ATMOSPHERIC BYWAYS
1. IGNIS FATUUS, OR WILL-O’-THE-WISP
Will-o’-the-wisp is proverbially elusive. It has thus far escaped the
fate of the rainbow, deplored by Keats. We do not know its woof and
texture, and it is not given in the dull catalogue of common things.
A strong argument in favor of the reality of this phenomenon is found
in the great number of names that have been applied to it. There are
forty or fifty in the British dialects alone. A myth generally carries
its nomenclature with it, as it spreads from one community to another,
while a fact of nature may give rise to a variety of local names.
It is certain, however, that a great many different phenomena have
been described as will-o’-the-wisp. Some of these are: (1) The
phosphorescence of decaying wood (“fox fire”) and other vegetable
matter. This is due to luminous fungi. According to H. Molisch there
are some forty-five species of fungi, including twenty species of
bacteria, that have the property of luminosity. Sometimes the ground
under a forest is illuminated on all sides with a soft, white light
from decaying leaves. (2) Fireflies, including glowworms (the wingless
females of the firefly and the larvæ). (3) Luminous birds and animals.
Their luminosity is supposed to be due to parasitic fungi. Certain
species of skunk have been described as giving off in the darkness a
continuous flame, the head being fiery red, which blends into a bright
blue at the tail. (4) Ball lightning. (5) St. Elmo’s fire. (6) Moving
lanterns, distant lights of houses, and other lights due to human
agency. (7) Burning gas ascending from marshes, stagnant pools, and the
like. Marsh gas and other inflammable gases commonly rise from such
places, and are often ignited by man, or by lightning, etc. Such fires
are sometimes seen by day as well as by night. (8) Burning naphtha
springs.
Excluding the numerous reported cases of will-o’-the-wisp in which the
phenomenon may be plausibly identified with one of those mentioned
above, there remain several cases, some of them reported by very
careful observers, which appear to belong to a different category. The
reports in question differ somewhat in details, but yield the following
composite description:
Small luminous bodies, “about as large as your fist,” or “the size of
a candle flame,” are seen hovering a few feet above the ground; not
only over marshes and pools, but also over dry land. Sometimes they
are stationary; at other times they appear to drift with the wind, or
even to move independently. They appear and disappear, after the manner
of fireflies. They do not set fire to objects with which they come in
contact, and are believed to be without sensible heat. Their color
is most often described as bluish, but may be yellow, purple, green,
etc.; rarely pure white. They are without odor and without smoke.
Traditionally they are associated with graveyards, but in very few of
the cases heretofore recorded were they actually seen in such places.
The popular idea that they flee from the traveler who tries to approach
them and follow him when he seeks to avoid them is also unsupported by
the evidence thus far adduced.
One of the most circumstantial accounts of these objects is that
published in the Belgian journal “Ciel et Terre” for July-August,
1920, by a retired army surgeon, Jules Rossignol, who observed them
repeatedly in the autumn of 1908 in and about some marshy woods near
Grupont. They were generally seen to rise from the ground, at first
in the shape of little white clouds, which changed to luminous globes
on attaining an altitude of a dozen yards, and returned by a circular
path toward the ground. They lasted from one to several minutes before
disappearing in the air.
It is astonishing that the phenomenon of _ignis fatuus_, though
reported from so many parts of the world, has not yet been made the
subject of direct scientific examination. Nobody has ever studied
its light with the spectroscope, for example. Chemists have, indeed,
attempted to reproduce the phenomenon, yet the chemical explanations
of it that have appeared in reference books down to a recent date
are quite untenable. It has sometimes been attributed to marsh gas
(methane, CH4), and sometimes to phosphureted hydrogen (phosphine,
PH3). But marsh gas, besides not being spontaneously combustible,
diffuses too rapidly in the air to produce the effects described,
while phosphureted hydrogen, though it takes fire spontaneously in the
air, produces thick wreaths of smoke when burning and has a powerful
odor--features never reported in connection with will-o’-the-wisp.
At least two more plausible explanations of _ignis fatuus_ have been
offered in the last few years. Mr. F. Sanford (“Scientific Monthly,”
Oct., 1919) believes that it is due to “swarms of luminous bacteria
which are carried up from the bottom of the marsh by rising bubbles of
gas.” A Belgian chemist, M. Léon Dumas (“La Nature,” Dec. 11, 1909),
claims to have produced little luminous clouds, corresponding to the
traditional descriptions of will-o’-the-wisp, by combining the two
gases sulphureted hydrogen and phosphine. Both these substances are
produced in the decay of animal matter, especially of the brain and
spinal cord. The body of an animal, buried in some wet place, would
accumulate the two gases under pressure in the skull and spinal canal,
and their escape, simultaneously, would fulfill the conditions of M.
Dumas’ experiments.
(At the request of the present writer, these experiments were repeated
at the Bureau of Standards, in Washington, with only partial success.
Further trials with these and other gases due to putrefaction are
desirable.)
2. THE RAIN TREE
From time to time the newspapers publish accounts of a wonderful tree,
said to grow wild in Peru or elsewhere, from the leaves of which falls
a continuous shower of rain, even in the driest weather. The writers
generally urge the introduction of this tree in regions where the
rainfall is deficient, and a so-called “rain tree” has actually been
sold for this purpose by nurserymen.
The story of this tree is very old. Early voyagers reported finding it
in the East Indies, Guinea, Brazil, and especially the island of Ferro,
in the Canaries. Nowadays the name “rain tree” is applied especially
to a magnificent tree of tropical America generally known to botanists
as _Pithecolobium_ (or _Enterolobium_) _saman_. One of its common names
is “guango.”
[Illustration: THE RAIN TREE
From “Voyageurs anciens et modernes”
(_By E. T. Charton_)
A legendary scene in the island of Ferro]
That many plants spontaneously exude moisture under suitable conditions
is well known. The phenomenon is called “guttation.” The moisture drawn
up from the roots is usually transpired from the leaves in the form
of invisible water vapor; i. e., it is evaporated on passing into the
air. If, however, the humidity of the surrounding air is sufficiently
high, or its temperature sufficiently low, to check evaporation, the
water will collect on the surface of the plant in liquid form, and may
ultimately trickle to the ground in considerable quantities. Guttation
occurs chiefly at night, or in cloudy or foggy weather. In a very dry
climate it does not occur at all; and for this reason, even if the
so-called rain tree could be successfully introduced in such a climate,
it would not help solve the problem of irrigation.
The dripping of moisture deposited on plants by drifting fog is
another common process that may have contributed to the legend of
the rain tree. A classic example of this process--technically called
“fog drip”--is that described by Dr. R. Marloth, who has made actual
measurements of the abundant moisture captured by the vegetation of
Table Mountain, South Africa, from the driving clouds of the southeast
trade winds during the nearly rainless summer months. Mr. Madison
Grant, writing of a similar phenomenon witnessed in the redwood forests
of California, tells us that “these forests are sometimes so wet that
the dripping from the high crowns is like a thin rain, and in summer it
is oftentimes hard to tell whether it is raining or not, so saturated
with moisture are the foliage and the trunks when the fog darkens the
forest.”
A copious production of “honeydew” by plant lice, scale insects, etc.,
may be at the bottom of some of the rain-tree stories. F. E. Lutz, in
his “Field Book of Insects,” writes of “weeping trees,” which drip
fluid of insect origin, and he says of the honeydew secreted by the
pear psylla (_Psylla pyricola_): “When the psyllas are numerous the
leaves and fruit become coated with this sticky substance and it even
drops from them like rain and runs down the trunk.”
The following account of the Peruvian rain tree, quoted from the
traveler Spruce, was published in “Nature” of Feb. 28, 1878, by Prof.
Thiselton Dyer:
“The Tamia-caspi, or rain tree of the eastern Peruvian Andes, is not
a myth, but a fact, although not exactly in the way popular rumor has
presented it. I first witnessed the phenomenon in September, 1855,
when residing at Tarapoto. I had gone one morning at daybreak, with
two assistants, into the adjacent wooded hills to botanize. A little
after seven o’clock we came under a lowish spreading tree, from which
with a perfectly clear sky over-head a smart rain was falling. A glance
upward showed a multitude of cicadas, sucking the juices of the tender
young branches and leaves and squirting forth slender streams of limpid
fluid.”
3. DEW PONDS
The Down country of southern England is one of the few places in the
world where the people go to the hilltops to seek water in dry weather.
On the summits of the Downs are found many artificial shallow ponds,
most of them very old. Some, indeed, date back to prehistoric times.
