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Full text of "Meteorology; or, Weather explained"

SERIES 




WEflTHER EXPLflHED 




,PH:D: 




of the 

of Toronto 



Mrs C. Dorothy Burns 







TvftHELL 5c CO, 



s 



HILLING 

CIENTIFIC 

ERIES 



METEOROLOGY; 

OR, 

WEATHEK EXPLAINED. 



BY 
V" > 

.1? G. M'PHERSON, Ph.D., F.RS.E., 

w 

GRADUATE WITH FIRST-CLASS HONOURS, AND FOR NINE YEARS 
EXTENSION LECTURER ON METEOROLOGY AND MATHEMATICAL 

EXAMINER IN THE UNIVERSITY OP ST. ANDREWS ; 
AUTHOR OF "TALES OF SCIENCE," ETC. 






LONDON : T. C. & E. C. JACK, 

34 HENRIETTA STREET, W.C. 

AND EDINBURGH. 

1905. 



THE 
SHILLING SCIENTIFIC SERIES 

The following Voln. are now ready or in the Press : 

BALLOONS, AIRSHIPS, AND FLYING MACHINES. 
By GERTRUDE BACON. 

MOTORS AND MOTORING. By Professor HARRY 
SPOONER. 

RADIUM. By Dr. HAMPSON. 

TELEGRAPHY WITH AND WITHOUT WIRES. By 
W. J. WHITE. 

ELECTRIC LIGHTING. By S. F. WALKER, R.N., 
M.I.E.E. 

LOCAL GOVERNMENT. By PERCY ASHLEY, M.A. 



Others in Preparation 



6043S9 

^2.3.^5- 



Printed by P.ALLANTYNK, HANSON <5r Co. 
At the Ballantyne Press 



CONTENTS 



CHAP. PAGE 

I. INTRODUCTION . . . . . . 9 

II. THE FORMATION OF DEW 13 

III. TRUE AND FALSE DEW 17 

IV. HOAR-FROST 20 

V. FOG . 23 

VI. THE NUMBERING OP THE DUST ... 26 

VII. DUST AND ATMOSPHERIC PHENOMENA . . 29 

VIII. A FOG-COUNTER 31 

IX. FORMATION OP CLOUDS 34 

X. DECAY OP CLOUDS 37 

XI. IT ALWAYS KAINS 40 

XII. HAZE 43 

XIII. HAZING EFFECTS OP ATMOSPHERIC DUST. . 47 

XIV. THUNDER CLEARS THE AIR .... 49 
XV. DISEASE GERMS IN THE AIR .... 53 

XVI. A CHANGE OP AIR . . . . . .55 

XVII. THE OLD MOON IN THE NEW MOON'S ARMS . 58 

XVIII. AN AUTUMN AFTERGLOW 62 

XIX. A WINTER FOREGLOW 65 

XX. THE RAINBOW 68 

XXI. THE AURORA BOREALIS . . . . .71 

XXII. THE BLUE SKY 74 

XXIII. A SANITARY DETECTIVE 78 

XXIV. FOG AND SMOKE 80 

XXV. ELECTRICAL DEPOSITION OP SMOKE ... 83 

XXVI. RADIATION PROM SNOW 86 

XXVII. MOUNTAIN GIANTS 88 

vii 



Vlll CONTENTS 

CHAP. PAGK 

XXVIII. THE WIND 92 

XXIX. CYCLONES AND ANTI-CYCLONES ... 95 

XXX. RAIN PHENOMENA 98 

XXXI. THE METEOROLOGY OF BEN NEVIS . . . 102 

XXXII. THE WEATHER AND INFLUENZA . . . 107 

XXXIII. CLIMATE 110 

XXXIV. THE "CHALLENGER" WEATHER REPORTS . 114 
XXXV. WEATHER-FORECASTING . . . . . 11G 

INDEX 124 



PREFATORY NOTE 

I AM very much indebted to Dr. John Aitken, 
F.R.S., for his great kindness in carefully re- 
vising the proof sheets, and giving me most 
valuable suggestions. This is a sufficient guar- 
antee that accuracy has not been sacrificed to 
popular explanation. 

J. G. M'P. 

RUTHVEN MANSE, 
June 10, 1905. 



METEOROLOGY 

CHAPTER I 
INTRODUCTION 

THOUGH by familiarity made commonplace, the 
"weather" is one of the most important topics of 
conversation, and has constant bearings upon the 
work and prospects of business -men and men of 
pleasure. The state of the weather is the password 
when people meet on the country road: we could 
not do without the humble talisman. " A fine day " 
comes spontaneously to the lips, whatever be the 
state of the atmosphere, unless it is peculiarly and 
strikingly repulsive ; then " A bitter day " would take 
the place of the expression. Yet I have heard 
Terrible guid wither " as often as " Terrible bad 
day " among country people. 

Scarcely a friendly letter is penned without a 
reference to the weather, as to what has been, is, or 
may be. It is a new stimulus to a lagging conversa- 
tion at any dinner-table. All are so dependent on 
the weather, especially those getting up in years or 
of delicate health. 

I remember, when at Strathpeffer, the great 
health-resort in the North of Scotland, in 1885, an 

9 



10 METEOROLOGY 

anxious invalid at " The Pump " asking a weather- 
beaten, rheumatic old gamekeeper what sort of a 
day it was to be, considering that it had been wet 
for some time. The keeper crippled to the baro- 
meter outside the doorway, and returned with the 
matter-of-fact answer : " She's faurer doon ta tay 
nur she wass up yestreen." The barometer had 
evidently fallen during the night. "And what are 
we to expect ? " sadly inquired the invalid. " It'll 
pe aither ferry wat, or mohr rain" a poor con- 
solation ! 

Most men who are bent on business or pleasure, 
and all dwellers in the country who have the instru- 
ments, make a first call at the barometer in the 
lobby, or the aneroid in the breakfast-parlour, to 
" see what she says." A good rise of the black needle 
(that is, to the right) above the yellow needle is a 
source of rejoicing, as it will likely be clear, dry, and 
hard weather. A slight fall (that is, to the left) 
causes anxiety as to coming rain, and a big depres- 
sion forebodes much rain or a violent storm of wind. 
In either case of " fall," the shutters come over the 
eyes of the observer. Next, even before breakfast, a 
move is made to the self-registering thermometer 
(set the night before) on a stone, a couple of feet 
above the grass. A good reading, above the freez- 
ing-point in winter and much above it in summer, 
indicates the absence of killing rimes, that are 
generally followed by rain. A very low register 
accounts for the feeling of cold during the night, 
though the fires were not out ; and predicts pre- 
carious weather. Ordinarily careful observers as I, 
who have been in one place for more than thirty 



INTRODUCTION 11 

years can, with the morning indications of these two 
instruments, come pretty sure of their prognostics 
of the day's weather. Of course, the morning news- 
paper is carefully scanned as to the weather-fore- 
casts from the London Meteorological Office direc- 
tion of wind ; warm, mild, or cold ; rain or fair, and 
so on and in general these indications are wonder- 
fully accurate for twenty-four hours; though the 
"three days'" prognostics seem to stretch a point. 
We are hardly up to that yet. 

The lower animals are very sensitive as to the 
state of approaching extremes of weather. "Thae 
sea beass," referring to sea-gulls over the inland leas 
during ploughing, are ordinary indicators of stormy 
weather. Wind is sure to follow violent wheelings 
of crows. "Beware of rain" when the sheep are 
restive, rubbing themselves on tree stumps. But all 
are familiar with Jenner's prognostics of rain. 

Science has come to the aid of ordinary weather- 
lore during the last twenty years, by leaps and 
bounds. Time-honoured notions and revered fic- 
tions, around which the hallowed associations of our 
early training fondly and firmly cling, must now 
yield to the exact handling of modern science ; and 
with reluctance we have to part with them. Yet 
there is in all a fascination to account for certain 
ordinary phenomena. " The man in the street," as 
well as the strong reading man, wishes to know 
the "why" and the "how" of weather-forecasting. 
They are anxious to have weather-phenomena ex- 
plained in a plain, interesting, but accurate way. 

The freshness of the marvellous results has an 
irresistible charm for the open mind, keen for useful 



12 METEOROLOGY 

information. The discoveries often seem so simple 
that one wonders why they were not made before. 

Until about twenty years ago, Meteorology was 
comparatively far back as a science ; and in one 
important branch of it, no one has done more to put 
weather-lore on a scientific basis than Dr. John 
Aitken, F.R.S., who has very kindly given me his 
full permission to popularise what I like of his 
numerous and very valuable scientific papers in the 
Transactions of the Royal Society of Edinburgh. 
This I have done my best to carry out in the follow- 
ing pages. " The way of putting it " is my only claim. 

Many scientific men are decoyed on in the search 
for truth with a spell unknown to others : the anti- 
cipation of the results sometimes amounts to a 
passion. Many wrong tracks do they take, yet they 
start afresh, just as the detective has to take several 
courses before he hits upon the correct scent. When 
they succeed, they experience a pleasure which is 
indescribable; to them fame is more than a mere 
" fancied life in others' breath." 

Dr. Aitken's continued experiments, often of rare 
ingenuity and brilliancy, show that no truth is 
altogether barren ; and even that which looks at 
first sight the very simplest and most trivial may 
turn out fruitful in precious results. Small things 
must not be overlooked, for great discoveries are 
sometimes at a man's very door. Dr. Aitken has 
shown us this in many of his discoveries which have 
revolutionised a branch of meteorology. Prudence, 
patience, observing power, and perseverance in 
scientific research will do much to bring about un- 
expected results, and not more BO in any science 



THE FORMATION OF DEW 13 

than in accounting for weather-lore on a rational 
basis, which it is in the power of all my readers to 
further. 

" The old order changeth, giving place to new." 
With kaleidoscopic variety Nature's face changes to 
the touch of the anxious and reverent observer. 
And some of these curious weather-views will be 
disclosed in these pages, so as, in a brief but read- 
able way, to explain the weather, and lay a safe 
basis for probable forecastings, which will be of great 
benefit to the man of business as well as the man of 
pleasure. 

" Felix, qui potuit rerum cognoscere causas." 

VIRGIL. 



CHAPTER II 
THE FORMATION OF DEW 

THE writer of the Book of Job gravely asked the im- 
portant question, " Who hath begotten the drops of 
dew ? " We repeat the question in another form, 
" Whence comes the real dew ? Does it fall from the 
heavens above, or does it rise from the earth beneath?" 
Until about the beginning of the seventeenth 
century, scientific men held the opinion of ordinary 
observers that dew fell from the atmosphere. But 
there was then a reaction from this theory, for 
Nardius denned it as an exhalation from the earth. 
Of course, it was well known that dew was formed by 
the precipitation of the vapour of the air upon a 
colder body. You can see., that any day for yourself 



14 METEOROLOGY 

by bringing a glass of very cold water into a warm 
room; the outer surface of the glass is dimmed at 
once by the moisture from the air. M. Picket was 
puzzled when he saw that a thermometer, suspended 
five feet above the ground, marked a lower tempera- 
ture on clear nights than one suspended at the 
height of seventy-five feet; because it was always 
supposed that the cold of evening descended from 
above. Again he was puzzled when he observed 
that a buried thermometer read higher than one 
on the surface of the ground. Until recently the 
greatest authority on dew was Dr. Wells, who care- 
fully converged all the rays of scientific light upon 
the subject. He came to the conclusion that dew 
was condensed out of the air. 

But the discovery of the true theory was left to 
Dr. John Aitken, F.R.S., a distinguished observer 
and a practical physicist, of whom Scotland has 
reason to be proud. About twenty years ago he 
made the discovery, and it is now accepted by all 
scientific men on the Continent as well as in Great 
Britain. What first caused him to doubt Dr. Wells' 
theory, so universally accepted, that dew is formed 
of vapour existing at the time in the . air, and to 
suppose that dew is mostly formed of vapour rising 
from the ground, was the result of some observations 
made in summer on the temperature of the soil at 
a small depth under the surface, and of the air over 
it, after sunset and at night. He was struck with 
the unvarying fact that the ground, a little below 
the surface, was warmer than the air over it. By 
placing a thermometer among stems below the sur- 
face, he found that it registered 18 Fahr. higher 



THE FORMATION OF DEW 15 

than one on the surface. So long, then, as the 
surface of the ground is above the dew-point (i.e. 
the temperature when dew begins to be formed), 
vapour must rise from the ground ; this moist air 
will mingle with the air which it enters, and its 
moisture will be condensed and form dew, whenever 
it comes in contact with a surface cooled below the 
dew-point. 

You can verify this by simple experiments. Take 
a thin, shallow, metal tray, painted black, and place 
it over the ground after sunset. On dewy nights 
the inside of the tray is dewed, and the grass inside 
is wetter than that outside. On some nights there 
is no dew outside the tray, and on all nights the 
deposit on the inner is heavier than that on the 
outside. If wool is used in the experiments, we are 
reminded of one of the forms of the dewing of 
Gideon's fleece the fleece was bedewed when all 
outside was dry. 

You therefore naturally and rightly come to the 
conclusion that far more vapour rises out of the 
ground during the night than condenses as dew on 
the grass, and that this vapour from the ground is 
trapped by the tray. Much of the rising vapour is 
generally carried away by the passing wind, however 
gentle ; hence we have it condensed as dew on the 
roofs of houses, and other places, where you would 
think that it had fallen from above. The vapour 
rising under the tray is not diluted by the mixture 
with the drier air which is occasioned by the passing 
wind ; therefore, though only cooled to the same 
extent as the air outside, it yields a heavier deposit 
of dew. 



16 METEOROLOGY 

If you place the tray on bare ground, you will 
find on a dewy night that the inside of the tray is 
quite wet. On a dewy night you will observe that 
the under part of the gravel of the road is dripping 
wet when the top is dry. You will find, too, that 
around pieces of iron and old implements in the 
field, there is a very marked increase of grass, owing 
to the deposit of moisture on these articles 
moisture which has been condensed by the cold 
metal from the vapour-charged air, which has risen 
from the ground on dewy nights. 

But all doubt upon this important matter is 
removed by a most successful experiment with a 
fine balance, which weighs to a quarter of a grain. 
If vapour rises from the ground for any length of 
time during dewy nights, the soil which gives oft' 
the vapour must lose weight. To test this, cut from 
the lawn a piece of turf six inches square and a 
quarter of an inch thick. Place this in a shallow 
pan, and carefully note the weight of both turf 
and pan with the sensitive balance. To prevent 
loss by evaporation, the weighing should be done 
in an open shed. Then place the pan and turf 
at sunset in the open cut. Five hours afterwards 
remove and weigh them, and it will be found 
that the turf has lost a part of its weight. The 
vapour which rose from the ground during the 
formation of the dew accounts for the difference 
of weight. This weighing-test will also succeed on 
bare ground. 

When dealing with hoar-frost, which is just frozen 
dew, we shall find visible evidence of the rising of 
dew from the ground. 



TRUE AND FALSE DEW 17 

You know the beautiful song, "Annie Laurie," 
which begins with 

" Maxwelton's braes are bonnie, 
Where early fa's the dew " 

well, you can no longer say that the dew "falls," 
for it rises from the ground. The song, however, 
will be sung as sweetly as ever; for the spirit of 
true poetry defies the cold letter of science. 



CHAPTER III 

TRUE AND FALSE DEW 

EVER since men could observe and think, they have 
admired the diamond globules sparkling in the rising 
sun. These " dew-drops " were considered to be shed 
from the bosom of the morn into the blooming 
flowers and rich grass-leaves. Ballantine's beautiful 
song of Providential care tells us that " Ilka blade o' 
grass keps it's ain drap o' dew." 

But, alas ! we have to bid " good-bye " to the appella- 
tion " dew-drop." What was popularly and poetically 
called dew is not dew at all. Then what is it ? 

On what we have been accustomed to call a 
"dewy" night, after the brilliant summer sun has 
set, and the stars begin to peep out of the almost 
cloudless sky, let us take a look at the produce of 
our vegetable garden. On the broccoli are found 
glistening drops ; but on the peas, growing next 
them, we find nothing. 

A closer examination shows us that the moisture 

B 



18 METEOROLOGY 

on the plants is not arranged as would be expected 
from the ordinary laws of radiation and condensa- 
tion. There is no generally filmy appearance over 
the leaves ; the moisture is collected in little drops 
placed at short distances apart, along the edges of 
the leaves all round. 

Now place a lighted lantern below one of the 
blades of the broccoli, and a revelation will be made. 
The brilliant diamond-drops .that fringe the edge 
of the blade are all placed at the points where the 
nearly colourless veins of the blade come to the 
outer edge. The drops are not dew at all, but the 
exudation of the healthy plant, which has been con- 
veyed up these veins by strong root-pressure. 

The fact is that the root acts as a kind of force- 
pump, and keeps up a constant pressure inside the 
tissues of the plant. One of the simplest experi- 
ments suggested by Dr. Aitken is to lift a single 
grass-plant, with a clod of moist earth attached to 
it, and place it on a plate with an inverted tumbler 
over it. In about an hour, drops will begin to exude, 
and the tip of nearly every blade will be found to 
be studded with a diamond-like drop. 

Next substitute water-pressure. Remove a blade 
of broccoli and connect it by means of an india- 
rubber tube with a head of water of about forty 
inches. Place a glass receiver over it, so as to check 
evaporation, and leave it for an hour. The plant 
will be found to have excreted water freely, some 
parts of the leaves being quite wet, while drops are 
collected at the places where they appeared at night. 

If the water pressed into the leaf is coloured with 
aniline blue, the drops when they first appear are 



TRUE AND FALSE DEW 19 

colourless ; but before they grow to any size, the blue 
appears, showing that little water was held in the 
veins. The whole leaf soon gets coloured of a fine 
deep blue-green, like that seen when vegetation is 
rank ; this shows that the injected liquid has pene- 
trated through the whole leaf. 

Again, the surfaces of the leaves of these drop- 
exuding plants never seem to be wetted by the 
water. It is because of the rejection of water by the 
leaf-surface that the exuded moisture from the veins 
remains as a drop. 

These observations and experiments establish the 
fact that the drops which first make their appearance 
on grass on dewy nights are not dew-drops at all, 
but the exuded watery juices of the plants. 

If now we look at dead leaves we shall find a 
difference of formation of the moisture on a dewy 
night: the moisture is spread equally over, where 
equally exposed. The moisture exuded by the 
healthy grass is always found at a point situated 
near the tip of the blade, forming a drop of some 
size; but the true dew collects later on evenly all 
over the blade. The false dew forms a large glisten- 
ing diamond-drop, whereas the true dew coats the 
blade with a fine pearly lustre. Brilliant globules 
are produced by the vital action of the plant, espe- 
cially beautiful when the deep-red setting sun 
makes them glisten, all a-tremble, with gold light; 
while an infinite number of minute but shining opal- 
like particles of moisture bedecks the blade-surfaces, 
in the form of the gentle dew 

M Like that which kept the heart of Eden green 
Before the useful trouble of the rain." 



20 METEOROLOGY 

CHAPTER IV 

HOAR-FROST 

ALL in this country are familiar with the beauty 
of hoar-frost. The children are delighted with the 
funny figures on the glass of the bedroom window 
on a cold winter morning. Frost is a wonderful 
artist; during the night he has been dipping his 
brush into something like diluted schist, and laying 
it gracefully on the smooth panes. 

And, as you walk over the meadows, you observe 
the thin white films of ice on the green pasture; 
and the clear, slender blades seem like crystal spears, 
or the " lashes of light that trim the stars." 

You all know what hoar-frost is, though most in 
the country give it the expressive name of " rime." 
But you are not all aware of how it is formed. 
Hoar-frost is just frozen dew. In a learned paper, 
written in 1784, Professor Wilson of Glasgow made 
this significant remark : " This is a subject which, 
besides its entire novelty, seems, upon other accounts, 
to have a claim to some attention." He observed, 
in that exceptionally cold winter, that, when sheets 
of paper and plates of metal were laid out, all began 
to attract hoar-frost as soon as they had time to cool 
down to the temperature of the air. He was struck 
with the fact that, while the thermometer indicated 
36 degrees of frost a few feet above the ground 
and 44 degrees of frost at the surface of the snow, 
there were only 8 degrees of frost at a point 3 inches 



HOAR-FROST 21 

below the surface of the snow. If he had only 
thought of placing the thermometer on the grass, 
under the snow, he would have found it to register 
the freezing-point only. And had he inserted the 
instrument below the ground, he would have found 
it registering a still higher temperature. That fact 
would have suggested to him the formation of hoar- 
frost ; that the water- vapour from the warm soil 
was trapped by a cold stratum of air and frozen 
when in the form of dew. 

One of the most interesting experiments, without 
apparatus, which you can make is in connection with 
the formation of hoar-frost, when there is no snow 
on the ground, in very cold weather. If it has been 
a bright, clear, sunny day in January, the effect can 
be better observed. Look over the garden, grass, 
and walks on the morning after the intense cold 
of the night ; big plane-tree leaves may be found 
scattered over the place. You see little or no hoar- 
frost on the upper surface of the leaves. But turn 
up the surface next the earth, or the road, or the 
grass, and what do you see? You have only to 
handle the leaf in this way to be brightly astonished. 
A thick white coating of hoar-frost, as thick as a 
layer of snow, is on the under surface. If a number 
of leaves have been overlapping each other, there 
will be no coating of hoar-frost under the top leaves ; 
but when you reach the lowest layer, next the bare 
ground, you will find the hoar-frost on the under 
surface of the leaves. Now that is positive proof 
that the hoar-frost has not fallen from the air, but 
has risen from the earth. 

The sun's heat on the previous day warmed the 



22 METEOROLOGY 

earth. This heat the earth retained till evening. 
As the air chilled, the water- vapour from the warmer 
earth rose from its surface, and was arrested by the 
cold surface of the leaves. So cold was that surface 
that it froze the water- vapour when rising from the 
earth, and formed hoar-frost in very large quantities. 
When this happens later on in the season, one may 
be almost sure of having rain in the forenoon. 

