almost the most dangerous sign of all.
It has, however, been stated already that it is not
safe to depend on the observations from our western
stations as to the direction and force of the wind,
owing to the hilly nature of the coasts, so that we
cannot implicitly trust the reports on this subject
which we receive.
Another very important sign as regards the wind, is
the indraught of air towards the storm area. This is
perfectly intelligible on the supposition that the air
really flows in towards the centre and rises there. On
Storm Warnings. 149
the approach of a cyclone to the west coast of Ireland,
we frequently find the winds South-westerly on the
west coast of France, as on November 28, 1874 (p. 90),
while we can hardly say that the barometer on that
coast, at such a distance from the centre of the disturb-
ance, had yet felt its influence.
The reports of sea disturbance are even more un-
certain guides to us than the observations of wind, as
is explained in Chapter I., p. n.
Temperature is also a very useful aid in gaining a
knowledge of coming disturbance, for it will be remem-
bered how the rise of the thermometer in front of a
storm is a marked characteristic of areas of low pres-
sure, but the indications of temperature have, for various
reasons, not yet been reduced to strict rules like those
of the barometer.
We know, however, that a great contrast of tempera-
ture between adjacent stations, being an indication of
serious atmospherical disturbance, is the precursor or
concomitant of a serious storm, so that if we find a great
difference between the reports of temperature, we are
at once warned of approaching disturbance. Some
striking instances of this fact may be cited. On
November 13, 1875, at 8 A - M -> tne thermometric report
from Scilly was 57, and from Wick 21. The result-
ing difference is 36. The gale of Sunday, November
14, with its accompanying high tide and consequent
inundations on the south coast and in London, was
long remembered by the residents in that part of
1 5 o Weather Charts and Storm Warnings.
England. Again, on December 8, 1886, an unusually
severe storm crossed the north of Ireland and England.
This had been preceded by remarkable unsteadiness of
temperature. On the 4th of the month the change in
24 hours had been 21 at Hurst Castle and Dungeness,
1 8 in London, and 17 at Loughborough. On the
6th the change had been 22 at Loughborough, 21 in
London, 20 at Oxford, and 19 at Cambridge and
Dungeness. Accordingly, the atmosphere had been in
a state of disturbed equilibrium for four days before the
Besides all the symptoms of the approach of a storm
which have been enumerated, there are the innumerable
local signs which enable the fisherman and shepherd,
not to speak of the inferior animals, to judge of coming
bad weather. Among all these, almost the most
important are the character and motion of the upper
clouds. Another great sign is the clearness of the
atmosphere, the unusual visibility of distant objects,
which is well known as a sign of a coming gale.
It must always be remembered that, in order to issue
perfectly correct storm warnings, we should require to
know the size, shape, position, and motion, in direction
and rate, of an advancing depression, and also whether
it is becoming deeper or the contrary, and that there is
not one of these conditions of which we have a really
sufficient knowledge at present, while of most of them we
can have no knowledge at all till the storm has burst
upon us. The problem which is put before the
Storm Warnings. 1 5 i
Meteorological Office daily, is similar to one which
astronomers would at once recognise as impossible of
solution, and that is to determine the elements of a
comet's path from a single observation taken, say, in
a brief clear interval on a cloudy night. The first
glimpse we get of a storm must suffice for us to issue
It is therefore evident that for our own exposed
western and northern coasts we can but rarely issue
timely warnings, but fortunately these iron-bound shores
are not frequented by an amount of coasting craft at
all to be compared with that navigating the compara-
tively calmer wafers of the two Channels and the North
The results of the warnings to our oivn coasts have
been printed in the Reports of the Office for several
years back. The following are the figures for the year
1885, being the last which have been published :
1 5 2 Weather Charts and Storm Warnings.
'C O "
vo" -t-J : "i : :
^ J W
od'in'S Sb 4^
c a. ta< c tj 'S
^<J <J t^O fe
S3Jt B 5S T W
jooag; ui sSuiuau^
sjojaq uon^jg SUQ JB
hH ; M H4 M N ; ; ;
p9LJDK9J O 9Z)JO^ 94"[
3DJO.I '8JBI SSUIUJB^
juanbasqng Aq pay
-psnf jou sSuiuaB^Y
g eu GJ
1/3 *o 6
9 ssoaoj ' S P U 'AV.
Xq payijsnf sSuiuaB^
*O r^ ro ^"OO O oo vO O
** Q) 2
* o %
-dn puB g aoaoj
I^M N ONONVO rM^
Xq paynsnf sSuiuae^
rj-rOrj-M co^j-Tl-W N
'Si 1 1 3
8 I I
-y^ pus jsioq oj sjap
r-( ff M
^xT'O T: 13" T3 r a'r3 w
If these figures be compared with those for the
preceding eight years, we see that the results in per-
centages are fairly constant.
Accordingly, it appears that more than half the
signals of approaching storms (force upwards of 8,
Beaufort scale, ' a fresh gale ') were fully justified, and
the same is the case for four out of five signals of
approaching strong winds (force upwards of 6, Beaufort
scale, ' a strong breeze ').
It is therefore evident that the system of storm
warnings renders it possible to give useful intelligence
to the coasts, but it need hardly be said that the system
for these islands is rather of the ' from hand to mouth '
type, and that our warnings would be far more useful if
they could be issued sooner, so as to render it possible
for captains to get intimation of a coming gale before
leaving port This, however, can hardly be hoped for
in the present state of weather telegraphy, and a few
154 Weather Charts and Storm Warnings.
instances will suffice to show some of the principal
causes of failure of warnings, in addition to those
arising from the imperfections of our arrangements,
which have been already described.
We shall commence with a case in which even a
practised seaman's experience was at fault, so that we
can hardly blame our telegraphic reporters, who are
mostly landsmen, for their failure to notice, from the ap-
pearance of the sky and sea, that a storm was imminent.
Nearly fifteen years ago, on November 22, 1872, there
was a tremendous gale in the Channel, when the Royal
Adelaide was lost on Chesil Bank. On that day at
noon the telegraphic reports had shown an apparent
improvement on the weather of the previous day, so that
the signals then flying were lowered on the south coast.
At night the storm came on, and of course the comments
on the Office were not favourable. On this day one
of our best sea-observers, the late Captain Thomas
Donkin, of the Inverness (one of the three ships that
rode out the Madras cyclone of May 2, 1872), was out
in the gale, and was blown back by it, hove to, from the
Lizard to the Casquets, off Alderney. We wrote to him
as soon as we heard that he was safe at anchor at
Portland, to ask him whether he, being at sea, had
anticipated the storm from the look of the sky and sea ;
and his answer was : ' With respect to the weather on
November 22, I may say that at noon I was standing in
towards the land, between Falmouth and Plymouth,
and a pilot cutter came alongside, and if I had had the
least apprehension of such a gale as followed being
near at hand, I should have taken a pilot and gone into
Plymouth. The appearance of the weather at the time
was fine, though the glass was falling, though not low at
the time for SW. wind and unsettled weather.'
In this case, therefore, the signals, once hoisted, had
been lowered too soon.
FIG. 49. October 20, 1874; 8 A.M. Depression approaching
coast of Norway.
The next case, which will be illustrated by charts,
affords specimens of a double failure of warning. In
the first instance the signals had been hoisted on the
north-west coasts on the morning of the 2Oth, and had
been lowered again in the afternoon, while subsequently
they were hoisted unnecessarily and had to be lowered.
156 Weather Charts and Storm Warnings.
The gale is that of October 21, 1874, which has already
been noticed, p. 72.
Taking the first chart (fig. 49, p. 155) for 8 A.M.
October 20, we find pressure highest over the entrance
of the Channel, and lowest in the far north, where
SW. gales are reported. These gales, with a falling
FIG. 50. October 20, 1874; 6 P.M. Depression off Christiansund.
barometer in Scotland, caused some alarm, but this was
allayed by our finding conditions unchanged at 2 P.M.
By 6 P.M., however (fig. 50), the depression existing in
the north had advanced to the coast of Norway, where
the barometer had fallen 0.6 inch, but the signs of
danger to ourselves were the bend southwards of the
isobar of 29.4 round the Butt of Lewis, and the backing
of the wind, though still light in force, to South-west
at Stornoway and over the Moray Firth, and, though
last not least, the steady rise of the barometer at the
entrance of the Channel.
During the night the storm came on, and at 8 A.M.
October 21, its centre lay half-way between Peterhead
and the Shetlands (fig. 5 I ), while a terrific Westerly
FIG. 51. October 21, 1874; 8 A.M.
New depression off north of
FIG. 52. October 21, 1874; 6 P.M.
Depression has advanced to the
coast of Norway.
gale was blowing over the whole of the United King-
dom, and the area of high pressure had been displaced,
and lay over the extreme south-west of France.
The next chart (fig. 5 2), for 6 P.M. on the 2 ist, shows
us that the disturbance had made rapid progress east-
1 5 8 Weather Charts and Storm Warnings.
wards, and now lay over western Norway, while the
winds in these islands had moderated in violence, and
had veered towards North-west
If we now turn back to fig. 17 (p. 83), we shall see
the cause of the unnecessary warnings to which allusion
has just been made.
At 8 A.M. on the 22nd, a brisk fall of the barometer
took place in the west of
Ireland, with a ' backing '
wind, and warnings were at
once issued, but, as will be
seen by fig. 17, this was
only a false alarm, for the
b fresh disturbance was only
secondary to the more
serious one which had pre-
ceded it, and its only effect
was to equalise pressure in
Ireland, by reducing the
gradients and moderating
the force of the wind.
FIG. 53-January 21, 1875; SA.M. The storm which has
Small depression over Belgium, been taken as a typical cy-
Mand diStUlbanCe appr achi " e clone, that of November 29,
1 874, whose course we have
traced (figs. 1922, pp. 90-92), is a good instance of a
partial success and partial failure. On the 28th,
warnings were issued to the west, north, and east of
England, but not to the Channel coast or to the
French stations. It will be seen from fig. 21 (p. 91)
that while the warning was quite successful on all the
coasts to which it was issued, its omission was a signal
failure at the southern stations.
It will be interesting to examine yet another case
of failure of warnings, and one which has arisen from
the unexpected direction of
motion of the storm.
Fig. 53 (p. 158), for 8 A.M.
January 21, 1875, shows us I"
no less than three cyclonic
disturbances over the area
of our chart. One large one
is disappearing over Nor-
way. A very small second-
ary one is lying near Dover,
while the third the one
we are about to trace is
just showing itself off the
west coast of Ireland.
