Subsequent promise of bribe

If after a public officer, juror or voter, has done any act as a public officer, juror or voter, any other person secretly agrees or offers to give or procure for him or for any other person any valuable consideration on account of such act, the person so agreeing or offering shall be presumed, until the contrary is shown, to have been guilty of having before the doing of such act corrupted such public officer, juror or voter, in respect of such act.