Snow on cholera

Mathematics is, at least in part, the science of abstraction. Mathematicians look at the rich complexity of the real world and replace it with a simple system which, at best, palely reflects one or two aspects of it. Roads become lines, towns become points, weather becomes a series of numbers (temperature, wind-speed, pressure, …) and human beings become units. The object of the first part of this book is to show how useful such abstraction can be.

In 1818 Europe became aware of a terrifying epidemic raging in parts of India. The disease, previously unknown to European science, struck suddenly, manifesting itself in violent diarrhoea and vomiting followed by agonising muscular cramps. An early description tells how

Often the skin turned blue or black and sometimes the convulsions were so severe that the body was contracted into a ball which could not be straightened out after death. The disease was named ‘Cholera Morbus’ and killed perhaps half its victims.