12 BULLETIN 119, U. S. NATIONAL MUSEUM. 



edgewise to the wind to stop it, or to regulate the position to conform 

 to the wind pressure. 



WATER WHEELS. 



It is quite probable that the current wheels used from time im- 

 memorial, particularly in the Orient, for raising water, and locally 

 known as the Persian wheel, the Noria and the Tympanum, were 

 the forerunners of the water wheel used for the development of 

 power. At all events, water wheels were used to turn mill stones in 

 50 B. C, according to Strabo, and from this time on were gradually 

 improved, particularly as to their efficiencies. This was brought 

 about mainly through the mode of directing the water to the wheel 

 so that there were developed many types, such as the overshot, under- 

 shot, breast, flutter, Barker, and several others whose efficiencies 

 ranged from as much as 75 per cent to as little as 25 per cent. 



The modern development of the water wheel is the turbine, a 

 water wheel revolving on a vertical axis and having peculiarly 

 shaped buckets or vanes. Its greater efficiency and ability to take 

 advantage of high as well as low falls of water has practically 

 caused the elimination of the earlier water wheel. Since its inven- 

 tion by Fourneyron in 1823, many types have been developed which, 

 however, may be classified into high and low pressure turbines, and 

 further subdivided according to the direction of flow of the water 

 through the machine. Fourneyron directed the water to the center 

 of the wheel and discharged it outward (radially). The Chase is 

 just the reverse, the water entering at all points around the cir- 

 cumference and escaping at the center and downward. Another 

 type, of which the Jonval is an example, invented in 1841, receives 

 the water above and directs it downward through a set of guides to 

 the wheel, the water discharging below. 



Model of Leffel Double Turbine Water Wheel. Made and Presented by 



James Leffel & Co. 



This belongs to the class of water wheels in which the water enters 

 the buckets tangentially at the surface and is discharged at the 

 center. This particular turbine has two sets of buckets, one with a 

 central and the other with a vertical discharge, each receiving its 

 water from the same set of guides at the same time and the water 

 leaving each wheel independently. The two sets are cast together 

 and attached to the same shaft. Cat. No. 180,193 U.S.N.M. 



STEAM ENGINES. 



Connected with the history of the steam engine are the names 

 Hero, Anthemius, da Vinci, Porta, Branca, de Caus, Marquis of 

 Worcester, Papin, Savery, Newcomen, and Watt, names of men 



