Where the second _s_ is not pronounced, as often happens, to avoid the prolonged hissing sound of another _s_, he recommends omitting it in print.
Moses' hat, for Moses's hat.
For conscience' sake.
3.

The apostrophe indicates the omission of letters in dialect, in familiar dialogue, and in poetry.
That's 'ow 'tis.
'Twas ever thus.
When two words are practically made into one syllable, a thin space may be put before the apostrophe, except that _don't_, _can't_, _won't_, and _shan't_ are consolidated.

This use of a space serves to distinguish between the possessive in _s_ and the contraction of _is_.
Where death 's abroad and sorrow 's close behind.
4.

Figures expressing dates are often abbreviated, but it is not good general practice.
The boys of '61.
It happened in '14.
5.

The apostrophe is used to form the plural of letters and figures.
Cross your t's and dot your i's.
Make 3's and 5's more plain.
Except in these cases the apostrophe is not a plural sign and should be so used only when it is intended to reproduce a dialect or colloquialism.
Wrong: All the Collins's were there.
Right: All the Collinses were there.
The final _ed_ of past tenses and past participles was formerly pronounced as a distinct syllable, thus: _clos-ed_, _belov-ed_, and this pronunciation continued in common use in poetry long after it was discontinued in prose.