Warnings were issued to FIG. 54. January 21, 1875; 2 P.M.
New disturbance near Pembroke.
all our own coasts except-
ing Scotland and the north-west of England, from
Fleetwood northwards. Fig. 54, for 2 P.M. on the
same day, shows us the disturbance with its centre
near Lundy Island, while pressure over the south of
France has barely changed since the morning.
At this time, however, the depression was becoming
deeper, and was extending rapidly to the southward.
160 Weather Charts and Storm Warnings.
55> f r 6 P - M - on the same day, shows us the
centre of the storm lying over Dover, and a very heavy
gale from North-west is blowing all along the west
coast of France, while our shores had nothing but
These warnings, therefore, were quite unnecessary for
FIG. 55. January 21, 1875 ; 6 P.M. New disturbance near
Dover, in same position as that at 8 A.M.
several of the English stations to which they were
issued, but they ought to have been transmitted to
France, where they would have been of good service.
Lastly, a storm like that of April 2024, 1872
(p. 103), which doubles back on its own course, naturally
causes much difficulty in the issue of warnings.
Storm Warnings. 161
The instances cited are sufficient to show that there
is great uncertainty in the practice of storm warnings,
owing to the deficiency of our information as regards
quality and quantity, and that even with all the in-
formation we can procure we are often to a great
extent in the dark as to the character and motion, in
direction and rate, of the storms which approach our
coasts, until they have wrought more or less damage.
With all these drawbacks, however, it has been
shown at p. 153 that we are able to maintain a
general success of about 80 per cent, for our warn-
ings, a result on which we may fairly congratulate
1 62 Weather Charts and Storm Warnings.
THE recognised value of storm warnings to the sea-
faring community soon led to a general demand, on
the part of the public, for predictions of the weather
day by day. These were issued by Admiral FitzRoy
almost at the first institution of storm warnings in
1 86 1, but the forecast service was suspended at the
end of 1866, and was not resumed for the space of
more than ten years.
Meanwhile, the Meteorological System of the United
States was organised, and it at once commenced the
issue of its ' Probabilities.' This service speedily
attained great popularity, owing to the very general
correctness of the predictions. In our own country,
however, forecasting was not taken up again until the
re-organisation of the Office in 1877. The country was
partitioned into eleven districts, the same division as
has been adopted for the Weekly Weather Report, and
which has reference to the predominant character of
the agriculture in the different parts of the United
Kingdom. The districts are shown in the accom-
panying map (fig. 56). The reason that Scotland
North is called o, is that when the division was first
planned it was considered that the Highlands of Scot-
land were not strictly agricultural.
The principles of preparation of the forecasts are on
the whole similar to those of the preparation of storm
warnings, but the task is evidently much more difficult ;
and besides the duty is constant, and not merely occa-
0. SCOTLAND, NORTH.
1. SCOTLAND, EAST.
2. ENGLAND, N.E.
3. ENGLAND, EAST.
4. MIDLAND COUNTIES.
5. ENGLAND, SOUTH.
6. SCOTLAND, WEST.
7. ENGLAND, N.W.
8. ENGLAND, S.W.
9. IRELAND, NORTH.
1 10. IRELAND, SOUTH.
FIG. 56. Chart shewing Districts.
sional. The great difficulty consists in the fact that the
weather is not, and cannot be, the same over the whole
of each of the districts, for the variations in the contour
of the country ; the hills and valleys ; the lie of the land,
whether it faces north, south, east or west ; and its
position with regard to the sea, all exert a great
influence on its weather. More especially is this the
case with regard to ranges of hills. Supposing such a
1 64 Weather Charts and Storm Warnings.
range to lie along a coast-line, the wind coming from
the sea will be forced to rise over it. As it rises it is
expanded by the reduction of pressure. In the process
of expansion the air is chilled, and a proportion of the
moisture in it is condensed and falls as rain. When
the air reaches the ridge of the hills it begins to
descend. It is compressed in the descent and warmed
thereby, so that its tendency is not to produce rain but
to absorb moisture. The air is accordingly damp on
the weather side of the hill and dry on its lee side.
To give a practical instance of what is meant, I may
say that in the month of August 1886 I was living
on Speyside, with the mountains of Perthshire and
Inverness-shire to the south and west. The weather
was uniformly dry, while at the same period the
residents in Argyllshire were complaining of constant
To prove this by figures is not difficult. The three
stations selected are Laudale on Loch Sunart, Argyll-
shire, among high hills, close to the coast ; Glasgow
Observatory, lying well to the south of the Grampians,
but at some distance from hills ; and Nairn, lying to
the north-east of the hills of Inverness-shire. The
following are the recorded rainfalls, in inches, in the
months of August and September 1886 :
Laudale . . .3.78 ... 9.50
Glasgow . . .1.81 ... 4.96
Nairn . . . .1.19 ... 2.47
It is not possible to frame forecasts which shall
Forecasting. 1 6 5
exactly suit these different conditions existing in one
district, but it is equally impossible for the forecaster in
London to subdivide in his mind the districts with
reference to all the local peculiarities of climate which
exist in each, and to frame several hundred special
Notwithstanding all these disadvantages, we are able
to point to a very good proportion of success for
our forecasts, as the figures shortly to be cited will
The forecasts are prepared three times a day, on
the receipt of the several telegraphic reports, for 8 A.M.,
2 P.M., and 6 P.M. respectively, as explained at p. 15.
Each forecast is intended to cover the interval of
twenty-four hours, and no more, from the time of its
The 1 1 A.M. forecasts are intended for the early
editions of the evening papers, for the clubs, and for
public exhibition in various parts of London.
The 3.30 P.M. forecasts are not generally published,
but in the summer-time they are issued to a limited
number of gentlemen to aid them in the saving of the
hay harvest. In this case the recipients engage to
send in regularly to the Office reports as to the
accuracy of the forecasts.
The 8.30 P.M. forecasts are supplied gratis to any
newspaper which will send for them to the Office, as
explained in the Annual Reports.
The forecasts are also issued to subscribers at a
1 66 Weather Charts and Storm Warnings.
small charge, and in addition the Office is always
ready to answer, to the best of its ability, inquiries as
to weather, for not more than twenty-four hours in
advance, on terms which are published in the Postal
In order to check the accuracy of the forecasts, they
are regularly compared with the weather reported in
the various districts on the days to which they referred,
and the results of this checking of the forecasts issued
at 8.30 P.M. during the year 1885 is as follows :
Success. ; Success.
Scotland, N. .
Scotland, E. .
England, E. .
53 3 1
51 34 n 4
Scotland, W. .
Ireland, N. ,
* Note, " partial" implies "more than half."
The forecasts have been issued and checked regu-
larly since the beginning of the year 1879, and the
following are the figures of the summary for the entire
period of seven years, under the same headings as
those just given :
The Office, however, does not rest content with its
own estimate of its own work, and accordingly the
reports of the Hay Harvest Forecasts, which are
furnished in the manner explained above, are tabulated
and reduced to percentages. These figures therefore
are quite independent of any possible colouring by the
Office. The tables correspond exactly to those just
given, except that they come down a year later, as the
results for the season of 1886 have already appeared.
NAMES OF STATIONS.
Golspie and Munlochy
England, N.E. .
Ulceby and Chatton, North-
14 * 85
Rothamsted and Thorpe
Circncester and East Ret-
England, S. .
Horsham, Maidstone, and
Dumbarton, Stranraer, and
England, N.W. .
Ley bum, Knutsford, and
England, S.W. .
Bridgend (Glamorgan), Clif-
ton. Glastonbury, and
Ireland, N. .
Ireland, S. .
Hollymount and Moynalty
Moneygall and Kilkenny .
Mean for all districts .
68 Weather Charts and Storm Warnings.
SUMMARY FOR THE LAST EIGHT YEARS.
At the risk of wearying the reader with a recapitu-
lation of dry figures, this summary of results may be
concluded with quotations of the figures obtained by
independent private observers during the last year
In the Times of February 7, 1887, a letter appeared
from the Rev. G. T. Ryves, of near Stoke-on-Trent,
giving his experience of the forecasts for the Midland
Counties in 1886. The writer says:
'The forecasts were tested under six heads viz.,
I. Prevalence of rain, snow, or sleet. 2. State of the
sky (whether clear, cloudy, overcast, or hazy). 3 and
4. Direction and force of wind. 5. Temperature
(whether warmer or colder). 6. Electrical disturbances
(lightning and hail). The success or failure of the
forecast as to each head referred to in it was entered
in its appropriate column, and the result was then
entered in one of these columns (according as the
actual weather agreed or disagreed with the forecast),
cither as an absolute success, an absolute failure, or a
partial or doubtful success.
'As no forecasts are issued on Sundays and Good
Friday, and there were t\vo days in December when it
was impossible to issue any, owing to the breakdown
of telegraphic communication, the number of forecasts
sent out by the Office during the year was 310. Of
these, 309 were tested in the manner above described,
with the following result : Absolute successes, 247 ;
absolute failures, 26 ; partial or doubtful successes, 36.
That is to say, we get, omitting small fractions, 80 per
cent, of successes, SJ per cent, of failures, and 1 1 \ per
cent, of doubtful cases.'
In the same connection it may not be without
interest to give the following figures showing the
results of the forecasts for England, SW., as tested
at the Observatory Rousdon, Lyme Regis, by Mr.
C. E. Peek, F.R.A.S., for the last three years. At this
observatory the forecasts, arriving by post, are delivered
about noon. The last entry of the weather for the
period covered by the forecast is made at 9 A.M., and
these facts are compared with the forecast on its
l g l
1 70 Weather Charts and Storm Warnings.
The results of our work may be compared very fairly
with those published by the other European Offices
which issue forecasts. It is undeniable that occasion-
ally complete failures of the forecasts occur, and these
are due very much to the same causes as the failures in
storm warnings already described. A notable instance
of this may be cited, being that to which the Bishop of
Carlisle drew notice in Nature for November 2, 1882.
The date of the occurrence was October 24 in the same
The two charts (figs. 5 7 and 5 8) will show the com-
pleteness of the failure of the forecast. On the evening
172 Weather Charts and Storm Warnings.
of the 23rd (fig. 57), there was nothing in the reports
from any of the stations to indicate the approach of any
disturbance ; accordingly, none was forecasted and no
warnings were issued.
Yet, at 8 A.M. next morning we find a well-marked
secondary depression with its centre near Southampton
(fig- 58), which has brought with it to the south of
England torrents of rain, subsequently turning to snow,
and to the French coast and the south-east of England
a storm of wind. Fortunately the wind on our south
coast was not at its worst until about noon, for at
8 A.M. not one of the south coast stations reported
a gale except Hurst Castle, and that only reported
The following are the reports of the wind force
collected afterwards by the Office :
Jersey, 8 A.M WNW. 9*.
