NOT FOR POSTCARD USE Fractal geometry. A computer graphics image, entitled Solar Particle, showing a Julia Set, one of a class of shapes plotted from complex number coordinates. Each point is assigned a colour depending upon its behaviour under a series of simple, but repeated, mathematical operations or mappings. The Julia Set was invented and studied during World War I by the French mathematicians Gaston Julia and Pierre Fatou. The better-known Mandelbrot Set arose as a result of attempts, made in the 1970's, to rationalise the massive variety of forms of the Julia Set.