Answer: b. songs the people on the urn appear to be playing.
In these lines, the speaker tells the musicians to play not to the physical ear, but to the spiritual one. This is a metaphorical ear that is meant to be receiving the music of the pipes. He tells us that these songs are "ditties of no tone," which means that the songs do not have tones or notes. They cannot be played, because they are imaginary. Therefore, the author is talking about the songs that the people on the urn are playing, which are similarly imaginary and cannot be heard with the "physical" ear.
