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”.