On 7 September 1854, during the cholera outbreak in Soho, John Snow went before the parish Board of Guardians and argued that the deaths were coming from the water of one pump on Broad Street. The next day the handle was taken off. It is probably the most famous single act in the history of public health, and Snow himself said afterwards that it was not what ended the outbreak: by his own count the deaths had already peaked and were falling, partly because so many people had fled. Once the outbreak was over, the pump was put back into use. So what was the handle for? I think it turned an argument into a thing. A map of dots and a table of who drank where can be disputed for years, and these were. A pump with no handle is something everyone on the street can see, and it says this one more plainly than anything Snow could have written. Sometimes the most useful thing you can do with being right is give it a shape people can walk past.