I have a simple question today. I’m copyediting a book on early modern Hebrew and Biblical studies, and the author cites Paul Joüon’s A Grammar of Biblical Hebrew in a footnote. Here’s what I’ve been able to find out about Joüon: he was born in Nantes in 1871, he was a Jesuit, he taught Hebrew at the University of St Joseph in Beirut (1907-14) and at the Pontifical Biblical Institute in Rome; and he died in 1940 (also in Nantes, judging by this Polish snippet from Google Books: “Paul SJ, ur. 26 II 1871 w Nantes, zm. 18 II 1940 tamże”). My question is, what the devil is that diaeresis doing there, and how (if at all) does it affect the pronunciation?