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_.)