_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.