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”.