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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | |
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First Edition Preface Second Edition Preface Acknowledgments
Section A A index 401-409 of 917 terms
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All-hallown summer—(Also called Allhallow summer, All Saints' summer.) In English folklore, an old name for a period, like Indian summer, of unseasonable warmth, supposed to occur on the eve of All Hallows day (All Saints Day, November 1). It is mentioned by Shakespeare, but its use appears to have died out. More frequently heard today are references to such as St. Luke's summer, St. Martin's summer, Old Wives' summer.
all-sky photometer—A photometer with a field of view that is wide enough to measure the amount of light energy emanating from the entire hemisphere or almost the entire hemisphere of sky above the instrument.
all-weather airport—An airport equipped with facilities to permit the landing of qualified aircraft and aircrewmen without regard to operational weather limits.
Allard's law—An equation used in predicting the night visual range of self-luminous targets. Assume a light source at distance x from an observer and having (monochromatic) luminous power Pv in that person's direction. Then for uniform extinction coefficient σ, the illuminance Ev reaching the observer is When Ev equals the threshold illuminance for a given background luminance and detection probability, x is the night visual range, or maximum distance for detecting the light source.
allerheiligenwind—In the Tyrol, the wind that sets in after Altweibersommer (“Old Wives' summer”).
allobaric—Of a change in pressure; of pressure tendency. Strictly, this term could be used in many instances in place of the more frequently used term, isallobaric.
allohypsography—(Rare.) The pattern exhibited by a height-change chart.
allowed transitions—A transition between two energy levels in an atom or a molecule that does not violate any selection rules. These transitions are characterized by large absorption cross sections.
alluvial aquifer—Aquifer with geologic materials deposited by a stream and that retains a hydraulic connection with the depositing stream.
alluvial—Geologic layers deposited by streams.
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