(1)  Any person who knowing, or having a reasonable opportunity of knowing, the nature thereof –

(a) .  .  .  .  .  .  .  .  

(b) publicly exhibits any disgusting object or indecent show –

is guilty of a crime.

Charge:  Exhibiting obscene matter.

(2)  In any prosecution for a crime under this section it shall be a defence to prove that the act alleged was done for the public good.

(3)  The questions whether any such act as aforesaid was capable of being for the public good, and whether there is any evidence in the circumstances of excess beyond the requirements of the public good, are questions of law.

(4)  The questions whether any such act as aforesaid was for the public good, and whether there was any such excess as aforesaid, are questions of fact.