A Brief Hiatus

On page 234 of Middlemarch (Penguin Books, 2003) I came across the word aërial ("... an immeasurable depth of aërial perspective"). Why did Eliot include the umlaut? Webster and OED both take me to the diacritic-less aerial. No mention of the umlaut. So I did what anyone would do: I checked Google's Ngram Viewer. Turns out aërial was indeed a standard usage until around 1920, whereupon it showed a steep decline. But why the umlaut? An old Webster's dictionary tells us it's a matter of pronunciation (and thus--and I correct myself--the diacritic is technically a dieresis). The word aërial (from aër) is derived from the Greek aēr (two syllables). So aërial was actually pronounced with what the linguists call a hiatus (OED: a break between two vowels coming together but not in the same syllable): /eɪˈi.rɪ.əl/ (four syllables). We have hiatuses in words like cooperate (coöperate), creator (creätor), and, a good one, zoönomia. Say the word: aërial. It's a pleasure, that extra syllable. Mellifluous, to my ear. Indeed, atmospheric.