r< >REST PRESERVATK )N 



21 



View Showing the Clear Length of a Noble Fir 



The demands on a central station, 

 however, are most exacting. Service 

 must be furnished every day and every 

 hour. Factories must have a uniform 

 supply. The demand of every cus- 

 tomer must be met on the instant zvith- 

 ont notice. While a factory develop- 

 ing its own water power will adjust its 

 business to bridge over low-water pe- 

 riods, the manufacturer who buys 

 power forgets that such adjustments 

 can be made. 



These considerations bring us to a 

 maxim in the electric supply busi- 

 ness the mimimum capacity of the 

 central station must equal the maxi- 

 mum demand of the service. No more 

 regular business can be handled by a 

 water power plant than can be sup- 

 plied in times of lowest water. Un- 

 less auxiliary power is provided, the 

 water wheel capacity is limited to this 

 minimum flow : and the excess water 

 above the minimum flow, amounting 

 perhaps to eighty to ninety per cent, of 

 the entire flow, is wasted. 



The discrepancy between maximum 

 and minimum stream flow is extraordi- 

 nary. The Pemigewasset at Plymouth, 

 representing a stream whose water- 

 shed is largely wooded, in a period of 

 ten years showed a maximum flow of 

 over 30,000 cubic feet per second 

 (July, 1897); and a minimum of 120 

 cubic feet per second (September, 

 1899). There is no artificial storage 

 on this stream. The minimum has 

 fallen to 350 cubic feet per second 

 every year for twenty years. 



It is obvious then that any means by 

 which the minimum flow can be pre- 

 served or increased is of vast import- 

 ance to the water-driven electric plant 



If the minimum flow is sufficient 

 to furnish adequate power, the rates to 

 consumers can be fixed at the lowest 

 point. Whenever an auxiliary be- 

 comes necessary, even for use only a 

 few days in the year, charges must be 

 advanced to earn- this additional in- 

 vestment. Interest an 1 fixed charges 

 are at least ten per cent, on the invest- 

 ment, an annual charge of $10 to $15 

 per horsepower. 



