This section is from the book "The Home Cyclopedia Of General Information", by Charles Morris. Also available from Amazon: Home Cyclopedia of Necessary Knowledge.
[Gk. gyros, a circle; and skopein, to see.] An apparatus consisting of a heavy rotating disk mounted on gimbals, so that it can turn in any direction. When rotating it will constantly point to the same star, and may therefore be employed to show that the apparent rotation of the heavenly bodies is due to the rotation of the earth on its axis in the opposite direction.
 
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