Hurst Castle .... WSW. 10.
Owers (Lightship), 10-11 A.M. . SW.byW. 12*.
Varne (do.), noon . . . SW.byW. 10.
Dover, 2 P.M WSW. 8.
London . . . . . SSW. 10.
Kentish Knock (Lightship), 3 P.M. W.byS. 10.
Yarmouth, ii A.M. . . . SE.byE., 62 miles per hour.
Leman & Ower (Lightship), 6 P.M. W. 10.
Spurn Head .... WNW. 9.
Where no hour is stated none is given in the report.
At the two stations marked, the force of 9 was reached
before the warnings, which were issued at 9 A.M., could
have reached the place, so that strictly speaking the
warnings were issued before the gale had reached
Forecasting. 1 7 3
a dangerous height, except in the Channel Islands
and at the Owers Lightship, off Selsea Bill.
Now as to the possibility of foreseeing this gale,
a careful examination of the photographic curves at
the observatories shows that at Falmouth, the first to
feel the influence of the disturbance, the barometer did
not begin to fall till 10 P.M.
In a paper by Mr. H. Harries, 'On the Typhoon
Origin of the Weather over the British Isles during the
Second Half of October 1882,' which appeared in the
Quarterly Journal of the Royal Meteorological Society,
vol. xii. p. 10, this particular disturbance comes under
notice, and the author says : ' I have examined the
records of many ships over a large area west and
south-west of the British Isles, but find nothing to
justify our supposing that the storm had any existence
at all until late on the night of the 23rd.'
After quoting facts to justify this assertion, Mr.
Harries goes on to say : ' At the earliest, therefore, no
prediction of an approaching storm could have been
issued from the Meteorological Office before 3 A.M. of
the 24th, and shortly after this hour the tempest was
raging over the Channel and the French coast.'
This failure of forecasts attracted much attention, and
various suggestions have been made to obviate the
possibility of its recurrence. If we come to analyse
these, we find they are two in number, and both of
them have been more than once mentioned in these
pages (pp. 15, 1 6). They are: I. More frequent
1 74 Weather CJiarts and Storm Warnings.
telegrams ; and II. More complete and accurate reports
of the state of the sky.
More frequent telegrams demand a greater ex-
penditure of money; the telegraph offices close before
nightfall, and to keep them open would cost a very
large sum. In fact, it has well been said ' meteor-
ology is money,' and at every turn we are met by the
same difficulty of providing funds for any improve-
ment. The second suggestion, that if a lunar halo,
which was noticed in London at 10 P.M., had been
reported two hours earlier, the Office might have had
some intimation of impending change, is more practical ;
but here, too, the fact is that the halo, if it existed at
6 P.M., was not reported from a single station, and
the storm therefore took the Office at unawares.
It is needless to cite more instances of incorrectness
of the forecasts ; they are all more or less similar in
character to that which has just been quoted. Their
correctness, on the contrary, is constantly being dis-
cussed in the newspapers, and in addition a large
number of anonymous letters and postcards relating to
the subject arrive at the Meteorological Office.
Many of these are very plain-spoken. One corre-
spondent, whose handwriting is perfectly familiar to
us, and who has been sending us postcards for years,
'Where is your violent cyclone to burst on British
coasts between nights of 1 4 and 1 6 ? The deadest
of calms, of course!' This individual holds the Office
Forecasting. 1 7 5
responsible for the announcements of the New York
Another gentleman is straightforward enough to sign
his name, and he says :
' If you cannot give better information in your
weather forecast you had better shut up your shop.
You have been quite wrong every day this week. Go
away, false prophet. I shall have a petition prepared
to abolish your Office.'
Some of the letters are of a different tenor, and call
for special forecasts. One arrived in June 1886,
bearing no less than ten postmarks. It was addressed
' Weather Office, Strand, London.' Its contents were :
' Three next days order to be fine.'
Another, of similar import, was addressed :
1 Clark of the Weather,
'No. i, Rainy Quarter.'
The Post Office added, 'Try Meteorological Office.'
This letter was dated and reached us by first post.
Another was addressed :
' Right Hon. Clerk of Weather,
1 9 Downing Street,
' London, W.C.'
It ran as follows :
' My Lord Clerk,
1 May it please your Lordship, you will greatly
oblige your humble servant by writing or sending me
176 Weather Charts and Storm Warnings.
a telegraph whether it will be fine or not on the 5th of
November 1867. I have the honour to remain,
' Your Lordship's most obedient servant,
' JOSEPH WILLIAM - .'
It need scarcely be said that this child received an
answer, the letter being evidently in good faith.
The last to be mentioned is the prettiest of all. It
reached me at Rome at the time of the meeting of the
International Congress in 1879, and created great
amusement among the savants assembled there. It was
' On Her Majesty's Service.
1 To the Clerk of the Weather,
1 Government Offices,
1 To the Cleark of the Weather [sic].
' Please Mr. Clerk of the Weather, tell the rain, snow,
and hail to stop for the afternoon and rain in the
"Good bye, my dear old Clark [sic].
1 Go on next page.
1 My name is Blanche
' Parsonage .'
Miss Blanche was duly informed that she was not
the only person who cherished such wishes, but that
her desires could not be fulfilled.
The number of weather prophets that write to us is
very large indeed. Here is a verbatim copy of one letter :
' April 28, 1879. Colliery.
'Notice Sir this to warn all shipowners and
captans and all seefarenmen that there wil be see
storm, on the 1 6 or 1 8 of May from North East with
rain lighting to get there ships trimed squalls of
wind.' This was duly signed.
The weather was perfectly calm between the I5th
and iQth of May 1879.
One gentleman issued on postcards monthly forecasts
for more than twelve months in 1882 and 1883. To
each forecast was appended the following note :
'These forecasts being founded on a universal law,
allowance must be made for local differences and
peculiarities. They are applicable to all places in the
Northern Temperate Zone.'
The reader will have gathered from the foregoing
pages that the weather is seldom quite the same on
any one day all over the limited area of the British Isles.
How then can we expect a forecast to be generally
applicable when the North Temperate Zone embraces
climates so different from ours as those of St. Peters-
burg and of Salt Lake City !
One thing is at all events admitted by all who have
experience of forecasting, and that is that as yet no
scientific principles have been established which enable
us in Western Europe to forecast the weather for more
than a few hours.
178 Weather Charts and Storm Warnings.
SUGGESTIONS FOR IMPROVEMENT.
IT will be seen, from what has been said in the fore-
going pages, that there is room for improvement in the
entire service, but improvement requires money, and
money is limited. There is no lack of criticisms,
friendly or the contrary, of our work, or of sugges-
tions of new sources of information.
In some quarters the Meteorological Office is often
expected to be far more venturesome in its announce-
ments of weather than it is at all prepared to be.
Once a gentleman called on us with the request that we
would prepare for a newspaper, which he had recently
started, a forecast of the probable weather for a week
in advance. On our declining the task, he remarked
that Admiral FitzRoy had issued forecasts for three
days in advance, and that we ought to be able to do so
for double that period. He quietly ignored the fact
that Admiral FitzRoy's three-day forecasts were not
successful enough for them to be continued, and that
accordingly they had not been kept up.
Other men call on us to be as precise in our
Suggestions for Improvement. i / 9
announcements of * probabilities ' as the Chief Signal
Office at Washington, in simple oblivion of the circum-
stance that while that Office has an immense continent
to deal with, and is itself situated on the eastern side of
its area of observation, so that the gradual march of
weather changes over the western stations can be
observed and reported long before they reach the more
thickly populated portions of the States, we have to
deal with an extended oceanic coast, and can by no
possibility have a series of stations on our western side,
so that, unless by the appearance of the clouds and sky,
we have no chance of learning what is going on out of
sight of land.
Our reporting system is shown on the frontispiece,
and a glance at it will prove how badly we are off for
stations on the west coast of Scotland. This is a most
important district for gaining early intelligence of
weather changes, but in the first instance telegraphic
communication is only very scantily developed in such
wild regions, and in the second place the habitable spots
are almost all in sheltered bays, where the true force of
the wind is hardly ever felt, owing to the fact that few
ordinary houses could bear the brunt of a winter
Atlantic gale, blowing, as it sometimes does, with a
velocity of over 80 miles in a single hour, and reaching
the speed of at least 100 or 120 in gusts. The
observers therefore cannot possibly send up perfectly
true reports of the direction and force of wind, as will
be at once admitted when the position of the stations in
i So Weather Charts and Storm Warnings.
western Ireland and Scotland is considered. Valencia
lies on the shore of a narrow sound, with high hills
about it. Belmullet is at the head of Blacksod Bay,
and is therefore quite sheltered from the sea, though its
wind reports are good enough, as the land is low in
the neighbourhood. Malin Head is well exposed.
Ardrossan is a valuable station, but it is far up the Firth
of Clyde, and at least fifty miles, as the crow flies, from
the extreme western point of Lslay. We have no other
station till we reach Stornoway in the Island of
The most obvious idea is to obtain information from
the westward, either from moored signal ships, from
islands such as the Azores, Faroes, Iceland, and New-
foundland, or lastly from the mainland of America.
Let us take these different suggestions in order.
The idea of the employment of ships moored at a dis-
tance from the coast, and connected by a telegraphic cable
with the shore, has already been noticed in Chapter I.
This plan has over and over again been suggested as
a most valuable mode of obtaining information, not
only of the position of vessels in distress or wind-bound,
but of the meteorological conditions prevailing out at
sea. Some scientific men, as the late Mr. Morse, have
even gone so far as to propose that these signal ships
need not even be manned, but might be simple buoys
provided with electrically self-registering apparatus,
which might record its indications automatically at the
nearest station on land !
Suggestions for Improvement. 1 8 1
The plain state of the case about any such visionary
projects is that, even if we were to overcome the diffi-
culty of mooring a ship in 1000 fathom water, we
should find it very difficult to maintain the telegraphic
cable in working condition. Some years ago the
Admiralty lent H.M.S. Brisk to be moored as a trial
signal ship at the entrance of the Channel. The experi-
ment was given up in six weeks, mainly on the ground
of the difficulty of maintaining the telegraphic connec-
tion in a perfect state, and it was stated that the venture
cost the promoters about as many thousand pounds as
the Brisk was days at sea.
