There is a class of post-office thieves who make a specialty of rifling the registered letters that pass through their hands in transit on journeys of greater or less length. Some of them have managed operations very shrewdly, in the evident belief that they had discovered an infallible method for doing the work and at the same time escaping detection. Too late they generally learn by sad experience that no patents can be taken out for the protection of crime. In this class of cases something tangible always remains to exhibit the peculiar style of workmanship belonging to each; and it would often surprise the uninitiated to learn how many traits of character, what indexes of habit and vocation, can be picked up by careful study of the minute points presented for inspection. Unless, however, an agent cultivates a taste for thoroughness even to details and trifles that might at first view appear utterly insignificant, he will never succeed in interpreting the hieroglyphics. At intervals of two or three weeks, beginning in the summer of 1871, registered packages passing to and fro from Chicago to a town in the interior of Dakota Territory, which for convenience will be called Wellington,--though that was not its name,--were reported to the department as rifled. As the season wore on, the complaints increased in frequency. Under the old method of doing business at headquarters, which often amounted practically to a distribution of the cases about equally "among the boys," the agent stationed at Chicago received most of them at first; then a part were sent to an agent in Iowa; and as the number multiplied, Furay, at Omaha, was favored with an occasional sprinkling. Under the present more perfect system, great care is taken to group together all the complaints growing out of each series of depredations, to locate the seat of trouble by comparisons carefully made in the department itself, and to give everything bearing on the subject to the officer specifically charged with the investigation. March came around before Mr. Furay found time to give personal attention to this particular thief. He then passed over the route to Wellington, eighty miles by stagecoach from the nearest railroad station, with ten intermediate offices. All the packages remained over night at Sioux City, Iowa, a fact sufficiently important to invite close scrutiny; but the detective soon became satisfied that he must look elsewhere for the robber. His suspicions were next directed to another office, where also the mails lay over night; but the postmaster bore a countenance so open and honest that he too was eliminated from the problem.