CABINET NOIR, the name given in France to the office where the letters of suspected persons were opened and read by public officials bef ore being forwarded to their destination. This practice had been in vogue since the establishment of posts, but it was not until the reign of Louis XV. that a separate office was created for the purpose, called the cabinet du secret des posies, or more popularly the cabinet noir. Although denounced at the time of the Revolution, it was used both by the revolutionary leaders and by Napoleon. The cabinet noir as such has disap peared, but the right to open letters in cases of emergency and especially in time of war is exercised in all civilized countries. In England this power was confirmed by the Post Office Act of 1837; its most famous use being the opening of Mazzini's letters in (See ESPIONAGE and CENSORSHIP.)