Although Leigh did not subscribe to a commonly held belief that smoke from burning coal had purifying properties, he did generally appear to accept the popular miasma theory as an explanation for transmission of diseases.
[13][14][15][c] Sir Robert Rawlinson, a noted sanitarian and engineer of the time, described how public policy in Manchester had affected the city's rivers by the 1840s: a semi-liquid compound is formed, an accurate idea of which no written description can convey.
[9][10] In 1850, he co-authored A History of the Cholera in Manchester in 1849, the aims of which have been described by Robert Kargon, a historian of science, as "nothing less than the scientific assessment of disease and the public health measures taken against it."
While movement of infected people from one place to another seemed to explain how the disease was introduced from affected areas to previously unaffected locations, often at a relatively large distance, the study suggested that direct contact with a carrier was not necessary for propagation.
Kargon quotes from the study:[9] ... whatever may have been observed in other parts of England, it is proveable then, that Cholera has almost entirely confined its ravages to those localities or particular streets in which noxious exhalations proceeding from putrifying or otherwise decomposing matters in rivers, canals, stagnant water, etc.
A subsequent formal recruitment process led by another committee resulted in a recommendation in March 1868 to appoint a different applicant but the aldermen over-ruled again, this time preferring Leigh to the proposed candidate.
[19] Fear of epidemic and reaction to emergencies were, according to the historian Anthony Wohl, the cause of rebalancing an official mindset that was general based on "corruption, lethargy, innate conservatism ... and parsimony.
[21] Although Manchester was considered to be a leader in efforts relating to smoke abatement, often acting in advance of national legislative measures, Leigh's reports as Medical Officer for Health were unremitting in their criticism of air quality.
He drew attention to and demanded vigorous action against smoke and other emissions, which he noted caused not only respiratory disease but also, for example, limited the impact of sunlight and thus exacerbated rickets and depression.
Despite a zealous personal desire for eradication and the emergence between 1870 and 1888 of a range of pressure groups in Manchester that sought abatement of emissions, the official belief throughout the century was that the nuisance was in fact being reduced.
Leigh's 1883 report supported this in noting a visible reduction in smoke density resulting from greater regulation and the deployment of more inspectors, although quantitative measurements were rare and the belief of success was thus mostly subjective.
Bowler and Brimblecombe say that, despite the history of progressive efforts by the civic authorities on this issue, abatement measures could not keep up with the rapid development of the town, whose industrial expansion had continued apace and whose population had grown from 70,000 to 243,000 between 1801 and 1841 alone.