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Possible Duplicate:
When did it become correct to add an ‘s’ to a singular possessive already ending in ‘s’?
Which singular names ending in “s” form possessives with only a bare apostrophe?

Which one is correct?
I thought the latter would be correct but apparently the former is always used; why?

###Edit:

Another (confusing) example: Charles'(s?) law

Possible Duplicate:
When did it become correct to add an ‘s’ to a singular possessive already ending in ‘s’?
Which singular names ending in “s” form possessives with only a bare apostrophe?

Which one is correct?
I thought the latter would be correct but apparently the former is always used; why?

Edit:

Another (confusing) example: Charles'(s?) law

Possible Duplicate:
When did it become correct to add an ‘s’ to a singular possessive already ending in ‘s’?
Which singular names ending in “s” form possessives with only a bare apostrophe?

Which one is correct?
I thought the latter would be correct but apparently the former is always used; why?

###Edit:

Another (confusing) example: Charles'(s?) law

Possible Duplicate:
When did it become correct to add an ‘s’ to a singular possessive already ending in ‘s’?
Which singular names ending in “s” form possessives with only a bare apostrophe?

Which one is correct?
I thought the latter would be correct but apparently the former is always used; why?

###Edit:

Another (confusing) example: Charles'(s?) law

Which one is correct?
I thought the latter would be correct but apparently the former is always used; why?

###Edit:

Another (confusing) example: Charles'(s?) law

Possible Duplicate:
When did it become correct to add an ‘s’ to a singular possessive already ending in ‘s’?
Which singular names ending in “s” form possessives with only a bare apostrophe?

Which one is correct?
I thought the latter would be correct but apparently the former is always used; why?

###Edit:

Another (confusing) example: Charles'(s?) law