As hoar-frost is just frozen dew, I can even more 
surely convince you of the formation of hoar-frost as 
rising from the ground by observations made by me 
at my manse in Strathmore, in June 1892. I mention 
this particularly because then was the most favourable 
testing-time that has ever occurred during meteoro- 
logical observations. June 9th was the warmest 
June day (with one exception) for twenty years. 
The thermometer reached 83 Fahr. in the shade. 
Next day was the coldest June day (with one 
exception) for twenty years, when the thermometer 
was as low as 51 in the shade. But during the 
night my thermometer on the grass registered 32 
the freezing point. On the evening of the sultry day 
I examined the soil at 10 o'clock. It was damp, and 
the grass round it was filmy moist. The leaves of 
the trees were crackling dry, and all above was void 
of moisture. The air became gradually chilly ; and 
as gradually the moisture rose in height on the 
shrubs and lower branches of small trees. The 
moon shone bright, and the stars showed their clear, 
chilly eyes. The soil soon became quite wet, the 
low grass was dripping with moisture, and the longer 
grass was becoming dewed. This gave the best 
natural evidence of the rising of the dew that I ever 



FOG 23 

witnessed. But everything was favourable for the 
observation the cold air incumbent on the rising, 
warm, moist vapour from the soil fixing the dew- 
point, when the projecting blades seized the moisture 
greedily and formed dew. Had the temperature 
been a little below the freezing-point, hoar-frost 
would have been beautifully formed. 



CHAPTER V 

FOG 

To many nothing is more troublesome than a 
dense fog in a large town. It paralyses traffic, it 
is dangerous to pedestrians, it encourages theft, it 
chokes the asthmatic, and chills the weak-lunged. 

In the country it is disagreeable enough ; but 
never so intensely raw and dense as in the city. 
On the sea, too, the fog is disagreeable and fraught 
with danger. The fog-horn is heard, in its deep, 
sombre note, from the lighthouse tower, when the 
strong artificial light is almost useless. 

But a peculiar sense of stagnation possesses the 
dweller of the large town, when enveloped in a dense 
fog. Sometimes during the day, through a thinner 
portion, the sun will be dimly seen in copper hue, 
like the moon under an eclipse. The smoke-impreg- 
nated mass assumes a peculiar " pea-soup " colour. 

Now, what is this fog ? How is it formed ? It 
has been ascertained that fogs are dependent upon 
dust for their formation. Without dust there could 



24 METEOROLOGY 

be no fogs, there would be only dew on the grass 
and road. Instead of the dust-impregnated air that 
irritates the housekeeper, there would be the constant 
dripping of moisture on the walls, which would annoy 
her more. 

Ocular demonstration can testify to this. If two 
closed glass receivers be placed beside each other, 
the one containing ordinary air, and the other 
filtered air (i.e. air deprived of its dust by being 
driven through cotton wool), and if jets of steam be 
successively introduced into these, a strange effect is 
noticed. In the vessel containing common air the 
steam will be seen rising in a dense cloud ; then 
a beautiful white foggy cloud will be formed, so 
dense that it cannot be seen through. But in the 
vessel containing the filtered air, the steam is not 
seen at all ; there is not the slightest appearance of 
cloudiness. In the one case, where there was the 
ordinary atmospheric dust, fog at once appeared ; in 
the other case, where there was no dust in suspension, 
the air remained clear and destitute of fog. Invisible 
dust, then, is necessary in the air for the formation of 
fogs. 

The reason of this is that a free-surface must exist 
for the condensation of the vapour-particles. The 
fine particles of dust in the air act as free-surfaces, on 
which the fog is formed. Where there is abundance 
of dust in the air and little water-vapour present, 
there is an over-proportion of dust-particles ; and 
the fog-particles are, in consequence, closely packed, 
but light in form and small in size, and take the 
lighter appearance of fog. Accordingly, if the dust is 
increased in the air, there is a proportionate increase 



FOG 25 

of fog. Every fog-particle, then, has embosomed in it 
an invisible dust-particle. 

But whence comes the dust ? From many sources. 
It is organic and inorganic. So very fine is the 
inorganic dust in the atmosphere that, if the two- 
thousandth part of a grain of fine iron be heated, and 
the dust be driven off and carried into a glass receiver 
of filtered air, the introduction of a jet of steam into 
that receiver would at once occasion an appreciable 
cloudiness. 

This is why fogs are so prevalent in large towns. 
Next the minute brine-particles, driven into the air 
as fog forms above the ocean surface, are the burnt 
sulphur -particles emanating from the chimneys in 
towns. The brilliant flame, as well as the smoky 
flame, is a fog-producer. If gas is burnt in filtered 
air, intense fog is produced when water-vapour is 
introduced. Products of combustion from a clear 
fire and from a smoky one produce equal fogging. 
The fogs that densely fill our large towns are gene- 
rally less bearable than those that veil the hills and 
overhang the rivers. 

It is the sulphur, however, from the consumed 
coals, which is the active producer of the fogs of a 
large town. The burnt sulphur condenses in the air 
to very fine particles, and the quantity of burnt 
sulphur is enormous. No less than seven and a half 
millions of tons of coals are consumed in London. 
Now, the average amount of sulphur in English coal 
is one and a quarter per cent. That would give no 
less than 93,750 tons of sul-phur burned every year in 
London fires. Now, if we reckon that on an average 
twice the quantity of coals is consumed there on a 



26 METEOROLOGY 

winter day that is consumed on a summer day, no 
less than 347 tons of the products of combustion 
(in extremely fine particles) are driven into the 
superincumbent air of London every winter day. 
This is an enormous quantity, quite sufficient to 
account for the density of the fogs in that city. 



CHAPTER VI 
THE NUMBERING OF THE DUST 

IF the shutters be all but closed in a room, when 
the sun is shining in, myriads of floating particles 
can be seen glistening in the stream of light. Their 
number seems inexhaustible. According to Milton, 
the follies of life are 

" Thick and numberless, 
As the gay motes that people the sunbeams." 

Can these, then, be counted ? Yes, Dr. Aitken has 
numbered the dust of the air. I shall never forget 
my rapt astonishment the day I first numbered the 
dust in the lecture-room of the Royal Society of Edin- 
burgh, with his instrument and under his direction. 

This wonderfully ingenious instrument was devised 
on this principle, that every fog-particle has entombed 
in it an invisible dust-particle. A definite small 
quantity of common air is diluted with a fixed large 
quantity of dustless air (i.e. air that has been filtered 
through cotton- wool). The mixture is allowed to be 
saturated with water-vapour. Then the few par- 



THE NUMBERING OF THE DUST 27 

tides of dust seize the moisture, become visible in line 
drops, fall on a divided plate, and are there counted 
by means of a magnifying glass. That is the secret ! 

I shall now give you a general idea of the apparatus. 
Into a common glass flask of carafe shape, and flat- 
bottomed, of 30 cubic inches capacity, are passed two 
small tubes, at the end of one of which is attached a 
small square silver table, 1 inch in length. A little 
water having been inserted, the flask is inverted, and 
the table is placed exactly 1 inch from the inverted 
bottom, so that the contents of air right above the 
table are 1 cubic inch. This observing table is 
divided into 100 equal squares, and is highly polished, 
with the burnishing all in one direction, so that 
during the observations it appears dark, when the 
fine mist-particles glisten opal-like with the reflected 
light in order that they may be more easily counted. 
The tube to which the silver table is attached is con- 
nected with two stop-cocks, one of which can admit 
a small measured portion of the air to be examined. 
The other tube in the flask is connected with an air- 
pump of 10 cubic inches capacity. Over the flask is 
placed a covering, coloured black in the inside. In 
the top of this cover is inserted a powerful magni- 
fying glass, through which the particles on the silver 
table can be easily counted. A little to the side of 
this magnifier is an opening in the cover, through 
which light is concentrated on the table. 

To perform the experiment, the air in the flask is 
exhausted by the air-pump. The flask is then filled 
with filtered air. One-tenth of a cubic inch of the 
air to be examined is then introduced into the flask, 
and mixed with the 30 cubic inches of dustless air. 



28 METEOROLOGY 

After one stroke of the air-pump, this mixed air is 
made to occupy an additional space of 10 cubic 
inches ; and this rarefying of the air so chills it that 
condensation of the water- vapour takes place on the 
dust-particles. The observer, looking through the 
magnifying-glass upon the silver table, sees the mist- 
particles fall like an opal shower on the table. He 
counts the number on a single square in two or three 
places, striking an average in his mind. Suppose 
the average number upon a single square were five, 
then on the whole table there would be 500 ; and 
these 500 particles of dust are those which floated 
invisibly in the cubic inch of mixed air right above 
the table. But, as there are 40 cubic inches of mixed 
air in the flask and barrel, the number of dust-par- 
ticles in the whole is 20,000. That is, there are 
20,000 dust-particles in the same quantity of common 
air (one-tenth of a cubic inch) which was introduced 
for examination. In other words, a cubic inch of the 
air contained 200,000 dust-particles nearly a quarter 
of a million. 

The day I used the instrument we counted 4,000,000 
of dust-particles in a cubic inch of the air outside of 
the room, due to the quantity of smoke from the 
passing trains. Dr. Aitken has counted in 1 cubic 
inch of air immediately above a Bunsen flame the 
fabulous number of 489,000.000 of dust-particles. 

A small instrument has been constructed which 
can bring about results sufficiently accurate for ordi- 
nary purposes. It is so constructed that, when the 
different parts are unscrewed, they fit into a case 4J 
inches by 2J by 1 J deep about the size of an ordinary 
cigar-case. 



DUST AND ATMOSPHERIC PHENOMENA 29 

After knowing this, we are apt to wonder why our 
lungs do not get clogged up with the enormous 
number of dust-particles. In ordinary breathing, 
30 cubic inches of air pass in and out at every breath, 
and adults breathe about fifteen times every minute. 
But the warm lung-surface repels the colder dust- 
particles, and the continuous evaporation of moisture 
from the surface of the air-tubes prevents the dust 
from alighting or clinging to the surface at all. 



CHAPTER VII 

DUST AND ATMOSPHERIC PHENOMENA 

DR. AITKEN has devoted a vast amount of attention 
to the enumeration of dust-particles in the air, on 
the Continent as well as in Scotland, to determine 
the effects of their variation in number. 

On his first visit to Hyeres, in 1890, he counted 
with the instrument 12,000 dust-particles in a cubic 
inch of the air: whereas in the following year he 
counted 250,000. He observed, however, that where 
there was least dust, the air was very clear ; whereas 
with the maximum of dust, there was a very thick 
haze. 

At Mentone, the corresponding number was 13,000, 
when the wind was blowing from the mountains ; 
but increased to 430,000, when the wind was blowing 
from the populous town. 

On his first visit to the Rigi Kulm, in Switzerland, 
the air was remarkably clear and brilliant, and the 



30 METEOROLOGY 

corresponding number never exceeded 33,000; bat, 
on his second visit, he counted no less than 166,000. 
This was accounted for by a thick haze, which 
rendered the lower Alps scarcely visible. The upper 
limit of the haze was well denned ; and though the 
sky was cloudless, the sun looked like a harvest 
moon, and required no eagle's eye to keep fixed 
on it. 

Next day there was a violent thunder-storm. At 
6 P.M. the storm commenced, and 60,000 dust- 
particles to the cubic inch of air were registered; 
but in the middle of the storm he counted only 
13,000. There was a heavy fall of hail at this time, 
and he accounts for the diminution of dust-particles 
by the down-rush of purer upper air, which displaced 
the contaminated lower air. 

At the Lake of Lucerne there was an exceptional 
diminution of the number in the course of an hour, 
viz. from 171,000 to 28,000 in a cubic inch. On 
looking about, he found that the direction of the 
wind had changed, bringing down the purer upper 
air to the place of observation. The bending down- 
wards of the trees by the strong wind showed that 
it was coming from the upper air. 

Returning to Scotland, he continued his observa- 
tions at Ben Nevis and at Kingairloch, opposite 
Appin, Mr. Rankin using the instrument at the top 
of the mountain. These observations showed in 
general that on the mountain southerly, south- 
easterly, and easterly winds were more impregnated 
with dust-particles, sometimes containing 133,000 
per cubic inch. Northerly winds brought pure 
air. The observations at sea-level showed a certain 



A FOG-COUNTER 31 

parallelism to those on the summit of the mountain. 
With a north-westerly wind the dust-particles reached 
the low number of 300 per cubic inch, the lowest 
recorded at any low-level station. 

The general deductions which he made from his 
numerous observations during these two years are 
that (1) air coming from inhabited districts is always 
impure ; (2) dust is carried by the wind- to enormous 
distances; (3) dust rises to the tops of mountains 
during the day ; (4) with much dust there is much 
haze ; (5) high humidity causes great thickness of 
the atmosphere, if accompanied by a great amount 
of dust, whereas there is no evidence that humidity 
alone has any effect in producing thickness ; (6) and 
there is generally a high amount of dust with high 
temperature, and a low amount of dust with low 
temperature. 



CHAPTER VIII 
A FOG-COUNTER 

NEXT to the enumeration of the dust-particles in 
the atmosphere is the marvellous accuracy of count- 
ing the number of particles in a fog. The same 
ingenious inventor has constructed a fog-counter 
for the purpose ; and the number of fog-particles in 
a cubic inch can be ascertained. This instrument 
consists of a glass micrometer divided into squares 
of a known size, and a strong microscope for observ- 
ing the drops on the stage. The space between the 



32 METEOROLOGY 

micrometer and the microscope is open, so that the 
air passes freely over the stage ; and the drops that 
fall on its surface are easily seen. These drops are 
very small ; many of them when spread on the glass 
are no more than the five-hundredth of an inch in 
diameter. 

In observing these drops, the attention requires 
to be confined to a limited area of the stage, as many 
of the drops rapidly evaporate, some almost as soon 
as they touch the glass, whilst the large ones remain 
a few seconds. 

In one set of Dr. Aitken's observations, in February 
1891, the fog was so thick that objects beyond a 
hundred yards were quite invisible. The number 
of drops falling per second varied greatly from time 
to time. The greatest number was 323 drops per 
square inch in one second. The high number 
never lasted for long, and in the intervals the 
number fell as low as 32, or to one-tenth. 

If we knew the size of these drops, we might be 
able to calculate the velocity of their fall, and from 
that obtain the number in a cubic inch. 

An ingenious addition is put to the instrument in 
order to ascertain this directly. It is constructed so 
as to ascertain the number of particles that fall from 
a known height. Under a low-power microscope, 
and concentric with it, is mounted a tube 2 inches 
long and 1 inch in diameter, with a bottom and a 
cover, which are fixed to an axis parallel with the 
axis of the tube, so that, by turning a handle, these 
can be slid sideways, closing or opening the tube 
at both ends when required. In the top is a small 
opening, corresponding to the lens of the microscope, 



A FOG-COUNTER 33 

and in the centre of the bottom is placed the observ- 
ing-stage illumined by a spot-mirror. The handle is 
turned, and the ends are open to admit the foggy air. 
The handle is quickly reversed, and the ends are 
closed, enabling the observer to count on the stage 
all the fog-particles in the two inches of air over it. 

The number of dust-particles in the air which 
become centres of condensation depends on the rate 
at which the condensation is taking place. The 
most recent observations show that quick condensa- 
tion causes a large number of particles to become 
active, whereas slow condensation causes a small 
number. After the condensation has ceased, a pro- 
cess of differentiation takes place, the larger particles 
robbing the smaller ones of their moisture, owing to 
the vapour-pressure at the surface of the drops of 
large curvature being less than at the surface of 
drops of smaller curvature. 

By this process the particles in a cloud are re- 
duced in number; the remaining ones, becoming 
larger, fall quicker. The cloud thus becomes thinner 
for a time. A strong wind, suddenly arising, will 
cause the cloud-particles to be rapidly formed : these 
will be very numerous, but very small so small that 
they are just visible with great care under a strong 
magnifying lens used in the instrument. But in 
slowly formed clouds the particles are larger, and 
therefore more easily visible to the naked eye. 

Though the particles in a fog are slightly finer, 
the number is about the same as in a cloud that is, 
generally. As clouds vary in density, the number of 
particles varies. Sometimes in a cloud one cannot 
see farther than 30 yards ; whereas in a few minutes 

c 



34 METEOROLOGY 

it clears up a little, so that we can see 100 yards. Of 
course, the denser the cloud the greater the number 
of water-particles falling on the calculating-stage of 
the instrument. 

Very heavy falls of cloud-particles seldom last 
more than a few seconds, the average being about 
325 on the square inch per second, the maximum 
reaching to 1290. This is about four times the 
number counted in a fog. Yet the particles are so 
very small that they evaporate instantly when they 
reach a slight increase of temperature. 



CHAPTER IX 

FORMATION OF CLOUDS 

IN our ordinary atmosphere there can be no clouds 
without dust. A dust-particle is the nucleus that 
at a certain humidity becomes the centre of con- 
densation of the water- vapour so as to form a cloud- 
particle ; and a collection of these forms a cloud. 

This condensation of vapour round a number of 
dust-particles in visible form gives rise to a vast 
variety of cloud-shapes. There are two distinct ways 
in which the formation of clouds generally takes 
place. Either a layer of air is cooled in a body 
below the dew-point ; or a mass of warm and moist 
air rises into a ma'ss which is cold and dry. The 
first forms a cloud, called, from being a layer, 
stratus; the second forms a cloud, called, from its 
heap appearance, cumulus. The first is widely 
extended and horizontal, averaging 1800 feet hi 






FORMATION OF CLOUDS 35 

height; the second is convex or conical, like the 
head of a sheaf, increasing upward from a level base, 
averaging from 4500 feet to 6000 feet in height. 

There are endless combinations of these two ; but 
at the height of 27,000 feet, where the cloud-particles 
are frozen, the structure of the cloud is finer, like 
" mares' tails," receiving the name cirrus. When 
the cirrus and cumulus are combined, in well-defined 
roundish masses, what is familiarly described as a 
" mackerel sky " is beautifully presented. The dark 
mass of cloud, called nimbus, is the threatening rain- 
cloud, about 4500 feet in height. 

At the International Meteorological Conference at 
Munich, in 1892, twelve varieties of clouds were 
classified, but those named above are the principal. 
In a beautiful sunset one can sometimes notice two 
or three distances of clouds, the sun shedding its 
gold light on the full front of one set, and only 
fringing with vivid light the nearer range, j 

Although no man has wrought so hard as Dr. 
Aitken to establish the principle that clouds are 
mainly due to the existence of dust-particles which 
attract moisture on certain conditions, yet even 
twenty years ago he said that it was probable that 
sunshine might cause the formation of nuclei and 
allow cloudy condensation to take place where there 
was no dust. 

Under certain conditions the sun gives rise to a 
great increase in the number of nuclei. Accordingly, 
he has carefully tested a few of the ordinary con- 
stituents and impurities in our atmosphere to see if 
sunshine acted on them in such a way as to make 
them probable formers of cloud-particles. 



36 METEOROLOGY 

He tested various gases, with more or less success. 
He found that ordinary air, after being deprived of 
its dust-particles and exposed to sunshine, does not 
show any cloudy condensation on expansion ; but, 
when certain gases are in the dustless air, a very 
different result is obtained. 

He first used ammonia, putting one drop into six 
cubic inches of water in a flask, and sunning this for 
one minute ; the result was a considerable quantity 
of condensation, even with such a weak solution. 
When the flask was exposed for five minutes, the 
condensation by the action of the sunshine was made 
more dense. 

Hydrogen peroxide was tested in the same way, 
and it was found to be a powerful generator of 
nuclei. Curious is it that sulphurous acid is puzzling 
to the experimentalist for cloud formation. It gives 
rise to condensation in the dark ; but sunshine very 
conclusively increases the condensation. 

Chlorine causes condensation to take place with- 
out supersaturation ; sulphuretted hydrogen (which 
one always associates with the smell of rotten eggs) 
gives dense condensation after being exposed to sun- 
shine. 

Though the most of these nuclei, due to the action 
of sunshine in the gases, remain active for cloudy 
condensation for a comparatively short space of time 
fifteen minutes to half-an-hour yet the experi- 
ments show that it is possible for the cloudy con- 
densation to take place in certain circumstances in 
the absence of dust. This seems paradoxical in 
the light of the former beautiful experiments ; but, 
in ordinary circumstances, dust is needed for the 






DECAY OF CLOUDS 37 

formation of clouds. However, supposing there is 
any part of the upper air free from dust, it is now 
found possible, when any of these gases experimented 
''on be present, for the sun to convert them into 
nuclei of condensation, and permit of clouds being 
formed in dustless air, miles above the surface of the 
earth. 

In the lower atmosphere there are always plenty 
of dust-particles to form cloudy condensation, 
whether the sun shines or not. These are produced 
by the waste from the millions of meteors that daily 
fall into the air. 

But in the higher atmosphere, clouds can be 
formed by the action of the sun's rays on certain 
gases. This is a great boon to us on the earth ; for 
it assures us of clouds being ever existing to defend 
us from the sun's extra-powerful rays, even when 
our atmosphere is fairly clear. This is surely of 
some meteorological importance. 



CHAPTER X 
DECAY OF CLOUDS 

FKOM the earliest ages clouds have attracted the 
attention of observers. Varied are their forms and 
colours, yet in our atmosphere there is one law in 
their formation. Cloud-particles are formed by the 
condensation of water- vapour on the dust-particles 
invisibly floating in the atmosphere, up to thousands 
and even millions in the cubic inch of air. 

But observers have not directed their attention so 



38 METEOROLOGY 

much to the decay of clouds in fact, the subject 
is quite new. And yet how suggestive is the 
subject ! 