In the year 1886, however, the Telegraph Construc-
tion and Maintenance Co. succeeded in keeping up
connection with the Sunk Lightship, off Harwich, for a
year, so that the possibility of working such a scheme
has been proved.
As regards reports from islands situated in mid-
Atlantic, there is but little prospect of our ever making
much progress in that direction. It has often been
suggested that a cable should be laid from Portugal to
the Azores, and that this country should bear a consider-
able share in the cost of daily telegrams frcm those
islands, as it was assumed that, as the Azores are situated
in the Atlantic, they must be, so to speak, pickets, to
give us early news of danger approaching from that
All this is very plausible, but when we come to test
the simultaneous reports taken daily in those islands
1 82 Weather Charts and Storm Warnings.
and at Valencia, as has been done at the Meteorological
Office for two years and a half (Quarterly Journal of
the Meteorological Society, vol. i. p. 183), we find
that there is very little connection between the pheno-
mena occurring at the two stations, so that we could get
no direct warnings of approaching storms from the
Azores, though of course a daily knowledge of the
conditions of weather over the part of the Atlantic
where those islands are situated could not fail to be of
value to us, as is evident from what has been said in
Chapter VI. In fact, the Azores lie to the southward
of the usual track of Atlantic storms, and it would
apparently be a far better investment of money for this
country to spend it in obtaining reports from the Faroes,
if ever a cable were laid to those islands, than in paying
for telegrams from the Azores, as many of the most
destructive storms on our north-east coast come down
on us from the northern part of the Atlantic Ocean and
pass over the Faroe Islands. The value of St. Kilda
as an outpost could hardly be overrated, but there is no
present hope of telegraphic connection with that island,
and in all cases it must be remembered that unless a
cable will pay commercially it is hopeless to look for
the establishment of telegraphic communication for
scientific purposes. The telegraphic connection of the
Azores with Europe has been talked about for a quarter
of a century, and repeatedly it has been announced that
a concession for laying a cable has been granted, but
up to the present date (April 1887) capitalists have not
Suggestions for Improvement. 1 8 3
been induced to put down the necessary sum. To give
some idea of the expense which would have to be met
if the cable were laid and maintained for scientific
purposes alone, it is sufficient to say that such a scheme,
for communication with the Faroes and Iceland, was
proposed to the International Meteorological Committee
at their meeting at Copenhagen in 1882, and that in
that scheme the annual contribution of this country,
ranged naturally in the first class for maritime import-
ance, was 3285 for three daily reports, being more
than we pay at present for all our home and European
telegrams put together ! The idea of maintaining cables
for meteorological service alone may therefore be dis-
missed as visionary.
As regards reports from the other side of the
Atlantic, in the year 1868 a direct service of reports
from Heart's Content, Newfoundland, was organised.
These messages were transmitted gratis, thanks to the
great liberality of the Anglo-American Telegraph Co.
It was found, however, that we could not turn them to
practical account, mainly owing to the fact that the
situation of the station of Heart's Content was in a
sheltered nook, where no storm could hurt the shore
end of the cable, and accordingly the wind reported by
the observers bore little relation to that blowing at sea
outside. The service was therefore discontinued in the
Speaking in general terms, we may say, as regards
storm warnings from America, that though storms do
1 84 Weather Charts and Storm Warnings.
sometimes cross the Atlantic from shore to shore, they
change their character en route, some increasing and
others dying out, so that Ave cannot predict which
storm, out of several starting from the States, will
reach us. Professer Loomis, a very high authority on
American weather, very strongly supports the view
just stated in the following words, taken from the
American Journal of Science and Art for January
* When storms from the American continent enter
upon the Atlantic Ocean they generally undergo im-
portant changes in a few days, and are frequently
merged in other storms which appear to originate over
the ocean, so that we can seldom identify a storm in its
course entirely across the Atlantic.'
To give an instance of a storm failing to advance
over any great distance, I shall take one which is very
striking. On November 30, 1874, the steamer La
Plata, with a telegraph cable on board, foundered in a
heavy gale near the Channel Islands. This storm
entirely died out and disappeared before it crossed the
These statements show how rash is the opinion
which is held by Professor Daniel Draper, of New
York, and announced in the Reports of the Central
Park Observatory for 1872 and 1873, to the effect that
out of eighty-six storms which he had investigated, as
having started from New York, only three had failed to
show themselves either at Valencia or Falmouth.
Suggestions for Improvement. 1 8 5
We now come to the practical results of Atlantic
Telegraphy, as it has been conducted of late years. In
February 1877, owing to the great public spirit of
Mr. J. G. Bennett, the Weather Bureau of the New
York Herald, under the late Mr. J. J. Collins, com-
menced the transmission by telegraph of Weather
Warnings to Europe. These messages have been
continued ever since ; they appear in the public press,
and so have attained an extensive circulation.
When these warnings were first issued, their general
purport was to the effect that a disturbance was on its
way across the Atlantic, and might be expected to
cause gales on the western coasts of Europe at a given
date. The following is a specimen of these messages
it arrived July 4, 1877 :
' Storm centre will arrive British, French coasts,
probably 5th or 6th ; NE. to SW. gales, rains and
lightning. Warn outward-bound ships.'
The practical utility of these warnings has been
carefully tested in our own Meteorological Office, for
the first year of their continuance, and of late by
Professor Cleveland Abbe, of the Chief Signal Office,
Washington : the results in both cases are much the
same. About one-quarter of the warnings are fol-
lowed by gales of any consequence on the British
The actual percentages which my discussion, published
in the Nautical Magazine for March 1878, yielded, were
as follows :
1 86 Weather Charts and Storm Warnings.
Absolute success . . 17.5
Partial ,, . . 25.0
Very slight ,, . .15.0
Absolute failure . . 42.5
The paper goes on to say : ' These figures show that
not 45 per cent, of the warnings (in 1877) can be
considered to be really successful. What is meant by
" really successful " is that the information conveyed by
them was of real value to seamen in British ports.'
Professor Cleveland Abbe, of the Chief Signal Office,
Washington, states in a letter addressed to myself:
' A full report on the verifications of the New York
Herald predictions was submitted by me to the late
General Myer, in January 1878 : this covered all cases of
published predictions up to November 29, 1877, and in
it I allowed the Herald 42 per cent, in all i.e., about
25 per cent, for well-verified predictions and 17 per
cent, for partial successes, and for the remaining 50 per
cent, [sic] of failures. This was for Great Britain, but for
France and Spain the percentages were decidedly less.
These were of course apparent verifications, and took no
account of the fact that sometimes storms arrived in
Great Britain and served to verify a prediction, whereas
they really were different and distinct from the storms
to which the predictions referred.'
It will be seen that Professor Abbe's investigation
refers to a portion of the same period to which my in-
quiry referred. It is very satisfactory to see that the
two discussions, totally independent of each other, con-
firm each other so completely.
Suggestions for Improvement. 187
Of late years the Herald warnings have been gene-
rally couched somewhat in the following words :
4 A disturbance is central near Newfoundland, and may
be expected to disturb the weather of the British Isles,
&c., at such and such a date.'
These telegrams have been much more successful
than the positive predictions of gales, as the phrase
' disturbance of weather ' allows considerable latitude,
and it is a fact that if a storm even approaches our
coasts, it cannot fail to disturb our weather to a certain
extent, at least in Ireland or Scotland.
To give an idea of the extent to which storms
striking our coasts could really be predicted by means
of reports from America, the late Captain HofTmeyer,
the head of the Danish Meteorological Service, who
himself had drawn and published daily weather maps
of the Atlantic for the space of three and a quarter
years, investigated the course of Atlantic storms in a
pamphlet which he published in 1880. He discussed
285 depressions in all, covering an interval of twenty-
one months, and found the following percentage propor-
tions of the storms prevailing over the ocean source of
Source of Depression. S^-W.
Arctic Regions .... 8
North America . . . -44
Probably Tropical ... 9
Secondary, arising at sea . . 37
It will be seen from this that not one-half of the
1 8 8 Weather Charts and Storm Warnings.
storms which existed in 40 W. came from the United
States. Now of the 285 storms only 145, or,* in round
numbers, one-half, passed the meridian of 10 W., and
these were thus divided in percentages:
Source of Depression. .
Arctic Regions . . . .12
North America . . . 47
Probably Tropical ... 5
Secondary, formed at sea . . 33
Untraceable .... 3
We see therefore that of the storms which reach us,
not quite one-half could possibly have been predicted
by telegrams from America. The figures given above
show that the actual successes attained by prediction
were much less than this.
For the last few years the Meteorological Office, in
conjunction with the Bureau Central Meteorologique in
Paris, has been in regular receipt of telegrams for-
warded by the Chief Signal Office, Washington, and
conveying intelligence of storms met with by steamers
arriving at American ports. It was considered that if
a steamer encountered a storm to the westward of the
meridian of 45 W., she could reach an American port
before the storm could reach Europe. Accordingly,
timely intelligence from her log might be transmitted
by telegraph to Europe. It has not, however, been
found practicable as yet to issue warnings based solely
on these telegrams, but their receipt puts us on our
Suggestions for Improvement. 1 8 9
We learn therefore from all this, that we in the
United Kingdom have to rely on our resources and our
own stations, for gaining information for storm-warning
purposes, and so we must only do our best to improve
our own arrangements.
It is evident that, if we had an extensive continent
like North America to deal with, we too, in the Meteoro-
logical Office, could probably make good our claim to
a proportion of successes for our warnings, rivalling that
with which the Chief Signal Office is justly credited.
That this is not an idle boast is shown by the following
figures taken from the Report of the Meteorological
Office (the Norddeutsche Seewarte) at Hamburg for
1874. A system of warning for Hamburg from our
Office had then been in operation since 1867, and the
general results were, that 301 warning messages were
issued from London in the course of the seven years.
72 per cent, of these warnings were followed by gales,
while in only three cases did the storm outrun the mes-
sage. Naturally in these figures no account is taken of
the gales missed owing to the Sunday interruption of
our service which prevailed up to 1877.
The reason of this success in issuing to Hamburg
timely warning of all storms, a success which is far
more brilliant than we can ever show for our own
coasts, is that our network of stations, as will be seen
from the frontispiece, entirely surrounds the North Sea,
and that no storm can reach Hamburg without passing
over our outposts, unless it comes from the Continental
Weather Charts and Storm Warnings.
side, a very unusual direction for its advance. As a
proof of this statement I may say that in the year 1869
twenty-three storms were felt in Hamburg, and twenty-
two of these had previously passed over some part of
the United Kingdom.
