This metaphor really stands out to me. It is a three tiered metaphor, which is very impressive. First, it is comparing poets and kings to "clerks of Time". A clerk is someone who keeps a record of something, so a clerk of Time would be keeping a record of what happens throughout all of time. The second tier of the metaphor says that these poets and kings, while they keep record of Time, are tiering, or ranking, "the same dull webs of discontent". Basically, that the kings and poets are trying to compare and contrast the suffering of people. And the third tier, "Clipping the same sad alnage of the years." is comparing the poems being written / kings reigning from their thrones to cloth clippings, pieces of clothing, and SAD pieces of clothing at that. The SAME SAD pieces of clothing, the alnage of the years. This whole three tiered metaphor is, I think, trying to get across the notion that basically everything a person is able to learn from reading in poetry, and everything a person is able to learn from living in society, is old news. History repeats itself. And there is no change big enough in the world that would ever allow us to escape from our history anyway. And so we are left with "the same sad alnage of the years." Sorry, sorry, I can't get over that line.