The process of decay in clouds takes place in 
various ways. A careful observer may witness the 
gradual wasting away and dilution into thin air of 
even great stretches of cloud, when circumstances 
are favourable. In May 1896 my attention was 
particularly drawn to this at my manse in Strath- 
more. In the middle of that exceptionally sultry 
month, I was arrested by a remarkable transforma- 
tion scene. It was the hottest May for seventy-two 
years, and the driest for twenty-five years. The 
whole parched earth was thirsting for rain. All the 
morning my eyes were turned to the clouds in the 
hope that the much-desired shower should fall. Till 
ten o'clock the sun was not seen, and there was no 
blue in the sky. Nor was there any haze or fog. 

But suddenly the sun shone through a thinner 
portion of the enveloping clouds, and, to the north, 
the sky began to open. As if by some magic spell 
there was, in a quarter of an hour, more blue to be 
seen than clouds. At the same time, near the 
horizon, a haze was forming, gradually becoming 
denser as time wore on. In an hour the whole 
clouds were gone, and the glorious orb of day dis- 
pelled the moisture to its thin-air form. 

This was a pointed and rapid illustration of the 
decay from cloud-form to haze, and then to the pure 
vapoury sky. It was an instance of the reverse 
process. As the sun cleared through, the temperature 
in the cloud-land rose and evaporation took place on 
the surface of the cloud-particles, until by an un- 



DECAY OF CLOUDS . 39 

traceable, but still a gradual process through fog, the 
haze was formed. Even then the heat was too great 
for a definite haze, and the water-vapour returned 
to the air, leaving the dust-particles in invisible 
suspension. 

But clouds decay in another way. This I will 
illustrate in the next chapter on " It always rains." 

What strikes a close observer is the difference of 
structure in clouds which are in the process of 
formation and those which are in the process of 
decay. In the former the water-particles are much 
smaller and far more numerous than in the latter. 
While the particles in clouds in decay are large 
enough to be seen with the unaided eye, when they 
fall on a properly lighted measuring table, they are 
so small in clouds in rapid formation that the 
particles cannot be seen without the aid of a strong 
magnifying glass. 

Observers have assumed that the whole explana- 
tion of the fantastic shapes taken by clouds is 
founded on the process of formation ; but Dr. Aitken 
has pointed out that ripple-marked clouds, for in- 
stance, have been clouds of decay. When what is 
called a cirro-stratus cloud mackerel-like against 
the blue sky is carefully observed in fine weather, it 
will be found that it frequently changes the ripple- 
marked cirrus in the process of decay to vanishing. 
Where the cloud is thin enough to be broken through 
by the clear air that is drawn in between the eddies, 
the ripple markings get nearer and nearer the centre, 
as the cloud decays. And, at last, when nearly 
dissolved, these markings are extended quite across 
the cloud. 



40 METEOROLOGY 

Whether, then, we consider the cases of clouds 
gradually melting away back into their original state 
of blue water-vapour, or the constant fine raining 
from clouds and re-formation by evaporation, or the 
transformation of such clouds as the cirro-stratus 
into the ripple-marked cirrus, we are forced to the 
conclusion that in clouds there is not always 
development, but sometimes degeneration; not 
always formation, but sometimes decay. 



CHAPTER XI 
IT ALWAYS RAINS 

ALL are familiar with the answer given by the 
native of Skye to the irate tourist on that island, 
who, for the sixth day drenched, asked the question : 
"Does it always rain here?" "Na!" answered the 
workman, without at all understanding the joke; 
" feiles it snaas " (sometimes it snows). Yet, strange 
to say, the tourist's question has been answered in 
the affirmative in every place where a cloud is over- 
head, visible or invisible. 

Whenever a cloud is formed, it begins to rain; 
and the drops shower down in immense numbers, 
though most minute in size " the playful fancies of 
the mighty sky." 

No doubt it is only in certain circumstances that 
these drops are attracted together so as to form large 
drops, which fall to the earth in genial showers to 
refresh the thirsty soil, or in a terrible deluge to 
cause great destruction. But when the temperature 



IT ALWAYS KAINS 41 

and pressure are not suitable for the formation of 
what we commonly know as the rain, the fine drops 
fall into the air under the cloud, where they imme- 
diately evaporate from their dust free-surfaces, if the 
air is dry and warm. This is, in other words, the 
decay of clouds. 

It is a curious fact that objects in a fog may 
not be wetted, when the number of water-particles 
is great. It seems that these water-particles all 
evaporate so quickly that even one's hand or face 
is not sensible of being wetted. The particles are 
minutely small ; and they may evaporate even before 
reaching the warm skin, by reason of the heated air 
over the skin, 

There is a peculiarly warm sensation in the centre 
of a cumulus cloud, especially when it is not dense. 
A glow of heat seems to radiate from all points. 
Yet the face and hands are quite dry, and exposed 
objects are not wetted; but it is really always 
raining. That is a curious discovery. 

It is radiant heat that is the cause of the re- 
markable result. The rays of the sun, which strike 
the upper part of the cloud, not only heat that 
surface but also penetrate the cloud and fall on the 
surface of bodies within, generating heat there. 
These heated surfaces again radiate heat into the 
air attached to them. This warm air receives the 
fine raindrops in the cloud, and dissolves the moisture 
from the dust-particles before the moisture can reach 
the surfaces exposed. That a vast amount of radiant 
heat rushes through a cloud is clearly shown by 
exposing a thermometer with black bulb in vacuo. 
On some occasions, a thermometer would indicate 



42 METEOROLOGY 

from 40 to 50 above the temperature of the air, 
thus proving the surface to be quite dry. 

These observations have been corroborated on 
Mount Pilatus, near Lucerne 1000 feet higher and 
more isolated than the Rigi. The summit was quite 
enveloped in cloud, and, though one might naturally 
conclude that the air was dense with moisture, yet 
the wooden seats, walls, and all exposed surfaces 
were quite dry. Strange to say, however, the ther- 
mometers hung up got wet rapidly, and the phis 
driven into the wooden post to support them rapidly 
became moist. A thermometer lying on a wooden 
seat stood at 60, while one hung up read only 48. 
This difference was caused by radiant heat. 

It is well known that, when bodies are exposed to 
radiant heat, they are heated in proportion to then- 
size ; the smaller, then, may be moist, when the larger 
are 'dry by radiation. The effect of the sun's pene- 
trating heat through the cloud is to heat exposed 
objects above the temperature of the air; and if the 
objects are of any size they are considerably heated, 
and retain their heat more, while at the same time 
around them is a layer of warm air which is quite 
sufficient to force the water- vapour to leave the dust- 
particles in the fine rain. 

Hence seats, walls, posts, &c., are quite dry, though 
they are in the middle of a cloud. They are large 
enough to throw off the moisture by the retained 
heat, or by the large amount of surrounding heat; 
whereas, small bodies, which are not heated to the 
same degree and cannot therefore retain their heat 
so easily, have not heat-power sufficient to withstand 
the moisture, and they become wetted. Hence, by 



HAZE 43 

the radiant heat, the large exposed objects are dry in 
the cloud ; whereas small objects are damp, and, in 
some cases, dripping with wet. 

The fact is, then, that whenever a cloud overhangs, 
rain is falling, though it may not reach the earth 
on account of the dryness of the stratum of air below 
the cloud, and the heat of the air over the earth. 
So that on a summer day, with the gold-fringed, 
fleecy clouds sailing overhead, it is really raining; 
but the drops, being very small, evaporate long 
before reaching the earth. As Ariel sings at the 
end of " The Tempest " of Shakespeare, " The rain, 
it raineth every day." It rains, but much of the 
melting of the clouds is reproduced by a wonderful 
circularity the moisture evaporating, seizing other 
dust-particles, forming cloud-particles, falling again, 
and so on ad infinitum, during the existing circum- 
stances. 



CHAPTER XII 

HAZE 

WHAT is haze ? The dictionary says, " a fog." Well, 
haze is not a fog. In a fog, the dust-particles in the 
air have been fully clothed with water- vapour ; in a 
haze, the process of condensation has been arrested. 

Cloudy condensation is changed to haze by the 
reduction of its humidity. Dr. Aitken invented a 
simple apparatus for testing the condensing power of 
dust, and observing if water- vapour condensed on the 
deposited dust in unsaturated air. 



44 METEOBOLOGY 

The dust from the air has first to be collected. 
This is done by placing a glass plate vertically, and 
hi close contact with one of the panes of glass in the 
window, by means of a little india-rubber solution. 
The plate being thus rendered colder than the air hi 
the room, the dust is deposited on it. 

Construct a rectangular box, with a square bottom, 
1J inches a side and f inch deep, and open at the 
top. Cover the top edge of the box with a thickness 
of india-rubber. Place the dusty plate a square glass 
mirror, 4 inches a side on the top of the india-rubber, 
and hold it down by spring catches, so as to make 
the box water-tight. The box has been provided with 
two pipes, one for taking in water and the other for 
taking away the overflow, with the bulb of a ther- 
mometer in the centre. Clean the dust carefully off 
one half of the mirror, so that one half of the glass 
covering the box is clean and the other half dusty. 
Pour cold water through the pipe into the box, so as 
to lower the temperature of the mirror, and carefully 
observe when condensation begins on the clean part 
and on the dusty part, taking a note of the difference 
of temperature. The condensation of the water- 
vapour will appear on the dust - particles before 
coming down to the natural dew-point temperature 
of the clean glass. And the difference between the 
two temperatures indicates the temperature above 
the dew-point at which the dust has condensed the 
water-vapour, 

Magnesia dust has small affinity for water- vapour ; 
accordingly, it condenses at almost exactly the same 
temperature as the glass. But gunpowder has great 
condensing power. All have noticed that the smoke 



HAZE 45 

from exploded gunpowder is far more dense in damp 
than in dry weather. In the experiment it will be 
found that the dust from gunpowder smoke begins 
to show signs of condensing the vapour at a tempera- 
ture of 9 Fahr. above the dew-point. In the case of 
sodium dust, the vapour is condensed from the air 
at a temperature of 30 above the dew-point. 

Dust collected in a smoking-room shows a decidedly 
greater condensing power than that from the outer air. 

We can now understand why the glass in picture 
frames and other places sometimes appears damp 
when the air is not saturated. When in winter the 
windows are not often cleaned, a damp deposit may 
be frequently seen on the glass. Any one can try the 
experiment. Clean one half of a dusty pane of glass 
in cold weather, and the clean part will remain un- 
dewed and clear, while the dusty part is damp to the 
eye and greasy to the touch. 

These observations indicate that moisture is de- 
posited on the dust-particles from air, which is not 
saturated, and that the condensation takes place 
while the air is comparatively dry, before the tem- 
perature is lowered to the dew-point. There is, then, 
no definite demarcation between what seems to us 
clear air and thick haze. The clearest air has some 
haze, and, as the humidity increases, the thickness of 
the air increases. 

In all haze the temperature is above the dew-point. 
The dust-particles have only condensed a very small 
amount of the moisture so as to form haze, before 
the fuller condensation takes place at the dew-point. 

At the Italian lakes, on many occasions when the 
air is damp and still, every stage of condensation 



46 METEOROLOGY 

may be observed in close proximity, not separated 
by a hard and fast line, but when no one could 
determine where the clear air ended and the cloud 
began. Sometimes in the sky overhead a gradual 
change can be observed from perfect clearness to 
thick air, and then the cloud. 

A thick haze may be occasioned by an increased 
number of dust-particles with little moisture, or of 
a diminished number of dust-particles with much 
moisture, above the point of saturation. The haze is 
cleared by this temperature rising, so as to allow the 
moisture to evaporate from the dust-particles. 

Whenever the air is dry and hazy, much dust is 
found in it; as the dust decreases the haze also 
decreases. For example, Dr. Aitken, at Kingairloch, 
in one of the clearest districts of Argyleshire, on a 
clear July afternoon, counted 4000 dust-particles in a 
cubic inch of the air; whereas, two days before, in 
thick haze, he counted no fewer than 64,000 in the 
cubic inch. At Dumfries the number counted on a 
very hazy day in October increased twenty-fold over 
the number counted the day before, when it was clear. 

All know that thick haze is usual in very sultry 
weather. The wavy, will-o'-the-wisp ripples near 
the horizon indicate its presence very plainly. 
During the intense heat there is generally much 
dust in the atmosphere; this dust, by the high 
temperature, attracts moisture from the apparently 
dry air, though above the saturation point. In all 
circumstances, then, the haze can be accounted for 
by the condensing power of the dust-particles in 
the atmosphere, at a higher temperature than that 
required for the formation of fogs, or mists, or rain. 



HAZING EFFECTS OF ATMOSPHERIC DUST 47 

CHAPTER XIII 
HAZING EFFECTS OF ATMOSPHERIC DUST 

THE transparency of the atmosphere is very much 
destroyed by the impurities communicated to it 
while passing over the inhabited areas of the country. 
Dr. Aitken devoted eighteen months to compare 
the amount of dusty impurities in different masses 
of air, or of different airs brought in by winds from 
different directions. 

He took Falkirk for his centre of observations. 
This town lies a little to the north of a line drawn 
between Edinburgh and Glasgow, and is nearly mid- 
way between them. If we draw a line due west 
from it, and another due north, we find ,that, in the 
north-west quadrant so enclosed, the population of 
that part of Scotland is extremely thin, the country 
over that area being chiefly mountainous. In all 
other directions, the conditions are quite different. 
In the north-east quadrant are the fairly well-popu- 
lated areas of Aberdeenshire, Forfarshire, and the 
thickly populated county of Fife. In the south-east 
quadrant are situated Edinburgh and the well-popu- 
lated districts of the south-east of Scotland. And 
in the south-west quadrant are Glasgow and the 
large manufacturing towns which surround it. The 
winds from three of these quadrants bring air 
polluted in its passage over populated areas, whereas 
the winds from the north-west come comparatively 
pure. 

The general plan of estimating the amount of 



48 METEOROLOGY 

haze is to note the most distant hill that can be 
seen through the haze. The distance in miles of 
the farthest away hill visible is then called "the 
limit of visibility " of the air at the time. For the 
observations made at Falkirk, only three hills are 
available, one about four miles distant, the Ochils 
about fifteen miles distant, and Ben Ledi about 
twenty-five miles distant all in the north-west 
quadrant. When the air is thick, only the near 
hill can be seen ; then the Ochils become visible as 
the air clears; and at last Ben Ledi is seen, when 
the haze becomes still less. After Ben Ledi is 
visible, it then becomes necessary to estimate the 
amount of haze on it, in order to get the limit of 
visibility of the air at the time. Thus, if Ben Ledi 
be half-hazed, then the limit of visibility will be 
fifty miles. In this way all the estimates of haze 
have been reduced to one scale for comparison. 

As the result of all the observations it was found 
that, as the dryness of the air increases, the limit of 
visibility also increases. A very marked difference 
in the transparency of the air was found with winds 
from the different directions. In the north-west 
quadrant the winds made the air very clear, whereas 
winds from all other directions made the air very 
much hazed. The winds in the other three areas 
are nearly ten times more hazed than those from 
the north-west quadrant. That is very striking. 

The conclusion come to is that the air from 
densely inhabited districts is so polluted that it is 
fully nine times more hazed than the air that comes 
from the thinly inhabited districts ; in other words, 
the atmosphere at Falkirk is about ten times thicker 



THUNDER CLEARS THE AIR 49 

when the wind is east or south than it would be if 
there were no fires and no inhabitants. 

It is interesting to notice that the limit varies 
considerably for the same wind at the same humidity. 
This is what might have been expected, because 
from the observations made by the dust-counter 
the number of particles varied greatly in winds 
from the same directions, but at different times. 
This depends upon the rise and fall of the wind, 
changes in the state of trade, season of the year, and 
other causes. During a strike, the dearth of coal 
will make a considerable diminution in the number 
of dust-particles in the air of large towns. With 
a north wind, the extreme limits of visibility are 
120 to 200 miles; and with a north-west wind, from 
70 to 250 miles. An east wind has as limits 4 to 50 
miles, and a south-east wind 2 to 60 miles. 

One interesting fact to be noticed, after wading 
through these tables, is this that, as a general result, 
the transparency of the air increases about 3*7 times 
for any increase in dryness from 2 to 8 of wet- 
bulb depression. That is, the clearness of the air is 
inversely proportional to the relative humidity ; or, 
put another way, if the air is four times drier it is 
about four times clearer. 



CH AFTER ' XIV 
THUNDER CLEARS THE AIR 

THE phrase " thunder clears the air " is familiar to 
all. It contains a very vital truth, yet even scientific 

D 



50 METEOROLOGY 

men did not know its full meaning until just the 
other day. It came by experience to people who 
had been for ages observing the weather ; and it is 
one of the most pointed of the "weather-lore" ex- 
pressions. Folks got to know, by a sort of rule-of- 
thumb, truths which scientifically they were unable 
to learn. And this is one. 

Perhaps, therefore, we should respect a little more 
what is called " folk-lore," or ordinary people's say- 
ings. Experience has taught men many wonderful 
things. In olden times they were keener natural 
observers. They had few books, but they had plenty 
of time. They studied the habits of animals and 
moods of nature, and they came wonderfully near to 
reaching the full truth, though they could not give 
a reason for it. The awe-inspiring in nature has 
especially riveted the attention of man. 

And no appearance in nature joins more power- 
fully the elements of grandeur and awe than a heavy 
thunder-storm. When, suddenly, from the breast of 
a dark thunder-cloud a brilliant flash of light darts 
zigzag to the earth, followed by a loud crackling 
noise which softens in the distance into weaker 
volumes of sound, terror seizes the birds of the air 
and the cattle in the field. The man who is born to 
rule the storm rejoices in the powerful display ; but 
kings have trembled at the sight. 

Byron thus pictures a storm in the Alps : 

" Far along 

From peak to peak, the rattling crags among 
Leaps the live thunder ! Not from one lone cloud, 

But every mountain now hath found a tongue, 
And Jura answers, through her misty shroud, 
Back to the joyous Alps, who call to her aloud ! " 



THUNDER CLEARS THE AIR 51 

Franklin found that lightning is just a kind of 
electricity. No one can tell how it is produced ; yet 
a flash has been photographed. When the flash is 
from one cloud to another there is sheet-lightning, 
which is beautiful but not dangerous; but, when 
the electricity passes from a cloud to the earth in a 
forked form, it is very dangerous indeed. The flash 
is instantaneous, but the sound of the thunder takes 
some time to travel. Roughly speaking, the sound 
takes five seconds or six beats of the pulse to the 
mile. 

All are now taught at school that it is the oxygen 
in the air which is necessary to keep us in life. If 
mice are put into a glass jar of pure oxygen gas, they 
will at once dance with exhilarating joy. It occurred 
to Sir Benjamin Richardson, some time ago, that it 
would be interesting to continue some experiments 
with animals and oxygen. He put a number of mice 
into a jar of pure oxygen for a time ; they breathed 
in the gas, and breathed out water-vapour and 
carbonic acid. After the mice had continued this 
for some time, he removed them by an arrangement. 
By chemical means he removed the water-vapour 
and carbonic acid from the mixed air in the vessel. 
When a blown-out taper was inserted, it at once 
burst into flame, showing that the remaining gas was 
oxygen. 

Again, the mice were put into this vessel to 
breathe away. But, strange to say, the animals soon 
became drowsy; the smartness of the oxygen was 
gone. At last they died ; there was nothing in the 
gas to keep them in life; yet, by the ordinary 
chemical tests, it was still oxygen. It had repeatedly 



52 METEOROLOGY 

passed through the lungs of the mice, and during 
this passage there had been an action in the air-cells 
which absorbed the life-giving element of the gas. 
It is oxygen, so far as chemistry is concerned, but 
it has no life-giving power. It has been devitalised. 

But the startling discovery still remains. Sir 
Benjamin had previously fitted up the vessel with 
two short wires, opposite each other in the sides 
part outside and part inside. Two wires are fastened 
to the outside knobs. These wires are attached to an 
electric machine, and a flash of electricity is made to 
pass between the inner points of the vessel. The 
wires are again removed ; nothing strange is seen in 
the vessel. But, when living mice are put into the 
vessel, they dance as joyfully as if pure oxygen were 
in it. The oxygen in which the first mice died has 
now been quite refreshed by the electricity. The 
bad air has been cleared and made life-supporting 
by the electric discharge. It has been again vitalised. 

Now, to apply this : before a thunder-storm, every- 
thing has been so still for days that the oxygen in 
the air has been to some extent robbed of its life- 
sustaining power. The air feels "close," a feeling 
of drowsiness comes over all. But, after the air has 
been pierced by several flashes of lightning, the life- 
force in the air is restored. Your spirits revive; 
you feel restored ; your breathing is far freer ; your 
drowsiness is gone. Then there is a burst of heavenly 
music from the exhilarated birds. Thus a thunder- 
storm " clears the air." 

After the passage of lightning through the air 
ozone is produced the gas that is produced after 
a flash of electricity. It is a kind of oxygen, with 



DISEASE- GERMS IN THE AIR 53 

fine exciting effects on the body. If, then, the life- 
sustaining power of oxygen depends on a trace of 
ozone, and this is being made by lightning's work, 
how pleased should we be at the occasional thunder- 
storm I 



CHAPTER XV 
DISEASE-GERMS IN THE AIR 

THE gay motes that dance in the sunbeams are not 
all harmless. All are annoying to the tidy house- 
keeper ; but some are dangerous. There are living 
particles that float in the air as the messengers of 
disease and death. Some, falling on fresh wounds, 
find there a suitable feeding-place; and, if not 
destroyed, generate the deadly influence. Others 
are drawn in with the breath ; and, unless the lungs 
can withstand them, they seize hold and spread 
some sickness or disease. From stagnant pools, 
common sewers, and filthy rooms, disease-germs are 
constantly contaminating the air. Yet these can be 
counted. 

The simplest method is that of Professor Frank- 
land. It depends on this principle: a certain 
quantity of air is drawn through some cotton- wool ; 
this wool seizes the organisms as the air passes 
through ; these organisms are afterwards allowed to 
feed upon a suitable nutritive medium until they 
reach maturity ; they are then counted easily. 

