The authors employ a number of literary devices or figures of speech to present the information using a figurative language that assists in adding details and depth to the writing and enhance its significance.
The simile is demonstrated as the figure of speech that aims to compare two distinct objects using 'as' and 'like' in order to elaborate on the meaning of the unfamiliar word through this comparison.
As per the question, the given excerpt from the popular romanticist Lord Byron's 'Child Harold, canto III' employs a 'simile' which is reflected by the comparison of the speaker himself 'I' with a 'weed' using 'as'. In these lines, the speaker aims to elaborate his present state by comparing himself to a 'weed which has "flung from the rock and on ocean's foam to sail"'.
