Eccentricity (of Orbit). Distance of focus from centre of ellipse of a planetary path.
Echelon. Formation of a line of ships in which each ship is on the quarter of ship ahead: thus allowing all guns to be used ahead, astern or on the beam.
Echo.Reflected sound. Travels at same speed, whatever its wavelength. In radar (2) the radio energy returned to the aerial as a result or reflection or scattering from an object. 3. The representation of (2) on a radar display. False echo, one whose position on the display does not indicate the correct range and/or bearing of the target.
Echo Box. A type of Performance Monitor which shows the performance of a radar set.
Echometer. Echo sounder produced by Marconi Sounding Device Co., Ltd.
Echo Sounder. Electrically operated instrument that emits a sound from vessel's submerged surface and then measures time interval until return to echo—which is recorded. Graduated scale converts interval to depth indication. May be of 'Sonic' or of 'Supersonic' type.
Echo Sounding. Ascertainment of depth of water by use of an echo sounder.
Eclipsareon. Instruction apparatus for explaining the occurrence of eclipses.
Eclipse. Cessation of light due to passing into a shadow. Applied to darkening of Moon's disc when she passes into shadow cast by Earth. Also applied to occultation of Sun by Moon. Strictly speaking, the latter is a misnomer, but is universally sanctioned by long-established usage.