Third Exception.-It is not defamation to express in good faith any opinion whatever respecting the conduct of any person touching any public question, and respecting his character, so far as his character appears in that conduct, and no further. Illustration It is not defamation in A to express in good faith any opinion whatever respecting Z's conduct in petitioning Government on a public question, in signing a requisition for a meeting on a public question, in presiding or attending at such meeting, in forming or joining any society which invites the public support, in voting or canvassing for a particular candidate for any situation in the efficient discharge of the duties of which the public is interested.