Finally, we come to the subject of high-level stations,
such as that on Ben Nevis. A considerable number of
such stations has been organised. Among these we
may mention, in the United States, Pike's Peak and
Mount Washington ; in Portugal, Sierra da Estrella ;
in France, the Pic du Midi, Puy de Dome, and Mont
Ventoux ; in Switzerland, the Santis ; in Italy, Mont
Cimone arrd others ; in Austria, the Sonnblick and
Hoch Obir ; in Germany, the Brocken and Schnee-
koppe ; and there are several others.
The discussion of the results they yield has led to
most interesting conclusions in relation to the diurnal
march of temperature, barometrical pressure, and the
force of wind at different levels, and more especially as
to the changes in the dampness and the temperature of
the air produced by its passage over mountain chains.
The popular idea of the value of these stations
is, however, that they are mainly of importance as
weather-reporting points. On this head I recently
inquired in Europe and the United States, of the chiefs
of the meteorological services which possess such
stations, as to what practical benefit their forecasting
service derived from these reports.
The outcome is very scanty and quite incommen-
Suggestions for Improvement. 1 9 1
suratc with the cost and labour of maintaining the
stations, supposing tJicsc to be kept up solely for forecasting
The late General Hazen replied that no telegraphic
reports were received from Pike's Peak, but that the
information from Mount Washington was of consider-
able value in weather prediction for the adjacent New
From Europe the replies were less decided. Professor
Mascart said that the reports from the Pic du Midi were
often of value in giving early warning of floods in the
low country, owing to the melting of snow. He also
stated that the reports from that station and from the
Puy de Dome indicated shifts of wind before any signs
of their approach were noticeable at the lower level.
The other directors gave no positive reply. On one
point all authorities are in accord, that the barometrical
readings cannot well be used in forecasting. This
arises mainly from difficulties connected with the reduc-
tion of the readings to sea-level. It is very interesting
to learn that the barometrical oscillations at the summit
of Ben Nevis are particularly sudden and extensive,
but no indication has yet been given of the mode of
using such information in forecasting.
It must always be remembered that the preparation
of forecasts and storm warnings is necessarily a rapid
proceeding, and it must be carried out with intelligence,
often defective, especially in stormy weather, when
completeness of information is most desirable. The
192 Weather Charts and Storm Warnings.
calculations therewith connected must above all be of
a simple nature, and such as can be carried out by
assistants of ordinary education.
In conclusion, I can only say that the foregoing
pages contain what is, necessarily, a very condensed
and brief abstract of the present state of our knowledge
of weather, in so far as this knowledge depends on the
system of Weather Telegraphy, a branch of investiga-
tion which is confessedly of great intricacy.
To do the subject justice, double the space, and at
least treble the number of charts and illustrations, would
have been required. If, however, the contents of these
pages shall have awakened in any of my readers a real
conception of what the weather work of the Meteoro-
logical Office is, and an interest in the careful study of
weather, one of the most enticing of all inquiries not
to mention its practical importance to every one the
trouble of putting together these notes will have been
far more than repaid.
The Weekly Weather Report. 193
THE WEEKLY WEATHER REPORT.
IN addition to the Daily Weather Reports, which have
been the theme of the preceding pages, the Office has
for the last nine years issued weekly returns contain-
ing information intended to be used in agricultural
and sanitary investigations. The subjects on which
data are given in this publication are Temperature,
Rainfall, and the Duration of Sunshine.
In the year 1884 the character of this Report was
much improved, and its size was considerably enlarged,
and a specimen of the summary of results which now
appears weekly will be found on pp. 194, 195.
This table appears in a somewhat abridged form in
the London newspapers on Thursday mornings, and in
several agricultural papers at the end of the week.
The nature of the information as to Rainfall and
Sunshine is easily intelligible : it consists of statements
of the amount of each recorded for the week, and of the
quantity which has accumulated since the beginning of
the year. In each case the difference from the average
194 Weather Charts and Storm Warnings.
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S g a" a" a a"
5 5 z 2 z z
1 < < < <
r r j j j j
o o g g S g
rj t > 2 SS .~ Z
CA dx M m X H
SCOTLAND, WEST .
ENGLAND, N.W. .
ENGLAND, S.W. . .
IRELAND, NORTH .
CHANNEL ISLANDS .
C 11 N CO -4- 10
vo t- 00 0% |
1 96 Weather Charts and Storm Warnings.
The statistics as to Accumulated Temperature,
however, are not so easily intelligible, as at the head of
the column we find the entry 'day-degrees/ which
calls for some explanation.
At one of the Conferences in connection with the
Health Exhibition in 1884, I read a paper on Cumu-
lative Temperature, which is here reproduced, as giving
an explanation which it is hoped will be sufficient for
'As to the growth of crops, Sir J. B. Lawes, Bart,
F.R.S., and Dr. Gilbert, F.R.S., have for many years
conducted with scrupulous accuracy extensive investiga-
tions into this subject at the famous experimental farm
of Rothamsted. Let us therefore hear what they have
to say :
' " On this point we may remark that we have found
the really most luxuriant and heavy crops, both of hay
and of wheat, to have been very materially influenced
by the characters of the winter and early spring periods
quantity in both cases depending very greatly on the
early development of the plant. With favourable
conditions in this respect some of our very heaviest
crops, both of hay and wheat, have been obtained under
by no means specially favourable meteorological
conditions during the period of most active above-
ground growth. On the other hand, high proportion of
corn to straw, which sometimes gives really high yield
per acre, depends more upon the conditions of the
periods of active above-ground growth and maturation.
The Weekly Weather Report. 197
In the same way, great weight of hay sometimes
depends upon the conditions of maturation rather than
4 " It is obvious, therefore, that in discussing the
relations of meteorological condition and agricultural
production, it is essential to be able to arrange the
records for any selected periods of the year."
* And again :
( " It is obvious that different seasons will differ
almost infinitely at each succeeding period of their
advance, and that, with each variation, the character of
development of the plant will also vary, tending to
luxuriance, or to maturation, that is, to quantity, or to
quality, as the case may be. Hence, only a very
detailed consideration of climatic statistics taken to-
gether with careful periodic observations in the field,
can afford a really clear perception of the connection
between the ever-fluctuating characters of season and the
equally fluctuating characters of growth and produce.
It is, in fact, the distribution of the various elements
making up the season, their mutual adaptations, and
their adaptation to the stage of growth of the plant,
which throughout influence the tendency to produce
quantity or quality. It not (infrequently happens, too,
that some passing conditions, not indicated by a
summary of the meteorological register, may affect the
crop very strikingly, and thus the cause will be over-
looked, unless careful observations be also made and
the stage of progress, and tendencies of growth, of
198 Weather Charts and Storm Warnings.
the crop itself at the time, be likewise taken into
1 Again :
' " Those characters of season which are very un-
favourable for land in poor condition, may be favourable
to land in high condition, and vice versa"
1 As regards the three elements represented on the
diagrams, 1 it is evident that the curves for rainfall and
sunshine require but little explanation, as the successive
steps of the curves show the successive weekly totals of
rain or sunshine.
' The case as regards temperature is, however,
different, and those who examine the diagrams will see
that there are two curves, one ascending, the other
descending. A certain arbitrary base line is assumed,
and the values are measured above or below that line.
' It is proved, almost beyond a doubt, that each plant,
say each individual cereal, requires a definite amount
of heat to bring it to maturity. Thus, maize requires
more than wheat, and wheat again more than barley or
1 We all know that maize is not an English crop at
all, and that wheat is not grown to much profit in
Ireland or the west of Scotland, being replaced by oats
or barley. The ordinary reason assigned for these
differences as to crops is that in each case the
temperature is not high enough for the particular crcp
1 Diagrams were exhibited in the Meteorological Annexe. These are
not reproduced here.
The U'cckly Weather Report. 199
which has failed. If the inquirer pursues the subject
further he generally finds out that his informant has no
very precise idea as to how the temperature acts.
' Now various investigators, and notably Boussingault
and Professor Alphonse de Candolle, of Geneva, have
devoted much attention to this subject, and the latter
writer, in his " Geographic Botanique," has come to the
conclusion that a certain total amount of temperature
above a definite base line is necessary for plant growth,
and that this amount, or, as he calls it, this " sum of
temperature," varies for each crop.
' He finds that plants, as a rule, do not begin to give
indications of active vegetation until the temperature
rose above 6 Cent. This temperature, 6 Cent., or in
round numbers, 42 Fahr., that is ten degrees above
the freezing-point, is taken as the base for all the
' Although Professor de Candolle propounded his
views some years ago, yet as recently as the year 1874,
at the Agricultural Conference at Vienna, meteorolo-
gists were quite at sea as to how these sums of tem-
perature were to be calculated.
' The credit of solving this problem belongs to
Lieut.-General Richard Strachey, the Chairman of the
Meteorological Council. He proposes to adopt a
certain unit of temperature to supply a standard for
calculation, the unit being one degree continued for
the unit of time, either one hour or one day, as the
case may be. Such a unit may be conveniently called
2oo Weather Charts and Storm Warnings.
an hour-degree, or a day-degree. The unit of time
adopted for the calculations to which I am about to
refer is a day, and the unit of what may be termed the
effective temperature is therefore a day-degree. A day-
degree therefore signifies one degree Fahr. of excess or
defect of temperature above or below 42 Fahr., con-
tinued for twenty-four hours, or any other number of
degrees for an inversely proportional number of hours.
' Now, the first idea I want you to take in about these
day-degrees is that, when we speak generally of the
mean or average temperature for a day, or month, or
year, we imply that the resulting temperature is the
same as would be observed if the thermometer indicated
this mean temperature throughout the entire period for
which the mean is taken. Thus, if we were dealing
with daily means, an average daily temperature of 62
Fahr., which is an ordinary temperature for a warm
summer's day, would indicate twenty day-degrees of
temperature for that day, starting from the assumed
base line of 42 Fahr., which has already been
'The first step therefore towards determining this
effective temperature in day-degrees resolves itself into
determining as speedily and simply as possible the
average temperature for the period under consideration.
'We have, fortunately, to our hands, a very simple
mode of arriving at the mean temperature with accuracy
sufficient for our purposes. Almost all observers record
the maximum and minimum temperatures once in the
The Weekly Weather Report. 201
twenty-four hours. It is found that the half sum of
these readings, the mean between them, is nearly, but
not exactly, the average for the day. It must, of
course, be understood that the instruments must be
read regularly and at the same hour every day.
* The next points which require attention are :
whether the maximum and minimum are both above
42, which occurs in summer, or both below that point,
which occurs in winter ; or, finally, whether one is
above, and the other below.
