Watt's Curve
A curve named after James Watt (1736-1819), the Scottish engineer who developed the steam engine (MacTutor Archive).The curve is produced by a Linkage of rods connecting two wheels of equal diameter. Let the two wheelshave Radius 
and let their centers be located a distance 
apart. Further suppose that a rod of length 
is fixed at each end to the Circumference of the two wheels. Let 
be the Midpoint of the rod. Then Watt'scurve 
is the Locus of .
The Polar equation of Watt's curve is
If
, then is a Circle of Radius with a figure of eight inside it.
References
Lockwood, E. H. A Book of Curves. Cambridge, England: Cambridge University Press, p. 162, 1967. MacTutor History of Mathematics Archive. ``Watt's Curve.''http://www-groups.dcs.st-and.ac.uk/~history/Curves/Watts.html.
- Extreme Value Distribution
- Extreme Value Theorem
- Extremum
- Extremum Test
- Extrinsic Curvature
- Fabry Imbedding
- Face
- Facet
- Faceting
- Factor
- Factor Base
- Factor (Graph)
- Factor Group
- Factorial
- Factorial Moment
- Factorial Number
- Factorial Prime
- Factorial Sum
- Factoring
- Factorion
- Factorization
- Factor Level
- Factor Ring
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- Fagnano's Point