Maybe there is an argument for a separate Empson blog. 'The stock device of the play [The Beggar's Opera] is a double irony like a Seidlitz powder, piling a dramatic irony onto what was already an irony. This forces one to read back a more complex irony onto the first one, and the composure of language of the characters makes us feel that the speaker took the whole sense for granted. So he is a pastoral character; he moves among fundamental truths.'
Seidlitz powder, the Pharmaceutical Journal tells us, was thought to help treat, among other things, the 'oedematous tumours of the legs in literary men'.