THE CONQUEST OF NATURE 



RUNNING WATER 



The aggregate amount of work accomplished with 

 the aid of the wind is but trifling, compared with that 

 which is accomplished with the aid of water. The 

 supply of water is practically inexhaustible, and this 

 fluid being much more manageable than air, can be 

 made a far more dependable aid to the worker. Every 

 stream, whatever its rate of flow, represents an enor- 

 mous store of potential energy. A cubic foot of water 

 weighs about sixty-two and a half pounds. The 

 working capacity of any mass of water is represented 

 by one-half its weight into the square of its velocity; 

 or, stated otherwise, by its weight into the distance of its 

 fall. Now, since the interiors of the continents, where 

 rivers find their sources, are often elevated by some 

 hundreds or even thousands of feet, it follows that the 

 working energy expended and for the most part 

 wasted by the aggregate water current of the world 

 is beyond all calculation. Meantime, however, a 

 portion of the energy which in the aggregate represents 

 an enormous working power is utilized with the aid 

 of various types of water wheels. 



Watermills appear to have been introduced in the 

 time of Mithridates, Julius Caesar, and Cicero. Strabo 

 informs us that there was a watermill near the residence 

 of Mithridates; and we learn from Pomponius Sabinus, 

 that the first mill seen at Rome was erected on the 

 Tiber, a little before the time of Augustus. That they 

 existed in the time of Augustus is obvious from the de- 

 scription given of them by Vitruvius, and the epigram 