1 In the first case all the accumulated temperature is
to the good ; it is all on the positive side. In the
second case it is all on the negative side. The third
case is the only one which presents difficulty, for when
the extreme temperatures are on either side of the line
of 42, one portion of the effective temperature for the
day is positive and the other negative.
1 Now, General Strachey carried out a long series of
calculations, based on the observed hourly temperatures
at Kew Observatory, and at other stations in the
United Kingdom, in order to ascertain the magnitude of
the co-efficient by which the difference between either
of these extreme temperatures and the base temperature
(42 Fahr.) should be multiplied in order to obtain the
values of the temperatures in excess or defect of 42
Fahr. expressed in day-degrees, and he found that this,
for a weekly period, was o.4.
' Accordingly we get the following rules :
' If the mean of the day is above 42 Fahr., we
202 Weather Charts and Storm Warnings.
multiply the difference between the minimum and 42
by o.4 (four- tenths), and call this the negative effective
' To find the positive effective temperature we subtract
from the difference between the mean for the day
and 42, the negative effective temperature just deter-
' If the mean of the day is below 42 Fahr. the
proceeding is similar ; but we first ascertain the positive
effective temperature, and subtract that from the differ-
ence between 42 Fahr. and the mean, thus obtaining
the negative effective temperature.
4 The method of determining the effective tempera-
ture, which may briefly be called the accumulated
temperature, is fully explained in a paper by General
Strachey, which was published in the volume of the
Quarterly Weather Report for 1878.
' The practical application of the data thus obtained
as standards of comparison for the growth and ripening
of various agricultural products must, of course, be left
to the agriculturists, and it will be interesting to learn
how far a correspondence between the character of the
several crops and the accumulated temperature of the
year can be established.
* The measure of temperature afforded by this system
of computation appears to be as well suited to supply
a standard of comparison of climates for hygienic
purposes as for agriculture, and the diagrams indicate
in a forcible manner the characteristic differences of
T/LC Weekly Weather Report* 203
climate, in respect of temperature, of the portions of our
islands to which they refer.'
Mia land Cauntiej
Diagram showing the curves of Accumulated Temperature, above and
below 42, for the period 1878-1885, in various districts.
204 Weather Charts and Storm Warnings.
By way of illustration of the foregoing, the curves of
accumulated temperature for four of the districts have
been reproduced in fig. 59 (p. 203). The districts selected
have been I. The Channel Islands ; II. Ireland South ;
III. The Midland Counties ; and IV. Scotland North.
The period is the interval of eight years, 1878-85. It
will be seen that the total amount of accumulated heat
above 42 Fahr. is highest, 3547, in the Channel
Islands ; Ireland South comes next, with 3064 ; then
follow the Midland Counties, with 2931 ; and last of all
comes Scotland North, with 1890, only one-half the
amount which falls to the share of the Channel Islands.
If we now look at the lower part of the diagram,
Showing the amount of accumulated heat below 42
Fahr., it will be seen what advantages the Channel
Islands and Ireland South derive, mainly from their
exposure to the sea and its warm currents. On the
other hand, the Midland Counties and Scotland North
run closely together in the amount of what may be
called negative accumulated heat, the inland position of
the former having the same effect on its winter climate
as the higher latitude of the Scotch Highlands.
All of these curves cf accumulated temperature
below 42 run parallel to the base during the summer,
inasmuch as at that season the temperature does not
fall below 42 ; but while in the Channel Islands the
point at which this condition is reached is 93, it is
239 in Ireland South, 504 in the Midland Counties,
and 510 in Scotland North.
The Weekly Weather Report.
It will also be noticed how very closely the curve for
Ireland South follows that for the Channel Islands at
the beginning of the year, while during the autumn
it practically coincides with that for the Midland
As regards the use which may be made of these
data, a paper on the Connection between the Accu-
mulated Temperature and Agricultural Production was
read by Professor J. H. Gilbert, F.R.S., before the
Societe Helvetique des Sciences Naturelles, and pub-
lished in the ' Bibliotheque Universelle/ vol. xvi. ($rd
Period), and of this some extracts may be interesting.
Dr. Gilbert gives the following table :
AGGREGATE EXCESS OF DAILY MEAN TEMPERATURE above 42 F. from
Fixed Dates, or from Commencement of Active Above-ground Growth ,
to Date of Harvest at Rothamsted.
From date of
From Date of
after a Break.
Dr. Gilbert says : * The results show that for wheat,
from the Meteorological Office figures, the total number
of aggregate degrees of heat is, for the last two columns.
1900 and 1836 respectively.
206 Weather Charts and Storm Warnings.
' Hervc Mangon's results, for north-west France,
give 1854, which is not far from the Rothamsted
' Risler's figures, for Nyon in Switzerland, correspond
' Boussingault and Herve Mangon have both investi-
gated the question for barley, and their results give
respectively, for spring-sown barley 2005 an ^ 1989,
nearly approaching the Rothamsted values for wheat.
' Boussingault's results for maize correspond to
35 1 5.'
The foregoing extract is sufficient to show one
direction in which the figures representing accumulated
temperature may be turned to account, but the number
of years for which this information is available is as yet
too small to allow of many important deductions being
drawn from them.
On Cirrus Cloud Observations. 207
ON CIRRUS CLOUD OBSERVATIONS.
THE following Instructions, devised by the Rev. W.
Clement Ley, were adopted by the Meteorological
Council in 1885, and have been issued to such of the
observers connected with the Office as are willing to
undertake the reporting of cirrus movements :
The attention of the observer is especially directed
to clouds of the 'cirrus' type, including what are heie
defined as true cirrus, sheet-cirrus, high cirro-cumulus,
and cirrus-haze. They are the highest kinds of cloud,
and it is to these types only that the following Instruc-
True Cirrus. When in moderate quantities it is
commonly white, though when seen through haze it is
usually somewhat cream-coloured, and when the sun's
rays have reached it through a long stratum of hazy
atmosphere, is often of either an orange or rosy tint.
In all cases it has a very delicate appearance. It is
sometimes arranged like bunches of fine hair ; and such
tufts of cirrus are often called ' mare's tails.' At other
times it resembles small curled feathers. Quite as
208 Weather Charts and Storm Warnings.
commonly, however, it lies in thin light strands, like
pale gossamer threads.
Sheet- Cirrus. When cirrus overspreads as a con-
tinuous sheet a large portion of the sky it becomes
what is here termed 'sheet-cirrus! In this state,
when not too thick, it produces 'halos' or large rings
round the sun and moon. The sheet-cirrus sometimes
appears fibrous, sometimes reticulated. When the veil
of this cloud becomes thick it assumes some neutral or
muddy tint, except in those cases when it is so disposed
that the rays of the rising or setting sun are reflected to
us from its under surface, which then appears of either
an orange or rosy colour.
1 High cirro-cumulus' differs from simple cirrus in
consisting of small detached masses somewhat rounded
in form, a great flotilla of which is often seen in the sky,
especially in fine summer weather. Clouds at lower levels
are frequently disposed in the same manner, but the
observer must be very careful to distinguish between
these and the high cirro-cumulus, which latter is either
white, or changes its colour under the same circumstances
as true cirrus, no part of any of the cloudlets ever seeming
to be decidedly throivn into shadoiv by another part.
The higJi cirro-cumulus also possesses the same faintness
and delicacy of outline which we observe in cirrus.
Cirrus-Haze. Sometimes cirrus is only visible as
either a milky or an oily-looking haze, which is here
termed ' cirrus-Jiaze?
On Cirrus Cloud Observations. 209
Amount. Whenever on looking round the sky the
observer notices clouds of the kinds above described, he
should in the first place endeavour to ascertain their
amount. In doing this he should observe whether they
cover, (i) only a trifling portion ; (2) about a quarter ;
(3) about a half; (4) about three-quarters; or finally,
the whole of the sky. The extent, not the density, of
the cloud is here referred to. If there be any consider-
able quantity of lower cloud in the sky, so that the
amount of upper cloud cannot be accurately ascertained,
it should be invariably entered as doubtful, by a ' ? '
Direction of Movement. The next thing to be
attended to is the direction from which the upper
clouds move. Considerable difficulty will here be en-
countered. If some of the clouds happen to be nearly
overhead, attention should at first be confined to such ;
and if possible the observer should so place himself as
to have the projecting corner of a roof or chimney,
the summit of a steeple, flagstaff, or other stationary
object, very close to the line between his eye and the
portion of cloud which he is about to watch.
A convenient plan is to set up a pole reaching 5 feet
7J inches above the level of the observer's eye ; a
mark or ring should be placed round the pole at the
2 1 o Weather Charts and Storm Warnings.
latter level. The summit of the pole must carry two
thin rods, fixed crosswise, and set truly to the four
cardinal points. Through or near the extremities
of these rods should pass a thin circular iron ring of
3 feet diameter, the use of which will be mentioned
presently. The observer should, when opportunity
offers, so station himself that some recognisable part of
a cloud appears to move vertically either upwards from
the top of the pole, or vertically downwards towards it.
The direction of the pole from the observer's position,
which may be judged of by the cross rods, is then, in
the first case, the direction of the upper current ; in the
second, its opposite. In watching the movements of
the clouds, the observer may conveniently use a staff,
one end of which is sharpened so as to stick in the
ground, while the other is fitted with a crescent-shaped
top in which to rest the arm, in order to support and
steady the head. If the clouds be observed from a
window it is some assistance to have a few wires some
horizontal, others vertical fastened across the window
to the wall on the outside.
When, however, no part of the cloud is moving
directly either towards or away from the observer, the
effects of the perspective render it difficult to estimate
the direction of movement exactly. To perfect oneself
in the art, it is advisable as often as possible to
endeavour to estimate the direction of movement of
some portion of the cloud which is inconveniently
placed, and then to find the actual direction of
On Cirrus Cloud Observations. 2 1 1
movement of another portion of the same cloud, or
same sort of cloud, which happens at the time to be
conveniently placed. By patiently practising the eye
in this process the observer eventually learns to make,
automatically, tolerably exact allowance for the errors
arising from perspective. In no case (should he have
the least doubt as to the direction of movement) must
any conjecture be telegraphed, but the figure for
' motion doubtful ' should be inserted in the telegram.
It is always well, when observing the movements of
the upper clouds, either to rest the head against a wall
or tree, or to support it on a staff, or by some other
means, so as to be quite motionless while taking an
Apparent Velocity. The next particular to be
attended to is the apparent velocity of motion in the
clouds i.e., the force of the current which carries them.