The bottom of these ponds consists of a layer of puddled chalk or clay
and is impervious to water, so that there is no loss by seepage. As
the ponds are not fed by springs or surface drainage, and as lack of
rain does not cause them to dry up, it is popularly believed that their
maintenance depends upon dew. Hence they are called “dew ponds.”
Kipling mentions them in his poetical description of Sussex:
We have no waters to delight
Our broad and brookless vales--
Only the dew pond on the height
Unfed, that never fails.
The leading authority on dew ponds is Mr. Edward A. Martin, who has
written a book about them. Mr. Martin’s experiments have demonstrated
that dew can make no important contribution to the water supply of
these ponds. The rainfall on the hilltops is somewhat higher than
in the valleys, and the greater part of the water in the ponds is
undoubtedly derived from this source. The real key to the mystery,
however, is found in the wet fogs that drift in from the sea. The
process of “fog drip,” which we have mentioned in connection with the
rain tree, supplies the deficiencies of the rainfall, and the name
“mist ponds,” occasionally applied to these bodies of water, is more
appropriate than “dew ponds.”
It remains, however, an interesting paradox that, in time of drought,
the farmers of the Downs drive their cattle to the hilltops to be
watered and send their carts uphill to procure water for household
use in the valleys below. Was it, perhaps, in this topsy-turvy
region--where uplands are called “downs”--that Jack and Jill went “up
the hill” on their ill-starred water quest?
4. BLOWING WELLS
Wells that predict weather changes are local curiosities in many parts
of the world. Such wells are not uncommon in the United States. If the
well is open at the top, its manifestations consist of occasional
disturbance of the water and the discharge of numerous bubbles. If it
is covered, a strong current of air is, at times, emitted from any
small orifice in the cover. This may be strong enough to lift and blow
away light objects placed over the aperture. Its emission is frequently
accompanied by a loud whistling or roaring sound. Such occurrences
are supposed to betoken an approaching storm. These wells are called
“blowing wells”; sometimes “weather wells” or “barometer wells.”
In certain cases an indraft of air is sometimes observed; i. e., the
well alternately “sucks” and “blows.”
As a rule these phenomena correspond to fluctuations in barometric
pressure, and therefore are, in a rough way, indicative of changes in
weather. It is obvious that a body of air inclosed in the earth and
communicating by one or a few small openings with the air above will
set up outdrafts and indrafts in adjusting its tension to that of
the latter. The amount of air contained in the well itself would not
suffice to produce the violent effects observed and it is therefore
assumed that the typical blowing well taps a subterranean reservoir of
air, probably filling the interstices of sand and gravel beds. When
the pressure of the external air is diminished, some of the imprisoned
air escapes. For a given body of inclosed air, the smaller the channel
or channels by which it emerges, the stronger the outdraft. When the
barometric pressure outside increases, the current of air flows in the
reverse direction. In winter the indraft of cold air in such a well
sometimes causes the water to freeze, even at a depth of 100 feet or
more below the surface of the ground, and is therefore a source of
inconvenience to the owner.
Various other circumstances may give rise to the bubbling and blowing
of wells. Carbon dioxide and other gases dissolved in the well water
account for the bubbling of many wells, and this process is more active
at times of low barometric pressure, because at a given temperature,
the amount of gas that the water can hold in solution varies with the
pressure.
Another cause of the blowing of a well is, in some cases, a sudden rise
in the water level (“water table”) in the surrounding ground, as after
a heavy rainstorm. If the ground is overlain by an impervious stratum,
the air imprisoned between this stratum and the surface of the ground
water over an extensive area will escape with violence through any
available channel, such as that supplied by the well.
Lastly, cases have been described in which subterranean air currents
arise from the friction of rapidly flowing underground streams, setting
up permanent indrafts or outdrafts through wells communicating with
such streams.
5. CURIOUS SHOWERS.
Showers of blood, sulphur, manna, frogs, fishes, and what not figure
in all the old chronicles, and are still frequently reported. Many
occurrences of this kind are recorded in Camille Flammarion’s book “The
Atmosphere,” Dr. E. E. Free’s “Movement of Soil Material by the Wind”
(U. S. Bureau of Soils, Bulletin 68), and Mr. W. L. McAtee’s article
“Showers of Organic Matter” in the “Monthly Weather Review” for May,
1917.
The power of the wind to whirl objects aloft is a matter of familiar
observation. McAtee tells of seeing a silk hat lifted from its owner’s
head and blown over a ten-story building in the city of Washington.
The vortex of a tornado or a waterspout furnishes the most favorable
skyward route for things that belong on _terra firma_. Objects weighing
scores or even hundreds of pounds are lifted by these whirls. Within
a mile or so of a tornado a shower of cart wheels or cook stoves
would not necessarily constitute a “prodigy.” A chicken coop weighing
75 pounds has been carried four miles and a church spire seventeen
miles. Oersted tells of a waterspout at Christiansö, on the Baltic,
that emptied the harbor to such an extent that the greater part of the
bottom was uncovered, while McAtee says that “waterspouts have been
observed to accomplish the comparatively insignificant feat of emptying
fish ponds and scattering their occupants.”
There is, in fact, no mystery about the way in which terrestrial
objects of many sorts get into the air; nor, considering the force
of the winds and their occasional strong vertical components, is it
strange that such objects sometimes travel a long way from home before
they return to earth.
There are, however, a great many cases of reported showers in which the
objects did not really fall, as supposed. McAtee gives the following
account of these spurious showers in the “Monthly Weather Review”:
“_Insect larvæ._--The rains of insect larvæ that have been investigated
have proved to be merely the appearance in large numbers on the
surface of the ground or upon snow of the larvæ of soldier beetles
(_Telephorus_), or sometimes caterpillars, which have been driven from
their hibernating quarters by the saturation of the soil by heavy rains
or melting snow.
“_Ants._--Accounts of showers of ants have usually been founded on
incursions of large numbers of winged ants, which of course needs no
assistance from the elements to follow out their habit of swarming
forth periodically in immense numbers.
“_Honey; sugar._--Showers of honey and of sugar are popular names for
what scientists know are exudations of certain plants, or of plant lice
which feed on a great variety of plants and whose product is often
known also as honeydew.
“_Grains._--Showers of grain, usually considered miraculous, have in
most cases been determined to be merely the accumulation by washing
during heavy rains of either the seeds or root tubercles of plants of
the immediate neighborhood.
“_Manna._--An account of manna ‘rains’ certainly pertains to the
discussion of showers of vegetable matter, for the substance manna
consists of lichens of the genus _Lecanora_ but in none of the numerous
recorded instances of manna ‘rains’ is there any direct evidence that
the substance really fell from the sky. These lichens form small,
round bodies that are easily blown over the surface of the ground and
accumulate in depressions; they are very buoyant also and hence easily
drifted into masses during the run-off of rain water. Manna ‘rains’
have not occurred except in countries where these lichens are common,
and as for statements of their falling down upon roofs or upon people,
or for any other proofs that they really rained down, I have seen none.
“_Blood rains._--The most frequently reported showers that are
spurious, at least in name, are the so-called blood rains. In all
times the phenomena going under this name have frightened the people
and have been taken as portents of terrific calamities. One of the
famous plagues of Egypt was a bloody rain which prevailed throughout
the whole land, continuing three days and three nights. Homer and
Virgil both allude to blood rains, and, in fact, the general subject of
preternatural rains was a favorite with the older writers.
“But scientific investigation has done away with the element of
mystery in these phenomena and has explained, with the others, the
rains of blood. Some blood rains have been found to be the meconial
fluid ejected by large numbers of certain lepidoptera simultaneously
emerging from their chrysalides; other red rains are due to the rapid
multiplication in rain pools of algæ and of rotifers containing red
coloring matter; “red snow” results from the presence of similar
organisms. But in no case have they rained down, except in the sense
that their spores or eggs have at some time been transported, probably
by the wind. The precipitation of moisture furnishes favorable
conditions for their rapid development and multiplication.”
Most of the reported showers of blood, however, have probably been
rainstorms in which the rain was colored with reddish dust. The
occurrence of such dust in the atmosphere is very common in some parts
of the world, as we have stated in a previous chapter. It has been
asserted that rain which fell at Oppido Mamertina, Italy, May 15, 1890,
actually contained blood, believed to be from birds.
Showers of supposed “sulphur” are due to pollen, chiefly from pine
trees. The air in the vicinity of pine forests is sometimes filled with
clouds of this material and the wind carries it for many miles. It is
reported that a pollen shower at Pictou, Nova Scotia, in June, 1841,
was so heavy that bucketfuls were swept up on a ship.
In the case of alleged showers of “paper” the material has been found
to be the crusts of dried algæ, which form on the surface of the ground
exposed by the evaporation of the water of shallow ponds.
