- Continental.--Same as International.
- International.--On the continent of Europe land lines use the Continental Morse alphabetic code. This code has come to be used throughout the world for wireless telegraphy and hence it is now called the International code. It is given on Page 305. [Appendix: International Morse Code].
- Morse.--The code devised by Samuel F. B. Morse and which is used on the land lines in the U. S.
- National Electric.--A set of rules and requirements devised by the National Board of Fire Underwriters for the electrical installations in buildings on which insurance companies carry risks. This code also covers the requirements for wireless installations. A copy may be had from the National Board of Fire Underwriters, New York City, or from your insurance agent.
- National Electric Safety.--The Bureau of Standards, Washington, D. C., have investigated the precautions which should be taken for the safe operation of all electric equipment. A copy of the Bureau of Standards Handbook No. 3 can be had for 40 cents from the Superintendent of Documents.
COEFFICIENT OF COUPLING.--See Coupling, Coefficient of.
COIL AERIAL.--See Aerial, Loop.
COIL ANTENNA.--See Aerial, Loop.
COIL, INDUCTION.--An apparatus for changing low voltage direct currents into high voltage, low frequency alternating currents. When fitted with a spark gap the high voltage, low frequency currents are converted into high voltage, high frequency currents. It is then also called a spark coil and a Ruhmkorff coil.
COIL, LOADING.--A coil connected in the aerial or closed oscillation circuit so that longer wave lengths can be received.
COIL, REPEATING.--See Repeating Coil.
COIL, ROTATING.--One which rotates on a shaft instead of sliding as in a loose coupler. The rotor of a variometer or variocoupler is a rotating coil.
COILS, INDUCTANCE.--These are the tuning coils used for sending and receiving sets. For sending sets they are formed of one and two coils, a single sending coil is generally called a tuning inductance coil, while a two-coil tuner is called an oscillation transformer. Receiving tuning coils are made with a single layer, single coil, or a pair of coils, when it is called an oscillation transformer. Some tuning inductance coils have more than one layer, they are then called lattice wound, cellular, basket wound, honeycomb, duo-lateral, stagger wound, spider-web and slab coils.
COMMERCIAL FREQUENCY.--See Frequency, Commercial.