Two objections to the publication of a work like the present, occurred to the author as well as to others whom he consulted, and caused him to hesitate in commencing the undertaking. First, the possibility that the detailed description of ingenious acts of dishonesty, might furnish information which could be obtained from no other source, and supply the evil-disposed with expedients for the prosecution of their nefarious designs. Second, the danger of again inflicting pain upon the innocent relatives and friends of those whose criminal biography would furnish material for the work. In reference to the first of these objections it may be said, that, although descriptions of skilful roguery are always perused with interest, and often with a sort of admiration for the talent displayed, yet when it is seen that retribution follows as certainly and often as closely as a shadow; that however dexterously the criminal may conceal himself in a labyrinth of his own construction, the ministers of the law track him through all its windings, or demolish the cunningly devised structure; and that when he fancies himself out of the reach of Justice, he sees, to his utter dismay, her omnipresent arm uplifted to strike him down; when these truths are brought to light by the record, an impressive view will be given of the resources which are at command for thwarting the designs of dishonesty, and of the futility of taking the field against such overwhelming odds. And in addition to the certainty of detection, the penalty inflicted for offences of this description is to be taken into the account. Doubtless many employés in Post-offices have committed crimes of which they never would have been guilty but for a mistaken idea of security from the punishment to which they were making themselves liable. It is well for all to be correctly informed on this subject, and to know that offences committed against this Department are not lightly dealt with. Information of this character the author has fully supplied. Again--Comparatively but few of the secret modes of detection are exhibited, and he who should consider himself safe in evading what plans are here described, will find to his sorrow that he has made a most dangerous calculation. As to the second objection above mentioned, namely, the danger of wounding the feelings of innocent parties, the author would observe that fictitious names of persons and places are generally substituted for the real ones; thus avoiding any additional publicity to those concerned in the cases given. And furthermore, he ventures to hope that few of the class to which this objection refers, would refuse to undergo such a trial of their feelings, if by this means a wholesome warning may be given to those who need it.