PNEUMATIC POWER TRANSMISSION. Every wind that blows is an instance of the pneumatic transmission of power, and every windmill or sail that catches the breeze ig a demonstra tion of it. The modern or technical use of the term, however, is confined to the compression of air at one point and its transmis sion to another point where it is used in motors to do work.
The first recorded instance of this being done was by Denis Papin (b. who compressed air with power derived from a water wheel and transmitted it through tubes to a distance. About i800 George Medhurst (1759-1827) took out patents in England for compressing air. He compressed and transmitted air which worked motors, and he built a pneumatic automobile. William Mann in 1829 took out a patent in England for a compound air compres sor. In his application he states : "The condensing pumps used in compressing I make of different capacities, according to the densities of the fluid to be compressed, those used to compress the higher densities being proportionately smaller than those previously used to compress it to the first or lower densities," etc. This is a very exact description of the best methods of compressing air to-day, omitting the very important inter-cooling. Baron Van Rathen in 1849 proposed to compress air in stages and to use inter-coolers between each stage to get 75o lb. pres sure for use in locomotives. For the next 4o years inventors tried without success all manner of devices for cooling air during compression by water, either injected into the cylinder or circu lated around it, and finally, with few exceptions, settled down to direct compression with no cooling worthy of mention. Only in the last ten years of the 19th century were the fundamental principles of economical air compression put into general practice, though all of them are contained in the patent of William Mann and the suggestion of Van Rathen.
The first successful application of compressed air to the trans mission of power, as we know it, was at the Mont Cenis tunnel in 1861. The form of compressor used was a system of water rams— several of them in succession—in which water was the piston, compressing the air upwards in the cylinder and forcing it out. Although the air came in contact with the water, it was not cooled, except slightly at the surface of the water and around the walls of the cylinders. The compressors were situated near the tunnel, and the compressed air was transmitted through pipes to drilling machines working at the faces in the tunnel. Rotary drills were tried first, hut were soon replaced by percussion drills adapted from drawings in the U.S. Patent Office, copied by a
French and Italian commission from the patent of J. W. Fowle of Philadelphia. H. S. Drinker (Tunneling, Explosive Compounds and Rock Drills, New York, 1893) states positively that the first percussion drill ever made to work successfully was patented by J. J. Couch of Philadelphia in 1849. Shortly afterwards Fowle patented his drills, in which the direct stroke and self-rotating principle was used as we use it now. The first successful drill in the Hoosac tunnel was patented in 1866 by W. Brooks, S. F. Gates and C. Burleigh, but after a few months was replaced by one made by Burleigh, who had bought Fowle's patent and improved it. Burleigh made a compressor, cooling the air during compression by an injected spray of water in the cylinders. The successful work in the Mont Cenis and Hoosac tunnels with the percussion drilling machines caused the use of compressed air to spread rapidly, and it was soon found there were many other purposes for which it could be employed with advantage.