6. THE YEAR WITHOUT A SUMMER
The Weather Bureau is a bureau of information, and one of the ways
in which it strives to give a good account of itself is by answering
endless questions about “the year without a summer.” This title has
been given to the year 1816.
Blodget, in his “Climatology of the United States,” tells us that all
the summers from 1811 to 1817 were cold in this country, and that in
every month of the summers of both 1812 and 1816 snows and frosts
occurred in the Northern States. It is the latter summer, however,
that has lived in popular tradition. The year 1816 is known further as
“poverty year,” or “eighteen hundred and froze to death.” It acquired
the name of “mackerel year” in New Hampshire, where people ate mackerel
as a substitute for pork, little of which was fattened on account of
the extreme scarcity of corn. Western Europe, also, had a cold summer
in 1816, and the year as a whole seems to have been a cold one over a
great part of the world.
Sources of information about the cold summer in this country, besides
Blodget’s book above mentioned, include Perley’s “Historic Storms
of New England,” which devotes a whole chapter to the subject, and
Charles Peirce’s “Weather in Philadelphia.” Peirce tells us that
at Philadelphia “there was ice during every month of the year, not
excepting June, July, and August, There was scarcely a vegetable
came to perfection north and east of the Potomac.” According to the
“Monthly Weather Review,” citing the recollections of James Winchester,
of Vermont: “It is said that in June of that year snow fell to the
depth of three inches in New York, Pennsylvania, and New Jersey on the
17th; five inches in all the New England States, except three inches
in Vermont. There was snow and ice in every month of this year. The
storm of June 17 was as severe as any that ever occurred in the depth
of winter; it began about noon, increasing in fury until night, by
which time the roads were impassable by reason of snowdrifts; many were
bewildered in the blinding storm and frozen to death.... There was
a heavy snowstorm August 30th.... The year 1816 had neither spring,
summer, nor autumn. The only crop of corn raised in that part of
Vermont that summer was saved by keeping bonfires burning around the
cornfield night and day.”
At the time of its occurrence the frigid weather of the summer of 1816
was popularly attributed to sun spots, which were big enough to be seen
with the naked eye in May and June. A present-day hypothesis on the
subject has been mentioned in our chapter on atmospheric dust. The dust
cloud from the eruption of Tomboro, in 1815, was so vast that for three
days there was darkness at a distance of 300 miles from the volcano.
A proximate cause of the cold summer is perhaps to be sought in an
unusual intensity and extent of the area of low barometric pressure
which is more or less permanently located in the vicinity of Iceland
and, as one of the principal atmospheric “centers of action,” has a
great deal to say about the weather of the countries adjacent to the
North Atlantic. Dr. C. F. Brooks has called attention to the fact that
the Arctic navigator, Scoresby, found unusually mild and open weather
that summer in the seas east of Greenland. This would be explained
by strong southerly winds, forming part of the “counter-clockwise”
circulation around the Iceland low; and if the same pressure system
extended its influence to our shores, persistent cold northwest winds
might be expected to result over the northeastern United States.
7. INDIAN SUMMER AND THE ICE SAINTS
Indian summer _weather_ is an undeniable fact. Every inhabitant of
the northern United States and southern Canada is familiar with the
mild, calm, hazy state of the atmosphere that frequently occurs in the
autumn, sometimes following a brief period of unseasonable cold known
as “squaw winter.” It is, however, one thing to recognize the existence
of a certain type of weather as characteristic of our autumns, and
quite another to admit that one definite spell of such weather occurs
more or less regularly from year to year. One true summer, and only
one, comes to pass each year, and occupies an approximately fixed place
in the calendar. Even the so-called “year without a summer,” which we
have just described, was merely a year in which the regular annual
rise of the temperature curve was less marked than usual. Indian
summer, on the contrary, has never been tied down to a particular part
of a particular month. In his notes on the meteorological conditions
at Concord, Massachusetts, during the ten years, 1851-1860, Thoreau
records the occurrence of Indian summer weather on dates all the way
from September 27 to December 13; a range of 77 days.
The belief in the definite occurrence, year after year, of what has
sometimes been called the “after-summer” is not peculiar to America. It
prevails also in Europe, where this supposed period of renewed warmth
has been assigned to certain dates, owing in part to its association
with the names of particular saints in the calendar. These dates vary
widely, however, from one region to another, ranging from August 15
(Julian calendar), the beginning of the “young women’s summer” of
Russia, to November 15, St. Martin’s day, a date popularly associated
with after-summer in Germany, Holland, France, Italy, and sometimes
England.
The supposed tendency of particular types of weather to occur at
about the same period every year, independently of and often in sharp
contrast to the regular march of the seasons, has been described by
R. Abercromby under the name of “recurrence,” and there is a large
literature on the subject; especially in connection with periods of
unseasonable temperature. While Indian summer is the most discussed
example of recurrence in the American weather calendar, in the Old
World more attention, both popular and scientific, has been devoted
to a frosty period supposed to recur in May. With the elaboration of
the ecclesiastical calendar, the frosts in question became definitely
associated with the days dedicated to Saints Mamertus, Pancras,
and Servatius (May 11, 12, 13), or, in south-central Europe, Saints
Pancras, Servatius, and Boniface (May 12, 13, 14), hence known as the
Ice Saints. These saints and their days are called in French _saints de
glace_, and in German _Eisheiligen_, _Eismänner_, or _gestrenge Herren_.
Yet other examples of the elusive phenomenon of recurrence are the
“January thaw” of New England, the April “blackthorn winter” of
England, and the June “sheep-cold” (_Schafkälte_) of Germany, dangerous
to newly shorn sheep.
In the middle of the last century the cold weather of the Ice Saints
was variously ascribed to the melting of the ice and snow of high
latitudes, the passage of periodic meteor showers between the earth and
the sun, and other far-reaching terrestrial or cosmical causes. FitzRoy
believed that the liberation of latent heat in autumn during the
formation of ice in the circumpolar regions was accountable for Indian
summer. A review of the whole body of literature concerning supposed
recurrent irregularities in the annual march of temperature will be
found in the “Monthly Weather Review” (Washington) for August, 1919.
Whether recurrence, in Abercromby’s sense of the term, is a
real phenomenon is still an unsettled question. Many periods of
unseasonable weather occur in the course of each year, and it is easy
for the uncritical observer to identify one of them with the Ice
Saints, another with Indian summer, and so on. About the best that
meteorologists can do at present is to explain each particular instance
of such weather by reference to barometric and other conditions shown
on the daily weather map.
GLOSSARY
The vast vocabulary of meteorology is very inadequately represented
in ordinary dictionaries, and has never been made the subject of a
comprehensive special glossary. The writer of this book has been
gathering material toward such a glossary for some years, and from the
material now in hand it appears that an approximately complete English
meteorological dictionary, embracing both scientific and nonscientific
terms relating to the atmosphere and its phenomena, would contain
upward of fifteen thousand definitions.
From this statement it will be evident that the brief glossary herewith
appended is of the most fragmentary character. It includes only a
selection of the _meteorological_ terms found in the present book. It
does not, in general, include terms pertaining primarily to physics,
chemistry, astronomy, physiology, etc., even though they figure to some
extent in meteorology, as all such terms used in the book are more
or less satisfactorily defined in the latest editions of the large
American dictionaries.
_Absolute Extremes._--The highest and lowest values of a
meteorological element (especially temperature) that have ever
been recorded at a station; known, respectively, as the _absolute
maximum_ and the _absolute minimum_. (The term is sometimes
improperly applied to the highest and lowest values for a specified
year.)
_Aeroclinoscope._--A semaphore formerly used in Holland for
displaying weather signals.
_Aerology._--The branch of meteorology dealing with the “free”
atmosphere; i. e., all parts of the atmosphere not near the earth’s
surface. Aerological investigations are made with kites and
balloons, and also include observations of clouds, meteor trails,
the aurora, etc.
_Afterglow._--1. The glow in the western sky after sunset. 2. A
renewal of rosy light on mountain peaks after the first sunset
illumination has faded; also called _recoloration_. This is one
stage of the _Alpenglow_.
_After-summer._--A renewal of mild weather in the autumn; called
Indian summer in America, St. Martin’s summer, etc., in Europe.
_Alpenglow._--Successive appearances and disappearances of rosy
light sometimes seen on mountain peaks in clear weather after
sunset or before sunrise.
_Altimeter._--A barometer used for measuring altitude.
_Alto-cumulus_; _Alto-stratus_.--Forms of cloud. (See Chapter VI.)
