372 12 MODERN GEOMETRIESFIGL TB2JL
Huygens' cycloidal pendulum, from his Horologium oscillatoriurn.
© Stock Montage, Inc.requires the same time to slide to the bottom of a cycloid no matter where it
begins; second, the involute of a cycloid is another cycloid. He therefore designed
a pendulum clock in which the pendulum bob was attached to a flexible leather
strap that is confined between two inverted cycloidal arcs. The pendulum is thereby
forced to fall along the involute of a cycloid and hence to be truly tautochronous.
Reality being more complicated than our dreams, however, this apparatus—like