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WATER-POWERS OF SOUTH CAROLINA. 



201 



The kind of mills and the amount of power employed by each may 

 be summarized thus : 



KIND OF MILL 



HORSE-POWER 



Grist and flour mills 

 Cotton factories . . . 



Saw mills 



Cotton gins 



Miscellaneous . . . . 



Total 



The water-power that a stream will furnish is determined by its fall and 

 its volume of water. The amount of fall is accurately determined by a 

 carefully made line of levels. The time allowed Mr. Swain to survey 

 the large field allotted to him enabled him to visit in person only a few 

 of the most important water-powers, and even in these instances the only 

 instrument of measurement he could use was a Locke pocket level, with 

 which he says he was in some cases " enabled to arrive at quite close ap- 

 proximation of the fall, while in others the results obtained are liable to 

 large errors." To determine the volume of water in a stream is a much 

 more difficult, tedious and delicate matter. Accurate gaugings of the 

 stream are to be made, and these are to be continued through the different 

 seasons of the year, and for a series of years, before the average amount 

 of flow to be relied on can be stated. " In the absence of such a series of 

 gaugings," Mr. Swain was forced, in order to arrive at any approximate 

 estimate of power, to adopt an entirely different method. He i)oints out 

 the uncertainty of this method, and is scrupulously careful that his errors, 

 whatever they may be, shall always be on the safe side — that is, below 

 tJie mark, but never above it. His method consists, first, in determining 

 the drainage area of the different streams by geometrical measurement 

 on the best maps accessible to him, and here he naturally remarks on the 

 inaccuracy and lack of agreement among the maps ; the next was the 

 determination of the average annual rainfall and the spring, summ.er, 



