In “To a Passer-By” the first stanza is descriptive as well as the first stanza in “A Passer-By”. Both stanzas are four lines and begin with a description of the surroundings; the street before describing the woman.
The differences are the rhyme scheme, the enjambment and the use of words. The rhyme scheme in “A Passer-By” is “ABAB” and the stanza rhymes where as “To Passer-By” does not have a regular rhyme scheme and does not rhyme. The enjambment in “A Passer-By” allows you to read the first and second line differently where in “To Passer-By” the punctuation tells you when to stop and when to break. The words in “A Passer-By” are more straight forward and understandable.
The effect of this difference is to really allow the reader to understand what is happening without defining so many words, the difference also makes the poem more descriptive and imaginative. The difference in the rhyme scheme helps in “A Passer-By” to understand the setting of the poem.