""State of the London Water Supply." Supplement to the Weekly Return"
In the annual compilation of Weekly Returns: volume 14, no. 49, pp. 429-32.
Farr restates his statistical conclusion that "the cause of cholera in an epidemic acts more or less on the whole of the population, but that its fatality bears a certain relation to the impurity of the soil, the water, and the air.
[Part of his reasoning combines sanitary and zymotic elements:] The dirty water and dirty air sink towards the bottom of the London basin, from which they also incessantly send up dank vapours; and it has been shown, that, when large numbers are taken, so as to render other circumstances nearly equal, the mortality decreases progressively in the dwellings at different elevations.
After correcting the above Table [see page 1 of the PFD] and the tables of cholera 1848-49, for the effects of elevation, it is found that a large residual mortality remains, which is fairly referable to the impurity of the water; for it is least where the water is known to be sweetest, greatest where the water is known to be impure" [and where Farr implies that Snow's theory may be applicable].