The posters illustrate five curves which are all envelopes of systems of circles:
Each poster describes how to draw the curve and also gives brief mathematical or historical information, such as the origin of the curve’s name, or where the curve occurs in nature.
See below for more information about the background notes as well as samples from the notes. Larger images of the posters may be seen by going to the Poster Gallery.
“Noli turbare circulos meos. [Do not disturb my circles!]”—Archimedes
A descriptive booklet accompanies the posters, explaining the mathematics behind the images in the posters and related topics.
The four pages of background notes give more information about the five curves and about envelopes in general. The topics covered are:
The notes help interested students and teachers explore further, and provide ideas for activities connected to the theme of the posters.
An envelope is a curve touching every member of a system of lines or curves, or, equivalently, the boundary of the region filled by the system. ‘Touching’ means ‘tangent to’; another name for a ‘system’ is a ‘family’.
A roulette is the path traced by a point attached to a curve, as the curve rolls without slipping along another fixed curve. The cardioid, limaçon and nephroid are roulettes obtained when one circle rolls along another.
Light rays reflected from a curved mirror form a family of straight lines; the envelope of this family is a caustic curve. Everyday examples of caustics may be seen when light is reflected by familiar objects like mugs and cups.
The cardioid and the nephroid are both caustics of a circle: if the light source is on the circle, a cardioid results; if the rays are parallel, a nephroid is formed.
The lemniscate appears as a section of a torus with ‘holes’ of equal radii, as shown.
© A K Jobbings 2004–2018
Clicking a link will scroll the page to the relevant section.
Visit the Poster Gallery to see larger images of the posters.Poster Gallery
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All posters are A2 size:
42 cm by 59.4 cm
The front face of each poster is covered with a wipe-clean laminated film.
Each booklet of background notes has four A4 pages and includes many diagrams.