This guy named dissolution is rising and falling, rising and falling. He goes seamlessly from end of a musical scale to the other, and then back down again, like playing a slide whistle. To the speaker this music sounds almost funereal, but he has to admit it’s not out of tune. In lines 5-7 the poem becomes more philosophical and does not suggest any particular image.
In line 8 the poem becomes visual again. We imagine a big word – "TRUTH" – all in capital letters. And then suddenly this figure starts melting like the wicked witch from The Wizard of Oz. Truth doesn’t disappear, exactly, it just looks, well, different. To illustrate the point, the speaker shows us a white frosty landscape that melts away to reveal the regular old English countryside.
Now that we’re in the countryside, why don’t we wander over to that old tower over there? Its stones are all mossy and eroded, and the top of the tower is covered in weeds and vines. Mother Nature gradually takes back what’s hers. We hear someone shout and then – CRASH – the sound waves from the shout were strong enough to bring the whole structure toppling down. The powerful tower now lies in a heap of stone on the ground.