About an inch from each end of a glass tube 
(5 inches long and 1 inch bore), the glass is pressed 



54 METEOROLOGY 

in during the process of blowing. Some cotton-wool 
is squeezed in to form a plug at the farther con- 
stricted part of the glass. The important plug is 
now inserted at the same open end, but is not allowed 
to go beyond the constricted part at its end. A piece 
of long lead tubing is attached to the former end by 
an india-rubber tube. The other end of the lead 
tubing is connected with an exhausting syringe. 
Sixty strokes of the 18 cubic inches syringe will 
draw 1080 cubic inches of the air to be examined 
through the plugs, the first retaining the organisms. 

The impregnated plug is then put into a flask 
containing in solution some gelatine-peptone. The 
flask is made to revolve horizontally until an almost 
perfectly even film of gelatine and the organisms 
from the broken-up plug cover its inner surface. 

The flask is allowed to remain for an hour in a 
cool place, and is then placed under a bell-jar, at a 
temperature of 70 Fahr. There it remains, to allow 
the germs to incubate, for four or five days. The 
surface of the flask having been previously divided 
into equal parts by ink lines, the counting is now 
commenced. If the average be taken for each 
segment, the number of the whole is easily ascer- 
tained. A simple arithmetical calculation then 
determines the number of organisms in a cubic foot, 
since the number is known for the 1080 cubic inches. 
That is the process for determining the number of 
living organisms in a fixed quantity of air. 

No less than thirty colonies of organisms were 
counted in a cubic foot of air taken from the Golden 
Gallery of St. Paul's Cathedral, London, and 140 
from the air of the churchyard. An ordinary man 



A CHANGE OF AIR 55 

would breathe there thirty-six micro-organisms every 
minute. 

Electricity has a powerful effect in destroying these 
organisms. Ozone is generated in the air by light- 
ning, and it is detrimental to them. In fine ozoned 
Highland air scarcely a disease-germ can be detected. 
Open sea air contains about one germ in two cubic 
feet. It has been found that in Paris the average in 
summer is about 140 per cubic foot of air, but in 
bedrooms the number is double. During the twenty- 
four hours of the day the number of germs is highest 
ahout 6 A.M., and lowest about mid-day. 

Raindrops carry the germs to the ground. Hence 
the advantage of a thunder plout in a sanitary way. 
A cubic foot of rain has been found to contain 5500 
organic dust-germs, besides 7,000,000,000 of inorganic 
dust-particles. In a dirty town the rain will bring 
down in a year, upon a square foot of surface, no 
less than 3,000,000 of bacteria, many of them being 
disease-bearing and death-bearing. No wonder, then, 
that scientific men are using every endeavour to 
protect the human frame, as well as the frame of 
the lower animals, from the baneful inroads of these 
floating nuclei of disease and death. 



CHAPTER XVI 
A CHANGE OF AIR 

FOR weakness of body and fatigue of mind a very 
common and essentially serviceable recommendation 
is " a change of air." Of course, the change of scene 



56 METEOROLOGY 

from coast to country, or from town to hillside, may 
help much the depressed in body or mind ; and this 
is very commendable. But, strange to say, there is a 
healing virtue in breathing different air. 

At first one is apt to think that air is the same all 
over, as he thinks water is especially outside smoky 
towns ; but both have varied qualities in different 
parts. You have only to be assured that in a cubic 
inch of bedroom air in the denser parts of a large 
town there are about 20,000,000 of dust-particles, 
and in the open air of a heathery mountain-side 
there are only some hundreds, to see that there is 
something after all on the face of it in the "old 
wives' saw." 

Not that the dust-particles are all injurious; for 
most of them are inorganic, and many of the organic 
particles are quite wholesome ; yet there is a change 
wrought, often very marked, in going from one place 
to another for different air. 

Even in the country, especially in summer-time, 
one distinctly notices the great difference in the air 
of lowland and highland localities. The ten miles 
change from Strathmore to Glenisla shows a marked 
difference in the air. Below, it is close, weakening, 
enervating ; above, it is exhilarating, invigorating, and 
strong. 

So people must have a change at least those who 
can afford it for health must be seen to first of all, 
if one has means to do so. Oh ! the blessing of good 
health ! How many who enjoy it never think of the 
misery of its loss ! In fact, health is the soul that 
animates all enjoyments of life; for without it those 
would soon be tasteless. A man starves at the best- 



A CHANGE OF AIR 57 

spread table, and is poor in the rnidst of the greatest 
treasures without health. 

In these days half of our diseases come from the 
neglect of the body in the overwork of the brain. 
The wear and tear of labour and intellect go on 
without pause or self-pity. Men may live as long as 
their forefathers, but they suffer more from a thousand 
artificial anxieties and cares. The men of old fatigued 
only the muscles, we exhaust the finer strength of 
the nerves. Even more so now, then, do we require 
a change of air to soothe our overwrought nervous 
system. 

And when that magic power, concealed from mortal 
view, works such wonders on the health, surely it 
is one's duty to save up and have it, when it is 
within one's means. For is not health the greatest 
of all possessions ? What a rich colour clothes the 
countenance of the young after a month's outing in 
the hill country ! How fine and pure has the blood 
become ! All stagnant humours, accumulated in 
winter town life, have been dispelled by the ozone- 
brightening charm. The weary looking office or 
shop man is now transfigured into a sprightly youth 
once more, ready with strongly recuperated power 
for another winter's labours. The pale wife, who has 
been stifled for months in close-aired rooms, has now 
a healthy flush on her becoming countenance that 
speaks of gladly restored health. And all this has 
been brought about by a " change of air " ! 

For a thorough change to a town man, he should 
make for the Highlands. There he is never tired of 
walking, for the air which he breathes is full of ozone. 
This revivifying element in the air is produced by 



58 METEOROLOGY 

the lightning-bursts from hill to hill. There is in 
the Highlands a continual rush of electricity, whether 
seen or not. Hence the air is very pure, free from 
organic germs, intensely exhilarating and buoyant. 

Sportsmen are livingly aware of the recuperative 
power of the Highland air. Perhaps these city men 
do not benefit so much by the easy walking exercise 
on the grouse moors as in breathing the splendidly 
delight-inspiring air. What a change one feels there 
in a very few hours ! 

" A change of ah* " is an old wives' adage. But 
much of the weather-lore of our forefathers was based 
on real scientific principles only now coming to 
light. Nature is ever true, but it requires patience 
to unravel her secrets. We therefore advocate an 
occasional " change of air " to improve the health 

" The chiefest good, 
Bestow'd by Heaven, but seldom understood." 



CHAPTER XVII 

THE OLD MOON IN THE NEW MOON'S ARMS 

AFTER the sun's broad beams have tired the sight, 
the moon with more sober light charms us to 
descry her beauty, as she shines sublimely in her 
virgin modesty. There is always a most fascinating 
freshness in the first sight of the new moon. The 
superstition of centuries adds to this charm. Why 
boys and girls like to turn over a coin in their pocket 
at this sight one cannot tell : yet it is done. No 



OLD MOON IN THE NEW MOON*S ARMS 59 

young lady likes to look at the new moon through a 
pane of glass. And farmers are always confident of 
a change of weather with a new moon : at least in 
bad weather they earnestly hope for it. 

But, banishing all superstition, we welcome the pale 
silver sickle in the heavens, once more appearing from 
the bosom of the azure. And no language can equal 
these beautiful words of the youthful Shelley : 

" Like the young moon, 
When on the sunlit limits of the night 

Her white shell trembles amid crimson air, 
And while the sleeping tempest gathers might, 

Doth, as the herald of his coming, bear 
The ghost of its dead mother, whose dim form 

Bends in dark ether from her infant's chair." 

That is a more charming way of putting the 
ordinary expression, " the old moon in the new 
moon's arms." We are regularly accustomed to the 
moonshine, but only occasionally is the earthshine 
on the moon so regulated that the shadowed part is 
visible. This is not seen at the appearance of every 
new moon. It depends upon the positions of the 
sun and moon, the state of the atmosphere, and the 
absence of heavy clouds. I never in my life saw the 
phenomenon so marvellously beautiful as on May 
7th, 1894, at my manse in Strathmore. I took par- 
ticular note of it, as some exceedingly curious things 
were connected with it. 

At nine o'clock in the evening, the new moon 
issued from some clouds in the western heavens, the 
sun having set, about an hour before. The crescent 
was thin and silvery, and the outline of the shadowed 
part was just visible. The sky near the horizon was 



60 METEOROLOGY 

clear and greenish-hued. As the night advanced the 
moon descended, and at ten o'clock she was ap- 
proaching a purple stratum of clouds that stretched 
over the hills, while the position of the sun was only 
known a little to the east, by the back-thrown light 
upon the dim sky. Through the moisture-laden air 
the sun's rays, reflected by the moon, threw a golden 
stream from the crescent moon, for the silvery shell 
became more golden-hued. 

The horns of the moon now seemed to project, and 
the shadowed part became more distinct, though the 
circle appeared smaller. By means of a field-glass I 
noticed that this was extra lighted, with points here 
and there quite golden-tinged. The darker spots 
showed the deep caverns; the brighter points 
brought into relief the mountain peaks. 

Why was the surface brighter than usual ? I can- 
not go into detail about the phases of the moon ; 
but, in a word, I may say that, while the sun can 
illuminate the side of the moon turned towards it, it 
is unable to throw any light on the shadow, seeing 
that there is no atmosphere around the moon to 
refract the light. 

If we, in imagination, looked from the moon 
upon the earth, we should see the same phases as are 
now noticed in the moon ; and when it is just before 
new moon on the earth, the earth will appear fully 
illuminated from the moon. We would also observe 
(from the moon) that the brightness of the illuminated 
part of the earth would vary from time to time, accord- 
ing to the changes in the earth's atmosphere. More 
light would be reflected to the moon from the clouds 
in our atmosphere than from the bare earth or 



OLD MOON IN THE NEW MOON'S ARMS 61 

cloudless sea, since clouds reflect more light than 
either land or sea. Accordingly, .we arrive at this 
curious fact that the extra brightness of the dark 
body of the moon is mainly determined by the 
amount of cloud in our atmosphere. 

Accordingly, I concluded that there must be 
clouds to the west, though I could not see them, 
which reflected rays of light and faintly illuminated 
the shadowed part of the moon. It had become 
much colder, and I concluded that during the night 
the cloud-particles, if driven near by the wind, would 
condense into rain. And, assuredly, next morning I 
was gratified to find that rain had fallen in large 
quantities, substantiating the theory. 

There is much pleasure in verifying such an inter- 
esting problem. The dark body of the moon being 
more than usually visible is one of our well-known 
and oldest indications of coming bad weather. And 
at once came to my memory the lines of Sir Patrick 
Spens, as he foreboded rain for his crossing the North 

Sea: 

'* I saw the new moon late yestreen 
Wi 3 the auld moon in her arm ; 
And if we gang to sea, master, 
I fear we'll come to harm." 

This lunar indication, then, has a sound physical 
basis, showing that near the observer there are vast 
areas of clouds, which are reflecting light upon the 
moon at the time, before they condense into rain by 
the chilling of the air. According to the old Greek 
poet, Aratus : " If the new moon is ruddy, and you 
can trace the shadow of the complete circle, a storm 
is approaching." 



62 METEOROLOGY 

CHAPTER XVIII 

AN AUTUMN AFTERGLOW 

A BRILLIANT afterglow is welcomed for its surpassing 
beauty and a precursor of fine fixed weather. 

A glorious sunset has always had a charrn for the 
lover of nature's beauties. The zenith spreads its 
canopy of sapphire, and not a breath creeps through 
the rosy air. A magnificent array of clouds of 
numberless shapes come smartly into view. Some, 
far off, are voyaging their sun-bright paths in silvery 
folds; others float in golden groups. Some masses 
are embroidered with burning crimson ; others are 
like " islands all lovely in an emerald sea." Over the 
glowing sky are splendid colourings. The flood of 
rosy light looks as if a great conflagration were below 
the horizon. 

I remember witnessing an especially brilliant 
sunset last autumn on the high-road between Kirrie- 
muir and Blairgowrie. The setting sun shone upon 
the back of certain long trailing clouds which were 
much nearer me than a range behind. The fringes 
of the front range were brilliantly golden, while the 
face of those behind was sparklingly bright. Then 
the sun disappeared over the western hills, and his 
place was full of spokes of living light. 

Looking eastward, I observed on the horizon the 
base of the northern line of a beautiful rainbow 
" the shepherd's delight " for fine weather. 

Soon in the west the light faded ; but there came 



AN AUTUMN AFTERGLOW 63 

out of the east a lovely flush, and the general sky 
was presently flamboyant with afterglow. The front 
set of clouds was darker except on the edges, the red 
being on the clouds behind ; and the horizon in the 
east was particularly rich with dark red hues. 

Gradually the eastern glow rose and reddened all 
the clouds, but the front clouds were still grey. 
The effect was very fine in contrast. The fleecy 
clouds overhead became transparently light red, 
as they stretched over to reach the silver-streaked 
west. The new moon was just appearing upright 
against a slightly less bright opening in the sky, 
betokening the firm hardness of autumn. 

Soon the colouring melted away, and the peaceful 
reign of the later twilight possessed the land. 

Now why that brilliancy of the east, when the 
west was colourless ? Most of all you note the 
immense variety and wealth of reds. These are 
due to dust in the atmosphere. We are the more 
convinced of this by the very remarkable and beau- 
tiful sunsets which occurred after the tremendous 
eruption at Krakatoa, in the Straits of Sunda, thirty 
years ago. There was then ejected an enormous 
quantity of fine dust, which spread over the whole 
world's atmosphere. So long as that vast amount of 
dust remained in the air did the sunsets and after- 
glows display an exceptional wealth of colouring. All 
observers were struck with the vividly brilliant red 
colours in all shades and tints. 

The minute particles of dust in the atmosphere 
arrest the sun's rays and scatter them in all direc- 
tions; they are so small, however, that they cannot 
reflect and scatter all; their power is limited to 



64 METEOROLOGY 

the scattering of the rays at the blue end of the 
spectrum, while the red rays pass on unarrested. 
The display of the colours of the blue end are found 
in numberless shades, from the full deep blue in the 
zenith to the greenish-blue near the horizon. 

If there were no fine dust-particles in the upper 
strata, the sunset effect would be whiter; if there 
were no large dust-particles, there would be no 
colouring at all. If there were no dust-particles in 
the air at all, the light would simply pass through 
into space without revealing itself, and the moment 
the sun disappeared there would be total darkness. 
The very existence of our twilight depends on the 
dust in the air ; and its length depends on the amount 
and extension upwards of the dust-particles. 

But how have the particles been increased in size 
in the east ? Because, as the sun was sinking, but 
before its rays failed to illumine the heavens, the 
temperature of the air began to fall. This cooling 
made the dust-particles seize the water-vapour to 
form haze-particles of a larger size. The particles in 
the east first lose the sun's heat, and first become 
cool ; and the rays of light are then best sifted, pro- 
ducing a more distinct and darker red. As the sun 
dipped lower, the particles overhead became a turn 
larger, and thereby better reflected the red rays. 
Accordingly, the roseate bands in the east spread 
over to the zenith, and passed over to the west, produc- 
ing in a few minutes a universal transformation glow. 

To produce the full effect often witnessed, there 
must be, besides the ordinary dust-particles, small 
crystals floating in the air, which increase the reflec- 
tion from their surfaces and enhance the glow effects. 



A WINTEB FOKEGLOW 65 

In autumn, after sunset, the water-covered dust- 
particles become frozen and the red light streams 
with rare brilliancy, causing all reddish and coloured 
objects to glow with a rare brightness. Then the air 
glows with a strange light as of the northern dawn. 
From all this it is clear that, though the colouring of 
sunset is produced by the direct rays of the sun, the 
afterglow is produced by reflection, or, rather, radia- 
tion from 1 the illuminated particles near the horizon. 
The effect in autumn is a stream of red light, of 
varied tones, and rare brilliancy in all quarters, unseen 
during the warmer summer. We have to witness 
the sunsets at Ballachulish to be assured that Waller 
Paton really imitated nature in the characteristic 
bronze tints of his richly painted landscapes. 



CHAPTER XIX 

A WINTER FOREGLOW 

LITTLE attention has been paid to foreglows com- 
pared with afterglows, either with regard to their 
natural beauty or their weather forecasting. But 
either the ordinary red-cloud surroundings at sunrise, 
or the western foreglow at rarer intervals, betokens to 
the weather-prophet wet and gloomy weather. The 
farmer and the sailor do not like the sight, they 
depend so much on favourable weather conditions. 

Of course, sunrise to the aesthetic observer has 
always its charms. The powerful king of day 
rejoices " as a bridegroom coming out of his 

E 



66 METEOROLOGY 

chamber " as he steps upon the earth over the dewy 
mountain tops, bathing all in light, and spreading 
gladness and deep joy before him. The lessening 
cloud, the kindling azure, and the mountain's brow 
illumined with golden streaks, mark his approach ; 
he is encompassed with bright beams, as he throws 
his unutterable love upon the clouds, " the beauteous 
robes of heaven." Aslant the dew-bright earth 
and coloured air he looks in boundless majesty 
abroad, touching the green leaves all a-tremble with 
gold light. 

But glorious, and educating, and inspiring as is the 
sunrise in itself in many cases, there is occasionally 
something very remarkable that is connected with it. 
Rare is it, but how charming when witnessed, though 
till very recently it was all but unexplained. This is 
the foreglow. 

It is in no respect so splendid as the afterglow 
succeeding sunset ; but, because of its comparative 
rarity, its beauty is enhanced. I remember a fore- 
glow most vividly which was seen at my manse, hi 
Strathmore, in January 1893. My bedroom window 
looked due west ; I slept with the blind up. On that 
morning I was struck, just after the darkness was 
fading away, with a slight colouring all along the 
western horizon. The skeleton branches of the 
trees stood out strongly against it. The colouring 
gradually increased, and the roseate hue stretched 
higher. The old well-known faces that I used to 
conjure up out of the thin blended boughs became 
more life-like, as the cheeks flushed. There was 
rare warmth on a winter morning, to cheer a half- 
despairing soul, tired out with the long hours of oil 



A WINTER FOREGLOW 67 

reading, and pierced to the heart by the never- 
ceasing rimes ; yet I could not understand it. 

I went to the room opposite to watch the sunrise, 
for I had observed in the diary that the appearance 
of the sun would not be for a few minutes. There 
were streaks of light in the east above the horizon, 
but no colour was visible. That hectic flush slight, 
yet well marked which was deepening in the western 
heavens, had no counterpart in the east, except the 
colourless light which marked the wintry sun's near 
approach. As soon as the sun's rays shot up into 
the eastern clouds, and his orb appeared above the 
horizon, the western sky paled, the colour left it, as 
if ashamed of its assumed glory. A foreglow like 
that I have very rarely seen, and its existence was 
a puzzle to me till I studied Dr. Aitken's explanation 
of the afterglows after sunset. I had never come 
across any description of a foreglow ; and, of course, 
across no explanation of the curious phenomenon. 
The western heavens were coloured with fairly bright 
roseate hues, while the eastern horizon was only 
silvery bright before the sun rose ; whereas, after the 
sun appeared and coloured the eastern hills and 
clouds, the western sky resumed its leaden grey and 
colourless appearance. Why was that ? What is the 
explanation ? 

I have not space enough to repeat the explanation 
given already in the last chapter of the glorious 
phenomenon of the afterglow. But the explanation 
is similar. Before sunrise, the rays of the sun are 
reflected by dust-particles in the zenith to the western 
clouds. The colouring is intensified by the frozen 
water-vapour on these particles in the west. 



08 METEOROLOGY 

One thing I carefully noted. Ere mid-day, snow 
began to fall, and for some days a severe snow- 
storm kept us indoors. Then, at any rate, the fore- 
glow betokened a coming storm. It was, like a 
rainbow in a summer morning, a decided warning 
of the approaching wet weather. 



CHAPTER XX 

THE RAINBOW 
THE poet Wordsworth rapturously exclaimed 

" My heart leaps up when I behold 
A rainbow in the sky." 

And old and young have always been enchanted 
with the beautiful phenomenon. How glorious is 
the parti-coloured girdle which, on an April morning 
or September evening, is cast o'er mountain, tower, 
and town, or even mirrored in the ocean's depths ! 
No colours are so vividly bright as when this 
triumphal arch bespans a dark nimbus: then it 
unfolds them in due prismatic proportion, " running 
from the red to where the violet fades into the 
sky." 

A plain description of the formation of the rain- 
bow is not very easily given, but a short sketch may 
be useful. Beautiful as is the ethereal bow, "born 
of the shower and colour'd by the sun," yet the 
marvellous effect is more exquisitely intensified in its 
gorgeous display when the hand of science points 



THE RAINBOW 69 

out the path in which the sun's rays, from above the 
western horizon, fall on the watery cloud, indicating 
line weather " the shepherd's delight." 

One law of reflection is that, when a ray of light 
falls on a plane or spherical surface, it goes oft* at 
the same angle to the surface as it fell. One law 
of refraction is that, when a ray of light passes 
through one medium and enters a denser medium 
(as from air to water), it is bent back a little. By 
refraction you see the sun's rays long after the sun 
has set ; when the sun is just below the horizon, an 
observer, on the surface of the earth, will see it 
raised by an amount which is generally equal to its 
apparent diameter. 

The rays of different colours are bent back (when 
passing through the water) at different rates, some 
slightly, others more, from the red to the violet end. 
The rainbow, then, is produced by refraction and 
reflection of the several coloured rays of sunlight in 
the drops of water which make up falling rain. 

The sun is behind the observer, and its rays fall 
in a parallel direction upon the drops of rain before 
him. In each drop the light is dispersively refracted, 
and then reflected from the farther face of the drop ; 
it travels back through the drop, and comes out with 
dispersing colours. 

