Stanza 9 Summary

Get out the microscope, because we’re going through this poem line-by-line.

Again the traffic lights that skim thy swift
Unfractioned idiom, immaculate sigh of stars,

Now afternoon has turned to night. We see the lights of cars going over the bridge. They "skim" the surface of the bridge like water.
The bridge is like a special phrase in a language – an idiom. Idioms are phrases that cannot be understood from their words alone. A "blessing in disguise" is one example. "Idiom" can also refer to a regional dialect.
Idioms are generally "unfractioned" – they cannot be split down into parts. You cannot understand "blessing in disguise" and how it is used just from looking up the meanings of each word in the dictionary.
The bridge speaks a private and mysterious language. It makes a complete statement that cannot be put into normal words. We're super-deep into the turf of metaphor here.
In another delicious image, the bridge is an "immaculate," or perfect, expression of the stars "sighing" down on earth.
Remember that in the Christian tradition, Jesus Christ had an "immaculate" birth. It's as if the stars gave birth to the bridge with their breath.

Beading thy path--condense eternity:
And we have seen night lifted in thine arms.

The language becomes very flowery and Romantic here.
The lights on the cars are like beads on a necklace, or like prayer beads.
These beads seem to "condense" the promise of eternity into a visual image.
The towers of the bridge are like "arms" that lift up the night sky.
The bridge is holding the sky above us. Notice all the attributes of motion that are given to a motionless object! That's poetry, baby.