This animal horsepower isn't a very efficient horsepower. In fact, it is less than three-fourths of an actual horsepower, as engineers use the term. A real horsepower will do the work of lifting 33,000 pounds one foot in one minute--or 550 pounds one foot in one second. Burn a pint of gasoline, with 14 pounds of air, in a gasoline engine, and the engine will supply one 33,000-pound horsepower for an hour. The gasoline will cost about 2 cents, and the air is supplied free. If it was the air that cost two cents a pound, instead of the gasoline, the automobile industry would undoubtedly stop where it began some fifteen years ago. It is human nature, however, to grumble over this two cents. Yet the average farmer who would get excited if sound young chunks and drafters were running wild across his pastures, is not inspired by any similar desire of possession and mastery by the sight of a brook, or a rivulet that waters his meadows. This brook or river is flowing down hill to the sea. Every 4,000 gallons that falls one foot in one minute; every 400 gallons that falls 10 feet in one minute; or every 40 gallons that falls 100 feet in one minute, means the power of one horse going to waste--not the $200 flesh-and-blood kind that can lift only 23,000 pounds a foot a minute--but the 33,000 foot-pound kind. Thousands of farms have small streams in their very dooryard, capable of developing five, ten, twenty, fifty horsepower twenty-four hours a day, for the greater part of the year. Within a quarter of a mile of the great majority of farms (outside of the dry lands themselves) there are such streams. Only a small fraction of one per cent of them have been put to work, made to pay their passage from the hills to the sea. The United States government geological survey engineers recently made an estimate of the waterfalls capable of developing 1,000 horsepower and over, that are running to waste, unused, in this country. They estimated that there is available, every second of the day and night, some 30,000,000 horsepower, in dry weather--and twice this during the eight wet months of the year. The waterfall capable of giving up 1,000 horsepower in energy is not the subject of these chapters. It is the small streams--the brooks, the creeks, the rivulets--which feed the 1,000 horsepower torrents, make them possible, that are of interest to the farmer. These small streams thread every township, every county, seeking the easiest way to the main valleys where they come together in great rivers.