New John Snow book reviewed

Steven Shapin has a long review of a new book on John Snow in the New Yorker. Shapin is a well known respected historian of science, and his review gets most of the story right, including the prominant role of the map in Snow's efforts to convince the authorities that cholera is spread through infected water:

As it turned out, the critical evidence came not from this study of commercially piped river water but from a fine-grained map showing the roles of different wells...

What Snow needed was not the biological or chemical identity of the “morbid poison,” or formal proof of causation, but a powerful rhetoric of persuasion. The map Snow produced, in 1854, plotted cholera mortality house by house in the affected area, with bars at each address that showed the number of dead. The closer you lived to the Broad Street pump, the higher the pile of bars. A few streets away, around the pump at the top of Carnaby Street, there were scarcely any bars, and slightly farther, near the Warwick Street pump, there were none at all.

Over the last ten years the story of John Snow has been repeatedly told. The story has gone from the straightforward one of the map being the way that Snow realized the Broad Street pump was contaminated (eg., in Tufte's 1983 book) to a realization that Snow used the map to powerfully illustrate his already-developed theory of contagion (then a minority opinion):

Maps like Snow’s allowed the modern city to remake itself and to understand itself in a new way. They collected different sorts of knowledge, represented them vividly on the scale of a tabletop, and made that representation available as a resource for urban reform: a plan and a plan of action.

This latter version, if more complicated, is more interesting. As Shapin points out, science does not proceed neatly from one idea to another but often involves highly contested competing claims, and the ones we now think are right don't always win out straight away.