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This glossary of historic aviation terms is reproduced from 'The Spotters Glossary' which appeared in 'The Aeroplane Spotter' from January 1940 onwards. 'The Aeroplane Spotter' was the first journal devoted exclusively to the study and practice of aircraft recognition.

We are pleased to have been able to reproduce the entire glossary from A-Z, offering a unique insight into aviation terminology (and therefore aviation history and technology) prior to and during the 1940s.

NB: In the interests of clarity we have substituted current equivalents where words and phrases used in the original publication have fallen from general use (eg, 'aero motor' has been replaced by 'aero engine').

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Maestro: A North-Westerly wind experienced in the Adriatic. It occurs most frequently in Winter and Spring; when it blows in the Summer it is followed by fine weather.

Magnetic Course: The angle (measured in a clockwise direction) between the course of an aeroplane - that is, the direction steered - and Magnetic North. It is measured on a map from the nearest magnetic meridian.

Magnetic Track-angle: The angle (measured in a clockwise direction) between the track of an aeroplane - that is, its path over the ground - and Magnetic North. It is measured on a map from the nearest magnetic meridian.

Main Float: The principal watertight body of a floatplane which provides the necessary buoyancy on the water.

Mainplane: A complete main lifting surface of an aeroplane or glider.

Main Step: A discontinuity in the under surface of a float or hull designed to help the seaplane "unstick" from the water.

Malleability: The property which allows a material to be permanently deformed, without fracture, when beaten or rolled.

Maneton: The detachable short end of the crankshaft in a rotary or radial engine.

Manoeuvrability: The ability of an aeroplane to change its attitude under the influence of its controls. Manoeuvrability and control are two conflicting requirements. The former is particularly desirable in fighters in which it can be developed at the expense of the stability. In bombers and transport stability is more important, although in some such machines a high degree of manoeuvrability is also obtained.

Maps: Four main types of air map were recognised internationally before the Second World War: (1) Basic Maps. These cover the whole World in 24 sheets and are intended for the planning of routes and to give general aeronautical information. (2) Route Maps. Drawn to a small scale, these are intended for navigational use on long journeys. (3) Local Maps: The normal one to one-million scale. International Maps of the World modified to meet the needs of air navigation. These are used for ordinary navigation work. (4) General Maps: Maps drawn to Mercator's projection to a scale in which one degree of longitude equals three centimetres. This type of map has special applications.

Marine Distress Signal: A pyrotechnic device for use by aircraft in distress after landing on water.

Marshal of the Royal Air Force: The highest rank in the RAF, equivalent to an Admiral of the Fleet in the Navy and a Field Marshal in the Army.

Martensite: A hard, brittle, constituent of carbon steel. It is formed when the steel is cooled rapidly by quenching.

Mask Microphone: A microphone mounted in a face mask used for radio and intercommunication transmission in flight.

Master Connecting Rod: In a radial aero engine the large connecting rod linking one of the pistons to the crankshaft. Articulated rods are connected to the big end of the master rod and transmit the power from the other pistons.

Master Pilot's Certificate: The highest grade of commercial pilot's certificate. This certificate is awarded to "B" license pilots who have at least five years' experience and have satisfied other stringent requirements.

Maximum Permissible r.p.m.: The number of revolutions per minute of the crankshaft of an engine which must not be exceeded or maintained beyond a specified time - usually five minutes.

Maximum Power: The power developed by an aero engine at maximum permissible r.p.m. (see above)

Maximum-Power Altitude: The lowest height at which full throttle is permissible at maximum rpm for level flight. With a supercharged engine it is also the greatest height at which maximum boost pressure can be maintained in continuous climbing flight.

McKee Trans-Canada Trophy: A trophy awarded annually to the Canadian pilot who does most towards the sound advancement of Canadian Aviation. It was presented in 1926 by the late J Dalzell McKee, who made the first aeroplane flight across Canada.

Mean Chord: The total area of an aerofoil divided by the span.

Medium Clouds: Average height between 8,000ft and 20,000ft. They are: (a) Alto-cumulus. A layer of small masses of cloud arranged in groups, lines or rolls. (b) Alto-stratus. A grey fibrous cloud resembling a veil, through which the sun or moon shows vaguely without the halo effect which occurs with cirro-stratus cloud.

Mesh Wiring: A wire network which prevents the gas bags of a rigid airship chafing against the longitudinals of the hull structure.

Meteorograph: An instrument which records two or more of the basic meteorological conditions of pressure, temperature or humidity.

Mid-Wing Monoplane: A monoplane in which the mainplane is located approximately midway between the top and bottom of the fuselage.

Millibar: The thousandth part of a bar, a bar being a unit of barometric pressure equal to 750·1mm (29·531in) of mercury at 0°C in latitude 45°.

Maximum Flying Speed: The lowest speed at which an aeroplane or glider can be maintained in level flight.

Mist: a slight fog caused by condensation of moisture.

Mistral: A cold, dry wind from the North or North-West, common on the Mediterranean coast of France.

Mixture Control: A device embodied in the carburettor of an aero engine for reducing the quantity of fuel supplied to the cylinders as height increases so as to maintain a constant ratio of fuel to air.

Monocoque: A method of construction in which the skin carries the whole or the greater part of the main loads; applied particularly to fuselages.

Monoplane: An aeroplane or glider with a single mainplane.

Monsoon: By definition: winds which in certain regions blow in opposite directions at different seasons of the year. In Eastern and Southern Asia the term is commonly used to denote seasonal rains without reference to wind.

Mooring Area: An area of water reserved as a place for the mooring of seaplanes.

Mooring Mast: A relatively short mast to which airships are moored by a quick-release attachment in the nose. Great Britain originated the mooring mast and developed it into the mooring tower. The Americans use a mobile motor-driven form of mast for all types of airship. This has the advantage that it can be used for manoeuvring the airship while on the ground.

Mooring Tower: An elaborate high mast for mooring rigid airships. Mooring towers provide a means of entry to the airship from a platform near the top across a gangway let down from the airship. A lift runs from the foot of the tower to the platform, as do fuel and water ballast pipes.

Mortar Signal: A signal flare which after reaching a height of about 1,000ft burns steadily for part of its descent.

Mountain Breeze: A local wind caused by the downward flow of cold air off high ground at night or in Winter.

Multiplane: An aeroplane or glider with two or more mainplanes one above the other. There have been several quadruplanes and many triplanes.