London (Notebook)
"mark" repetition
Blake repeats 'mark' three times in four lines—the word shifts from verb (to notice) to noun (a sign). He's watching suffering become visible, permanent, written on bodies.
Chimney sweeper detail
[CONTEXT: Child labor was legal; sweepers as young as 4 cleaned flues.] Blake uses a specific, real victim instead of abstract suffering. The 'blackening' of churches ties religious institutions to child exploitation.
"blood down Palace walls"
The soldier's sigh becomes literal blood on the monarch's residence. Blake collapses metaphor into accusation—the king's walls are stained by those who die in his wars.