_Anemogram._--The record traced by a self-registering anemometer.
_Anemometer._--An instrument for measuring the force or speed of
the wind.
_Aneroid Barometer._--A barometer consisting of a thin-walled metal
vacuum-box, which changes its shape with changes of atmospheric
pressure. The movements of the box are communicated, by levers, to
an index or (in the barograph) to a recording pen.
_Anthelion._--A rare species of halo, consisting of a brilliant,
usually white image of the sun opposite the latter in azimuth.
(This term has also been applied to the _glory_, q. v.)
_Anticrepuscular Rays._--The continuation of the crepuscular rays
converging toward a point in the sky opposite to the sun.
_Anticyclone._--An area of high barometric pressure and its
attendant system of winds. (Cf. _cyclone_.)
_Antitrades._--Term formerly applied to the prevailing westerly
winds of middle latitudes, but now more frequently applied to the
westerly return-currents lying over the trade winds. Some writers
prefer to call the former the _antitrades_ and the latter the
_countertrades_.
_Antitwilight Arch._--The pink or purplish zone of illumination
bordering the shadow of the earth (_dark segment_) in the part of
the sky opposite the sun after sunset and before sunrise.
_Arcs of Lowitz._--A pair of rare halo phenomena. These arcs are
directed obliquely downward from the parhelia of 22 degrees on
either side of the sun toward the halo of 22 degrees.
_Astraphobia._--A pathological condition experienced by certain
persons before and during thunderstorms.
_Atmometer._--An instrument for measuring evaporation; also called
_atmidometer_, _evaporimeter_, etc.
_Aureole._--(See _corona_. 1).
_Aurora._--A luminous phenomenon due to electrical discharges
in the atmosphere; probably confined to the tenuous air of high
altitudes. It is most commonly seen in sub-Arctic and sub-Antarctic
latitudes. Called _aurora borealis_ or _aurora australis_,
according to the hemisphere in which it occurs. Observations with
the spectroscope seem to indicate that a faint “permanent aurora”
is a normal feature of the sky in all parts of the world.
“_Backstays of the Sun._”--A sailor’s name for crepuscular rays
extending downward from the sun.
_Baguio._--The name current in the Philippines for a tropical
cyclone.
_Ballistic Wind._--A military term applied to a fictitious wind
which, if affecting a projectile throughout its flight, would
produce the same total effect in deflecting it from its course
and altering its range as do the various winds that it actually
encounters.
_Ballon-sonde._--A sounding-balloon.
_Bar._--A unit of pressure equal to 1,000,000 dynes per square
centimeter. A bar = 100 _centibars_ = 1,000 _millibars_. A
barometric pressure of one bar is sometimes called a “C. G. S.
atmosphere,” and is equivalent to a pressure of 29.531 inches of
mercury at 32 degree F. and in latitude 45 degrees.
_Barisal Gun._--Same as _brontide_.
_Barocyclonometer._--One of several instruments that have been
devised for locating tropical hurricanes without the aid of a
weather map.
_Barograph._--A self-registering barometer.
_Barometer._--An instrument for measuring the pressure of the
atmosphere. The two principal types are the _mercurial_ and the
_aneroid_. The _microbarometer_ is used to show minute changes
of pressure. Certain forms of hygroscope are popularly miscalled
“barometers.”
_Barometer Well._--Same as _blowing well_.
_Barometric Tendency._--The change of barometric pressure within
a specified time (usually three hours) before one of the regular
observations.
_Beaufort Scale._--A scale of wind force, originally devised for
use at sea, but now used also on land. The scale runs from 0 = calm
to = hurricane. Many other scales are similarly employed in the
noninstrumental observation of wind force.
_Bioclimatic Law._--A phenological law, announced by Dr. A. D.
Hopkins, according to which periodical events of plant and animal
life advance over the United States at the rate of 1 degree of
latitude, 5 degrees of longitude, and 400 feet of altitude every
four days--northward, eastward, and up-ward in spring, and
southward, westward, and downward in autumn.
_Bishop’s Ring._--A large corona due to fine dust in the
atmosphere. It has been seen after certain great volcanic
eruptions, especially that of Krakatoa, in 1883.
_Blizzard._--A violent, intensely cold wind, laden with snow.
_Blowing Well._--A well which emits a strong current of air
from any small opening in its cover during a fall of barometric
pressure. During a rise of barometric pressure such wells are
sometimes observed to “suck.” Wells that are thus responsive to
barometric changes are sometimes called “barometer wells” or
“weather wells.”
_Bora._--A cold wind of the northern Adriatic, blowing down from
the high plateaus to the northward. Also, a similar wind on the
northeastern coast of the Black Sea.
_Brave West Winds._--The boisterous westerly winds blowing over the
ocean between latitudes 40 and 50 degrees S. This region is known
as the “roaring forties.”
_Bright Segment._--The broad band of golden light that, in clear
weather, borders the western horizon just after sunset and the
eastern just before sunrise.
_Brontide._--A sound resembling a distant muffled detonation,
usually indefinite as to direction. Brontides are rather common
in certain parts of the world. They are called _mistpoeffers_ on
the Belgian coast, _Barisal guns_ in the Ganges delta, _bulldag_,
_desert sounds_, or _Hanley’s guns_ in parts of Australia,
_gouffre_ in Haiti, _Moodus noises_ at Moodus, Connecticut,
_Nebelzerteiler_, _Seedonner_, _Seeschiessen_, etc., in Germany,
_baturlio_, _boniti_, _bombiti_, etc., in Italy. These sounds are
probably of subterranean origin in most cases.
_Bump._--An upward jolt experienced by an aviator, as if running
over an obstruction. A bump may be caused by any condition that
suddenly increases the lift of the machine, but is perhaps most
frequently due to rising air currents. Air in which bumps are
experienced is said to be “bumpy.” (Cf. _hole in the air_.)
_Callina._--A Spanish name for dry fog.
_Calms of Cancer_; _Calms of Capricorn_.--The belts of high
pressure lying north of the northeast trade winds and south of the
southeast trade winds, respectively.
_Center of Action._--Any one of several large areas of high and low
barometric pressure, changing little in location, and persisting
through a season or through the whole year; e. g., the Iceland
low, the Siberian winter high, etc. Changes in the intensity and
positions of these pressure systems are associated with widespread
weather changes.
_Ceraunograph._--A self-registering thunderstorm recorder.
_Chinook_, or _Chinook Wind_.--A foehn blowing down the eastern
slopes of the Rocky Mountains over the adjacent plains, in the
United States and Canada. In winter, this warm, dry wind causes
snow to disappear with remarkable rapidity, and hence it has been
nicknamed the “snow-eater.” (Cf. _foehn_.) The “wet chinook” is a
wind of a different character, blowing from the Pacific Ocean over
the northwestern United States.
_Circumscribed Halo._--A halo formed by the junction of the upper
and lower tangent arcs of the halo of 22 degrees, when the luminary
is about 40 degrees or more above the horizon. As the altitude of
the luminary increases, the circumscribed halo gradually assumes an
elliptical form and finally merges into the halo of 22 degrees.
_Circumzenithal Arc._--A rainbow-tinted halo, often very bright,
convex to the luminary and 46 degrees or a little more above it. It
is sometimes called the _upper quasi-tangent arc of the halo of 46
degrees_, but the circumzenithal arc and the halo of 46 degrees are
rarely seen at the same time.
_Cirro-cumulus_; _Cirro-stratus_; _Cirrus_.--Forms of cloud. (See
Chapter VI.)
_Cistern._--The cup, containing mercury, at the base of a mercurial
barometer.
_Climatography._--1. Descriptive and statistical climatology. 2. An
account of the climate of a particular place or region.
_Climatology._--1. The science of climate. 2. A body of knowledge
concerning the climate of any place or region; as, “the climatology
of Panama.”
_Climograph._--A diagram introduced by Dr. Griffith Taylor,
of Australia, for showing the mean monthly values of wet-bulb
temperature and relative humidity at any place, and for comparing
such data as recorded at different places throughout the world;
especially with reference to the effects of climate on mankind.
Other pairs of elements can be used in constructing climographs:
e. g., the dry-bulb temperature and the relative humidity.
_Cloud-banner._--A bannerlike cloud streaming off from a mountain
peak.
_Cloud-burst._--A sudden and extremely heavy downpour of rain;
especially one in which the water falls in a continuous stream
rather than in drops. The term has been most commonly applied to
downpours in mountainous regions.
_Cloud-cap._--A caplike cloud crowning (1) a mountain summit, or
(2) another cloud, especially a mass of cumulo-nimbus.
_Col._--The neck of low pressure between two anticyclones; also
called a _saddle_.
