At 01:30 PM 12/11/2000 -0500, Kirstin Schwartz wrote:
>  Christopher Columbus' birthday or is it Christopher Columbus's birthday?

This is one of those messy areas where there's divided opinion. For
example, Hacker's A Writer's Reference says either is okay. My practice is
to add  the apostrophe plus "s" because another syllable gets pronounced,
so I'd write "Columbus's." Others would leave off the second "s." Being
consistent in one's practice is the important thing.

Of course, all agree that only the apostrophe is added when the word ends
in the plural ending "s": "the sisters' families," "the Joneses' house."

Dick Veit