The concept of "modernity" is credited to French author Charles Baudelaire who uses modernité to encapsulate the experience of living in Industrial Era urban metropolis settings. It is applied to the art forms that try to capture that "ephemeral experience" life.
Realism was a literary period that developed as a reaction to the idealism, emotionalism and sentimentality of Romanticism. Begun in France around 1850 with the writing of authors like Honoré de Balzac and Gustave Flaubert, in English literature, Realism coincided roughly with the Victorian period and was represented by authors like Charles Dickens and Charlotte Brontë.
Dickens' Our Mutual Friend is a tale of disguised identities, corruption and escape from corruption, romance, decay and death. In it, Dickens explores modernity as he traverses through experiences of urban living where liberated ideals clash with traditional hierarchy and where desire clashes with integrity. In it, he explores realism as he describes the grim, bleak, oppressive darkness that exists on various levels of urban life.
Literary devices are of two kinds: elements and techniques. Elements are the composite elements that are required in narrative fiction: setting, plot, mood, tone, point of view, characters, theme, etc. Techniques are the rhetorical and literary conventions that an author may choose from to develop a mood and tone, symbolism, imagery, figures of speech, etc. [Thus your question should be what literary devices, which are literary elements and literary techniques, does Dickens use ...?]
One technique that Dickens uses to establish setting, mood and tone (literary elements) is the literary technique of imagery, the first instance of which occurs in the opening phrases: "In these times of ours ... a boat of dirty and disreputable appearance ...." The setting is set as the contemporaneous readers' own time. The mood is set by connecting the "times" to "dirty" and "disreputable." The tone is set in a very subtle turn of words of the opening phrase which uses a prepositional phrase to draw attention to the times without judgement, praise or censure but with a sorrow expressed in the prolonged phrase, the repeated sibilant /s/ (consonance) and the post-modifying possessive "of ours": The times may be "dirty" and "disreputable" but they are our times and we are in them, feeling them, suffering them, causing them. He follow this up with hard, desperate words and phrases like iron, stone, autumn, closing in.
In these times of ours, though concerning the exact year there is no need to be precise, a boat of dirty and disreputable appearance, with two figures