_Cold Wave._--A rapid and marked fall of temperature during the
cold season of the year. The United States Weather Bureau applies
this term to a fall of temperature in 24 hours equaling or
exceeding a specified number of degrees and reaching a specified
temperature or lower; the specifications varying for different
parts of the country and for different periods of the year.
_Collector._--A device used in measurements of atmospheric
electricity for determining the potential gradient.
_Continental Climate._--The type of climate characteristic of
the interior of a continent. As compared with a marine climate,
a continental climate has a large annual and daily range of
temperature.
_Corona._--1. A colored luminous circular area formed, by
diffraction; around the sun, moon, or other source of light seen
through clouds or dust haze. Coronas invariably show a brownish-red
inner ring, which, together with the bluish-white inner field
between the ring and the luminary, forms the so-called _aureole_.
Most frequently the aureole alone is visible. Well developed
coronas show one or more series of spectral colors outside the
aureole. 2. A luminous circle formed by the apparent convergence
of auroral beams about the place in the sky toward which the
dipping-needle points.
_Corposant._--(See _St. Elmo’s fire_.)
_Countertrades._--(See _antitrades_.)
_Crepuscular Rays._--Beams of light radiating from the sun, seen
both before and after sunrise and sunset. The beams are made
visible by the presence of water-drops or dust in the atmosphere,
and the intervening dark spaces are the shadows of clouds. The
beams are actually parallel; their apparent divergence is the
result of perspective.
_Critical Period._--A period in the growth of a plant when it is
especially susceptible to the effects of atmospheric conditions.
_Cumulo-nimbus_; _Cumulus_.--Forms of cloud. (See Chapter VI.)
_Cyclone._--An area of low barometric pressure with its attendant
system of winds. The cyclones of the region within the tropics
(_tropical cyclones_) are violent storms; those of higher latitudes
(_extra-tropical cyclones_) may be stormy or otherwise. Tropical
cyclones are also called _hurricanes_, _typhoons_ or _baguios_.
Extra-tropical cyclones are commonly known as _lows_ or _barometric
depressions_.
_Cyclonopathy._--The abnormal sensitiveness of certain persons to
the weather changes attending the passage of barometric depressions.
_Cyclonoscope._--A pasteboard dial formerly used in the West Indies
for locating cyclones.
_Dark Segment._--The shadow of the earth which, in clear weather,
rises from the eastern horizon at sunset and sinks below the
western horizon at sunrise.
_Deperditometer._--An instrument devised by A. Piche for measuring
the cooling power of the atmosphere, with reference to its
physiological effects.
_Depression._--A cyclonic area, or low.
_Desert Sounds._--(See _brontide_.)
_Devil._--The name applied to a dust whirlwind in India. The term
is also current in South Africa.
_Dew._--Atmospheric moisture condensed, in liquid form, upon
objects cooler than the air, especially at night.
_Dew-point._--The temperature at which, under ordinary conditions,
condensation of water vapor begins in a cooling mass of air. It
varies with the absolute humidity.
_Dew Pond._--The name applied in southern England to certain
artificial ponds on the uplands. They contain water in the driest
weather, and are popularly supposed to be fed by dew.
“_Doctor._”--A colloquial name for the sea breeze in tropical
climates. The name is sometimes applied to other cool, invigorating
breezes.
_Doldrums._--The equatorial belt of calms or light, variable winds,
lying between the two trade-wind belts.
_Drought._--A protracted period of dry weather. In the United
States a drought has been defined as a period of thirty or more
consecutive days during which precipitation to the amount of 0.25
inch does not occur in twenty-four hours. Other quantitative
definitions have been used in other countries.
_Dry Fog._--A haze due to the presence of dust or smoke in the air.
_Dust-counter._--An instrument for determining approximately the
number of dust particles or condensation nuclei per unit volume in
a sample of air.
_Dynamic Meteorology._--The branch of meteorology that treats
of the motions of the atmosphere and their relations to other
meteorological phenomena.
_Earth-air Current._--The electrical current that passes between
the earth and the air on account of their difference of potential.
_Eddy._--A more or less fully developed vortex in the atmosphere,
constituting a local irregularity in a wind. All winds near the
earth’s surface contain eddies, which at any given place, produce
“gusts” and “lulls.” Air containing numerous eddies is said to be
“turbulent.”
_Electric Niagara._--(See _hail rod_.)
_Evaporimeter._--(See _atmometer_.)
_Eye of the Storm._--A calm region at the center of a tropical
cyclone, or a break in the clouds marking its location.
_Fall Wind._--A wind blowing down a mountain-side; or any wind
having a strong downward component. Fall Winds include the foehn,
mistral, bora, etc.
_False Cirrus._--Cirruslike clouds at the summit of a thundercloud;
probably identical in structure with true cirrus, or cirro-stratus.
Sometimes more appropriately called “thunderstorm cirrus.”
_Fata Morgana._--A complex form of mirage, characterized by marked
distortion of images.
_Festoon Cloud._--Mammato-cumulus.
_Flashing Arcs._--Visible atmospheric sound waves, or explosion
waves.
_Flat._--Featureless; said of weather maps.
_Foehn._--A dry fall wind warm for the season, characteristic
of many mountainous regions. The air is cooled dynamically in
ascending the mountains, but this leads to condensation, which
checks the fall in temperature through the liberation of latent
heat. The wind deposits its moisture as rain or snow. In descending
the opposite slope it is strongly heated dynamically and arrives in
the valleys beyond as a warm and very dry wind. Some writers apply
this term to any wind that is dynamically heated by descent; e. g.,
the sinking air of an anticyclone.
_Foehn-sickness._--Headache, lassitude, depression, etc.,
attributed, in the Alpine valleys, to the blowing of the foehn.
_Foehn-wall_ (German: _Föhnmauer_).--A wall of cloud that forms
along the crest of a mountain ridge over which the foehn is blowing.
_Fog._--A cloud at or near the earth’s surface. A fog and a
cloud are identical in structure, though the former is due to
thermal conditions of the earth’s surface, while the latter is
most frequently clue to the dynamic cooling of ascending air. In
ordinary speech, the term “fog” generally implies an obscurity of
the atmosphere sufficiently great to interfere with navigation or
locomotion. (Cf. _dry fog_.)
_Fogbow._--A rainbow, colorless or nearly so, formed in a fog.
_Fog-drip._--Moisture that is deposited on terrestrial objects by
fog, and drips from them to the ground.
_Fracto-cumulus_; _Fracto-nimbus_; _Fracto-stratus_.--Forms of
cloud. (See Chapter VI.)
_Freeze._--1. Freezing of plants without deposit of hoarfrost.
2. Freezing temperatures prevailing generally over a region; not
exclusively nocturnal and not confined to the air close to the
earth’s surface. (Cf. _frost_.)
_Frost._--1. The act or state of freezing. In America, a “frost”
generally means the occurrence, near the beginning or end of
the growing season, of nocturnal temperatures low enough to be
injurious to vegetation; distinguished from a “freeze,” which is
more general and severe. The Weather Bureau classifies frosts,
according to their effects, as “light,” “heavy,” and “killing.” 2.
Atmospheric moisture condensed upon terrestrial objects in the form
of ice; sometimes frozen dew. Also called _hoarfrost_.
_Frost-smoke._--Frozen fog rising from the water.
_Fulgurite._--A glassy tube formed in sandy soil or in rock by the
passage of lightning.
_Garúa._--A wet fog of the west coast of South America.
_Geocoronium._--The name applied by Dr. A. Wegener to a
hypothetical atmospheric gas, supposed to be much lighter than any
gas now known to chemists.
_Glaze._--Term applied by the U. S. Weather Bureau to a smooth
coating of ice on terrestrial objects due to the freezing of rain;
often popularly called “sleet.” In Great Britain such a deposit is
called _glazed frost_. A deposit of glaze on an extensive scale
constitutes an “ice storm.”
_Glory._--A series of concentric colored rings seen around the
shadow of the observer, or of his head only, cast upon a cloud or
fog bank. It is due to the diffraction of reflected light.
_Gouffre._--(See _brontide_.)
_Gradient._--Change of value of a meteorological element per unit
of distance. The gradients commonly discussed in meteorology are
the horizontal gradient of barometric pressure, the vertical
gradient of temperature, and the vertical gradient of electric
potential. British meteorologists now prefer the term _lapse-rate_
to _vertical gradient_.
_Graupel._--A kind of granular snow, sometimes called _soft hail_.
_Green Flash._--A bright green coloration of the upper edge of the
sun’s disk, sometimes seen when the rest of the disk is below the
horizon, at sunrise or sunset.
