68 PRACTICAL LESSONS IN SCIENCE. 



is interesting to notice how widespread their application is. 

 Every motion of the body, every tool, and nearly every article 

 we use, involves the action of some form of a simple machine. 



Water wheels are simple machines, something like the wheel 

 and axle, designed for the utilization of the force of gravity 

 through running water. One of the most common forms is the 

 undershot wheel, which is driven by the current flowing under the 

 wheel against the floats. In the case of the breast wheel, the 

 water falls on the wheel near its center and more power is ex- 

 erted. In the case of the overshot wheel the water falls upon the 

 top of the wheel, and more force is exerted than in either of the 

 other cases. The undershot wheel, with plane floats, transmits 

 about 30% of the power of the water. With curved floats it 

 transmits from 50% to 60%. The breast wheel transmits from 

 40% to 50%, and the overshot wheel transmits from 70% to 80%. 



The turbine wheel is the most valuable and economical of the 

 water wheels. While the other wheels are horizontal the axis of 

 the turbine wheel is vertical. In the center of the wheel is a sta- 

 tionary disk of cast-iron, circular in form and horizontal in posi- 

 tion. On the upper surface of this disk are fastened curved 

 guides. The wheel proper revolves outside of this disk. It con- 

 sists of two cast-iron plates, one above the other, the space 

 between them being divided into numerous channels by curved 

 partitions. The partitions in the wheel, and the guides on the 

 disk, curving in opposite directions. To the bottom of this 

 wheel is fastened a cast-iron plate which extends under the cen- 

 tral disk, and to the center of this plate is attached a vertical 

 shaft which comes up through the disk. The revolving part, 

 therefore, consists of an outside wheel, an iron plate underneath, 

 and the vertical shaft. This wheel is placed at the bottom of a 

 column of water. The weight of water upon the disk forces the 

 water between the curved guides on the disk against the curved 

 partitions of the wheel. The energy of these streams turns the 

 wheel and the shaft, and by means of cogs and belts this motion 

 is transferred to machinery. The turbine wheel transmits 80 

 per cent, or more of the computed energy of the falling water. 



