World Library  
Flag as Inappropriate
Email this Article

Lemniscate of Bernoulli

Article Id: WHEBN0000250908
Reproduction Date:

Title: Lemniscate of Bernoulli  
Author: World Heritage Encyclopedia
Language: English
Subject: Jacob Bernoulli, Giulio Carlo de' Toschi di Fagnano, Pedal equation, Watt's curve, Quasi-one-dimensional models
Collection: Algebraic Curves, Curves, Spiric Sections
Publisher: World Heritage Encyclopedia

Lemniscate of Bernoulli

A lemniscate of Bernoulli and its two foci
Lemniscate of Bernoulli is the pedal curve of rectangular hyperbola
Sinusoidal spirals: equilateral hyperbola (n = -2), line (n = -1), parabola (n = -1/2), cardioid (n = 1/2), circle (n = 1) and lemniscate of Bernoulli (n = 2), where rn = 1n cos(nθ) in polar coordinates and their equivalents in rectangular coordinates.

In geometry, the lemniscate of Bernoulli is a plane curve defined from two given points F1 and F2, known as foci, at distance 2a from each other as the locus of points P so that PF1·PF2 = a2. The curve has a shape similar to the numeral 8 and to the symbol. Its name is from lemniscus, which is Latin for "pendant ribbon". It is a special case of the Cassini oval and is a rational algebraic curve of degree 4.

This lemniscate was first described in 1694 by Jakob Bernoulli as a modification of an ellipse, which is the locus of points for which the sum of the distances to each of two fixed focal points is a constant. A Cassini oval, by contrast, is the locus of points for which the product of these distances is constant. In the case where the curve passes through the point midway between the foci, the oval is a lemniscate of Bernoulli.

This curve can be obtained as the inverse transform of a hyperbola, with the inversion circle centered at the center of the hyperbola (bisector of its two foci). It may also be drawn by a mechanical linkage in the form of Watt's linkage, with the lengths of the three bars of the linkage and the distance between its endpoints chosen to form a crossed square.[1]


  • Equations 1
  • Arc length and elliptic functions 2
  • Applications 3
  • See also 4
  • Notes 5
  • References 6
  • External links 7


(x^2 + y^2)^2 = 2a^2 (x^2 - y^2)\,
r^2 = 2a^2 \cos 2\theta\,
x = \frac{a\sqrt{2}\cos(t)}{\sin^2(t) + 1}; \qquad y = \frac{a\sqrt{2}\cos(t)\sin(t)}{\sin^2(t) + 1}

In two-center bipolar coordinates:

rr' = a^2\,

In rational polar coordinates:

Q = 2s-1\,

Arc length and elliptic functions

The determination of the arc length of arcs of the lemniscate leads to elliptic integrals, as was discovered in the eighteenth century. Around 1800, the elliptic functions inverting those integrals were studied by C. F. Gauss (largely unpublished at the time, but allusions in the notes to his Disquisitiones Arithmeticae). The period lattices are of a very special form, being proportional to the Gaussian integers. For this reason the case of elliptic functions with complex multiplication by the square root of minus one is called the lemniscatic case in some sources.


Dynamics on this curve and its more generalized versions are studied in quasi-one-dimensional models

See also


  1. ^ Bryant, John; Sangwin, Christopher J. (2008), How round is your circle? Where Engineering and Mathematics Meet, Princeton University Press, pp. 58–59,  .


  • J. Dennis Lawrence (1972). A catalog of special plane curves. Dover Publications. pp. 4–5,121–123,145,151,184.  

External links

  • Weisstein, Eric W., "Lemniscate", MathWorld.
  • "Lemniscate of Bernoulli" at The MacTutor History of Mathematics archive
  • "Lemniscate de Bernoulli" at Encyclopédie des Formes Mathématiques Remarquables (in French)
  • Coup d'œil sur la lemniscate de Bernoulli (in French)
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.