I'm writing a lab for a simple diffraction experiment, and I am stuck on this grammatical point:
Is it more appropriate to say "Huygens' Principle" or "Huygens's Principle"*? A cursory glance at Google seems to indicate that the most common usage seems to be "Huygens' Principle"; but as the apostrophe is at the end of the word as in the plural possessive, my inner grammarian is screaming that it should be "Huygens's". Which is correct?
*I know it can also be rendered as the Huygens-Fresnel Principle, obviating the need for my query.