The justices of the Supreme Court, the judges of the court of appeals and the district judges are each entitled to receive for their services a compensation to be fixed by law and paid in the manner provided by law, which must not be increased or diminished during the term for which they have been elected, unless a vacancy occurs, in which case the successor of the former incumbent is entitled to receive only such salary as may be provided by law at the time of his election or appointment. A provision must be made by law for setting apart from each year?s revenue a sufficient amount of money to pay such compensation.