PLYMOUTH BOCK 280 PNEUMATIC TOOLS Their chief founder was a lawyer, named Darby, who had taken _ orders. Their communities are of what is known as the Evangelical Calvinistic type, and many of them maintain that only among them- selves is true Christianity to be found. They have no regular ministry, every brother being at liberty to prophesy or E reach whenever moved to do so. They aptize all adults, whether previously baptized or not, and observe the Sacra- ment of the Lord's Supper weekly. They are rigid Predestinarians and ex- pect the millennium. by Latimer Clark in 1853, improveff my Varley in 1858, and again by Siemens in 1863. The invention of Latimer Clark and Varley required a separate tube be- tween each pair of stations, and admit- ted of only a single dispatch at a time; but a system of laying tubes in circuit for the continuous transmission of dis- patches, by means of an uninterrupted air current in one direction, was adopted in Berlin by Siemens and Halske in 1863, and introduced in London in 1870. Both systems are in use in London with modifications to suit special traffic. PLYMOUTH ROCK PLYMOUTH ROCK. See Plymouth (Mass). PLYMOUTH SOUND, an arm of the sea, on the S. W. coast of England, be- tween the counties of Devon and Corn- wall. It is about 3 miles wide at its en- trance, bounded by elevated land, which descends abruptly to the sea. It con- tains Drake Island, which is fortified, and the celebrated Pljrmouth breakwater. See Plymouth. PNEUMATIC DISPATCH, propulsion by means of compressed air or by form- ing a vacuum. Pneumatic railways have thus far proved abortive, but propulsion by compressed air has of recent years been successfully applied to a variety of practical uses. Parcels are thus con- veyed, and internal communication in warehouses, hotels, etc., is carried on by its ^ means. The most developed appli- cation of compressed air as a motive force is in connection with the telegraph service of large cities. Pneumatic dis- patch, which has proved a most useful auxiliary in securing prompt and cheap collection and distribution of telegraphic messages, was first introduced in London Pneumatic tubes are in use in Liver- pool, Manchester, Glasgow, Dublin, etc. The circuit system, but not with a con- tinuous current, is extensively used in Paris. The tubes are of iron two feet in diameter. Trains leave the central station at fixed intervals and make the circuit. Other European cities have similar systems. New York, ^ Philadel- phia, and other American cities use a pneumatic mail dispatching system. This is being superseded to some extent (1920) by swift motor vehicles. PNEUMATIC GUN, a gun operated by compressed air. PNEUMATIC TIRE, a rubber tire made hollow and then inflated with air. In common use for the wheels of motor- cars, bicycles, etc. PNEUMATIC TOOLS, a class of tools which operate by compressed air. They are usually portable, and used for metal, wood or stone work. The tools are of great variety and are put to many uses, but all of them are one of two types- percussion or rotary. In both types the motor is contained in the tool, and air