The observer is requested to notice whether the cloud
be actually motionless, or whether its motion is very
slight, moderate, rapid, or very rapid. Clouds of the
cirrus type are seldom really motionless, but owing to
their great distance they commonly, though not always,
appear to move more slowly than the lower clouds. To
estimate, even according to the very rough scale pro-
posed, the apparent velocity of movements, we have to
encounter precisely the same difficulties which have
presented themselves in finding the direction, and the
2 1 2 Weather Charts and Storm Warnings.
training of the eye requisite for deciding this is identical.
A cloud which is near the horizon of course presents
much less movement to the eye than one which is near
the zenith, because it is at a much greater distance ; and
further, the apparent movement of clouds which are
travelling either across, or more or less obliquely to,
the line of sight, is different from that of clouds which
are travelling directly to or from the zenith. To test
the accuracy of his estimate of the apparent velocity of
clouds moving crossways and obliquely, the observer
should, when occasion offers, compare it with his
estimation of the apparent velocity of clouds in the
same stratum passing overhead at the time. To test
the accuracy of his latter estimation he will do well
occasionally to notice how many seconds of time a
recognisable portion of upper cloud takes in travelling
15 on the sky, to or from the zenith. The pole
arrangement already described can be employed for
this purpose. In the last case a recognisable portion of
cloud must be first caught in the zenith, the observer
looking up the pole, applying his eye as closely as he
can to the ring or mark above mentioned. He should
then note the time, and again at the moment when the
selected portion of cloud, as viewed from this spot,
reaches the circular wire. The time taken by the cloud
in passing over this distance from the zenith, which
is (approximately) 15, should be then noted. When
clouds of the cirrus type take a longer time than
600 seconds (or ten minutes) in traversing 15 to
On Cirrus Cloud Observations. 2 1 3
or from the zenith, their motion should be regarded as
' very slight/ When a less time than this, but a longer
time than 300 seconds, or five minutes, as 'moderate ;'
when less than 300 seconds but more than 60, as
' rapid ; ' and lastly, whenever they take a less time
than 60 seconds, as ' very rapid.'
It may be mentioned that in simply looking at the
sky without the aid of any appliance, inexperienced
observers commonly estimate the position of the zenith
wrongly because they do not throw the head far enough
' R.-point? Clouds of the cirrus kind very com-
monly lie in streaks, lines, or bands. Attention must
next be given to the direction of these lines i.e., their
position with respect to the points of the compass
altogether irrespective of the motion of the clouds. When
one of these bands happens to pass through the
zenith, the point at which it reaches, or, if continued,
would reach, the horizon, is to be noted. This point
is called, for convenience' sake, the R.-point, or ' point
of radiation,' because the cirrus bands, while really
parallel, appear in perspective to radiate from this
point, or rather from one beyond it, and beneath the
horizon. It is, however, comparatively seldom that a
cirrus band happens to lie immediately over the
observer's head : the bands usually appearing in per-
spective as arches, or portions of arches, lying in any
2 1 4 Weather Charts and Storm Warnings.
part of the sky, and variously inclined to the horizon,
according to their distance from the observer. It is
easy in these cases to find the R.-point, if we imagine
ourselves able to travel over the earth's surface so as to
get immediately under one of these bands. The best
plan, however, is to note, first, the point on the horizon
which lies beneath the summit of any visible complete
arch of cirrus. If there be no complete arch, but only
a short thread visible, the observer should extend his
arm so as to point with the forefinger towards this
thread, and then pass the arm briskly two or three
times backwards and forwards from one part of the
horizon to another, continuing as closely as he can the
curve of the cirrus thread. The point on the horizon
which is immediately beneath the highest part of the
curve so formed should then be noted, and in every
case the R.-point will be a point at right angles to this
point on the horizon.
It is obvious that there must always be two R.-points
opposite to each other. Although it is in itself im-
material upon which of these the observer fixes, he is
requested as a matter of convenience, when he has
already found a point from which the upper clouds move,
to report the R.-point which is nearest to that direction,
if one of the two be nearer than the other. For
example, if cirrus travels from WNW. and lies in strands
which are disposed lengthwise NW. and SE., the
R.-point NW. should be reported in preference to the
On Cirrus Cloud Observations. 2 1 5
The * selvedge ' or margin of a sheet of cirrus
usually gives the R.-point in the same way as a streak
of detached cirrus. And when sheet-cirrus or cirrus-
haze completely covers the sky, a warp may frequently
be seen in it which supplies the same datum.
Cross rays or tangled threads may very often be
noticed, frequently transverse or nearly so to the cirrus
bands. These are especially discernible in some
varieties of sheet-cirrus, when they form what we may
call the 'woof of the cloud sheet, and give to the
latter the reticulated appearance already mentioned.
No notice of these threads is required in the telegrams.
In rather common cases, however, the cross threads are
so marked that it is impossible to decide whether a
particular point of the compass, or one at about right
angles to it, is rightly to be regarded as the R.-point.
Lastly, whenever a bank of cloud of this type appears
on any horizon, or whenever being overhead, or nearly
so, such a bank appears thicker in one part of the sky
than in the other parts, the observer is to report the
position of bank (z>., the direction in which the bank
lies or in which it is thickest) and its density. The
direction will not necessarily be at right angles to the
R.-point, though it most commonly is so.
As to results from these observations, our experience
of them is too short to enable us to say much, but the
2 1 6 Weather Charts and Storm Warnings.
following is a brief summary of the most obvious appli-
cations of cirrus observations in weather prediction :
During bright weather and Westerly (NW. to SW.)
airs or light winds, the appearance of very high clouds
of the mare's-tail type, moving from the North-west-
ward, is usually an indication of a backing of the wind
to the Southward, and its increase in force, probably to
a fresh or strong gale. This movement of the very
high clouds under such conditions is especially dan-
gerous, if at the same time a batch of such clouds be
rising in the west, and the barometer, after rising, is
inclined to fall again.
Again, when the wind is Westerly or North-westerly
of moderate strength, if high hair-like or thready clouds
appear moving from N. or NNE., they very commonly
portend a great increase of wind from the North-
westward, with snow, sleet, or soft hail in winter.
Again, if the wind be Easterly, and high clouds
appear, similar to those just mentioned, but moving
steadily from SSW., they point to an increase in the
force of the Easterly wind ; and during sultry summer
weather, to the early approach of thunderstorms,
followed probably by a shift of wind to the South-
In all these cases, however, the direction of the wind
at the surface must be carefully noted ; and it may be
added that the value of the sign is increased when it
occurs after a spell of exceptional bright weather and
a sudden rise of the barometer.
6 oj o
sanojj tz ISTJJ m ipyure^;
moo * oo *
" o o o o 'dodo
>i oj o 'jpnoQ jo lunouiy *********
(31 01 0)
(zi 01 o)
1 ^- 1 ^- "^OO v> m t^ VOOO CO O CO
t^ t> O
W W W
W W '->
VO TJ-00 r<1 H-I M M TJ-M r^- r~ I-N. l^ O rj-v3 ON OJ
r i i i r r i i i i i i i r i i i i
-" >-" O OOOOOn-.
For explanation of the columns see p. 220.
Appendices. 2 1 9
i-Ht>r^i-ir< 1 5r^N vO ^ O rovO O
oo l ~ l Q *> O\vO t^.# rOTt-N^J-i-ifcdfcfcc}
d d dd"~ddpd'-<dc)6'- : 06666 6 6 6 d_P __ 6
O ""> t^oo OOO* OOt^OO*** O* O
O M VO N vO \O
MVO w O
** "-" 1OO fOiOt^^-^JvO x^)00 10
odcxjooooooooooo \o 06
NOVEMBER 28, 2 P.M., REPORTS AND REMARKS.
The barometer continues to fall, excepting at Rochefort, most on our
SW. coasts, and the wind at Valencia has backed to E. The sea is
increasing at the mouth of the Channel, and rain falls along our western
coasts. Warnings issued to our W. and N. coasts.
EXPLANATION OF COLUMNS.
BAROMETER. The letters r (rising), f (falling), and s (steady), indicate
the motion of the mercury in last 14 hours. EXTREME WIND is the
strongest wind experienced in past 24 hours. WEATHER : see p. 10.
* An Asterisk is inserted in all places for which information is not
usually received. The ' extreme ' wind for the Swedish, Norwegian, and
Danish stations is an observation taken at 8 P.M.
For Sunday \ November 29, 1874, at 8 a.m.
During the past twenty-four hours a serious fall of the barometer has
taken place over the United Kingdom, amounting to more than an inch at
Nottingham ; and the centre of a very deep and well-defined depression
has advanced to Wales and the western central parts of England. From
Corunna to Pembroke there is a gradient of 0.13 inch per 50 miles for
W. winds ; while from Skudesnaes to Holyhead there is one of o.io inch
for SE. winds.
Temperature has risen very considerably at all but the most western
stations. Over central England the change amounts to 14 in the twenty-
Strong SE. gales have set in on our NE. coast, while very strong W. to
NW. gales are felt in the SW. and Bay of Biscay, and S. winds in the SE.
of England. The sea runs very high, especially in the N. and NE.
Very heavy rain has fallen over the whole of the United Kingdom,
accompanied by hail and snow in some places ; the fall continues at most
stations. The weather is extremely unsettled.
NOTE. The chart which faces this page is reduced from the Daily
Weather Chart, but is printed in the form in use in 1887, not in that which
actually appeared in 1874.
Weather Charts & Storm Warnings.
BAROMETER. WIND X SEA
( Explanation of Map )
ecu*, truth if an. i/..*
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ivuui <"<^ tlw barkf and* tnvBitrs rtftr tft t'vt'tx.
. - fonm, abort TO. > -fijrcM 8 to ,
.-fonM. * to 7, fvw > to 4,
MEAN HEIGHT ^ ^. BAROMETER
at ^$rjs'fi *&o.
_^T-.* T|OM *-
TEMPERATURE, K. WEATHER at 8 A.M..
PAST 2fi- WOUflS.
A dotted, luu ttpantUf te dietnct* in. wftiA rauv
kxu falim rtwn riw Arr <Ar hat been, nan*
FatU of Sin* or mart, arr </u,</ ii^figurrs.
MEANS OF TEMPERATURE IH SHADE.
, of July.
upcraftira mjaw < ftr *
arc nuvd^ <hor Ibr ttu- tC vt
WEATHER CHARTS, Nov.29.1874-.8AJ4.
Reduced from the Daily Weather Report.
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1co O tXi C^ O *O PO POvO * OO t^ vo ro O ^O O ^ O ^"
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A BBE, Cleveland, on results of
New York Herald warnings,
Aberdeen Observatory, curves for
October 21, 1874, 73 ; readings
for same period, 222.
