>>An before a muted H as in An hourglass (the h is silent in hourglass)
>>A before historical because the h is not silent.
>>(Although you will see and hear it both ways and it is acceptable - and probably common which is what you asked - to always use "AN" before any word that begins with "H")
>>
>I agree. I'm checking my husband's manuscript (he is transalting his book in English) and when I saw "an historical" it stroke me as wrong. That's why I want a correct literary usage.

Send him my expressions of solidarity. Been done, done that, and the translator often despised the author and vice versa.