I find it amusing that we've gotten off on a tangent about grammar here, but since the question came up it made me curious and I had to check the "manual." Although the use of "an historian" is commonplace among historians (we're an odd lot), technically you are correct Fyron. According to the Chicago Manual of Style, "an" is not used before a word that begins with a consonant sound (y, h, and w included). This is the style for American "English," of course, I don't if it's true for real English.