Accumulated temperature, calcula-
tion of, 196 ; curves of, for
United Kingdom, 203.
America, value of telegraphic re-
ports from, 184 ; present service
of telegrams from, 188.
Anticyclones defined, 36, 40 ; illus-
tration of, 40 ; characteristics of,
57 ; typical, 59 ; motion of, 93.
Ascending motion, effect of, on air,
Atlantic Ocean, advance of storms
over, 15, 117, 183; cost of tele-
graphy across the, 183.
Atlantic weather, Hoffmeyer on,
Aurora as sign of storm, 1 1 7.
Azores, possible value of telegraphic
reports from, 181.
1 g ACKING ' of wind explained,
31 ; reasons of, 78 ; why
considered dangerous, 78, 148.
Balaclava storm, experience of, 138.
Ball, John, suggestion of storm
warnings, 138, 139.
Barometer, corrections of, 2 ; for
capillarity, 2 ; for capacity, 2 ;
reduction of, to 32 F., 3 ; to
sea-level, 3 ; a single reading of,
at any time, no indication of wind
or weather, 27 ; scales, wording
on, misleading, 49 ; rise and fall
of, not infallible sign of weather,
53 ; instances of serious fall of
with calm weather, 54.
Beaufort, Sir F., scale for wind, 8 ;
notation of weather, 10.
Belt, Thomas, theory of origin of
| Bennett, J. G., Neiv York Herald
i Ben Nevis, difficulty of using re-
ports from, 191.
Boussingault, M., on accumulated
temperature, 199, 206.
Brisk, II. M.S., as signal-ship,
Buys Ballot, Prof., law of motion of
wind, 26, 44.
CARLISLE, Bishop of, on failure
of forecasts, 171.
Charts, weather, explained, 37.
Circulation of wind with cyclones,
39 ; with anticyclones, 42.
Cirrus -cloud observations, instruc-
tions for, 207 ; some results from,
Cirrus-clouds, value of, as signs of
change of weather, 1 14.
Clearness of atmosphere as sign of
Clouds, deficiency of information
respecting, in the Daily Weather
Reports, 13 ; accompanying a cy-
clonic storm, 64.
Co-existing depressions, 84.
Collins, J. J., New York Herald
Crops, dependence of, on tempera-
Currents, equatorial and polar, 24.
Curves from self-recording instru-
ments at times of storm, 68,
Cyclone, typical, diagram of clouds
and weather in, 65.
Cyclones defined, 36, 58 ; illustra-
tions of, 37, 58 ; typical, 62 ;
passage of, on the northern side
of a station, 68, 72 ; passage of,
on the southern side of a station,
75 ; advance of, 65 et seq. ;
probable rate of, unknown, 89 ;
affected by surface of ground,
95 ; probable direction of, known
to some extent, 95 ; affected by
conditions of pressure, 96.
T~\E CANDOLLE on accumu-
lated temperature, 199.
Depressions defined, 36 ; very ex-
tensive, instance of, 54; secondary,
80 ; co-existing, 84. See Cyclones.
Descending motion, effect of, on
air, 57, 164.
Districts of British Isles, arrange-
ment of, 163.
Draper, Prof. D., on storms crossing
the Atlantic, 184.
EQUINOCTIAL gales, supposed
recurrence of, disproved, Scott,
129 ; Prince, 134 ; in North
Germany, 136 ; in Adriatic,
Evans, Lewis, first published state-
ment of motion of storms, 87.
P ALMOUTH Observatory, curves
for February 2, 1873, 75 ; read-
ings for same period, 223.
Faroe Islands, importance of infor-
mation from, 182.
Faye, M., theory of origin of storms,
FitzRoy, Admiral, institution of
storm warnings, 140 ; storm-sig-
nal system, 119.
Fogs with anticyclones, 61.
Forecast?, FitzRoy, 162 ; Signal
Office, Washington, 162 ; resump-
tion of, in England, 162 ; prepa-
ration of, 165 ; hay harvest, 165 ;
failure of, Oct. 24, 1882, 171 ;
criticisms of, 174.
Forecasting, difficulty of, 163 ; re-
sults of, 1 68; Ryves, 168;
Franklin, Benjamin, first recognition
of motion of storms, 87.
Q.ALE of Oct. 24, 1882, 172.
Gales, equinoctial, their recur-
rence disproved, 129.
Germany, results of warnings from
London to, 189.
Gilbert, Dr. J. H., on accumulated
temperature, 196, 205
Gradients explained, 45, 53; in-
stances of, 47, 52; for certain
winds, 53 ; relation of, to winds,
Gyration of wind, law of, stated,
30 ; explained, 77.
T-TAMBURG, warnings from
London to, 189.
Harries, H., on storm of Oct. 24,
Heart's Content, telegraphic reports
from, value of, 183.
Iloffmeyer, on Atlantic weather,
Hoffmeyer's charts, 96.
Humidity, importance of, as indi-
cation of weather, 6 ; changes of,
during progress of storms, 70, 73,
Humidity of air, action of ascend-
ing and descending motion on,
Hurricanes, 44, 88.
ICELAND, cost of proposed tele-
grams from, 183.
Isobars defined, 33 ; mode of draw-
T7"OEPPEX, Dr., on sun-spots
and temperature, 123; on
periodicity of weather, 124.
JAW, Buys Ballot's, 26, 44 ; of
Gyration, 30, 77 ; of Storms,
Lawes, Sir J. B., on accumulated
Leverrier, M., first proposal of
storm warnings in Europe, 138 ;
ideas as to object of storm warn-
ings, I39 ! 46.
Ley, Rev. W. Clement, theory of
motion of storms, 118; diagram
of typical cyclone, 65 ; cirrus-
cloud observations, 207.
Loomis, Prof., on storms crossing
the Atlantic, 184.
A/TELDRUM, C, theory of origin
of storms, 119; periodicity
of rainfall, 120.
Mistiness of atmosphere a sign of
Mohn, Prof., theory of origin of
storms, 1 1 8.
Motion of cyclones in different di-
rections, effects of, 78 ; probable
rate of, comparatively unknown,
89; in relation to mountains, 95;
in relation to distribution of pres-
sure, 95 et scq. ; erratic, instance
Mountains, effects of, on motion of
cyclones, 95 ; effects of, on winds,
179 ; effects of, on weather, 164.
Mountain stations, 190; value of,
Gen. Hazen, 191 ; Prof. Mas-
Miiller, Dr. R., on equinoctial gale?,
phic reports from, value of, 183.
New York Herald warnings, 185 ;
results of, 186.
pEEK, C. E., on results of fore-
Periodicity of weather, 124 ; of
Pressure, relation of, to wind, 47 ;
to motion of cyclones, 99.
Prince, C. L., on equinoctial gales,
"D AIN, not properly indicated by
telegraphic weather reports,
7 ; with cyclones, 67 ; with
easterly winds, 77; produced by
ascending currents of air, 57, 164.
Rainfall, periodicity of, 120.
Rate of motion of storm', 89.
Redfield, discoverer of the Law of
Reid, Law of Storms, 137.
Reports, telegraphic, defects of, 12.
Results of Storm Warnings for the I
British Isles, 152; of Forecast?, I
Reye, Prof., theory of origin of I
Ryves, Rev. G. T., on results of j
CT. KILDA, value of, as a pos-
sible reporting station, 182.
Sea disturbance, scale for, n ;
value of, as indication of weather,
Sea-level, reduction of barometrical
readings to, 3.
Secondary depressions, instances of,
80 ; effects of, on their primaries,
Shower, with shift of wind to north-
west, 65, 72.
Signal-ships, proposal of, 15, 181 ;
proved to be possible, 181.
Signals, storm, explanation of, 142.
Signs of storm, 146.
Storms, definition of, 8; with high
barometer, 27 ; vertical depth of,
slight, 29 ; advance of, 87 ; rate
of advance of, unknown, 89 ;
probable direction of advance of,
95 et see/.; advance of, over the
Atlantic, 15, 118, 184; distri-
bution of, in the British Isles,
Storm warnings, institution of, 138;
difficulty of issuing correct, 148;
results of, 152; suggestion of,
Ball, 138 ; Leverrier, 138.
Strachey, Gen. R., on calculation
of accumulated temperature, 199.
Straight-line gales, explanation of,
Summary of principles recognised
in weather study, no.
Sunday interruption to weather re-
Sunk light - ship connected with
Sun-spots, relation of, to rainfall,
121-5; an d temperature in
England, 123; over the globe,
TEMPERATURE, correction of
barometer for, 3 ; information
respecting, given in Daily Weather
Reports, 5; mean, definition of, 5;
mode of ascertaining, 5 ;
instances of sudden falls of, 65,
76 ; regular daily course of, dis-
turbed by storms, 70, 73 ; differ-
ences of, as sign of storm, 149 ;
accumulated, calculation of,
196 ; effect of, on crops, 196.
Thermometer, attached, 2 ; wet and
dry bulb, 6.
Tornado in Sweden, 29.
Trade winds, 24.
Typhoons, 44, 88.
"yALENCIA Observatory, curves
for March 27, 1874, 69 ; read-
ings for same period, 221.
Veering of wind explained, 31 ;
reasons of, 78.
storm, first pro-
posal of, in America, 136;
first proposal of, in Europe, 138 ;
first proposal of, in England, 139;
results of, for Hamburg, 189 ;
results of, for the United King-
dom, 152; instances of failure of,
Washington, Chief Signal Office,
14, 179, 188.
Weather, Beaufort notation for, 10 ;
value of reports of general ap-
pearstnce of, 12 ; charts, explana-
tion of, 33 ; with anticyclones,
5$i 59 J with cyclones, 58, 62 ;
charts, mode of using, 113 ; local
characteristics of, 115; periodi-
city of, Koppen, 124.
Weather Reports in 1887, specimen
of, 18; in 1874, specimen of,
Weekly Weather Report, institution
of the, 193.
Wind, Beaufort scale for, 7 ; cannot
well be measured instrumentally
at telegraph stations, 8 ; measure-
ment of, by velocity instead of
pressure, 9 ; characteristics of
main currents of, 23 ; currents,
polar and equatorial, 24 ; Trade,
25 ; Buys Ballot's law for, 26 ;
motion of, in cyclones, 40 ; mo-
tion of, in anticyclones, 42 ;
cause of, 45 ; relation of, to gra-
dients, 52 ; reports of, from tele-
graphic stations sometimes de-
Wording on barometer scales, mis-
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