MEASUBEMENT OF STEEAMS. 35 



high every second, or 6. quarts to a hight of 30 feet. The 

 small size windmills are about one-sixth of one horse- 

 power. 



Where streams are available, the supply of water will 

 be found most ample and most economical. No storage 

 tanks are needed in which the water must remain for a 

 time, that its temperature may be raised nearly to that of 

 the soil, as when wells are used. The water may be 

 taken directly from the stream and flowed upon the 

 ground. A low dam of two feet in hight may be con- 

 structed of planks across the stream, by which power to 

 run a small undershot wheel may be secured. Where 

 there is facility for backing the water to a greater extent, 

 or of procuring a greater fall, a breast- wheel may be used. 

 A dam four or five feet high will be sufficient for a wheel 

 of this kind, if the stream is four feet wide and six inches 

 deep, and runs with a velocity of two miles per hour. 

 Such a stream with this fall of water would give sufficient 

 power to elevate 11 quarts of water per second a hight of 

 30 feet, or a sufficient supply for about 12 acres of ground, 

 or more in proportion to the less hight that the water 

 would have to be raised. To calculate the nominal 

 horse-power furnished by a fall of water, the velocity of 

 the stream in feet per minute, the hight of fall, and the 

 sectional area (the width and depth) of the stream in 

 square feet, must be multiplied together, and by 62 1 !,, 

 and divided by 33,000. 



For instance, if the stream is found to be 5 feet wide 

 at the surface, and 3 feet at the bottom, with banks evenly 

 sloping from the surface to the bottom, the mean diame- 

 ter is found by adding the surface and bottom widths to- 

 gether and taking half the sum. In this case the mean 

 width will be 4 feet. If the depth in the middle is 6 

 inches or half a foot, this mean width is multiplied by 

 the depth and the product is the sectional area, which in 

 this case is two square feet. To find the velocity of the 



