Glossary - Part M

•  Mangin Mirror: Alphonse Mangin, a Colonel in the French Army, designed a form of glass spherical mirror where the reflecting material was deposited on the rear, or second surface, of a glass lens.

•  Manufacturer’s Name: The manufacturer’s name is usually affixed to the lens by means of a stamping into the lens bottom ring or through the use of a name plate attached to the lens frame.

•  Masonry: A Lighthouse built of brick or stone, rarely found in the Maritime region and sometimes hidden by shingle cladding.

•  Mercury Drain Valve: A valve or drain (sometimes called a petcock, drain tap or clean out) in the bottom of the mercury trough that allows the removal of the mercury for cleaning or repair.

•  Mercury Float: The donut shaped cast-iron ring attached to the bottom of the lens that floats upon the mercury in the mercury trough.

•  Mercury Trough: A circular iron trough containing a quantity of mercury in which a lens apparatus floats and revolves.

•  Modern Optic: Term applied to a broad range of lightweight, weatherproof beacons used in modern devises.