London's great fogs in the nineteenth century were seasonal. They began in late autumn, were especially severe in winter, and eased somewhat in spring. They were not, as some accounts described them, thick fogs that lingered at all times.
Nor were the fogs then as suffocating as they would become later. Factory emissions were not yet so severe. Although a great fire had nearly destroyed London, it had allowed people to redesign the city. Yet as the number of workers in the City of London and the West End grew, poor people's homes were demolished. They were forced to move into slums, or places so overcrowded that they were about to become slums.
Some suburban areas had originally been intended to attract wealthy residents, such as Notting Hill. Unfortunately, the property developers had not anticipated that the nearby pigsties and brickworks would keep the rich away from this upscale residential district. Thus, this building investment failed, and the houses were divided into rental rooms for the poor.
At the beginning of the nineteenth century, London had more than a dozen large slums. This did not include the later-famous Whitechapel district, which was still an industrial area packed with factories, though its heavy Irish population had already given it signs of decline. Agatha Christie had a novel called The Seven Dials Mystery. In one scene, there was a letter that mentioned a place called Seven Dials. It really existed, and it was also one of London's notorious slums.
By then, people already regarded prisons and slums as much the same. Prisons housed poor people who had committed crimes, while slums housed poor people who were about to commit them. Some reporters even visited slums and prisons, describing their encounters as though they had ventured into another world for their middle-class readers.