. Conservation. Forests and forestry. FOREST PRESERVATION 21. View Showing tlic Clear Length of a Noble Fir The demands on a central station, however, are most exacting. Service must be furnished every day and everv hour. Factories must have a uniform supply. The demand of every cus- tomer must be met on the instant zuith- out 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
. Conservation. Forests and forestry. FOREST PRESERVATION 21. View Showing tlic Clear Length of a Noble Fir The demands on a central station, however, are most exacting. Service must be furnished every day and everv hour. Factories must have a uniform supply. The demand of every cus- tomer must be met on the instant zuith- out 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 eight}' 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 carry 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
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