The prothonotary of the court of common pleas of Philadelphia shall be first appointed by the judges of said court on the first Monday of December, in the year one thousand eight hundred and seventy-five, and the present prothonotary of the district court in said county shall be the prothonotary of the said court of common pleas until said date when his commission shall expire, and the present clerk of the court of oyer and terminer and quarter sessions of the peace in Philadelphia shall be the clerk of such court until the expiration of his present commission on the first Monday of December, in the year one thousand eight hundred and seventy-five.