tplangency

[Eng. plangen (t); -cy.] The quality or state of being plangent; a dashing or beating with noise. appear to retrograde in the sky. Shining only with reflected light, they shine with a steady radiance in place of twinkling like the fixed stars. Planets are plăn-et-siaal, a. [Eng. planetoid ; al.] Of or primary or secondary, the former revolving around pertaining to the planetoids; relating to a planet the sun, the latter around the primaries. The oid. primary planets known to the ancients were five: Mercury, Venus, Mars, Jupiter, and Saturn. Omitting asteroids, comets, and meteoric rings, eight are now known: Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Twenty-one secondary planets are known, the Moon, two satellites of Mars, five of Jupiter, eight of Saturn, four of Uranus, and one of Neptune. The existence of an inter mercurial primary planet has been suspected but not proved. The planets Mercury and Venus, being nearer than the Earth to the Sun, are called inferior planets; the others, being more distant, are termed superior. Another cla ification is sometimes adopted, that into intra and extra asteroidal planets; that is, those nearer and those more remote from the sun than the asteroids. Under the first are included, Mercury, Venus, the Earth, and Mars, all of which are comparatively small, while the others, Jupiter, Saturn, Uranus, and Neptune are the giants of the system. For instance, the Earth is 7,918 miles in diameter, and Mars 4,200, but Jupiter is 85,000. The intra-asteroidal planets complete the annual revolution in short periods, the Earth, for example, in 365-26 days, while Neptune takes to do so 60,127 days, or about 165 years. The minor planets, planetoids, or asteroids are between Mars and Jupiter. IMG:content-1169.png:[blocks in formation] Gearing: The exterior revolving wheel of the "sun and planet" motion, invented by James Watt. So called from its rotation around another gearwheel, which is termed the sun-gear. The axis of the planet-gear is preserved concentric with the axis of the central or sun-wheel by means of an The planet-wheel sometimes gears with an arm. internally cogged wheel, and may be driven by the latter, rolling around inside the larger gear-wheel instead of outside. [SUN-AND-PLANET-WHEELS.] plăn-ě-tär-i-ŭm, subst . [Lat., from planet a =a planet.] A machine for exhibiting the relative motions of the planets and their positions in respect to the sun and one another. [ORRERY.]