According to the height of the sun, or the slope 
of its rays, a higher or lower rainbow will be formed. 
And, strange, no two people can see the very same 
bow ; in fact the rainbow, as seen by the one eye, is 
not formed by the same water-drops as the rainbow 
seen by the other eye. 

When the primary bow is seen in most vivid 



70 METEOROLOGY 

colours on a dark cloud, a second arch, larger and 
fainter, is often seen. But the order of the colours is 
quite reversed. At a greater elevation, the sun's ray 
enters the lower side of a drop of rain-water, is re- 
fracted, reflected twice, and then refracted again before 
being sent out to the observer's eye. That is why 
the colours are reversed. 

A one-coloured rainbow is a curious and rare 
phenomenon. It is a strange paradox, for the very 
idea of a rainbow brings up the seven colours red, 
orange, yellow, green, blue, indigo, and violet. Yet 
Dr. Aitken tells us of a rainbow with one colour 
which he observed on Christmas Day, in 1888. 

He was taking his walk on the high ground south 
of Falkirk. In the east he observed a strange pillar- 
like cloud, lit up with the light of the setting 
sun. Then the red pillar extended, curved over, and 
formed a perfect arch across the north-eastern sky. 
When fully developed, this rainbow was the most 
extraordinary one which he had ever seen. There 
was no colour in it but red. It consisted simply 
of a red arch, and even the red had a sameness 
about it. 

Outside the rainbow there was part of a secondary 
bow. The Ochil Hills were north of his point of 
observation. These hills were covered with snow, 
and the setting sun was glowing with rosy light. 
Never had he seen such a depth of colour as was 
on them on this occasion. It was a deep, furnacy 
red. The sun's light was shorn of all the rays of 
short-wave length on its passage through the atmos- 
phere, and only the red rays reached the earth. 
The reason why the Ochils glowed with so deep a 



THE AURORA BOREALIS 71 

red was owing to their being overhung by a dense 
curtain of clouds, which screened off the light of the 
sky. The illumination was thus principally that of 
the direct softer light of the sun. 



CHAPTER XXI 
THE AURORA BOREALIS 

HE must be a very careless observer who has not 
been struck with the appearance of the streamers 
which occasionally light up the northern heavens, 
and which farmers consider to be indicators of 
strong wind or broken weather. 

The time was when the phenomenon was con- 
sidered to be supernatural and portentous, as the 
chroniclers of spectral battles, when "fierce, fiery 
warriors fought upon the clouds, in ranks and- 
squadrons, and right form of war." And even in 
the rural districts of Britain, the blood-coloured 
aurora, of October 24th, 1870, was considered to be 
the reflection of an enormous Prussian bonfire, fed by 
the beleaguered French capital. 

In joyful spirit, the Shetlanders call the beautiful 
natural phenomenon, " Merry Dancers." Burns asso- 
ciated their evanescence with the transitoriness of 
sensuous gratification : " they flit ere you can point 
their place." And Tennyson spoke of his cousin's face 
lit up with the colour and light of love, " as I have 
seen the rosy red flushing in the northern night." 

Yet this phenomenon is to a great extent under 
the control of cosmical laws. One of the most diffi- 



72 METEOROLOGY 

cult problems of our day has been to disentangle the 
irregular webwork of aurorse, and bring them under 
a law of periodicity, which depends upon the fluctua- 
tions of the sun's photosphere and the variations or 
the earth's magnetism, and which have such an 
important influence upon the fluctuations of the 
weather. 

The name "Aurora Borealis" was given to it by 
Gassendi in 1621. Afterwards, the old almanacs 
described it as the "Great Amazing Light in the 
North." In the Lowlands of Scotland, the name it 
long went by, of " Lord Derwentwater's Lights," was 
given because it suddenly appeared on the night 
before the execution of the rebel lord. In Ceylon 
aurorse were called " Buddha Lights." 

The first symptom of an aurora borealis is com- 
monly a low arch of pale, greenish-yellow light, 
placed at right angles to the magnetic meridian. 
Sometimes rays cover the whole sky, frequently 
showing tremulous motion from end to end ; and 
sometimes they appear to hang from the sky like 
the fringes of a mantle. They are among the most 
capricious of natural phenomena, so full of indi- 
vidualities and vagaries. To the glitter of rapid 
movement they add the charm of vivid colouring. 
It is strongly asserted that aurorse are preceded by 
the same general phenomena as thunder-storms. 
This was borne out by Piazzi Smith (late Astron- 
omer-Royal for Scotland), who observed that their 
monthly frequency varies inversely with that of 
thunder-storms both being safety-valves for the 
discharge of surplus electricity. 

Careful observers have, moreover, noticed a re- 



THE AURORA BOREALIS 73 

markable coincidence between the display of aurorae 
and the maxima of the sun's spots and of the earth's 
magnetic disturbances. Some have supposed that 
the light of the aurora is caused by clouds of 
meteoric dust, composed of iron, which is ignited 
by friction with the atmosphere. But there is this 
difficulty in the way, shooting stars are more frequent 
in the morning, while the reverse is the case with 
the aurora. The highest authorities have concluded, 
pretty uniformly, that aurorge are electric discharges 
through highly rarefied air, taking place in a mag- 
netic field, and under the sway of the earth's 
magnetic induction. They are not inappropriately 
called " Polar lightnings," for when electricity misses 
the one channel it must traverse the other. 

The natives of the Arctic regions of North America 
pretend to foretell wind by the rapidity of the 
motions of the streamers. When they spread over 
the whole sky, in a uniform sheet of light, fine 
weather ensues. Fitzroy believed that aurorae in 
northern latitudes indicated and accompanied stormy 
weather at a distance. The same idea is still current 
among many farmers and fishermen in Scotland. 

Is there any audible accompaniment to the brilliant 
spectacle? The natives of some parts, with subtle 
hearing-power, speak of the " whizzing " sound which 
is often heard during auroral displays. Burns tells 
of their " hissing, eerie din," as echoes of the far-off 
songs of the Valkyries. Perhaps the most striking 
incident which corroborates this opinion occurred 
during the Franco-Prussian War. Holier, a practised 
aeronaut, left Paris in a balloon, on his mission of 
city defence, and fourteen hours afterwards landed 



74 METEOROLOGY 

in Norway. He had reached the height of two and 
a half miles. When descending, he passed through 
a peculiar cloud of sulphurous odour, which emitted 
flashed light and a slight scratching or rustling 
noise. On landing, he witnessed a splendid aurora 
borealis. He must, therefore, have passed through 
a cloud in which an electrical discharge of an auroral 
nature was proceeding, accompanied with an audible 
sound. There is, moreover, no improbability of such 
sounds being occasionally heard, since a somewhat 
similar phenomenon accompanies the brush dis- 
charge of the electric machinery, to which the 
aurora bears considerable resemblance. 

Though no fixed conclusions are yet established 
about the causes of the brilliant auroral display, yet, 
as the results of laborious observations, we are assured 
that the stabler centre of our solar system holds in 
its powerful sway the several planets at their re- 
spective distances, supplying them all with their 
seasonable light and ;heat, vibrating sympathetic 
chords in all, and even controlling under certain 
though to us still unknown laws the electric 
streamers that flit, apparently lawlessly, in the distant 
earth's atmosphere. 



CHAPTER XXII 

THE BLUE SKY 

IF we look at the sky overhead, when cloudless 
in the sunshine, we wonder what gives the air 
such a deep-blue colour. We are not looking, as 



THE BLUE SKY 75 

children seem to do, into vacancy, away into the far 
unknown. And even, if that were the case, would 
not the space be quite colourless ? What, then, pro- 
duces the blueness ? 

Some of the very fine dust-particles, even when 
clothed with an exceedingly thin coating of water- 
vapour, are carried very high ; and, looking through 
a vast accumulation of these, we find the effect of 
a deep-blue colour. 

Why so ? Because these particles are so small 
that they can only reflect the rays of the blue end of 
the spectrum ; and the higher we ascend, the smaller 
are the particles and the deeper is the blue. But 
it is also because water, even in its very finest 
and purest form, is blue in colour. For long this 
was disputed. Even Sir Robert Christison con- 
cluded, after years of experimenting on Highland 
streams, that water was colourless. 

Of course, he admitted that the water in the 
Indian and Pacific Oceans has frequent patches of 
red, brown, or white colour, from the myriads of 
animalcules suspended in the water. Ehrenberg 
found that it was vegetable matter which gave to 
the Red Sea its characteristic name. But these, and 
similar waters, are not pure. 

It is to Dr. Aitken that the final discovery of the 
real colour of water is due. When on a visit to 
several towns on the shores of the Mediterranean, he 
set about making some very interesting experiments, 
which the reader will follow with pleasure. 

It is a well-known fact that colour transmitted 
through different bodies differs considerably from 
colour reflected by them. In his first experiment he 



76 METEOROLOGY 

took a long empty metal tube, open at one end, and 
closed at the other end by a clear-glass plate. This 
was let down vertically into the water, near to a fixed 
object, which appeared of most beautiful deep and 
delicate blue at a depth of 20 feet. Scientific men 
know that, if the colour of water is due to the light 
reflected by extremely small particles of matter sus- 
pended in the water, then the object looked at through 
it would have been illuminated with yellow (the 
complementary colour of blue). A blackened tube 
was then filled with water (which had a clear-glass 
plate fixed to the bottom), and white, red, yellow, 
and purple objects were sunk in the water, and these 
colours were found to change in the same way as if 
they were looked at through a piece of pale-blue glass. 
The white object appeared blue, the red darkened 
very rapidly as it sank, and soon lost its colour; 
at the depth of seven feet a very brilliant red was so 
darkened as to appear dark brick-red. The yellow 
object changed to green, and the purple to dark blue. 

But, still further to satisfy himself that water is 
really blue in itself, even without any particles sus- 
pended in it, he tested the colour of distilled water. 
He filled a darkened tube with this water (clear-glass 
plates being at the ends of the tube), and looked 
through it at a white surface. The effect was the 
same as before, the colour was blue, almost exactly 
of the same hue as a solution of Prussian blue. 

This is corroborated by the fact that, the purer 
the water is in nature, the bluer is the tint when a 
large quantity is looked through. Some Highland 
lochs have crystal waters of the most extraordinary 
blue. Of course, some cling to the old idea that tbia 



THE BLUE SKY 77 

is accounted for by the reflected blue of the clear 
heavens above. No doubt, if the sky be deep blue, 
then this blue light, when reflected by the surface of 
the water, will enrich and deepen the hue. But the 
water itself is really blue. 

At the same time, the dust-particles suspended in 
the water have a great effect in making the water 
appear more beautiful, brilliant, and varied in its 
colouring; because little or no light is reflected by 
the interior of a mass of water itself. If a dark 
metal vessel be tilled with a weak solution of 
Prussian blue, the liquid will appear quite dark 
and void of colour. But throw in some fine white 
powder, and the liquid will at once become of a 
brilliant blue colour. This accounts for the change 
of depth and brilliancy of colour in the several 
shores of the Mediterranean. 

When, then, you look at the face of a deep-blue 
lake on a summer evening the heavens all aglow 
with the unrivalled display of colour from the zenith, 
stretching in lighter hues of glory to the horizon 
though to you the calm water appears like a lake of 
molten metal glowing with sky-reflected light, so 
powerful and brilliant as entirely to overpower the 
light which is internally ^reflected, yet blue is the nor- 
mal colour of the water : blueness is its inherent hue 

Looking upwards, we observe three distinct kinds 
of blue in the sky from the horizon to the zenith. 
All painters in water-colours know that. Newton 
thought that the colour of the sky was produced in 
the same way as the colours in thin plates, the order 
of succession of the colours gradually increasing in 
intensity. 



78 METEOROLOGY 

CHAPTER XXIII 

A SANITARY DETECTIVE 

THE impure state of the air in the rooms of a house 
can now be determined by means of colour alone. 
Dr. Aitken has invented a very simple instrument 
for that purpose ; and this ought to be of great service 
to sanitary officers. It is called the koniscope or 
dust-detective. 

The instrument consists of an air-pump and a 
metal tube with glass ends. Near one end of the 
test-tube is a passage by which it communicates with 
the air-pump, and near the other end is attached a 
stop-cock for admitting the ah* to be tested. It is 
not nearly so accurate as the dust-counter ; but it is 
cheaper, more easily wrought, and more handy for 
quick work. All the grades of blue, from what is 
scarcely visible to deep, dark blue, may be attached 
alongside the tube on pieces of coloured glass; 
and opposite these colours are the numbers of dust- 
particles in the cubic inch of the similar air, as 
determined by the dust-counter. 

While the number of particles was counted by 
means of the dust-counter, the depth of blue given 
by the koniscope was noted ; and the piece of glass 
of that exact depth of blue attached. A metal tube 
was fitted up vertically in the room, in such a way 
that it could be raised to any desired height into the 
impure air near the ceiling, so that supplies of air of 
different degrees of impurity might be obtained. To 



A SANITARY DETECTIVE 79 

produce the impurity, the gas was lit and kept burn- 
ing during the experiments. The air was drawn 
down through the pipe by means of the air-pump of 
the koniscope, and it passed through the measuring 
apparatus of the dust-counter on its way to the 
koniscope. It may be remarked that, by a stroke of 
the air-pump, the air within the test- tube is rarefied 
and the dust-particles seize the moisture in the 
super-saturated air to form fog- particles ; through 
this fog the colour is observed, and the shade of 
colour determines the number of dust-particles in 
the air. These colours are named "just visible," 
"very pale blue," "pale blue," "fine blue," "deep 
blue," and " very deep blue." 

When making a sanitary inspection, the pure air 
should be examined first, and the colour corre- 
sponding to that should be considered as the normal 
health colour. Any increase from the depth would 
indicate that the air was being gradually contami- 
nated ; and the amount of increase in the depth 
of colour would indicate the amount of increase 
of pollution. 

As an illustration of what this instrument can 
detect, a room of 24 by 17 by 13 feet was selected. 
The air was examined before the gas was lighted, 
and the colour in the test-tube was very faint, in- 
dicating a clear atmosphere. In all parts of the 
room this was found the same. A small tube was 
attached to the test-tube, open at the other end, for 
taking air from different parts of the room. Three 
jets of gas were then lit in the centre of the room, 
and observations at once begun with the koniscope. 

Within thirty-five seconds of striking the match to 



80 METEOROLOGY 

light the gas, the products of combustion had 
extended near the ceiling to the end of the room; 
this was indicated by the colour in the koniscope 
suddenly becoming a deep blue. In four minutes 
the deep-blue-producing air was got at a distance 
of two feet from the ceiling. In ten minutes there 
was strong evidence of the pollution all through the 
room. In half-an-hour the impurity at nine feet 
from the floor was very great, the colour being an 
intensely deep blue. 

The wide range of the indications of the instru- 
ment, from pure clearness to nearly black blue, 
makes the estimate of the impurity very easily 
taken with it; and, as there are few parts to get 
out of order, it is hoped it may come into general 
use for sanitary work. 



CHAPTER XXIV 

FOG AND SMOKE 

JUST two hundred and forty years ago, Mr. John 
Evelyn, F.R.S., a well-known writer on meteorology, 
sent a curious tract to King Charles II., which was 
ordered to be printed ~by his Majesty. It was 
entitled " Fumifugium," and dealt with the great 
smoke nuisance in London. I find from the thesis 
that he had a very hazy idea of the connection 
between fog and smoke; and no wonder, for it is 
only lately that the connection has been fully 
explained. 

We know that without dust- par tides there can 



FOG AND SMOKE 81 

be no fog, and that smoke supplies a vast amount of 
such particles. Therefore, in certain states of the 
atmosphere, the more smoke the more fog. In 
Mr. Evelyn's day the fog, which he called "pre- 
sumptuous smoake," was at times so dense that men 
could hardly discern each other for the " clowd." 
His Majesty's only sister had complained of the 
damage done to her lungs by the contamination, 
and Mr. Evelyn was disgusted at the apathy of the 
people to do anything to remedy the nuisance. He 
deplored that that glorious and ancient city of 
London should wrap her stately head in " clowds of 
smoake, so full of stink and darknesse." He was 
of opinion that a method of charring coal so as to 
divest it of its smoke, while leaving it serviceable 
for many purposes, should be made the object of a 
very strict inquiry. And he was right. For it is 
now known that fog in a town is intensified by much 
smoke. 

In a city like London or Glasgow, where a great 
river, fed by warm streams of water from gigantic 
works, passes through its centre, fogs can never 
be entirely obliterated, for the dust-particles in the 
air (often four millions and upwards in the cubic 
inch) will seize with terrible avidity the warm 
vapour rising from the river. That is the main 
reason why fogs cannot there be put down. Smoke 
is being consumed to a great extent ; yet we find 
particles of sulphur remaining, which seize the warm 
vapour and form fogs dense enough to check all 
traffic. The worst form of city fogs seems to be 
produced when the air, after first flowing slowly in 
one direction, then turns on its tracks and flows 

F 



82 METEOROLOGY 

back over the city, bringing with it a black pall, the 
accumulated products of previous days, to which 
gets added the smoke and other impurities produced 
at the time. 

What irritated Mr. Evelyn was that, outside of 
London, the air was clear when passengers could 
not walk in safety within the city. So vexed was 
he about the contamination, that he made it the 
occasion of all the " cathars, phthisicks, coughs, and 
consumption in the city." He appealed to common 
sense to testify that those who repair to London soon 
take some serious illness. " I know a man," he said, 
"who came up to London and took a great cold, 
which he could never afterwards claw off again." 

Mr. Evelyn proposed that, by an Act of Parliament, 
the nuisance be removed; enjoining that all breweries, 
dye-works, soap and salt boilers, lime-burners, and 
the like, be removed five or six miles distant from 
London below the river Thames. That would have 
materially helped his cause. 

But there is more difficulty in the purification 
than he anticipated. Yet there was pluck in the 
old man pointing out the killing contamination and 
suggesting a possible remedy. He had the fond idea 
that thereby a certain charm, " or innocent magick, 
would make a transformation scene like Arabia, 
which is therefore "styl'd the Happy, attracting all 
with its gums and precious spices." In purer air 
fogs would be less dense, breathing would be easier, 
business would be livelier, life would be happier. 

Few, I suppose, have laid their hands on this 
curious Latin thesis, or its quaint translation, direct- 
ing the King's attention to the fogs that were ruining 



ELECTRICAL DEPOSITION OF SMOKE 88 

London. Since that time the city has increased, from 
little more than a village, to be the dwelling-place of 
six millions of human beings, yet too little improve- 
ment has been made in the removal of this fog nuis- 
ance. King Edward's drive through London would 
be even more dangerous on a muggy, frosty day than 
was Charles II.'s, when science was little known. 



CHAPTER XXV 
ELECTRICAL DEPOSITION OF SMOKE 

A GOOD deal of scientific work is being done in the 
way of clearing away fog and smoke; and this, 
through time, may have some practical results in 
removing a great source of annoyance, illness, and 
danger in large towns. Sir Oliver Lodge and Dr. 
Aitken have been throwing light upon the deposi- 
tion of smoke in the air by means of electricity. 

If an electric discharge be passed through a jar 
containing the smoke from burnt magnesium wire, 
tobacco, brown paper, and other substances, the dust 
will be deposited so as to make the air clear. Brush 
discharge, or anything that electrifies the air itself, 
is the most expeditious. 

If water be forced upwards through a vertical tube 
(with a nozzle one-twentieth of an inch in diameter), 
it will fall to the ground in a fine rain ; but, if a piece 
of rubbed (electrified) sealing-wax be held a yard 
distant from the place where the jet breaks into 
drops, they at once fall in large spots as in a thunder- 
shower. If paper be put on the ground during the 



84 METEOEOLOGY 

experiment, the sound of pattering will be observed 
to be quite different. If a kite be flown into a cloud, 
and made to give off electricity for some time, that 
cloud will begin to condense into rain. 

Experiments with Lord Kelvin's recorder show that 
variations in the electrical state of the atmosphere 
precede a change of weather. Then, with a very 
large voltaic battery, a tremendous quantity of elec- 
tricity could be poured into the atmosphere, and its 
electrical condition could be certainly disturbed. If 
this could be made practically available, how useful 
it would be to farmers when the crops were suffering 
from excessive drought ! It might be more power- 
fully available than the imagined condensation of a 
cloud into rain by the reverberation caused by the 
firing of a range of cannon. 

But what is the practical benefit of this informa- 
tion? If electricity deposits smoke, it might be 
made available in many ways. The fumes from 
chemical works might be condensed ; and the air in 
large cities, otherwise polluted, might be purified and 
rendered innocuous. The smoke of chimneys in 
manufacturing works might be prevented from en- 
tering the atmosphere at all. In flour-mills and 
coal-mines the fine dust is dangerously explosive. 
In lead, copper, and arsenic works, it is both 
poisonous and valuable. 

Lead smelters labour under this difficulty of con- 
densing the fume which escapes along with the 
smoke from red-lead smelting furnaces ; and it was 
considered that an electrical process of condensation 
might be made serviceable for the purpose. At 
Bagillt, the method used for collecting or condensing 



ELECTRICAL DEPOSITION OF SMOKE 8.5 

the lead fume is a large flue two miles long ; much 
is retained in this flue, but still a visible cloud of 
white-lead fume continually escapes from the top of 
the chimney. There is a difficulty in the way of 
depositing fumes in the flue by means of a sufficient 
discharge of electricity, viz. the violent draught 
which is liable to exist there, and which would 
mechanically blow away any deposited dust. 

But Dr. Aitken suggests that regenerators might 
be used along with the electricity. The warm fumes 
might be taken to a cold depositor, where (by the 
ordinary law of cold surfaces attracting warm dust- 
particles) the impurities would be removed, and, 
when purified, the air would again be taken through 
a hot regenerator before being sent up the chimney. 
By a succession of these chambers, with the assist- 
ance of electric currents, the air, impregnated with 
the most deleterious particles, or valuable dust, could 
be rendered innocuous. 

