"The question concerns the appropriate use of the words historic and historical. When is one prefered over the other?"
This is a great question, for which the American Heritage Book of English Usage has an excellent answer:
Historic and historical have different usages though their senses overlap. Historic refers to what is important in history: the historic first voyage to the Moon. It is also used of what is famous or interesting because of its association with persons or events in history: a historic house. Historical refers to whatever existed in the past, whether regarded as important or not: a minor historical character. Historical also refers to anything concerned with history or the study of the past: a historical novel, historical discoveries. While these distinctions are useful, don't be surprised if you see these words used interchangeably, as in historic times or historical times.