Inform harbour-master of vessel sunk or dangerous wreckage adrift, Report wrecks to Lloyd's. There is more--much more. For instance, all manner of craft have to be watched to see that they do not carry more passengers than their licence permits, that obstruction is not caused by mooring across public stairs, that more than the fixed fare is not demanded by watermen, that no boat is navigated for hire without a licence, and so on. Detective-Inspector Helden and his staff of the Criminal Investigation Department of the division are the most dreaded enemies of the river thieves. Time was, when the "light-horsemen" of the river were in their heyday, that L25,000 worth of property was stolen annually. That has been reduced to less than a couple of hundred pounds--a comparatively trivial, insignificant figure. It is to both branches of the river police that those who use the river owe this complete immunity from theft. Every man of the C.I.D. in the division has a complete knowledge of thieves and receivers on whom it is necessary to maintain constant surveillance. Marine store dealers and old metal dealers are kept in close touch, for it is to them that the odds and ends of ship equipment might be taken by a dishonest sailor or watchman. One of the most famous of river thieves was a man whom the public knew as "Slippery Jack." He made a rich harvest until he was laid by the heels. Almost naked, and his skin greased lavishly, he would slip aboard likely-looking craft in search of plunder. If he were disturbed, he would dodge away, his greased skin aiding him if anyone attempted to seize him. He was tracked down one evening to Blackfriars, where he backed his boat into midstream and turned at bay with a vicious sheath-knife. Only after a fierce struggle, in which the police did not escape scot free, was he arrested. His exploits cost him ten years' penal servitude. It was the detective branch of the Thames Police that solved the complicated mystery of a supposed case of murder which attracted much public attention at the time. The full facts have never been made public, and may be interesting. In August, 1897, the body of a naked man was found floating near the Tower Bridge. A line was woven tightly round the body, arms and neck, and a doctor stated that the body must have been in the water about three weeks, that death was due to strangulation, and that he thought it impossible for the man to have tied the rope round himself, though it must have been tied before death. A woman identified the body as that of her husband, Von Veltheim--he who shot Woolf Joel in Johannesburg and was later sentenced at the Old Bailey for the blackmail of Mr. Solly Joel--and a jury brought in a verdict that "death was caused by strangulation whether amounting to murder the evidence fails to show."