  In a pioneering exposition of mathematical astronomy for the public, Sir John
Herschel attributed the stability of the ring of Saturn to its being eccentric
with respect to the planet and lopsided (asymmetric in mass) by a minute
amount. Tracing the sources and effects of this error reveals several lessons
of general relevance to science: on the formulation and interpretation of
calculations, the use of cutting-edge observations and the combining of
observations with theory. I emphasise the phenomenon of reinforcing errors.
