Wouldn't it be "Shuigh sé ar an gcathaoir." ? I am just learning a little Irish, working through "Progress in Irish" on my own, and having just recently done Ch. 17, I thought "ar an" was one of those prepositional phrases which cause úru?
Cad é mar atá tú, it really depends where you are from regarding this. In ulster irish instead of eclipsing the noun it willl be aspirated.
Go raibh maith agat! I appreciate the explanation. I am *always* getting tripped up by the regional differences, it seems. :-)