This is a mere common-place transaction, compared with the achievements of the staff of the little army of Detective policemen at head-quarters. Sometimes they are called upon to investigate robberies; so executed, that no human ingenuity appears to ordinary observers capable of finding the thief. He leaves not a trail or a trace. Every clue seems cut off; but the experience of a Detective guides him into tracks quite invisible to other eyes. Not long since, a trunk was rifled at a fashionable hotel. The theft was so managed, that no suspicion could rest on any one. The Detective sergeant who had been sent for, fairly owned, after making a minute examination of the case, that he could afford no hope of elucidating the mystery. As he was leaving the bed-room, however, in which the plundered portmanteau stood, he picked up an ordinary shirt-button from the carpet. He silently compared it with those on the shirts in the trunk. It did not match them. He said nothing, but hung about the hotel for the rest of the day. Had he been narrowly watched, he would have been set down for an eccentric critic of linen. He was looking out for a shirt-front or wristband without a button. His search was long and patient; but at length it was rewarded. One of the inmates of the house showed a deficiency in his dress, which no one but a Detective would have noticed. He looked as narrowly as he dared at the pattern of the remaining fasteners. It corresponded with that of the little tell-tale he had picked up. He went deeper into the subject, got a trace of some of the stolen property, ascertained a connexion between it and the suspected person, confronted him with the owner of the trunk, and finally succeeded in convicting him of the theft.—At another hotel-robbery, the blade of a knife, broken in the lock of a portmanteau, formed the clue. The Detective employed in that case was for some time indefatigable in seeking out knives with broken blades. At length he found one belonging to an under-waiter, who proved to have been the thief. The swell mob—the London branch of which is said to consist of from one hundred and fifty to two hundred members—demand the greatest amount of vigilance to detect. They hold the first place in the “profession.” Their cleverness consists in evading the law; the most expert are seldom taken. One “swell,” named Mo. Clark, had an iniquitous career of a quarter of a century, and never was captured during that time. He died a “prosperous gentleman” at Boulogne, whither he had retired to live on his “savings,” which he had invested in house property. An old hand named White lived unharmed to the age of eighty; but he had not been prudent, and existed on the contributions of the “mob,” till his old acquaintances were taken away, either by transportation or death, and the new race did not recognise his claims to their bounty. Hence he died in a workhouse. The average run of liberty which one of this class counts upon is four years.