Water-power plants in the United States. Letter from the Acting Chairman of the Federal Power Commission transmitting in response to Senate Resolution No. 164, a report showing the installed capacity, ownership, and kilowatt-hour output for the calendar year 1938, where available, for all water-power plants in the United States having an installed capacity of 100 horsepower or more, together with a list of the 200 largest water-power plants in the United States.