Nikola Tesla U.S. Patent 1,061,142 - Fluid Propulsion Patent Wrapper Page 47

31 T for measuring torque. Both of these machines were provided with reversing nozzels as shown in the photographs. Their rotors were composed of plane disks riveted together, as indicated, with spaces between them. The steam entered tangentially and, after describing its free spiral path, issued from the center through the three openings at both sides into the exhaust chamber. I recognize photographs G and H as showing th two turbines installed at the Edison Waterside Plant, New York City, and I know these machines were constructed and operated in accordance with the descriptions and illustrations in the above mentioned Tesla applications for patent. They were coupled together by a torsion spring shown in photograph H so that horse power measurements could be taken without recourse to reduction gears, one turbine being used as a driver and the other as a brake. The Tesla turbine is particularly valuable on account of its reversibility, its efficiency being the same for both directions of rotation. Other advantageous features are its extreme simplicity and adaptability to varying speeds without the marked drop in efficiency which is unavoidable in bucket turbines. The great torque at low speed which it possesses makes it especially adaptable for traction work, and by its compactness and small weight per horse power yield it is superior to existing machines. It is also a prominent characteristic of the Tesla turbine, and this is a matter of the greatest practical importance, that there is a very much smaller slip or relative velocity of steam and metal surface than in any other practical types of turbines. This contributes very greatly to its efficiency. I may also note that I believe it is the only turbine which utilizes the viscosity of the steam to transmit the kinetic energy of the intermediate -6H.P. 847