n.1.(Astron.) An instrument, intended to represent the revolution of a comet round the sun.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
The Wayward Comet: A Descriptive History of Cometary Orbits, Kepler's Problem and the Cometarium
The cometarium turns the complex physics that underlies a comet's motion in space into the indomitable and certain roll of meshed gearing, he says, though in the end the tameness portrayed by the cometarium turns out to be a chimera; the comet is a beast that moves beyond the certainty encoded within finely interlocking gears.
These include a wonderful "cometarium" from 18th-century England, which uses hand crank, dials, a pointer, and an elliptical track to mechanically trace the orbit of the comet of 1682, which we now call Comet Halley.