The laws of the land are intended not only to preserve the person and material property of every citizen sacred from intrusion, but to secure the privacy of his thoughts, so far as he sees fit to withhold them from others. Silence is as great a privilege as speech, and it is as important that every one should be able to maintain it whenever he pleases, as that he should be at liberty to utter his thoughts without restraint. Now the post-office undertakes to maintain this principle with regard to written communications as they are conveyed from one person to another through the mails. However unimportant the contents of a letter may be, the violation of its secrecy while it is in charge of the Post-Office Department, or even after having left its custody, becomes an offence of serious magnitude in the eye of the law; and as the quantity and importance of mail matter is continually increasing, it has been found necessary to adopt means for its security, which were not required in the earlier history of the Post-Office. One kind of danger to which the mails were exposed before the days of railroads and steamboats, namely, highway robbery, is now almost unknown. The principal danger at present to be apprehended, is from those connected with their transportation and delivery, and a system of _surveillance_ has been adopted, suited to the exigency of the case, namely, the creation of Special Agents, who have become a fixed "institution," likely to be essential to the efficiency of the Department, as long as any of its employés are deficient in principle or honesty. The origin of this Special Agent System will be given elsewhere. It is sufficient to say here, that the curious developments of character, and combinations of circumstances, which will be found in the following pages, were mainly brought to light by the operation of this system, as carried out by one of its Agents. "Ten years" of experience have given the author (or at least ought to have given him) an ample supply of material for the illustration of nearly every phase in Post-Office life. His principal difficulty is the "_embarras des richesses_;" yet he has endeavored to select such cases as are not only interesting in themselves, but well calculated to benefit those for whose use the present work is especially designed. CONTENTS. CHAPTER I. No "Ear-Biters" employed--The Commission--A whole School robbed--Value of a "quarter"--Embargo on Trunks--Unjust Suspicion--The dying Mother--Fidelity of Post Masters--A venerable pair of Officials--President Pierce assists--A clue to the Robberies--The Quaker Coat--An insane Traveler--The Decoy Letters--Off the Road--The dancing Horse--The Decoy missing--An official Visit by night--Finding the marked Bills--The Confession--The Arrest Page 25 CHAPTER II.