What links does Arthur Conan Doyle make to life in London (1880-1925) in "The Sign of Four"?

In "The Sign of Four," Doyle makes numerous references to life in London during the late Victorian and Edwardian periods.

First of all, Doyle's references to fog are very representative of life in Victorian London and they are abundant throughout the text. In Chapter One, for instance, Holmes refers to the "yellow fog" which "swirls down the street," while, in Chapter Three, Doyle describes as a "dense, drizzly fog" which lies across the "great city." 

...

In "The Sign of Four," Doyle makes numerous references to life in London during the late Victorian and Edwardian periods.

First of all, Doyle's references to fog are very representative of life in Victorian London and they are abundant throughout the text. In Chapter One, for instance, Holmes refers to the "yellow fog" which "swirls down the street," while, in Chapter Three, Doyle describes as a "dense, drizzly fog" which lies across the "great city." 

In the late nineteenth century, fog was a great problem for the people of London. It was thicker and more frequent than it is today, exacerbated by the great number of factories and manufacturers which dominated the nation's capital. The fog is also used in "The Sign of Four" as a literary device to create suspense, build atmosphere and as a metaphor for the difficulties surrounding the case of the Sholto murder and the missing jewels. 

Secondly, there are a number of references in "The Sign of Four" to contemporary ideas about race. In Chapter Eight, for instance, Holmes and Watson refer to Indians as "savages" and as being "monkey-faced." At this time, people of other races were portrayed as uncivilised, uncouth and culturally inferior to the British. You can find supporting evidence of this in the poem, "White Man's Burden," by Rudyard Kipling, which was published in 1899. (Please see the reference link provided). By espousing this attitude, then, Doyle shows himself to be a man of the times.