168 



ELEMENTS OF GENERAL SCIENCE 



FIG. 85. An undershot water 

 wheel 



The wheel is turned by the pressure 

 of the water against the paddles 



electric current is transmitted as far as St. Louis, Missouri, 

 and possibly it may be found advantageous to transmit it 



even greater distances. 



186. Undershot water wheels. 

 A simple type of water wheel is 

 one which consists essentially of 

 a wheel with a number of paddles 

 projecting from its circumfer- 

 ence. The wheel is so mounted 

 that paddles dip into a swiftly 

 flowing stream which flows be- 

 neath it, and the push of the 

 water revolves the wheel (fig. 

 85). Somewhat similar wheels 

 are often made and used as toys and offer excellent oppor- 

 tunities for individual ingenuity in constructing a water- 

 driven machine. 



187. Overshot water wheels. The rim of the overshot wheel 

 is provided with boxes, called buckets, which are placed in posi- 

 tions indicated in the illustration (fig. 86). Water is carried 

 out over the wheel in a pipe 



or a flume and allowed to run 

 upon the upper part of the 

 wheel. The upward-facing 

 buckets of one half of the 

 wheel are filled, and the weight 

 of the water turns the wheel. 

 Each descending bucket grad- 

 ually turns over as it descends, 

 and spills out the water, re- 

 turning empty up the other 

 side. The wheel is called an overshot wheel because the 

 water passes over it and then into the current. 



188. Turbines. A third kind of water wheel is the turbine. 

 In this type many streams of water under pressure are directed 



FIG. 86. An overshot water wheel 



The wheel is turned by the weight of 

 the water in the buckets 



