Cycloid gear
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A cycloidal gear is a toothed gear with a cycloidal profile. Such gears are used in mechanical clocks and watches, rather than the involute gear form used for most other gears. Cycloidal gears have advantages over involute gears in such applications in being able to be produced flat, and having fewer points of contact.
Drawing showing the tooth and leaf profile of a cycloidal wheel and pinion
Ole Rømer
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Ole Christensen Rømer was a Danish astronomer who, in 1676, made the first measurement of the speed of light and discovery that light travels at a finite speed. Rømer also invented the modern thermometer showing the temperature between two fixed points, namely the points at which water respectively boils and freezes.
Rundetårn ("round tower") in Copenhagen, on top of which the university had its observatory from the mid 17th century until the mid 19th century when it was moved to new premises. The current observatory there was built in the 20th century to serve amateurs.
Ole Rømer at work