In Chapter 4, David bites Mr. Murdstone in self-defense and is locked away in isolation. He uses metaphorical imagery to describe how it felt to spend five days alone like this:
[…] the setting in of rain one evening, with a fresh smell, and its coming down faster and faster between me and the church, until it and gathering night seemed to quench me in gloom, and fear, and remorse—all this appears to have gone round and round for years instead of days, it is so vividly and strongly stamped on my remembrance.
The rain imagery allows the narrator not only to depict an accurate scene, but also to conjure the feeling of the memory for the reader. The rain can hardly be an effect of what is happening to David. It simply happened to rain while he was locked away, and Mr. Murdstone and others may not even have remarked upon the rain. Still, in David's memory, the rain's “fresh smell” combines with the “gathering night” as a metaphorical punishment. The physical sensations brought on by the rainy night come to represent the emotional sensation of biting Mr. Murdstone and of being locked away. By describing the physical sensations, David helps the reader access the emotional sensations as well.
The way the rain magnifies the length of time David spends locked away also stands in metaphorically for the way memory can distort reality like a lens that makes everything appear out of proportion. The narrator is always conscious of the way certain memories are drawn out when he begins to investigate them. In this instance, he recalls the days locked in his room with such intensity that everything seems like it has "gone round and round for years instead of days." The way he describes this effect is sensory: he claims that the time is "vividly and strongly stamped" on his memory, so it seems more expansive than it actually was. The memory is David's attempt to describe his life story, and everything comes to the reader through the sensations and experiences that have stuck with him through the years.
In Chapter 8, David goes home from Salem House for the holidays, and the Murdstones are absent for his first afternoon there. He uses imagery and a simile to describe how their return to the house shatters the nostalgic fantasy of life back with his mother and Peggotty:
It appeared to my childish fancy, as I ascended to the bedroom where I had been imprisoned, that they brought a cold blast of air into the house which blew away the old familiar feeling like a feather.
In a literal sense, the cold blast of air is simply an effect of the time of year. If someone opens the door during winter in England, cold air will come inside. The reason David remembers the cold air, however, is because of its metaphorical significance. It contrasts the warmth he felt in his mother’s arms when it was just her, Peggotty, and David’s new half-brother. Just as winter kills off a lot of life, the Murdstones bring with them the death of the lively atmosphere in the house.
Although the Murdstones hold a lot of power over David, his mother, and Peggotty, the simile comparing the "old familiar feeling" to a feather that is easily blown away indicates how fragile the feeling of warmth was to begin with. Even at his young age, David is already indulging in nostalgia when he spends this perfect afternoon with his mother, brother, and Peggotty. Their collective warmth and happiness is an attempt to reclaim something that was lost as soon as Clara Copperfield brought Mr. Murdstone into their lives. The cold blast of winter air is a cold blast of reality. The Murdstones and the cold air alike are reality knocking down the door of the little family’s warm fantasy. Even if the Murdstones had remained out, David would eventually have had to go to "the bedroom where I had been imprisoned" because the house has been indelibly transformed by the Murdstones' abuse.