[rabidralph]

“an history”? Is the “h” in history suddenly silent?

[Verginius Rufus]

The "h" in "history" should be pronounced because the word is accented on the antepenult. But in "historian" and "historical" the first syllable is not accented so "an historian" or "an historical" would be correct.

Actually, it's my impression that some people pronounce an unaccented "h" and some don't...so "a historian" might not be incorrect.

It also works in the middle of a word--"h" in "vehicle" silent, but "h" in "vehicular" pronounced.