The lituus is a transcendental curve that can be graphed with the polar equation
r = k/√θ 
r2 = a2/θ.
The inverse of the lituus is Fermat’s spiral — a type of Archimedean spiral (the littus is the inverse of Fermat’s Spiral only when the inversion is take as the origin). However, the lituus itself isn’t technically a spiral because its curvature doesn’t strictly increase or decrease as a function of its arc length.
The curve can also be described as the locus of the point P moving so that the area of a circular sector — a wedge of a circle with a central angle of less than π radians — remains constant.
The name Lituus means a ‘crook,’ like a bishop’s crosier (a staff without knots and curved at the top) .
History of the Littus Curve
The curve was first described by Roger Cotes in a paper collection titled Harmonia Mensurarum, published in 1722 — six years after his death. He is well known for editing the second edition of Newton’s Principia .
Maclaurin also used the term lituus in his book Harmonia Mensurarum in 1722.
Image created with Desmos.
 Dunham, D. Hyperbolic Spirals and Spiral Patterns. Retrieved July 30, 2022 from: https://www.d.umn.edu/~ddunham/dunbrid03.pdf
 Kokosa, S. Fifty Famous Curves, Lots of Calculus Questions, And a Few Answers. Retrieved July 30, 2021 from: http://facstaff.bloomu.edu/skokoska/curves.pdf
 MacTutor. Roger Coates. Retrieved July 29, 2022 from: https://mathshistory.st-andrews.ac.uk/Biographies/Cotes/