The sewage of our towns must be cleaned of its 
deleterious parts before being run into the streams 
which give drink to the lower animals, because an 
Act of Parliament enforces the process. Why, then, 
ought we not to have similar compulsion for making 
the smoke from chemical and other noxious works 
quite harmless before being thrown into the air which 
contains the oxygen necessary for the life of human 
beings ? 

There seems to be a good field before electricians 
to catch the smoke on the wing and deposit its dust 
on a large scale. This seems to be a matter beyond 
our reach at present, except in the scientist's labora- 
tory ; but certainly it is a " consummation devoutly 
to be wished." 



86 METEOROLOGY 

CHAPTER XXVI 

RADIATION FROM SNOW 

ONE night a most interesting paper by Dr. Aitken, on 
" Radiation from Snow," was read by Professor Tait 
to the Fellows of the Royal Society of Edinburgh. 
I remember that Dr. Alex. Buchan the greatest 
meteorologist living spoke afterwards in the very 
highest terms of the subject-matter of the paper. 
This was corroborated by Lord Kelvin, Lord Mac- 
Laren, and Professor Chrystal. 

Dr. Aitken had been testing the radiating powers 
of different substances. Snow in the shade on a 
bright day at noon is 7 Fahr. colder than the air 
that floats upon it, whereas a black surface at the 
same is only 4 colder. This difference diminishes 
as the sun gets lower; and at night both radiate 
almost equally well. 

I select, among the careful and numerous obser- 
vations, the notes on January 19, 1886 ; for I took note 
of the cold of that day in my diary. It was the coldest 
day of the whole of that winter. The barometer 
was 28-8 inches, and the thermometer 4 that is, 
28 of frost. According to Dr. Buchan, that January 
had only two equal in average cold for fifty years. 

On January 19, at 10 A.M., when the air was at 20 
and the sky clear, a black surface registered 16 and 
the upper layer of snow 12, showing a difference of 
4 when both surfaces were colder than the superin- 
cumbent air. It is curious to note that, on February 5 



RADIATION FROM SNOW 87 

of the same year, at the same hour, when the sky 
was overcast, the air was at 23, the black surface 
registered 29, and the snow 25, showing again the 
difference of 4 ; but, in this case, both surfaces were 
warmer than the air. In both cases the radiation at 
night was equal. 

This small absorbing power of snow for heat re- 
flected and radiated from the sky during the day 
must have a most important effect on the tempera- 
ture of the air. The temperature of lands when 
covered with snow must be much lower than when 
free from it. And, when once a country has become 
covered with snow, there will be a tendency towards 
glacial conditions. 

But, besides being a bad absorber of heat from the 
sky, snow is also a very poor conductor of heat. On 
that very cold night (January 18), when there was a 
depth of 5J inches of snow on the ground, and the 
night clear, with strong radiation, the temperature 
of the surface of the snow was 3 Fahr., and a mini- 
mum thermometer on the snow showed that it had 
been down to zero some time before. A thermometer, 
plunged into the snow down to the grass, gave the 
most remarkable register of 32. Through the depth 
of 5J inches of snow there was a difference of tem- 
perature of 29. This was confirmed by removing 
the snow, and finding that the grass was unfrozen. 
As the ground was frozen when the snow fell, it would 
appear that the earth's heat slowly thawed it under 
the protection of the snow. 

The protection afforded by the bad-conducting 
power of snow is of great importance in the economy 
of nature. How vegetation would suffer, were it ex- 



88 METEOROLOGY 

posed to a low temperature, unprotected by the 
snow-mantle ! So that, though the continued snow 
cools the air for animals that can look after their 
own heating, it keeps warm the soil ; and vegetation 
prospers under the genial covering. The fine rich 
look of the young wheat -blades, after a continued 
snow has melted, must strike the most careless 
observer. Instead of the half-blackened tips and 
semi-sickly blades, which we see in a field of 
young wheat after a considerable course of dry frost 
without snow, we have a rich, healthy green which 
shows the vital energy at work in the plants. Or 
even in the town gardens, after a continued snow has 
been melted away by a soft, western breeze, we are 
struck with the white, peeping buds of the snowdrop 
and the finely springing grass in the sward. 

Yet the snow-covering gives durability to cold 
weather. This has been demonstrated by Dr. 
Wceikof, the distinguished Russian meteorologist. 
On this account the spring months of Russia and 
Siberia are intensely cold. The plants, then, which 
in winter are unable by locomotion to keep them- 
selves in health, are protected by the snow-mantle 
which chills the air for animals that can keep them- 
selves in heat by exercise. What a grand compen- 
sating power is here ! 

CHAPTER XXVII 
MOUNTAIN GIANTS 

SOME mysterious physical phenomena can be clearly 
explained by the aid of science. The mountain 



MOUNTAIN GIANTS 89 

giants that at times haunt the lonely valleys, and 
strike with fear the superstitious dwellers there, are 
only the enlarged shadows of living human beings 
cast upon a dense mist. 

The two most startling of these " eerie " phe- 
nomena are the spectres of Adam's Peak and the 
Brocken. 

The phenomena sometimes to be observed at 
Adam's Peak, in Ceylon, are very remarkable. Many 
travellers have given vivid accounts of these. On 
one occasion the Hon. Ralph Abercromby, in his 
praiseworthy enthusiasm for meteorological research, 
went there with two scientific friends to witness the 
strange appearance. The conical peak, a mile and a 
half high, overlooks a gorge west of it. When, then, 
the north-east monsoon blows the morning mist up 
the valley, light wreaths of condensed vapour pass 
to the right of the Peak, and catch the shadows 
at sunrise. 

This party reached the summit early one morning 
in February. The foreglow began to brighten the 
under-surface of the stratus-cloud with orange, and 
patches of white mist filled the hollows. Soon the 
sun peeped through a chink in the clouds, and they 
saw the pointed shadow of the Peak lying on the 
misty land. Then a prismatic circle, with the red 
inside, formed round the shadow. The meteorologist 
waved his arms about, and immediately he found 
giant shadowy arms moving in the centre of the 
rainbow. 

Soon they saw a brighter and sharper shadow of 
the Peak, encircled by a double bow, and their own 
spectral arms more clearly visible. The shadow, 



90 METEOROLOGY 

the double bow, and the giant forms, combined to 
make this phenomenon the most marked in the 
whole world. 

The question has been frequently asked : Why are 
such aerial effects not more widely observed ? There 
are not many mountains of this height and of a 
conical shape ; and still fewer can there be where a 
steady wind, for months together, blows up a valley 
so as to project the rising morning mist at a suitable 
height and distance on the western side, to catch the 
shadow of the peak at sunrise. 

The most famous place in Europe for witnessing 
the awe-inspiring phenomenon is the Brocken, in 
Germany 3740 feet in height. The only great dis- 
appointment there is that the conditions rarely 
combine at sunrise or sunset to have " the spectre " 
successful. 

In July 1892, my daughter and I were spending 
some weeks at Harzburg, and, of course, we had to 
visit the Brocken and take stock of the world-known 
phenomenon. At mid-day, the air at the flat 
summit was cold, clear, and hard. The boulders 
are of enormous size; and near the "Noah's Ark" 
Hotel and Observatory many are piled up in a mass, 
on which the observers stand at the appointed time 
for having their shadows projected on the misty air 
in the valleys. 

At five o'clock in the afternoon the sky was 
brilliantly clear on the summit of the Brocken ; but 
the wind was rising from the sun's direction, and the 
mist was filling up the wide-spread eastern valley. 
We stood on the " spectre " boulders, and our shadows 
were thrown on the grass, just as at home. How- 



MOUNTAIN GIANTS 91 

ever, they fell upon large patches of white heather, 
which there is very plentiful. 

At six o'clock the sun was still shining beautifully, 
and we anxiously waited for the time when it would 
be low enough to raise our shadows to the misty wall. 
An hour afterwards, a hundred visitors were out, and 
many of us were on the "spectre" stones. There was 
great excitement in anticipation of the weird appear- 
ances, which had attracted us from such a distance. 

But, almost at the moment of success, the sun 
descended behind a belt of purple cloud, and all we 
saw was part of a rainbow on the misty hollow. For 
the sun never appeared again. This was intensely 
saddening, seeing that, but for that stratum of cloud 
above the horizon, the phenomenon would have been 
graphically displayed. 

The cold became suddenly intense, and we had to 
sleep with a freezing mist enveloping the hotel. In 
vain did we wait for the wakening call, to tell us of 
sunrise ; for the sun could not pierce the mist, and 
we had to return home disappointed. 

Sometimes the rainbow colours assume the shapes 
of crosses instead of circles. Occasionally a bright 
halo will be seen above the shadow-head of the 
observer, concentric rainbows enclosing all. In some 
recorded cases the grand effect must have been 
simply glorious. 

Scientific observation has done much to dispel 
the superstition which has clung so tenaciously to 
the Highland mind. The lonely grandeur of the 
weird mountain giants has been clearly explained as 
perfectly natural, yet the awe-striking feeling cannot 
be entirely driven off. 



92 METEOROLOGY 

CHAPTER XXVIII 
THE WIND 

ONCE was the remark pointedly made: "The wind 
bloweth where it listeth." And that is nearly true 
still. The leading winds are under the calculation 
of the meteorologist, but the others will not be 
bound by laws. 

Yet there are instruments for measuring the 
velocity and force of the wind, after it is on; but 
" whence it comes " is a different matter. A gentle 
air moves at the rate of 7 miles an hour ; a hurricane 
from 80 to 150 miles, pressing with 50 Ibs. on the 
square foot exposed to its fury. Some of the gusts 
of the Tay Bridge storm, in 1879, had a velocity of 
150 miles an hour, with a pressure of 80 to 90 Ibs. 
to the square foot. 

Before steamers supplanted so many sailing vessels, 
seamen required to be always on the alert as to the 
direction and strength of the wind, and the likelihood 
of any sudden change ; and they chronicled twelve 
different strengths from "faint air" to a "storm." 

In general, the wind may be considered to be the 
result of a change of pressure and temperature in the 
atmosphere at the same level. The air of a warmer 
region, being lighter, ascends, and gives place to a 
current of wind from a colder region. These two 
currents the higher and the lower will continue 
to blow until there is equilibrium. 

The trade winds are regular and constant. These 



THE WIND 93 

were much followed in the days of old. A vast 
amount of air in the tropics gets heated and ascends, 
being lighter, and travels to the colder north. A 
strong current rushes in from the north to take its 
place. But the earth rotates round its axis from 
west to east, and the combined motions make two 
slant wind directions, which are called the "trade 
winds," because they were so important in trade 
navigation. 

Among the periodical winds are the "land and 
sea breezes." During the day, the land on the sea 
coast is warmer than the sea; accordingly, the air 
over the land becomes heated and ascends, the fine 
cool breeze from the sea taking its place. Towards 
evening there is the equilibrium of temperature 
which produces a temporary calm. Soon the earth 
chills, and the sea is counterbalancing^ warm as 
sea-water is steadier as to temperature than is land 
the air over the sea becomes warmer, and ascends, 
the current from the land rushing in to take its 
place. Hence during the night the wind is reversed, 
until in the morning again the equilibrium is re- 
stored and there is a calm, so far as these are con- 
cerned. These are therefore called the " land and sea 
breezes." Of course, it is within the tropics that 
these breezes are most marked. By the assistance 
of other winds, a hurricane will there occasionally 
destroy towns and bring about much damage and loss 
of life ; but better that hundreds should perish by a 
hurricane than thousands by the pestilence which, but 
for the storm, would have done its dire work. 

In countries where the differences of pressure are 
more marked than the differences of temperature, 



94 METEOROLOGY 

in the surrounding regions the strength of the wind 
thereby occasioned is far stronger than the land and 
sea breezes. 

The variable winds are more conflicting. These 
depend on purely local causes for a time, such as 
" the nature of the ground, covered with vegetation 
or bare ; the physical configuration of the surface, 
level or mountainous ; the vicinity of the sea or lakes, 
and the passage of storms." Among these winds are 
the simoom and sirocco. 

The east winds, which one does not care about 
in the British Islands during the spring time, are 
occasioned by the powerful northern current which 
rushes south from the northern regions in Europe. 
Dr. Buchan points out a very common mistake 
among even intelligent observers who shudder at the 
hard east winds. It is generally held that these 
winds are damp. They are unhealthy, but they are 
dry. It is quite true that many easterly winds are 
peculiarly moist ; all that precede storms are so far 
damp and rainy ; and it is owing to this circumstance 
that, on the east coast of Scotland, the east winds are 
searching and carry most of the annual rainfall there. 
But all of these moist easterly winds, however, soon 
turn to some westerly point. The real east wind, 
so much feared by invalids, does not turn to the 
west ; it is exceeding dry. Curious is it that brain 
diseases, as well as consumption, reach their height in 
Britain while east winds prevail. Once in Edinburgh, 
during the early spring, I had rheumatic fever, and 
during my convalescence my medical adviser, Dr. 
Menzies, would not let me have a short drive until 
the wind changed to the west. The first thing I 



CYCLONES AND ANTI-CYCLONES 95 

anxiously watched in the morning was the flag on 
the Castle ; and for nearly two months it always 
waved from the east. How heart-depressing ! 

Creatures are we in the hands of nature's mes- 
sengers. We so much depend upon the weather for 
our happiness. Joyful are we when the honey- 
laden 'zephyr waves the long grass in June, or when 

" The gentle wind, a sweet and passionate wooer, 
Kisses the blushing leaf." 

Compared with this, how terrible is Shakespeare's 
allusion to the appalling aspects of the storm : 

" I have seen tempests, when the scolding winds 
Have rived the knotty oaks ; and I have seen 
The ambitious ocean swell, and rage and foam, 
To be exalted with the threat'ning clouds ; 
But never till to-night, never till now, 
Did I go through a tempest dropping fire." 



CHAPTER XXIX 
CYCLONES AND ANTI-CYCLONES 

THE criticism of the weather in the meteorological 
column of our daily newspapers invariably speaks 
of " cyclones." It is, therefore, advisable to give 
as plain an explanation of these as possible. Cyclones 
are " storm- winds." Their nature has to be carefully 
studied by meteorologists, who are industriously at 
work to ascertain some scientific basis for the 
atmospheric movements. 

What is the cause of the spiral movement in 



96 METEOROLOGY 

storm-winds ? In their centre the depression of the 
barometer is lowest, because the atmosphere there 
is lightest. As the walls of the spiral are approached, 
the barometer rises. 

Dr. Aitken has ingeniously hit upon an experiment 
to illustrate a spiral in air. All that is necessary 
is a good fire, a free-going chimney, and a wet cloth. 
The cloth is hung up in front of the fire, and pretty 
near it, so that steam rises readily from its surface ; 
and, when there are no air-currents in the room, the 
steam will rise vertically, keeping close to the cloth. 
But if the room has a window in the wall, at right 
angles to the fireplace, so as to cause the air coming 
from it to make a cross-current past the fire, then 
a cyclone will be formed, and the vapour from the 
cloth will be seen circling round. When the 
cyclone is well formed, all the vapour is collected 
into the centre of the cyclone, and forms a white 
pillar extending from the cloth to the chimney. 
This experiment shows that no cyclone can form 
without some tangential motion in the air entering 
the area of low-pressure. 

Now to illustrate the spiral approach. Fill with 
water a cylindrical glass vessel, say 15 inches in dia- 
meter and 6 inches deep. Have an orifice with a plug 
a little from the centre of the bottom. Kemove the 
plug, the water runs out, passing round the vessel 
in a vortex form. But, as the passage between the 
orifice (or centre of the cyclone) and the temporary 
division is narrower than in any other place, the 
water has to pass this part much more quickly than 
at any other place. And this curious result is ob- 
served: the top of the cyclone no longer remains 



CYCLONES AND ANTI-CYCLONES 97 

over the orifice, but travels in the direction of the 
water which is moving most speedily. Similar to 
this is the cyclone in the atmosphere ; its centre also 
moves in the direction of the quickest flowing wind 
that enters it. 

Dr. Aitken is of opinion that, in forecasting storms, 
too little attention has been paid to the anti-cyclones. 
They do more than simply follow and fill up the 
depression made by the cyclones. They initiate and 
keep up their own circulation, and collect the mate- 
rials with which the cyclones produce their effect. 
Neither could work efficiently without the other. 

Suppose a large area on the earth over which the 
air is still in bright sunshine. After a time, when 
the air gets heated and charged with vapour, 
columns of air would begin to ascend in a dis- 
orderly fashion. But suppose an an ti- cyclone is 
blowing at one side of this area. When the upper 
air descends to the earth, it spreads outwards in 
all directions; but the earth's rotation interferes 
and changes the radial into a spiral motion. The 
an ti- cyclonic winds will prevent the formation of 
local cyclones, and drive all the moist, hot air to its 
circumference, just above the earth. The anti-cyclone 
forces its air tangentially into the cyclone, and gives 
it its direction and velocity of rotation, also the 
direction and rate of travel of the centre of depres- 
sion. The earth's rotation is the original source of 
the rotatory movements, but both intensify the initial 
motion. 

Accordingly, the cyclone must travel in the direc- 
tion of the strongest winds blowing into it, just as 
the vortex in the vessel with the eccentric orifice 

G 



98 METEOROLOGY 

travelled in the direction of the quickest moving 
water. This is verified by a study of the synoptic 
charts of the Meteorological Office. 

The sun's heat has always been looked upon as 
the main source of the energy of our winds, but 
some account must also be taken of the effects of 
cold. It is well known that the mean pressure over 
Continental areas is high during winter and low 
during summer. As the sun's rays during summer 
give rise to the cyclonic conditions, so the cooling of 
the earth during winter gives rise to anti-cyclonic 
conditions. It is found during the winter months 
in several parts of the Continent that as the tempera- 
ture falls the pressure rises, producing anti-cyclones 
over the cold area ; whereas, when the temperature 
begins to rise, the pressure falls, and cyclones are 
attracted to the warming area. 

Small natural cyclones are often seen on dusty 
roads, the whirling column having a core of dusty 
air, and the centre of the vortex travelling along the 
road, tossing up the dust in a very disagreeable way 
to pedestrians. Sometimes such a cyclone will toss 
up dry leaves to a height of four or five feet. They 
are very common ; but it is only when dust, leaves, 
or other light material is present that they are visible 
to the eye. 

CHAPTER XXX 

RAIN PHENOMENA 

THE soft rain on a genial evening, or the heavy 
thunder-showers on a broiling day, are too well known 



RAIN PHENOMENA 99 

to be written about. Sometimes rain is earnestly 
wished for, at other times it is dreaded, according to 
the season, seed-time or harvest. Some years, like 
1826, are very deficient in rainfall, when the corn is 
stunted and everything is being burnt up ; other 
years, like 1903, there is an over-supply, causing 
great damage to agriculture. The year 1903 will long 
be remembered for its continuous rainfall; it is the 
record year ; no year comes near it for the total rain- 
fall all over the kingdom. 

Rain is caused by anything that lowers the tem- 
perature of the air below the dew-point, but especially 
by winds. When a wind has blown over a consider- 
able area of ocean on to the land, there is a likelihood 
of rain. When this wind is carried on to higher 
latitudes, or colder parts, there is a certainty of rain. 
Of course, in the latter case the rain will fall heavier 
on the wind side than on the lee side. 

For short periods, the heaviest falls or " plouts " of 
rain are during thunder-storms. When the raindrops 
fall through a broad, cold stratum of air, they are 
frozen into hail, the particles of which sometimes 
reach a large size, like stones. Of course, water- 
spouts now and again are of terrible violence. 

One of the heaviest rainfalls yet recorded in Great 
Britain was about 2J inches in forty minutes at Led- 
nathie, Forfarshire, in 1887. Now 1 inch deep of 
rain means 100 tons on an imperial acre; so the 
amount of water falling on a field during that short 
time is simply startling. The heaviest fall for one 
day was at Ben Nevis Observatory, being fully 7J 
inches in 1890. In other parts of the world this is 
far exceeded, In one day at Brownsville, Texas, 



100 METEOROLOGY 

nearly 13 inches fell in 1886. On the Khasi hills, 
India, 30 inches on each of five successive days were 
registered. At Gibraltar, 33 inches were recorded in 
twenty-six hours. 

The heaviest rainfalls of the globe are occasioned 
by the winds that have swept over the most extensive 
ocean-areas in the tropics. On the summer winds 
the rainfall of India mainly depends ; when this fails, 
there is most distressing drought. Reservoirs are 
being erected to meet emergencies. 

From Dr. Buchan's statistics it is found that the 
annual rainfall at Mahabaleshwar is 263 inches; 
at Sandoway 214; and at Cherra-pungi 472 inches, 
the largest known rainfall anywhere on the globe. 
Over a large part -of the Highlands of Scotland more 
than 80 inches fall annually, while in some of the 
best agricultural districts there it does not exceed 
30 inches. 

Of all meteorological phenomena, rainfall is the 
most variable and uncertain. Symons gives as 
tentative results from twenty years' observations in 
London (1) In winter, the nights are wetter than 
the days ; (2) in spring and autumn, there is not 
much difference ; (3) in summer, nearly half as 
much again by day as by night. 

The wearisomeness of statistics may be here re- 
lieved by a short consideration of the splash of a 
drop of rain. Watching the drop-splashes on a rainy 
day in the outskirts of the city, when unable to get 
out, I brought to my recollection the marvellous series 
of experiments made by Professor A. M. Worthington 
in connection with these phenomena. Of course, I 
could not see to proper advantage the formation of 



RAIN PHENOMENA 101 

the splashes, as the heavy raindrops fell into these 
tiny lakes on the quiet road. There is not the effect 
of the huge thunder-drops in a stream or pool. The 
building up of the bubbles is not here perfect, for 
the domes fail to close, nor are the emergent columns 
visible to the naked eye. It is a pity ; for R. L. 
Stevenson once wrote of them in his delightful 
" Inland Voyage," when he canoed in the Belgian 
canals, as thrown up by the rain into "an infinity 
of little crystal fountains." 

