Power 3813 Power demand for the oil. There is a prevalent idea ! that hydraulic power may be developed in the future to such an extent as eventually to dis- place the present major use of coal and oil as a source of energy. The late Dr. Steinmetz made a comprehensive study of this possibility and demonstrated with certanty that no such substitution could be expected. If the equiv- alent of natural gas and oil is included in the estimate, the annual consumption of coal in the United States at present is nearly one bil- lion tons. The annual potential eneigy of the water powers of the United States, determined by multiplying the average height of the land above sea leve1 by the average fl.Tmi.ia] rainfall, gives a value of approximately one billion kilo- watt-years or che power of one billion kilo- watts developed continuously throughout one year. Much of this rainfall must be utilized, however, for agricultural purposes, and a con- siderable portion of it is lost for power pur- poses by seepage into the ground and evapora- tion into the air, so that according to Stein- metz, not more than 20 per cent, of the theo- retical total supply, or 200 million kilowatt- years, could be utilized for power develop- ment. Since one ton of coal contains about o*ne kilowatt-year of energy it is obvious that the energy equivalent of the present annual coal and oil consumption is five times greater than the total possible amount of energy avail- able each year from all sources of hydraulic power. Another factor which opposes the gen- eral use of hydraulic power is that it is not adapted to lie operation of most portable conveyances. From this survey of our resources in energy it will be seen that the nation must depend primarily upon its deposits of coal. Hydro- electric power will be developed and utilized most effectively on the Pacific Coast where coal is scarce and hydraulic power is abundant It has been estimated that the available hy- draulic power of the western States is six times greater than the total power demand of tha region for all purposes. The bituminous coa resources in the middle-western and eastern part of the country are so great that their de pletion at the present rate of consumption i not expected for many centuries. One carefu estimate indicates that the coal supply will last for 4,000 years. The future power suppl} in the United States is evidently dependen upon the construction of larger and more efft cient steam-electric 'power stations supple mented by hydro-electric power station wherever a source of hydraulic power can b conomically utilized. Present practice favors le location of the steam-electric plant on ide-water, lake, or river, in the general vicin- :y of the region where the major portion of he power is consumed. Thoughtful consideration has recently been iven to the question of safeguarding the con- inuity of service of the existing electric trans- mission systems which have grown to such an xtent that millions of people distributed over large area are dependent upon a single sys- em for their supply of power. These systems .re usually supplied by several power plants Derated by steam or a combination of steam and hydraulic power. The reliability of such ystems may be increased by interconnecting he various parts of the system by transmis- ion lines which form a network, so that the ailure of any transmission line or the suspen- sion of service of any power plant will not pre- vent the continuous delivery of power to most of the consumers. An interconnected system of this nature which covers the States of Cali- ornia and Oregon extends in one direction for a distance of over one thousand miles. A sim- lar system in the southeastern part of the Jnited States extends for 600 miles from Ala- jama to North Carolina. In the plan known as the super-power system it is proposed that all sources of power in the United States he ultimately interconnected to form a single na- tional network of power supply. One advantage of a super-power system would be the decreased coal consumption which would result from the operation of few- er but larger power plants on a system of large power capacity. Another factor which favors the tying together of existing power systems is the consequent improvement in the uniform- ity of the power demand upon the combined systems. While the major economic advan- tages of a super-power system relate to a sav- ing in fuel consumption and a decrease in the capital invested in the associated power plants, many other specific arguments may be offered for lie plan. A large power network may be made to serve a greater population, since the interconnecting lines may be constructed through regions which previously possessed no power supply. The electrification of railroad trunk lines could be executed with less diffi- culty by reason of the probable closer proxim- ity of some source of electric power. Wherever a transmission line came within reasonable dis- tance of a possible source of hydraulic power a hydro-electric plant could be constructed which might otherwise have been unjustified by reason of its isolated location.