The duties of a Special Agent of the Post-Office Department involve a constant and vigilant supervision of all its interests. This embraces a much wider range of action, and requires much higher qualifications on the part of those who undertake it, than any simply "detective" service. It is believed that neither Congress nor the public generally attach such a degree of importance to the office in question as it really possesses, both in itself and in the estimation of the Department. This is perhaps owing to the fact that so great a proportion of its duties have of late been connected with the investigation of cases of depredation upon the mails. This has given the corps of Special Agents the apparent character of mere "detective officers," while in truth they are much more than this. The qualifications which a Special Agent should possess are numerous and diverse; some, indeed, not often found in connection with one another. A high degree of shrewdness and tact is required, in order to estimate probabilities rightly, and to pursue investigations in such a way as to avoid attracting attention or exciting alarm. And an essential pre-requisite to success is a good knowledge of human nature. To calculate beforehand with correctness what a given person will do under certain circumstances, and thus to anticipate his movements, and make him subservient to the execution of your plans; to vary the mode of approach to suspected persons, according to the combinations of circumstances and the shades of character existing in the case in hand; to do all this, and much more of a like description, demands no small knowledge of the workings of the human mind. It is comparatively an easy matter to follow up a mail robber when once upon his track, (though there is often nicety even in this,) but to collect the scattered rays of suspicion and conjecture, and to bring them together into one focus, throwing its revealing glare upon the criminal, requires a higher order of intellect than any after operations. And the caution which is always necessary in the conducting of these cases, in order to secure a successful result, is called for not only for the sake of detecting the guilty, but in order that the innocent may not suffer blame. It often happens that circumstances of the strongest kind indicate the guilt of some person, who, notwithstanding, is entirely free from all connection with the crime. Never, perhaps, is a stronger temptation to hasty and indiscreet procedures offered than by such a state of things. Yet he who is guided by discretion, is not led away by the dazzling hope of immediate success in his investigation, but, aware how fallacious are sometimes the strongest appearances, he considers the question before him with coolness and deliberation, fully conscious of the priceless value of character, and reluctant to make any movement that might unjustly throw a shadow upon it.