Beautiful is this effect if one is under shelter, 
every dome seeming quite different in contour and 
individuality from all the rest. But terrible is it 
when out fishing on Loch Earn, even with the good- 
humoured old Admiral, when the heavy thunder- 
drops splash up the crystal water, and one gets soaked 
to the skin, sportsman-like despising an umbrella. 

There is, however, a scientific interest about the 
splash of a drop. The phenomenon can be best seen 
indoors by letting a drop of ink fall upon the surface 
of pure water in a tumbler, which stands on white 
paper. It is an exquisitely regulated phenomenon, 
which very ideally illustrates some of the funda- 
mental properties of fluids. 

When a drop of milk is let fall upon water 
coloured with aniline dye, the centre column of the 
splash is nearly cylindrical, and breaks up into drops 
before or during its subsequent descent into the 
liquid. As it disappears below the surface, the 
outward and downward flow causes a hollow to be 
again formed, up the sides of which a ring of milk 
is carried ; while the remainder descends to be torn 
a second time into a beautiful vortex ring. This 



102 METEOROLOGY 

shell or dome is a characteristic of all splashes made 
by large drops falling from a considerable height, 
and is extremely pretty. Sometimes the dome closes 
permanently over the imprisoned air, and forms a 
large bubble floating upon the water. The most 
successful experiments, however, have been carried 
through by means of instantaneous photography, 
with the aid of a Leyd en-jar spark, whose duration 
was less than the ten-millionth 'of a second. But 
the simple experiments, without the use of the 
apparatus, will while away a few hours on a rainy 
afternoon, when condemned to the penance of keeping 
within doors. 



CHAPTER XXXI 

THE METEOROLOGY OF BEN NEVIS 

SEVERAL large and very important volumes of the 
Royal Society of Edinburgh are devoted to statistics 
connected with the meteorology of Ben Nevis. Most 
of the abstracts have been arranged by Dr. Buchan ; 
while Messrs. Buchanan, Omond, and Rankine have 
taken a fair share of the work. 

This Observatory, as Mr. Buchanan remarks, is 
unique, for it is established in the clouds; and the 
observations made in it furnish a record of the 
meteorology of the clouds. It is 4406 feet above the 
level of the sea; and as there is a corresponding 
Observatory at Fort William, at the base of the 
mountain, it is peculiarly well fitted for important 
observations and weather forecasting. The moun- 



THE METEOROLOGY OF BEN NEVIS 103 

tain, too, is on the west sea-coast of Scotland, exposed 
immediately to the winds from the Atlantic, catching 
them at first hand. It is lamentable to think that, 
when the importance of the observations made at 
the two Observatories was becoming world known, 
funds could not be got to carry them on. Ben Nevis 
is the highest mountain in the British Islands, best 
fitted for meteorological observations ; yet these have 
been stopped for want of money. 

Dr. Buchan's valuable papers were published before 
any one dreamed of the stoppage of the work, which 
had such an important bearing on men engaged in 
business or taken up with open-air sport. From 
these I shall sift out a few facts that even <c mute, 
inglorious" meteorologists may be interested in 
knowing. 

For a considerable time the importance of the 
study of the changes of the weather has come 
gradually to be recognised, and an additional im- 
petus was given to the prosecution of this branch 
of meteorology when it was seen that the subject 
had intimate relations to the practical question of 
weather forecasts, including storm warnings. Weather 
maps, showing the state of the weather over an 
extensive part of the surface of the globe, began to 
be constructed ; but these were only indicators from 
places at the level of the sea. 

The singular advantages of a high-level observatory 
occurred to Mr. Milne Home in 1877 ; and Ben 
Nevis was considered to be in every respect the 
most suitable in this country. The Meteorological 
Council of the Royal Society of London offered in 
1880, unsolicited, 100 annually to the Scottish 



104 METEOROLOGY 

Meteorological Society, to aid in the support of an 
Observatory, the only stipulation being that the 
Council be supplied with copies of the observations. 

From June to October, in 1881, Mr. Wragge made 
daily observations at the top of the Ben ; and simul- 
taneous observations were made, by Mrs. Wragge, at 
Fort William. A second series, on a much more 
extended scale, was made in the following summer. 

Funds were secured to build an Observatory ; and, 
in November 1883, the regular work commenced, 
consisting of hourly observations by night as well 
as by day. Until a short time ago, these were carried 
on uninterruptedly. Telegraphic communications 
of each day's observations were sent to the morning 
newspapers; and now we are disappointed at not 
seeing them for comparison. 

The whole of the observations of temperature and 
humidity were of necessity eye-observations. For 
self -registering thermometers were comparatively 
useless when the wind was sometimes blowing at the 
rate of 100 miles an hour. Saturation was so com- 
plete in the atmosphere that everything exposed to 
it was dripping wet. Every object exposed to the 
outside frosts of winter soon became thickly incrusted 
with ice. Snowdrifts blocked up exposed instruments. 
Accordingly, the observers had to use their own eyes, 
often at great risks. 

The instruments in the Ben Nevis Observatory, 
and in the Observing Station at Fort William, were 
of the best description. Both stations were in 
positions where the effects of solar and terrestrial 
radiation were minimised. No other pair of meteoro- 
logical stations anywhere in .the world are so favour- 



THE METEOROLOGY OF BEN NEVIS 105 

ably situated as these two stations, for supplying the 
necessary observations for investigating the vertical 
changes of the atmosphere. It is to be earnestly 
hoped, therefore, that funds will be secured to re- 
sume the valuable work. 

The rate of the decrease of temperature with 
height there is 1 Fahr. for every 275 feet of 
ascent, on the mean of the year. The rate is 
most rapid in April and May, when it is 1 for 
each 247 feet; and least rapid in November and 
December, when it is 1 for 307 feet. This rate 
agrees closely with the results of the most care- 
fully conducted balloon ascents. The departures 
from the normal differences of temperature, but 
more especially the inversions of temperature, and 
the extraordinarily rapid rates of diminution with 
height, are intimately connected with the cyclones 
and anti-cyclones of North- Western Europe; and 
form data, as valuable as they are unique, in fore- 
casting storms. 

The most striking feature of the climate of Ben 
Nevis is the repeated occurrence of excessive droughts. 
For instance, in the summer and early autumn of 
1885, low humidities and dew-points frequently 
occurred. Corresponding notes were observed at 
sea-level. During nights when temperature falls 
through the effects of terrestrial radiation, those 
parts of the country suffer most from frosts over 
which very dry states of the air pass or rest ; whereas, 
those districts, over which a more humid atmosphere 
hangs, will escape. On the night of August 31 of 
that year, the potato crop on Speyside was totally 
destroyed by the frost ; whereas at Dalnaspidal, in the 



106 METEOROLOGY 

district immediately adjoining, potatoes were scarcely 
if at all blackened. 

The mean annual pressure at Ben Nevis was 
25-3 inches, and at Fort William 29 -8, the difference 
being 4J inches for the 4400 feet. 

For the whole year, the difference between the 
mean coldest hour, 5 A.M., and the warmest hour, 
2 P.M., is 2. For the five months, from October 
to February, the mean daily range of temperature 
varied only from 0-6 to 1/5. This is the time of the 
year when storms are most frequent ; and this small 
range in the diurnal march of the temperature is an 
important feature in the climatology of Ben Nevis ; 
for it presents, in nearly their simple form, the great 
changes of temperature accompanying storms and 
other weather changes, which it is so essential to 
know in forecasting weather. 

The daily maximum velocity of the wind occurs 
during the night, the daily differences being greatest 
in summer and least in winter. A blazing sun in 
the summer daily pours its rays on the atmosphere, 
and a thick envelope of cloud has apparently but 
little influence on the effect of the sun's rays. 
Thunder-storms are essentially autumn and winter 
phenomena, being rare in summer. 

According to Mr. Buchanan, the weather on Ben 
Nevis is characterised by great prevalence of fog 
or mist. In continuously clear weather it practically 
never rains on the mountain at all. In continuously 
foggy weather, on the other hand, the average daily 
rainfall is 1 inch. There is a large and continuous 
excess of pressure in clear weather over that of foggy 
weather. The mean temperature of the year is 



THE WEATHER AND INFLUENZA 107 

3J degrees higher in clear than in foggy weather. 
In June the excess is 10 degrees. The nocturnal 
heating in the whiter is very clearly observed. This 
has been noticed before in balloons as well as on 
mountains. The fog and mist in winter are much 
denser than in summer. Whether wet or dry, the 
fog which characterises the climate of the mountain 
is nothing but cloud under another name. 



CHAPTER XXXII 
THE WEATHER AND INFLUENZA 

SOME remarkable facts have been deduced by the 
late Dr. L. Gillespie, Medical Registrar, from the 
records of the Royal Infirmary of Edinburgh. He 
considered that it might lead to interesting results 
if the admissions into the medical wards were con- 
trasted with the varying states of the atmosphere. 
The repeated attacks of influenza made him pay 
particular attention to the influence of the weather 
on that disease. 

The meteorological facts taken comprise the 
weekly type of weather, i.e. cyclonic or anti-cyclonic, 
the extremes of temperature for the district for each 
week, and the mean weekly rainfall for the same 
district. More use is made of the extremes than of 
the mean, for rapid changes of temperature have a 
greater influence on disease than the actual mean. 

The period which he took up comprises the seven 
years 1888-1895. There was a yearly average of 
admissions of 3938 ; so that he had a good field for 



108 METEOROLOGY 

observation. Six distinct epidemics of influenza, 
varying in intensity, occurred during that period; 
yet there had been only twenty-three attacks between 
1510 and 1890. Accordingly, these six epidemics 
must have had a great influence on the incidence 
of disease in the same period, knowing the vigorous 
action of the poison on the respiratory, the circula- 
tory, and the nervous systems. The epidemics of 
influenza recorded in this country have usually 
occurred during the winter months. 

The first epidemic, which began on the 15th of 
December 1889 and continued for nine weeks, was 
preceded by six weeks of cyclonic weather, which 
was not, however, accompanied by a heavy rainfall. 
Throughout the course of the disease, the type 
continued to be almost exclusively cyclonic, with a 
heavy rainfall, a high temperature, and a great 
deficiency of sunshine. iThe four weeks immediately 
following were also chiefly cyclonic, but with a 
smaller rainfall. 

The summer epidemic of 1891 followed a fine 
winter and spring, during which anti-cyclonic con- 
ditions were largely prevalent. But the epidemic was 
immediately preceded by wet weather and a low 
barometer. It took place in dry weather, and was 
followed by wet, cyclonic weather in turn. 

The great winter epidemic of 1891 followed an 
extremely wet and broken autumn. Simultaneously 
with the establishment of an anti-cyclone, with east 
wind, practically no rain, and a lowering temperature, 
the influenza commenced. Great extremes in the 
temperature followed, the advent of warmer weather 



THE WEATHER AND INFLUENZA 109 

and more equable days witnessing the disappearance 
of the disease. 

The fourth epidemic was preceded by a wet period, 
ushered in by dry weather, accompanied by great 
heat; and its close occurred in slightly wetter 
weather, but under anti-cyclonic conditions. The 
fifth outbreak began after a short anti-cyclone had 
become established over our islands, continued 
during a long spell of cyclonic weather with a 
considerable rainfall, but was drowned out by heavy 
rains. The last appearance of the modern plague, 
of which Dr. Gillespie's paper treats, commenced 
after cold and wet weather, continued in very cold 
but drier weather, and subsided in warmth with 
a moderate rainfall. 

The conditions of these six epidemics were very 
variable in some respects, and regular in others. The 
most constant condition was the decreased rainfall at 
the time, when the disease was becoming epidemic. 
Anti-cyclonic weather prevailed at the time. 

According to Dr. Gillespie, the tables seem to 
suggest that a type of weather, which is liable to 
cause catarrhs and other affections of the respiratory 
tract, precedes the attacks of influenza ; but that the 
occurrence of influenza in epidemic form does not 
appear to take place until another and drier type 
has been established. As the weather changes, the 
affected patients increase with a rush. 

He is of opinion that the supposed rapid spread 
of influenza on the establishment of anti-cyclonic 
conditions may be explained in this way. The air in 
the cyclonic vortex, drawn chiefly from the atmos- 
phere over the ocean, is moist, and contains none of 



110 METEOROLOGY 

the contagion ; the air of the anti-cyclone, derived 
from the higher strata, and thus from distant 
cyclones, descending, blows gently over the land 
to the nearest cyclone, and, being drier, is more able 
to carry suspended particles with it. He considers 
that temperature has nothing to do with the 
problem, except in so far as the different types of 
weather may modify it. The Infirmary records 
point to the occurrence of similar phenomena, re- 
corded on previous occasions. Accordingly, if such 
meteorological conditions are not indispensable to 
the spread of influenza in epidemic form, they at 
least afford favourable facilities for it. 



CHAPTER XXXIII 
CLIMATE 

ONE is not far up in years, in Scotland at any rate, 
without practically realising what climate means. 
He may not be able to put it in words, but easterly 
haars, chilling rimes, drizzling mists, dagging fogs, 
and soddening rains speak eloquently to him of the 
meaning of climate. 

Climate is an expression for the conditions of a 
district with regard to temperature, and its influence 
on the health of animals and plants. The sun is the 
great source of heat, and when its rays are nearly 
perpendicular as at the Tropics the heat is greater 
on the earth than when the slanted rays are 
gradually cooled in their passage. As one passes 
to a higher level, he feels the air colder, until he 



CLIMATE 111 

reaches the fluctuating snow-line that marks per- 
petual snow. 

The temperature of the atmosphere also depends 
upon the radiation from the earth. Heat is quite 
differently radiated from a long stretch of sand, a dense 
forest, and a wide breadth of water. Strange is it that 
a newly ploughed field absorbs and radiates more heat 
than an open lea. The equable temperature of the 
sea-water has an influence on coast towns. The Gulf 
Stream, from the Gulf of Mexico, heats the ocean on 
to the west coast of Britain, and mellows the climate 
there. 

The rainfall of a district has a telling effect on the 
climate. Boggy land produces a deleterious climate, 
if not malaria. Over the world, generally, the pre- 
vailing winds are grand regulators of the climate 
in the distinctive districts. A wooded valley like 
the greatest in Britain, Strathmore has a health- 
invigorating power : what a calamity it is, then, that 
so many extensive woods, destroyed by the awful 
hurricane twelve years ago, are not replanted ! 

Some people can stand with impunity any climate ; 
their "leather lungs" cannot be touched by extremes of 
temperature ; but ordinary mortals are mere puppets 
in the hands of the goddess climate. Hence health- 
resorts are munificently got up, and splendidly patro- 
nised by people of means. The poor, fortunately, have 
been successful in the struggle for existence, by innate 
hardiness, otherwise they would have had a bad 
chance without ready cash for purchasing health. 

It may look ludicrous at first sight, but it seems 
none the less true, that the variation of the spots on 
the sun have something to do with climate, even to 



112 METEOROLOGY 

the produce of the fields. On close examination, 
with a proper instrument, the disc of the sun is found 
to be here and there studded with dark spots. These 
vary in size and position day after day. They 
always make their first appearance on the same side 
of the sun, they travel across it in about fourteen 
days, and then they disappear on the other side. 
There is a great difference in the number of spots 
visible from time to time ; indeed, there is what is 
called the minimum period, when none are seen for 
weeks together, and a maximum period, when more 
are seen than at any other time. The interval between 
two maximum periods of sun-spots is about eleven 
years. This is a very important fact, which has won- 
derful coincidences in the varied economy of nature. 
Kirchhoff has shown, by means of the spectroscope, 
that the temperature of a sun-spot must be lower 
than that of the remainder of the solar surface. As 
we must get less heat from the sun when it is 
covered with spots than when there are none, it may 
be considered a variable star, with a period of eleven 
years. Balfour Stewart and Lockyer have shown 
that this period is in some way connected with the 
action of the planets on the photosphere. As we have 
already mentioned, the variations of the magnetic 
needle have a period of the same length, its greatest 
variations occurring when there are most sun-spots. 
Aurorse, and the currents of electricity which 
traverse the earth's surface, follow the same law. 
This remarkable coincidence set men a-thinking. 
Can the varying condition of the sun exert any 
influences upon terrestrial affairs ? Is it connected 
with the variation of rainfall, the temperature and 



CLIMATE 113 

pressure of the atmosphere, and the frequency of 
storms ? Has the regular periodicity of eleven years 
in the sun-spots .no effect upon climate and agricul- 
tural produce ? 

Mr. F. Chambers, of Bombay, has ' taken great 
trouble to strike, as far as possible, a connection 
between the recurring eleven years of sun-spots and 
the variation of grain prices. He arranged the years 
from 1783 to 1882 in nine groups of eleven years ; 
and, from an examination of his tables, we find that 
there is a decided tendency for high prices to recur 
at more or less regular intervals of about eleven years, 
and a similar tendency for low prices. An occasional 
slight difference can be accounted for by some 
abnormal cause, as war or famine. 

Amid all the apparently irregular fluctuations of 
the yearly prices, there is in every one of the ten 
provinces of India a periodical rise and fall of prices 
once every eleven years, corresponding to the regular 
variation which takes place in the number of sun- 
spots during the same period. If it were possible to 
obtain statistics to show the actual out-turn of the 
crops each year, the eleven yearly variations calcu- 
lated therefrom might reasonably correspond with 
the sun-spot variations even more closely than do 
the price variations. 

This is a remarkable coincidence, if nothing more. 
What if it were yet possible to predict the variations 
of prices in the coming sun-spot cycle ? Such a 
power would be of immense service. By its aid it 
could be predicted that, as the present period of low 
prices has followed the last maximum of sun-spots, 
which was in the year 1904, it will not last much 

H 



114 METEOROLOGY 

longer, but that prices must gradually keep rising 
for the next five years. Could science really predict 
this, it would be studied by many and blessed by 
more. Yet the strange coincidence of a century's 
observations renders the conclusions not only possible, 
but tg some extent probable, 



. CHAPTER XXXIV 

THE "CHALLENGER" WEATHER REPORTS 

THE Challenger Expedition, commenced bySirWyville 
Thomson, and after his death continued by Sir John 
Murray, with an able staff of assistants for the several 
departments, was one of the splendid exceptions to 
the ordinary British Government stinginess in the 
furtherance of science. The results of the Expedition 
were printed in a great number of very handsome 
volumes at the expense of the Government. 

And the valuable deductions from the Challenger's 
Weather Reports by Dr. Alex. Buchan, in his "Atmos- 
pheric Circulation," have thrown considerable light 
upon oceanic weather phenomena. For some of his 
matured opinions on these, I am here much indebted 
to him. 

Humboldt,in 181 7, published a treatise on "Isother- 
mal Lines," which initiated a fresh line for the study of 
atmospheric phenomena. An isotherm is an imagi- 
nary line on the earth's surface, passing through 
places having a corresponding temperature either 
throughout the year or at any particular period. An 
isobar is an imaginary line on the earth's surface. 






THE "CHALLENGER WEATHER REPORTS 115 

connecting places at which the mean height of the 
barometer at sea-level is the same. To isobars, as well 
as to isotherms, Dr. Buchan has devoted consider- 
able attention. In 1868, he published an important 
series of charts containing these, with arrows for 
prevailing winds over the earth for the months of 
the year. In this way what are called synoptic 
charts were established. 

In the Challenger Report are shown the various 
movements of the atmosphere, with their corre- 
sponding causes. It is thus observed that the pre- 
vailing winds are produced by the inequality of 
the mass of air at different places. The air flows 
from a region of higher to a region of lower pressure, 
i.e. from where there is an excessive mass of air to 
fill up some deficiency. And this is the great prin- 
ciple on which the science of meteorology rests, not 
only as to winds, but as to weather changes. 

Of the sun's rays which reach the earth, those that 
fall on the land are absorbed by the surface layer of 
about 4 feet in thickness. But those that fall on 
the surface of the ocean penetrate, as shown by the 
observations of the Challenger Expedition, to a depth 
of about 500 feet. Hence, in deep waters the tem- 
perature of the surface is only partially heated by 
the direct rays of the sun. In mid-ocean the tem- 
perature of the surface scarcely differs 1 Fahr. 
during the whole day, while the daily variation of 
the surface layer of land is sometimes 50. The 
temperature of the air over the ocean is about three 
times greater than that of the surface of the open 
sea over which it lies ; but, near land, this increases 
to five times. 



116 METEOROLOGY 

The elastic force of vapour is seen in its simplest 
form on the open sea, as disclosed by these Reports. 
It is lowest at 4 A.M. and highest at 2 P.M. The 
relative humidity is just the reverse. When the 
temperature is highest, the saturation of the air is 
lowest, and vice versa. So on land when the air, by 
radiation of heat from the earth, is cooled below the 
dew-point, dew is produced, and, at the freezing-point, 
hoar-frost. 

The Challenger Reports, too, show that the force of 
the winds on the open sea is subject to no distinct 
and uniform daily variation, but that on nearing land 
the force of the wind gives a curve as distinctly 
marked as the ordinary curve of temperature. That 
force is lowest from 2 to 4 A.M., and highest from 
2 to 4 P.M. Each of the five great oceans gives the 
same result. At Ben Nevis, on the other hand, these 
forces are just reversed in strength. 

It is also shown by the Challenger observations 
that on the open sea the greatest number of thunder- 
storms occur from 10 P.M. to 8 A.M. And, from this, 
Dr. Buchan concludes that over the ocean terrestrial 
radiation is more powerful than solar radiation in 
causing those vertical disturbances in the equilibrium 
of the atmosphere which give rise to the thunder- 
storm. 

