were ranged in columns before me; (line 2)
If you really wanted to get carried away with symbolism, you might compare those columns to prison bars. At any rate, they represent the kind of artificial order that society opposes on the natural world.
where he lectured with much applause in the lecture-room, (line 4)
We don't learn that the speaker is in a crowded lecture until this point in the poem. He feels alone and isolated despite the crowd. The other people are mentioned indirectly, through their "applause," but otherwise we know nothing about them.
How soon, unaccountable, I became tired and sick; (line 5)
The speaker is a sensitive soul in the crowd. He's the only one who reacts so negatively to the lecture that he must escape. That is, we assume that the poor astronomer doesn't have everyone running for the exits.