Section 14. Whoever has custody of any public records shall, upon the expiration of his term of office, employment or authority, deliver over to his successor all such records which he is not authorized by law to retain, and shall make oath that he has so delivered them, according as they are the records of the commonwealth or of a county, city or town, before the state secretary, the clerk of the county commissioners or the city or town clerk, who shall, respectively, make a record of such oath.