_Growing Season._--In agricultural meteorology, the interval
between the last killing frost in spring and the first killing
frost in autumn.
_Gust._--A sudden brief increase in the force of the wind. Most
winds near the earth’s surface are made up of alternate gusts and
_lulls_, the majority of which are too brief to be registered by an
ordinary anemometer.
_Hail._--Balls or irregular lumps of ice, often of considerable
size, having a complex structure; large hailstones generally
have a snowlike center, surrounded by layers of ice, which may
be alternately clear and cloudy. Hail falls al-most exclusively
in connection with thunderstorms. For so-called “soft hail” see
_graupel_. (Cf. _sleet_.)
_Hail Rod._--A device analogous to a lightning rod, supposed to
have the property of averting the fall of hail. Hail rods have been
especially popular in France, where they are called _paragrêles_.
Large hail rods of recent construction are known as “electric
Niagaras.”
_Hail-shooting._--Bombarding the clouds to prevent the fall of hail.
_Halo._--A generic name for a large group of optical phenomena
caused by ice crystals in the atmosphere. The commonest of these
phenomena is the _halo of 22 degrees_ (i. e., of 22 degrees radius)
surrounding the sun or moon. The _halo of 46 degrees_ and the rare
_halo of 90 degrees_, or _halo of Hevelius_, also surround the
luminary. Other forms of halo are the _tangent arcs_, _parhelia_
(_or paraselenæ_), _parhelic_ (or _paraselenic_) _circle_,
_anthelion_, etc.
_Harmattan._--A dry, dusty wind of the west coast of Africa,
blowing from the deserts.
_Haze._--A lack of transparency in the atmosphere; sometimes due
to irregularities in the density of the air (_optical haze_),
sometimes to dust (_dust haze_, which when dense constitutes _dry
fog_), sometimes to fine particles of water or ice (grading into
true _fog_).
_Helm and Bar._--A pair of clouds seen when the “helm wind” is
blowing over Crossfell, an English mountain; the “helm” capping the
mountain and the “bar” lying to leeward of it.
_High._--An area of high barometric pressure; an anticyclone.
_Hoarfrost._--(See _frost_.)
_Hole in the Air._--A colloquial name for any condition in the
atmosphere that suddenly decreases the lift of an aeroplane. (Cf.
_bump_.)
_Horse Latitudes._--The regions of calms and variable winds
coinciding with the subtropical high-pressure belts lying on the
poleward sides of the trade winds. (The term has generally been
applied only to the northern of these two regions, in the North
Atlantic Ocean, or to the portion of it near Bermuda.)
_Hot Wave._--A period of abnormally high temperatures. It has
sometimes been defined, in the United States, as a period of
three or more consecutive days during each of which the maximum
temperature is 90 degrees F. or over.
_Hot Wind._--A hot, parching wind characteristic of certain
continental interiors; especially Australia, northern India and the
prairie region of the United States.
_Humidity._--The degree to which the air is charged with water
vapor; viz., the actual amount of water vapor present (_absolute
humidity_, which may be expressed in terms of weight per unit
volume or as vapor pressure), or the ratio which this amount
bears to the maximum amount the air can contain at the prevailing
temperature (_relative humidity_, expressed in percentage).
_Hurricane._--A tropical cyclone; especially one of the West Indies
region. (A cyclone originating in this region and passing northward
into the temperate zone is still called a “West India hurricane,”
even after it has assumed the character of an extratropical
cyclone, and, if sufficiently severe, justifies the display of
“hurricane warnings” at ports of the United States. “Hurricane”
is also the designation of the highest wind force on the Beaufort
scale, and is thus applied to any wind exceeding about seventy-five
miles an hour.)
_Hygrograph._--A self-registering hygrometer.
_Hygrometer._--Any instrument for measuring the humidity of the air.
_Hygroscope._--A device that gives a rough indication of the
relative humidity of the air. Most hygroscopes are mere toys.
_Ice Rain._--1. A rain that causes a deposit of glaze. 2. Falling
pellets of clear ice (called _sleet_ by the U. S. Weather Bureau).
_Ice Saints._--A period of cold weather popularly reputed in Europe
to occur yearly about May 11-13 (or, in south-central Europe, May
12-14); also, the saints whose days in the ecclesiastical calendar
fall on these dates.
_Ice Storm._--(See _glaze_.)
_Ignis Fatuus._--Will-o’-the-wisp. (See Chapter XXII.)
_Indian Summer._--A period of mild, calm, hazy weather occurring in
autumn or early winter, especially in the United States and Canada;
popularly regarded as a definite event in the calendar, but weather
of this type is really of irregular and intermittent occurrence.
(Cf. _St. Martin’s Summer_.)
_Instrument-shelter._--The American name of the cage or screen in
which thermometers are exposed at meteorological stations. Called
_thermometer-screen_ in Great Britain.
_Inversion._--More fully _temperature inversion_; an increase of
air temperature with increase of altitude, instead of the normal
decrease.
_Ion-counter._--An instrument for determining the number of ions
present, per unit volume, in a sample of air.
_Isobar._--A line of equal barometric pressure. (Isobars are
generally drawn on maps to show the horizontal distribution of
pressure reduced to sea level, or the pressure at some specified
altitude; but in a broader sense any line on a chart or diagram
drawn through places of equal pressure is an isobar.)
_Isohyet._--A line of equal rainfall.
_Isotherm._--A line of equal temperature.
_Isothermal Layer._--(See _stratosphere_.)
_January Thaw._--A period of mild weather popularly supposed to
recur each January, especially in New England.
_Katathermometer._--A device consisting of a dry-bulb and a
wet-bulb thermometer, designed for measuring the cooling power of
the atmosphere, with reference to its physiological effects. It was
invented by Leonard Hill.
_Kiosk._--The name given by the U. S. Weather Bureau to a small
street pavilion in which are displayed meteorological instruments,
maps, tables, etc.
_Land and Sea Breezes. Land and Lake Breezes._--The breezes that,
on certain coasts and under certain conditions, blow from the land
by night and from the water by day.
_Lenticular Cloud._--A cloud having approximately the form of a
double-convex lens, marking the position of a standing wave in the
atmosphere. (See Chapter VI.)
_Lightning._--A disruptive electrical discharge in the atmosphere,
or, generally, the luminous phenomena attending such a discharge.
The various forms of lightning are named and described in Chapter
IX.
_Lightning Print._--A collection of marks, often treelike in form,
sometimes found on the body of a person or animal that has been
struck by lightning.
_Lightning Rod._--A metallic rod, connected with a suitable
“ground,” in earth or water, set up for the purpose of protecting
some structure from lightning.
_Light-pillar._--A form of halo, consisting of a column of light,
vertical or nearly so, extending from or through the sun or moon.
Called a _sun-pillar_, or a _moon-pillar_, as the case may be.
_Line-squall._--A more or less continuous line of squalls and
thunderstorms traveling broadside over the country.
_Looming._--An apparent elevation of distant objects by mirage.
_Low._--An area of low barometric pressure, with its attendant
system of winds. Also called a _barometric depression_ or _cyclone_.
_Mackerel Sky._--An area of sky covered with cirro-cumulus clouds;
especially when the clouds resemble the patterns seen on the backs
of mackerel.
_Mammato-cumulus._--A form of cloud showing pendulous sacklike
protuberances. (See Chapter VI.)
_March._--The variation of a meteorological element in the course
of a day, year, or other interval of time; e. g., the diurnal
march of temperature; the annual march of barometric pressure.
_Mares’-tails._--Cirrus in long slender streaks.
_Marine Climate._--A type of climate characteristic of the ocean
and oceanic islands. Its most prominent feature is equability of
temperature.
_Meteorograph._--Autographic apparatus for recording simultaneously
two or more meteorological elements. Certain types of meteorograph
are connected, electrically or otherwise, with some of the
instruments at meteorological stations; others are sent aloft
attached to kites and balloons.
_Meteorology._--The science of the atmosphere.
_Millibar._--(See _bar_.)
_Mirage._--An apparent displacement or distortion of distant
objects by abnormal atmospheric refraction. Sometimes the images of
objects are inverted, multiplied, etc.
_Mist._--Generally, a wet fog or a very fine drizzle of rain; hence
the expression, “it is misting.” The “Scotch mist” of mountainous
or hilly regions is a combination of thick fog and heavy drizzle;
it has been suggested that this occurs when the rain clouds
actually rest on the earth.
_Mistpoeffer._--(See _brontide_.)
