24 BULLETIN 173, U. S. NATIONAL MUSEUM 



The turbine shown in the model is one of the seven of the present 

 installation. The wheel of the original is IT feet 9 inches in diameter, 

 weighs about 240,000 pounds, and develops 54,000 horsepower. It 

 turns 81 revolutions per minute and requires 6,000 cubic feet of water 

 a second at full operation. The model shows the scroll case that 

 conducts the water to the runner and the butterfly valve at the en- 

 trance to the scroll. This valve is actually 27 feet in diameter and was 

 the largest ever built. The valve is sealed after closing by admitting 

 water pressure to a rubber tube 3 inches in diameter set in the inside 

 face of the valve housing. The valves are used also as head gates. 

 The draft tube is the Moody type, with a concrete cone extending 

 from the bottom to the hub of the runner. A water-wheel governor 

 of the actuator type of oil-pressure, relay governor, having fiyballs 

 mechanically driven from the main shaft of the water wheel, is 

 shown. A curtain wall protects the water entrances from ice, and 

 trash racks are located in each intake opening. Gantry cranes for 

 handling the trash racks and emergency sectional head gates are 

 shown in the model. 



The Conowingo station is (1934) the second largest hydroelectric 

 generating plant in the United States, being surpassed only by in- 

 stallations at Niagara Falls. It has a present capacity of 378,000 

 horsepower, with an ultimate development of 11 54,000-horsepower 

 units, or 594,000 horsepower. The dam provides a head of 89 feet 

 and is seven-eighths of a mile in length. The station was first 

 operated in March 1928. 



ADDITIONAL WATER MOTORS IN THE COLLECTION, NOT 



DESCRIBED 



Rotary engine (water-wheel), Patent Office model, Patent no. 51389, Decem- 

 ber 5, 1865, issued to G. A. Lamb. U.S.N.M. no. 309202. 



Water motor. Patent Office model. Patent no. 185946, January 2, 1887, issued 

 to Kelsey L. Mills. U.S.N.M. no. 309205. 



Water motor, Patent Office model, Patent no. 236554, January 11, 1881, issued 

 to H. M. Col ton. U.S.N.M. no. 309206. 



THE STEAM ENGINE 



The early history of the steam engine has been written so often 

 that little more than the briefest outline is necessary here. 



In a review of the technical knowledge of his time. Heron of 

 Alexandria (about 150 A. D.) suggested some elementary mechanical 

 devices to use the pressure of steam and described the earliest form 

 of steam engine, a simple reaction turbine, or "aeolipile." No prac- 

 tical use of these devices was ever made, and steam itself remained 

 a mysterious gas until comparatively recent times. The work of 

 Cardan (1501-1576), and Porta (1543-1615), and de Cans (1576- 



