It's based on the vowel sound. The author may be someone who drops the h when they pronounce "historic". See: http://www.betterwritingskills.com/tip-w005.html h

It's based on the vowel sound. The author may be someone who drops the h when they pronounce "historic". See: http://www.betterwritingskills.com/tip-w005.html http://www.betterwritingskills.com/tip-w005.html