_Mistral._--Along the Mediterranean coast, from the mouth of the
Ebro to the Gulf of Genoa, a stormy, cold northerly wind, blowing
down from the mountains of the interior. (The name is sometimes
applied to northerly winds on the Adriatic, in Greece, and in
Algeria.)
_Monsoon._--A wind that reverses its direction with the season,
blowing more or less steadily from the interior of a continent
toward the sea in winter, and in the opposite direction in the
summer.
_Moon Dog._--A paraselene.
_Mountain and Valley Breezes._--The breezes that, in mountainous
regions, normally blow up the slopes by day (_valley breeze_) and
down the slopes by night (_mountain breeze_).
_Nephoscope._--An instrument for measuring the movements of clouds.
_Nieve Penitente._--Fields of pinnacled snow found on certain high
mountains in tropical or subtropical regions.
_Nimbus._--The rain cloud. (See Chapter VI.)
_Noctilucent Clouds._--Luminous, cirruslike clouds sometimes
visible throughout the short nights of summer; supposed to be
clouds of dust at great altitudes shining with reflected sunlight.
Such clouds were observed during several summers after the eruption
of Krakatoa (1883) and are still occasionally reported.
_Normal._--The average value which, in the course of years, any
meteorological element is found to have on a specified date or
during a specified month or other portion of the year, or during
the year as a whole. Also used as an adjective in such expressions
as “normal temperature,” etc. Thus, for any station at which
records have been maintained for many years, we may compute the
normal temperature of January 1, the normal pressure of February,
the normal rainfall of the year, etc. The normal serves as a
standard with which values occurring in a particular year may be
compared in order to determine the _departure from the normal_.
_Nucleus._--A particle upon which condensation of water vapor
occurs in the free atmosphere in the form of a water drop or an ice
crystal.
_Oblique Arcs of the Anthelion._--A rare form of halo, consisting
of intersecting arcs, usually white, passing through the anthelion
or the place where the anthelion would occur if visible.
_Ozone._--An allotropic form of oxygen, which occurs transiently
in small quantities in the lower atmosphere, and is supposed to be
permanently present and relatively abundant at high atmospheric
levels.
_Painter._--A dirty fog frequently experienced on the coast of
Peru. The brownish deposit from it is sometimes called “Peruvian
paint.”
_Paragrêle._--A hail rod.
_Paranthelion._--A halo phenomenon similar to a parhelion, but
occurring at a distance of 90 degrees or more in azimuth from the
sun. The solar distance of the ordinary paranthelia is 120 degrees.
(Analogous phenomena produced by the moon as source of light are
called _parantiselenæ_.)
_Paraselene._--(Plu. _paraselenæ_.) (See _parhelion_.)
_Paraselenic Circle._--(See _parhelic circle_.)
_Parasitic Clouds._--The name formerly given to clouds capping the
summits of mountains.
_Parhelic Circle._--A halo consisting of a white circle passing
through the sun and parallel to the horizon. A similar phenomenon
in connection with the moon is called a _paraselenic circle_.
_Parhelion._--A mock sun, or sun dog; a form of halo consisting
of a more or less distinctly colored image of the sun at the
same altitude as the latter above the horizon, and hence lying
on the parhelic circle, if present. The ordinary parhelia are 22
degrees from the sun in azimuth, or a little more, according to
the altitude of the luminary. Parhelia have occasionally been
seen about 46 degrees from the sun. Analogous phenomena seen in
connection with the moon are called _paraselenæ_, _mock moons_, _or
moon dogs_.
_Penetrating Radiation._--A form of radiation that has the property
of passing through a great extent of air without being absorbed and
of ionizing the air inside hermetically sealed metal vessels. It
is supposed to consist of a special kind of Gamma rays and to come
from the higher levels of the atmosphere.
_Phenology._--The study of the periodic phenomena of animal and
plant life and their relations to weather and climate.
_Photochemical Climate._--The chemical activity of sunlight
characteristic of any place or region. The variations of this
feature of solar radiation are more or less strikingly different
from those of solar heat and the brightness of solar light. Certain
types of “chemical actinometer” are used in its measurement.
_Pilot Balloon._--A small free balloon the drift of which, as
observed from the ground, indicates the movements of the air aloft.
_Pocky Cloud._--Mammato-cumulus.
_Pogonip._--A fog, composed of fine needles of ice, which occurs in
mountainous regions of the western United States and is reputed to
be very injurious to the lungs.
_Pollution Gauge._--A gauge for measuring soot and other impurities
found in the atmosphere.
_Pontias._--A wind that blows by night from a narrow valley at
Nyons, France.
_Potential Gradient._--(See _gradient_.)
_Precipitation._--The collective name for deposits of atmospheric
moisture in liquid and solid form, including rain, snow, hail, dew,
hoarfrost, etc.
_Pressure._--An elliptical expression, current in meteorological
literature, for _atmospheric pressure_, or _barometric pressure_.
_Prevailing Westerlies._--The belts of winds lying on the poleward
sides of the subtropical high-pressure belts.
_Psuchrainometer._--An instrument devised by J. R. Milne for
measuring the cooling power of the atmosphere with reference to
physiological effects.
_Psychrometer._--An instrument for measuring atmospheric humidity,
consisting usually of a _dry-bulb thermometer_ and a _wet-bulb
thermometer_. The former is an ordinary mercurial thermometer.
The latter has its bulb covered with muslin or other fabric,
which is either permanently wet or is wetted before use. In some
psychrometers there is only one thermometer, readings being taken
both before and after moistening the bulb.
_Purple Light._--The purple or rosy glow observed over a large
area of the western sky after sunset and the eastern sky before
sunrise; it lies above the _bright segment_ that borders the
horizon.
_Pyrheliometer._--An instrument that measures solar radiation by
its heating effects.
_Qobar._--A dry fog or heat haze of the upper Nile region. (Also
spelled _kobar_ and _gobar_ and occasionally applied to a hazy
condition of the atmosphere in other parts of the world.)
_Rain Balls._--Mammato-cumulus.
_Rainbow._--A luminous arc formed by the refraction and reflection
of light in drops of water. (See Chapter X.)
_Rainfall._--A term sometimes synonymous with _rain_, but most
frequently used in reference to amounts of precipitation (including
snow, hail, etc.).
_Rain Gauge._--An instrument for measuring rainfall.
_Rain Tree._--A mythical tree which is alleged to exude copious
showers of water even in the driest weather. (“Rain tree” is also
the common name of an ornamental tree variously known to botanists
as _Albizzia saman_, _Pithecolobium saman_, _Enterolobium saman_,
and _Samanea saman_.)
_Recoloration._--(See _afterglow_.)
_Recurrence._--The alleged tendency of any particular type of
weather to occur at about the same period every year, independently
of and generally in contrast to the regular march of the seasons.
_Refraction._--_Astronomical refraction._ Change in the apparent
position of a heavenly body, due to atmospheric refraction.
_Terrestrial refraction._ Change in the apparent position of
distant terrestrial objects, due to the same cause.
_Relative Wind._--In aeronautics, the motion of the air with
reference to an aeroplane or airship moving through it.
_Réseau._--A collection of meteorological stations operating under
a common direction, or in the same territory. An _international
réseau_ is a group of stations in different countries cooperating
for any purpose. The _Réseau mondial_ is a world-wide system of
selected stations, the observations of which may be utilized in
studies of the meteorology of the globe.
_Rime._--1. Hoarfrost. 2. A rough or feathery coating of ice
deposited on terrestrial objects by fog. (The second meaning is the
one now used in technical literature.)
_Roaring Forties._--(See _brave west winds_.)
_Saddle._--(See _col_.)
_Saint Elmo’s Fire._--A luminous brush discharge of electricity
from elevated objects, such as the masts and yardarms of ships,
lightning rods, steeples, etc., occurring in stormy weather. Also
called corposant.
_St. Martin’s Summer._--One of several names given in Europe to a
mild period in autumn, corresponding approximately to the Indian
summer of North America.
_Scarf Cloud._--A thin cirruslike cloud which often drapes the
summits of tall cumulo-nimbus clouds.
_Scotch Mist._--(See _mist_.)
_Scud._--Shreds or small detached masses of cloud moving rapidly
below a rain cloud or other heavy clouds.
_Sea Breeze._--(See _land and sea breezes_.)
_Secondary._--A small cyclone developed, or tending to develop, on
the border of a large one.
_Sensible Temperature._--The temperature felt at the surface of
the human body; formerly identified, by some authorities, with the
temperature indicated by the wet-bulb thermometer.
_Silence, Areas, Zones, or Regions of._--Regions within which a
sound is not heard, though heard in regions more distant from the
source.
_Silver Thaw._--A term variously applied to rime, glaze, and a thin
coating of ice deposited on cold objects by a damp wind.
