stupes, et cetera, doing it herself to as many as she could manage". By talking to local residents (with the help of Reverend Henry Whitehead), Snow identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street) at Cambridge Street. Although Snow's chemical and microscope examination of a sample of the water from this Broad Street pump water did not conclusively prove its danger, his facts about the patterns of illness and death among residents in Soho persuaded the St James parish authorities to disable the well pump by removing its handle. Although this action has been popularly reported as ending the outbreak, the epidemic may have already been in rapid decline, as explained by Snow: There is no doubt that the mortality was much diminished, as I said before, by the flight of the population, which commenced soon after the outbreak; but the attacks had so far diminished before the use of the water was stopped, that it is impossible to decide whether the well still contained the cholera poison in an active state, or whether, from some cause, the water had become free from it. Snow later used a dot map to illustrate how cases of cholera occurred around this pump. Snow's efforts to connect the incidence of cholera with potential geographic sources was based on creating what is now known as a Voronoi diagram. He mapped the locations of individual water pumps and generated cells which represented all the points on his map which were closest to each pump. The section of Snow's map representing areas in the city where the closest available source of water was the Broad Street pump included the highest incidence of cholera cases. Snow also performed a statistical comparison between the Southwark and Vauxhall Waterworks Company, and a waterworks at Seething Wells (owned by the Lambeth Waterworks Company) that was further upriver and hence had cleaner water; he showed that houses supplied by the former had a cholera mortality rate 14 times that of those supplied by the latter. Regarding the decline in cases related to the Broad Street pump, Snow said: It will be observed that the deaths either very much diminished, or ceased altogether, at every point where it becomes decidedly nearer to send to another pump than to the one in Broad street. It may also be noticed that the deaths are most