152 HYDROKINETICS. 



opposite to that of the water jets. The principle involved 

 was explained in 230. (See Appendix F.) 



265. The Turbine Wheel. The turbine wheel, of 

 which there are many varieties, is the most effective water- 

 wheel yet known, utilizing, in some cases, 85 per cent, of 

 the total energy of the stream. 



FIG. 92. 



(a.) Fig. 92 represents one form in perspective and in horizontal 

 section through the centre of the wheel and case complete. The 

 wheel B and the enclosing case D are placed on the floor of a pen- 

 stock wholly submerged in water, under the pressure of a consid- 

 erable head. The water enters, as shown by the arrows, through 

 openings in I), which are so constructed that it strikes the buckets 

 of B in the direction of greatest efficiency. After leaving the 

 buckets, the " dead-water " escapes from the central part of the 

 wheel, sometimes by a vertical draft tube, best made of boiler-iron. 

 The weight of the water in this tube increases the velocity with 

 which the water strikes the buckets. A central shaft, A, is carried 

 by the wheel and communicates its motion to the machinery above. 

 The wheel itself rests upon a central pivot carried by cross-arms 

 from the bottom of the outer case. The case D is covered with a 

 top T, which protects the wheel from the vertical pressure of the 

 water. The axis of the wheel passes through the centre of this 

 cover. The openings by which the water passes to the wheel are 

 called chutes. Sometimes a cylindrical collar, (7, is placed between 



