Half looking-glass,
For why should he
Be doubled?
The glass must stretch
Down his middle,
Or rather down the edge.
But he's in doubt
As to which side's in or out
Of the mirror.
There's little margin for error,
But there's no proof, either.
And if half his head's reflected,
Thought, he thinks, might be affected.
But he's resigned
To such economical design.
If the glass slips
This poetry seems to be light, but it is in fact about very serious ideas. The gentlemen is trying to hold himself together. 
 Bishop is disorientingly casual. There is no blank verse, as in Frost, the poem moves in and out of rhyme. The poem is closest to the poetry of Auden. 
 Bishop alters her forms under the occasions of her writing. She sees the world, and she responds to it. This is essential to Bishops' poetry. 
 (Source:  Open Yale Courses.  )
The Gentleman of Shalott