_Simoom._--An intensely hot and dry wind of Asian and African
deserts; often described as a sand storm or dust storm, but certain
authorities state that the typical simoom is free from sand or dust.
_Sirocco._--A name applied to various types of warm wind in the
Mediterranean region. Some of these siroccos are foehns. The term
is also used as the generic name for winds blowing from a warm
region toward an area of low pressure in a normally colder region.
_Sleet._--1. Frozen or partly frozen rain; frozen raindrops in the
form of particles of clear ice. 2. Snow and rain falling together.
(Other definitions have been proposed and the proper technical
application of this term is still a subject of controversy. In
popular and engineering use the word is often applied to a coating
of glaze on trees, wires, rails, etc.)
_Snow Bin._--A large receptacle for collecting the snowfall of an
entire winter, or other long period, for measurement at one time.
_Snow Garland._--An elongated mass of snow suspended at the ends
and sagging in the middle.
_Snow Mushroom._--An overhanging cap of snow resting on a tree
stump, post, or the like.
_Snow Roller._--A mass of snow rolled by the wind; generally
muff-shaped.
_Snow Sampler._--A device for collecting a sample of snow, cut
vertically through a snowfield, for the purpose of determining the
depth and density of the snow.
_Snow Survey._--A measurement of the total amount of snow lying
over a particular area, especially with a view to determining the
total amount of water it will yield, when melted, for purposes of
irrigation, etc.
_Soft Hail._--Graupel.
_Sounding Balloon._--A free, unmanned balloon carrying a set of
self-registering meteorological instruments.
_Specter of the Brocken._--The shadow of an observer and of objects
in his immediate vicinity cast upon a cloud or fog bank; sometimes
attended by a series of colored rings, called the _glory_ or
_Brocken-bow_.
_Squall._--1. A sudden storm of brief duration; closely akin to a
thunderstorm but not necessarily attended by thunder and lightning.
2. A sudden brief blast of wind, of longer duration than a gust.
_Squaw Winter._--In North America, a brief cold spell popularly
reputed to precede Indian summer.
_Static._--(See _stray_.)
_Storm Card._--A device intended for use on shipboard in
determining the direction of a storm center from the ship.
_Storm Water._--The water resulting from a heavy and rapid fall of
rain; especially the portion that occurs as run-off. (The term has
been used mainly in connection with the subject of sewers.)
_Strato-cumulus._--A form of cloud. (See Chapter VI.)
_Stratosphere._--The upper region of the atmosphere, formerly
called the _isothermal layer_, in which there is no marked or
systematic decrease of temperature with altitude. The stratosphere
is free from clouds (except occasional dust clouds) and from strong
vertical air currents, and its circulation appears to be more or
less independent of that of the lower atmosphere. The height of its
base, which varies with latitude and otherwise, averages between 6
and 7 miles. (Cf. _troposphere_.)
_Stray._--A natural electromagnetic wave in the ether. The term
is used in reference to the effects of such waves in producing
erratic signals in radiotelegraphic receivers. Strays are known
collectively as _static_.
_Summer Day._--A day in which the temperature reaches or exceeds 77
degrees F.
_Sun Dog._--A mock sun or parhelion.
“_Sun Drawing Water._”--The sun popularly said to be “drawing
water” when crepuscular rays extend down from it toward the horizon.
_Sunshine Recorder._--An instrument for recording the duration of
sunshine; certain types also record the intensity of sunshine.
_Synchronous Chart._--A form of synoptic chart, such as the
ordinary weather map, which shows the meteorological conditions
prevailing over any area at a given moment of time.
_Synoptic Chart._--A chart showing the distribution of
meteorological conditions over an area at a given moment or the
average conditions during a given period of time, such as a month
or a year.
_Table-cloth._--A sheet of cloud that sometimes spreads over the
flat top of Table Mountain, near Cape Town.
_Tangent Arc._--Any halo that occurs as an arc tangent to one of
the heliocentric halos.
_Term Hours._--Prescribed hours for taking meteorological
observations.
_Thermal Belt._--A well-defined zone, found on some mountain-sides,
in which vegetation is particularly exempt from frosts in spring
and autumn. Also called _verdant zone_.
_Thermograph._--A self-registering thermometer.
_Thermometer._--An instrument for measuring temperature; in
meteorology, generally the temperature of the air. _Maximum_
and _minimum thermometers_ indicate, respectively, the highest
and lowest temperatures occurring between the times of setting
the instruments. A _wet-bulb thermometer_ is used in measuring
humidity. (See _psychrometer_.)
_Thermometer Screen._--A cage, or sometimes merely a roof, for
protecting thermometers from direct sunshine and other radiation
that would cause the readings to indicate a temperature different
from that of the air. In the United States generally called an
_instrument shelter_.
_Thunder._--The sound produced by a lightning discharge.
_Thunderstorm._--A storm attended by thunder and lightning.
Thunderstorms are local disturbances, often occurring as episodes
of cyclones, and, in common with squalls, are marked by abrupt
variations in pressure, temperature, and wind.
_Thunderstorm Recorder._--Any device that furnishes a record of
thunderstorms, either near or distant. Most thunderstorm recorders
register, by radiotelegraphy, the strays set up by lightning
discharges.
_Tornado._--1. A violent vortex in the atmosphere, usually attended
by a pendulous, more or less funnel-shaped cloud. 2. In West
Africa: A violent thundersquall.
_Totalizer._--A form of snow gauge used chiefly in the Alps,
designed to be read only once a year. (French, _totalisateur_.)
_Trade Winds._--Two belts of winds, one on either side of the
equatorial doldrums, in which the winds blow almost constantly from
easterly quadrants.
_Troposphere._--The part of the atmosphere lying below the
stratosphere.
_Trough._--1. A line drawn at right angles to the path of a
cyclonic area through all points at which the pressure has reached
a minimum and is about to rise. 2. An elongated area of low
barometric pressure.
_Twilight._--_Astronomical twilight_ is the interval between
sunrise or sunset and the total darkness of night. _Civil twilight_
is the period of time before sunrise and after sunset during which
there is enough daylight for ordinary outdoor occupations.
“_Twister._”--A tornado; also, a small whirling dust storm.
_Typhoon._--The name applied in the Far East to a tropical cyclone.
_Ulloa’s Ring._--1. A glory. 2. A halo (also called _Bouguer’s
halo_) surrounding a point in the sky diametrically opposite the
sun; sometimes described as a “white rainbow.”
_Vane._--A device that shows which way the wind blows; also called
_weather vane_ or _wind vane_.
_Variability._--_Interdiurnal variability_ is the mean difference
between successive daily means of a meteorological element.
_Verdant Zone._--(See _thermal belt_.)
_Visibility._--The transparency and illumination of the atmosphere
as affecting the distance at which objects can be seen. It is often
expressed on a numerical scale. (This term was formerly applied
by British meteorologists to a state of unusual clearness of the
atmosphere, regarded as a weather prognostic.)
_V-shaped Depression._--A trough of low barometric pressure bounded
on the weather map by V-shaped isobars.
_Waterspout._--A tornadolike vortex and cloud occurring over a body
of water.
_Weather Well._--(See _blowing well_.)
_Wedge._--A wedge-shaped area of high barometric pressure.
_Wet-bulb thermometer._--(See _psychrometer_.)
_Wind._--Moving air; especially a mass of air having a common
direction of motion. The term is generally limited to air moving
horizontally, or nearly so; vertical streams of air are usually
called “currents.”
_Wind Aloft._--The wind blowing at high levels as distinguished
from that near the earth’s surface.
_Wind Rose._--1. A diagram showing the relative frequency and
sometimes also the average strength of the winds blowing from
different directions in a specified region. 2. A diagram showing
the average relation between winds from different directions and
the occurrence of other meteorological phenomena.
_Winter Day._--A day on which the temperature does not at any time
rise above the freezing point.
_Wool-pack Cloud._--Cumulus.
Transcribers’ Notes
Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in this book; otherwise they were not
changed.
Simple typographical errors were corrected; occasional unbalanced
quotation marks retained.
Ambiguous hyphens at the ends of lines were retained.
In versions of this book that do not support accented letters, “Canon”
(with a tilde over the middle “n”) is spelled “Canyon”.
Page 103: For consistency with the preceding enumerated definitions,
the Transcriber added extra spacing after the last of them, just before
“We have given”.
Page 348: In some versions of this eBook, the chemical symbols for
methane and phosphine are represented as CH4 and PH3.
Page 367: “The scale runs from 0 = calm to = hurricane” is missing the
value for hurricane, which is “12”.