CHAPTER XXXV 
WEATHER-FORECASTING 

To foretell with any degree of certainty the state of 
the weather for twenty-four hours is of immense 



WEATHER-FORECASTING 117 

advantage to business men, tourists, fishermen, and 
many others. The weather is everybody's business. 
And the probabilities of accurate forecasts are so 
improving that all are more or less giving attention 
to the morning meteorological reports. 

Weather-forecasting depends on the principle from 
vast experience that, if one event happens, a second 
is likely to follow. According to the extent and 
accuracy of the data, will be the strength of the 
probability of correct forecasts. And the great end 
of popular meteorology is to demonstrate this. 

We have given some explanations of the weather 
in some respects unique ; and a careful consideration of 
these explanations will the more convince the reader 
of the importance of the subject. No doubt the 
changes of the weather are extremely complex, at 
times baffling ; and the wonder is that forecasts come 
so near the truth. 

For instance, the year 1903 almost defied the 
ordinary rules of weather, for it broke the record for 
rainfall. And, last year, so repulsive and unseason- 
able was the spring, that there seemed to be a virtual 
" withdrawal " of the season. I wrote on it as " The 
Recession of Spring." Speak about Borrowing Days ! 
We had the equinoctial gales of March about the 
middle of April. On very few days had we "clear 
shining to cheer us after rain," for the bitter cold 
dried up any genial moisture. An old farmer re- 
marked that "We're gaun ower faur North." No 
one could account for the backwardness of the 
season. Unless for the cheering songs of the grove- 
charmers, one would have forgotten the time of the 
year. 



118 METEOROLOGY 

In March of this year, at Strathmore, the barometer 
fell from 30*5 inches (the highest for years) to 28*65 in 
five days without unfavourable weather following. It 
again rose to 30*05, then fell to 28*45, followed by a rise 
to 28*7 without any peculiar change. But in two days 
it fell to 28*4 (the lowest for years), followed by a 
deluge of rain and a perfect hurricane for several 
hours, while the temperature was fortunately mild. 
It was only evident at the end that this universal 
storm had been "brewing" some days before. 

All are familiar with the ordinary prognostics of 
good and bad weather. A " broch " round the moon, 
in her troubled heaven, indicates a storm of rain or 
wind. When the dark crimson sun in the evening 
throws a brilliant bronzed light on the gables and 
dead leaves, we are sure that there is an intense 
radiation from the earth to form dew, or even hoar- 
frost. 

According to the meteorological folk-lore, the 
weather of the summer season is indicated by the 
foliation of the oak and ash trees. If the oak comes 
first into leaf, the summer will be hot and dry, if the ash 
has the precedence it will be wet and cold. Looking 
over the observations of the budding of these two trees 
for half a century, I find that the weather-lore adage 
has been pretty correct. The ash was out before the 
oak a full month in the years 1816, '17, '21, '23, '28, 
'29, '30, '38, '40, '45, '50, and '59 ; and the summer and 
autumn in these years were unfavourable. Again, 
the oak was out before the ash several weeks in the 
years 1818, '19, '20, '22, '24, '25, '26, '27, '33, '34, '35, 
'36, '37, '42, '46, '54, '68, and '69 ; the summers during 
these years were dry and warm, and the harvests were 



WEATHER-FORECASTING 119 

abundant. One can never think of this weather 
prognostic from nature without recalling the Swallow 
Song of Tennyson's " Princess " : 

"Why lingereth she to clothe her heart with love, 
Delaying, as the tender ash delays 
To clothe herself, when all the woods are green ? " 

On a muggy morning a sudden clearness in the 
south "drowns the ploughman." And yet enough 
blue in the sky " tae mak' a pair o' breeks " cheers 
one with the assurance of coming dry and sunny 
weather. The low flying of the swallows betokens 
rain, as well as any unseasonable dancing of midges 
in the evening. Sore corns on the feet, and rheu- 
matism in the joints, are direful precursors. The 
leaves are all a-tremble before the approach of 
thunder. But throughout this volume I have given 
many illustrations. 

But one of the largest and most important practical 
problems of meteorology is to ascertain the course 
which storms follow, and the causes by which that 
course is determined, so that a forecast may thereby 
be made, not only of the certain approach of a 
storm, but the particular direction and force of the 
storm. The method of conducting this large in- 
quiry most effectively was devised by the French 
astronomer, Le Verrier the great aspirant, with our 
own Couch Adams, for the discovery of the planet 
Neptune. He began to carry this out in 1858 by 
the daily publication of weather data, followed by 
a synchronous weather map, which showed graphi- 
cally for the morning of the day of publication the 
atmospheric pressure and the direction and force of 



120 METEOROLOGY 

the wind, together with tables of temperature, rain- 
fall, cloud, and sea disturbances from a large number 
of places in all parts of Europe. It is from similar 
maps that forecasts of storms are still framed, and 
suitable warnings issued ; and a mass of information 
is being collected by telegraph from sixty stations 
in the British Islands, &c., of the state of the weather 
at eight o'clock every morning, and analysed and 
arranged at the Meteorological Office in London for 
the evening's forecasts over the different districts 
of the country. A juster knowledge is being now 
acquired of those great atmospheric movements, 
and other changes, which form the groundwork of 
weather-forecasting. 

The Meteorological Office, Westminster (entirely 
distinct from the Royal Meteorological Society), is 
administered by a Council (Chairman, Sir R. Strachey ; 
Scottish member, Dr. Buchan), selected by the Royal 
Society. It employs a staff of over forty. The chief 
departments relate to: (1) Ocean Meteorology, in- 
cluding the collection, tabulation, and discussion of 
meteorological data from British ships, the prepara- 
tion of ocean weather charts, and the issue of meteoro- 
logical instruments to the Royal Navy and Mercantile 
Marine; (2) Weather Telegraphy, including the re- 
ception of telegrams thrice a day from selected stations 
for the preparation of the daily reports and weather 
forecasts. Representatives of newspapers, &c., receive 
copies of the 11 A.M. forecast based on the 8 A.M. 
observations ; and also of the 8.30 P.M. forecasts based 
on the observations received earlier in the day. In 
summer and autumn harvest forecasts are issued by 
telegraph to individuals who will defray the cost. 






WEATHER-FORECASTING 121 

The Office also collects climatological data from a 
number of voluntary and some subsidised stations. 
The " first order " stations include Valentia, Falmouth, 
Kew, and Aberdeen. These have self-recording in- 
struments of high precision, giving a continuous 
record of the meteorological elements. 

A Government Commission which sat last year, 
under the Rt. Hon. Sir Herbert Maxwell, Bart., have 
issued a Report, recommending a number of changes 
in the management and constitution of the Meteoro- 
logical Office ; and considerable modifications are not 
unlikely to take place in the near future. In his 
evidence before that Commission, the Chairman of 
the Council acknowledged that the great function of 
meteorologists is the collection of facts ; but the in- 
terpretation of those collected facts, in a scientific 
manner, is still in a very immature condition. Dr. 
Buchan, in his evidence, confessed that forecasting 
by the Council is purely " by rule of thumb." It is 
not possible to lay down hard and fast rules for 
forecasting. 

With regard to the storm-warning telegrams, as a 
rule, the earliest trustworthy indication of the ap- 
proach of a dangerous storm to the coasts of the 
British Isles precedes the storm by only a few hours. 
Delays are therefore very serious. 

It is admitted by the best British meteorologists 
that the observations of the United States are better 
conducted, although the best instruments in the 
world are set and registered at Kew, in England. 
The work of weather forecasts and storm warnings 
is carried on with the highest degree of promptitude 
and efficiency at the Washington Central Office. 



122 METEOROLOGY 

This is because the work of predictions has been 
hitherto the chief work of the Office : the entire time 
of the observers, on whose telegraphic reports the 
forecasts are based, is controlled by the United States 
Weather Bureau ; and the right of precedence in 
the use of wires is maintained. 

Professor Bruckner, of Berne, has devoted a lifetime 
to the comparatively new treatment of climatic 
oscillations, based upon observations made at 321 
points on the earth's surface, distributed as follows : 
Europe, 198 ; Asia, 39 ; N. America, 50 ; Cen. and S. 
America, 16; Australia, 12; Africa, 6. One of his 
conclusions is that an average time of about thirty- 
live years is found to intervene between one period 
of excess or deficiency of warmth and the next, 
accompanied by the opposite relative condition of 
moisture. 

All are familiar with the hoisting of cone- warning 
as indication of a coming storm. This work is 
exceedingly important, especially for those connected 
with the sea by business or pleasure. On the known 
approach of a cyclone of dangerous intensity, special 
messages are sent from the London Meteorological 
Office, warning the coasts likely to be affected. 
When the cone is hoisted with its apex downwards, 
it means that strong south or south-west winds are 
to be looked for. When the cone is hoisted with 
its apex upwards, it indicates that strong winds from 
the north or north-east are expected. Of course 
they are merely useful precautions; but they are 
universally attended to by people on the sea-coast. 

Though one may have reasonable doubts about 
the use that can be made of weather forecasts for 



WEATHER-FORECASTING 123 

three days, such as are now regularly issued, on 
account of the finical, coy, spasmodic interludes on 
short notice, yet there is a wonderful certainty in the 
daily prognostics of the direction and strength of the 
wind, the temperature of the air, and the likelihood 
of rainy or fair weather, dependent on the broad 
uniformity of nature. This is very serviceable for 
people who have now to live at high pressure in 
business, in the enthralling days of keen competition. 
And it is a great boon to those who are in search of 
health by travelling, or who, in innocent pleasure, 
desire to live as much as possible in the open air. 
Very little credit is given to the " gas " of the isolated 
" weather prophet " ; but those who have confidence 
in the usual weather forecasts from the Meteorological 
Office are satisfied in their belief ; and those who, in 
self-confidence, ignore all weather prognostics, are still 
weak enough to read them and act up to them. 

In practical meteorology, in the scientific explana- 
tion of popular weather-lore, and in the study of 
atmospheric phenomena, which so powerfully influ- 
ence us, for gladness or discomfort, we may, as with 
other branches of science, even all our days, cheer- 
fully go on in " the noiseless tenor of our way," 

" Nourishing a youth sublime, 
With the fairy tales of science and the long results of time." 



INDEX 



ABBROROMBY, spectre on Adam's 
Teak, 89 

Adam's Peak, spectre, 89 

Afterglow described, 62 ; dust-par- 
ticles to form, 64 

Air, change of, 55 ; clearness and 
dry ness, 49 ; devitalised, 52 ; 
disease-germs in, 53 ; thunder- 
clouds, 49 

Aitken, Dr. , afterglows, 67 ; anti- 
cyclones, 97 ; colour of water, 
75 ; condensing power of dust, 
2 ; decay of clouds, 39 ; dew- 
formation, 14 ; dust and atmos- 
pheric phenomena, 29 ; electri- 
cal deposition of smoke, 83 ; 
false dew, 18 ; fog-counter, 82 ; 
foreglows, 67 ; formation of 
clouds, 35 ; haze, 44 ; hazing 
effects of atmospheric dust, 47 ; 
Kingairloch experiments, 30 ; 
one-coloured rainbow, 70 ; radia- 
tion from snow, 86 ; regenera- 
tors, 85 ; sanitary detective, 78 

Ammonia and cloud formation, 36 

Annie Laurie, 17 

Anti-cyclones, forecasting by, 97 ; 
formation, 97 ; cause of influ- 
enza, 109 

Aratus, forecasting by moon, 61 

Ariel's song, 42 

Aurora Borealis, 71 ; forebodings, 
71-73 ; name by Gassendi, 72 ; 
other names, 72 ; safety valve of 
electricity, 72 ; sun's spots, 72 ; 
sun control, 74 ; symptoms, 72 

BAGILLT, condensing lead fumes, 84 
Ballachulish, sunsets, 64 
Ballantiue's song, 17 
Barometer, indications, 10 
Ben Nevis, dust-particles, 30 ; in- 
struments, 104 ; meteorology, 

102 ; observations, 105 ; rainfall, 

103 ; regret at stoppage of Obser- 
vatory, 103 

Blairgowrie, personal description 

of afterglow, 62 
Blue sky, 74 ; cause of, 75, 77 
Borrowing days, 117 
Brocket), spectre, 89 ; personal 

description, 90 ; Noah's Ark, 90 
Bruckner, climatic oscillations, 122 



Buchan, Dr., Aitken's radiation 
from snow, 86 ; Ben Nevis, papers 
on, 103; Challenger Reports, 114 ; 
cold of 1886, 86; east winds, 
94 ; isobars, 115 ; rainfall statis- 
tics, 100 ; on forecasting, 121 

Buchanan, Ben Nevis Observatory, 
102 ; great prevalence of f ojr, 106 

Buddha's Lights, of Ceylon, 72 

Burns, allusions to aurora, 71, 73 

Byron, storm in Alps, 50 

Challenger Expedition, 114 ; tem- 
perature, 115 ; thunder-storms, 
116 ; winds, 116 

Chambers on sun-spots and grain 
prices, 113 

Change of air, 55 ; Strathmore to 
Glenisla, 56 

Charles II., fog and smoke, 80 

Chlorine and cloud formation, 36 

Christison and colour of water, 75 

Chrystal on Aitken's radiation 
from snow, 86 

Cirro-stratus cloud, mackerel-like, 
39 

Climate, Challenger notes, 115 ; 
con^-warnings, 120; Gulf Stream, 
111 ; oscillations, 120 ; rainfall, 
111 ; sun-spots on, 112 ; wooded 
country on, 111 

Clouds, decay of, 37 ; distances of, 

35 ; dry, 42 ; even without dust, 

36 ; formation of, 34 ; height of, 
34; numbering of cloud-particles, 
34 ; sunshine on cloud formation, 
35 ; varieties of, 35 

Cone-warnings, 121 
Continental winds, 98 
Cyclones, 95; formation of, 96, 
98 ; small natural, 98 

DECAY of clouds, 37 ; in thin rain, 
41 ; process, 38 ; ripple mark- 
ings, 39 

Dew, evidence of rising, 22 ; ex- 
periments, 15, 16 ; false dew, 
17 ; formation of, 13 

Disease-germs in air, 53; causes, 
53 ; deposited by rain, 55 

Diseases, and east wind, 94 ; per- 
sonal notes, 95 

Dumfries, dust in air at, 46 



124 



INDEX 



125 



Dust, condensing power, 43 ; from 
meteors, 37 ; generally necessary 
for cloud formation, 26 ; hazing 
effects, 47 ; numbering, 26 ; in- 
struments for numbering, 27 ; 
produces afterglows, 64 ; pro- 
duces foreglows, 67 ; quantity 
in Bunsen flame, 28 ; at Ben 
Nevis, 30; Hyeres, Mentone, 
Rigi Kulm, 29; Lucerne, Kin- 
gairloch, 30 ; when not neces- 
sary, 36 

Dustenumeration,deductionson,31 

EARN, Loch, splash of drop at, 

101 

Earth shine, 59 

Ehrenberg, on colour of water, 75 
Evelyn, fumifugium, 80 ; remedy 

for smoke, 82 

FALKIRK, Dr. Aitken's experiments 
on haze, 47 

False dew, 19 

Fitzroy on aurora as a foreboder, 73 

Fog, counter, 31 ; dry, 41 ; forma- 
tion, 24; more in towns, 25; 
and smoke, 80 

Folk-lore, 50 

Foreglow, described, 66 ; how pro- 
duced, 67 

Fort William Observatory, 102 

Frankland, disease-germs, 53 

Franklin, lightning, 51 

GASSENDI, named aurora, 72 
Gillespie, Dr., on weather and 

influenza, 107 
Glasgow, fog, 81 
Glass, appearing damp, 44 
Glenisla, ozoned air, 56 
Grain crops and sun-spots, 112 ; 

Chambers' tables, 113 
Great amazing light in the north, 72 
Gulf Stream, effects on climate, 111 
Gunpowder, great condensing 

power, 44 

HAZE, what is, 43 ; how produced, 
44; in clearest air, 45; stages 
of condensation, 46 ; in sultry 
weather, 46 ; dryness of air and 
visibility, 48 

Health improved by change of air, 56 
Highland air, few disease-germs, 55 
Hoar-frost, frozen dew, 20 ; on 

under surfaces, 21 
Hydrogen peroxide and cloud for- 
mation, 36 



Hyeres, dust-particles, 29 
Humboldt, isotherms, 114 

INDIAN Ocean, colour, 75 
Influenza, weather and, 107 ; six 
distinct epidemics, 108 ; spread 
of anti-cyclonic conditions, 109 
Isobars by Buchan, 115 
Isotherms by Humboldt, 114 
Italian lakes, stages of condensa- 
tion, 45 

JOB, on dew formation, 13 

KELVIN recorder, 84; Aitken's 

radiation from snow, 86 
Kew, instruments set, 121 
Kingairloch, dust-particles, 30, 46 
Kirchhoff, lower temperature of 

sun-spot, 112 

Krakatoa, eruption of, dust-par- 
ticles, 63 

LE VERRIER and weathercharts,119 
Lockyer, and sun-spots, 112 
Lightning, electricity, 51 ; photo- 
graphed, 51 ; sheet and forked, 
51 ; ozone, 52 
Lodge, electrical deposition of 

smoke, 83 

London, coals consumed, 25 ; sul- 
phur and fog, 25 ; fog in reign of 
Charles II., 81; Meteorological 
Office, 11, 120 

Lord Derwentwater's Lights, 72 
Lower animals, sensitiveness, 11 
Lucerne, dust-particles, 30 

MACLAREN, Aitken's radiation from 

snow, 86 

Magnesia, small affinity for water- 
vapour, 44 

Man in the street, 11 
Mediterranean, brilliant colour, 77 
Mentone, dust-particles, 29 
Merry Dancers of Shetland, 71 
Meteors, producing dust, 37 
Meteorological Council, London, 
103 ; Office, 120 ; cone-warnings, 
121 ; regular forecasts, 123 
Milne Home on Ben Nevis, 103 
Milton, dust numberless, 26 
Moon, old, in new moon's arms, 58 ; 

weather indications, 59, 61 
Mountain giants, 88 ; Adam's Peak, 

89.; Brocken, 89 

Munich, International Meteorolo- 
gical Conference, 35 
Murray, Challenger Expedition, 114 



126 INDEX 



NARDIUS, dew exhalation , 13 
Newton, colour of sky, 77 
Nimbus, cloud, 35 

OAK and ash, on climate, 118 
Ochils, one-coloured rainbow, 70 

PACIFIC, colour, 75 

Paris, aurora, 71; disease-germs, 55 

Paton, Waller, bronze tints in 

sunsets, 64 

Piazzi Smith, aurora, 72 
Picket, dew-formation, 14 
Pilatus, fine rain, 42 
Polar lightnings, 72 

RADIANT heat, producing fine rain, 

41 

Radiation from snow, 86 
Rain, 98; heavy rainfalls, 99 
Rainbow, 68; forecasts, 62, 69; 

formation, 69 ; one-coloured, 70 
Rains, it always, 40 ; radiant heat 

in process, 41 ; Ariel's song, 43 
Rankin, dust-particles, Ben Nevis, 

30 

Richardson, devitalised air, 51 
Rigi Kulm, dust-particles, 29 
Rolier, aurora, 73 

ST. PAUL'S, London, disease-germs 
in air, 54 

Sanitary detective, 78 

Shakespeare, tempest, 95 

Shelley, old moon in new moon's 
arms, 59 

Simoom and sirocco, 94 

Skye, rainy, 40 

Smoke, electrical deposition of, 
83 ; regenerators, 85 

Smoking-room, condensing power, 
44 

Suow, bad conducting, 87 ; radia- 
tion from, 86 

Sodium dust, condensing power, 45 

Spens, forebodings of moon, 61 

Splash of a drop, experiments, 101 

Stevenson, R. L., splash of drop, 101 

Stewart, sun-spots, 112 

Strachey on forecasts, 121 

Strathmore, observations on hoar- 
frost, 22 ; on decay of clouds, 38 ; 
to Glenisla, change of air, 56 ; 
observations on old moon in new 



moon's arms, 59; afterglow de- 
scribed, 62 ; foreglow, 66 ; cold of 
1886, 86 ; healthy by woods, 111 ; 
observations on barometer, 118 

Strathpeffer, 9 

Sulphur as a fog-former, 25 

Sulphuretted hydrogen and cloud- 
formation, 36 

Sunshine on cloud-formation, 35 

Sun's spots, and aurora, 72, 112 ; 
and grain crops, 112 

Symons, rainfall, 100 

Synoptic charts, 98 

TAIT, on Aitken's radiation from 
snow, 86 

Tay Bridge, fall of, 92 

Tennyson, aurora, 71 ; dew, 19 ; 
oak and ash, 119 

Thermometer, indications, 10 

Thomson, Wyville, Challenijer Ex- 
pedition, 114 

Thunder-storm described, 50 

VALKYRIES, aurora, 73 
Visibility, limit of, 48 

WASHINGTON, Meteorological 
Office, 121 

Water, pressure to show plant 
exudation, 18 ; colour of, 75 ; 
experiments on distilled, 76 ; 
dust-par Jcles vary colour, 77 

Weather and influenza, 107 

Weather-forecasting, 116 ; advan- 
tages, 117 ; principle, 117 ; ex- 
amples, 118 ; old moon in new 
moon's arms, 59 ; by moon, 61 ; 
oak and ash, 118 ; cone- warnings, 
122; three days', 123 

Weather-lore, 50, 118 

Weather talisman, 9 ; call on 
barometer and thermometer, 10 ; 
exceptional years, 117 

Wells, Dr., on dew, 14 

Wilson, Prof., on hoar-frost, 20 

Wind, 92; rates, 92; trade, 93; 
land and sea, 93 

Wreikof, durability of cold, 88 

Wordsworth, rainbow, 68 

Worthington, splash of drop. 100 

Wrasse, observations at Ben Nevis, 
104 






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