Main Circuit. (See [Circuit, Main].)
Main Feeder. The main wire in a district to which all the feeder wires are attached.
Main Switch. The switch connected to the main wire of a line, or the main-switch controlling a number of auxiliary switches.
Mains, Electric. The large conductors in a system of electric light or power distribution.
Make and Break, Automatic. An apparatus which enables the armature of a magnet to make and break its circuit automatically.
Make-and-break Current. (See [Current, Make-and-break].)
Mercurial Air-pump. An air-pump operated by mercury to obtain a high vacuum, and used extensively for exhausting incandescent-lamp bulbs.
Mercury Tube. A glass tube sealed and containing mercury. It is so arranged as to give out fluorescent light when shaken or agitated by an electric current. For example, the Geissler tubes, the Cooper-Hewitt light, Crook’s tubes, etc.
Metallic Arc. An arc which forms between metallic electrodes.
Metallic Circuit. (See [Circuit, Metallic].)