GLOSSARY OF TERMS USED IN RADIO TELEPHONY - VI:
DIELECTRIC - The insulator between the plates of a condenser. In the case of variable condensers this insulator is air. Mica is used as the dielectric for fixed condensers. Every insulator is a dielectric, even the rubber covering the wire.
DIODE - A vacuum tube containing two elements, a filament and a grid. Diode meaning two electrodes. A tube of this kind is to be only used in the place of a crystal detector and not in place of a regular three-element vacuum tube.
DIRECT COUPLING - When a coil is part of two circuits the are said to be directly coupled.