68 THE ART AND PRACTICE OF LANDSCAPE GARDENING. 



this : Select some part of it where the cross section is for a given 

 distance constant. Find the area of this cross section in square 

 feet. Prepare a float, and start it from the upper end of the 

 measured space. Count the number of seconds this float occupies 

 in passing the given distance ; then multiply the number of square 

 feet by the observed mean velocity in feet per second, and you will 

 obtain the discharge in cubic feet per second. To find the area of 

 a pipe, or a channel-way, or the mean velocity, or the quantity dis- 

 charged (according to Trautwine) when the other two are given : 



Area in discharge in cubic feet per second 



square feet mean velocity in feet per second. 



Mean velocity discharge in cubic feet per second 



=z. ------- . . _. . 



in feet per second area in square feet. 



Discharge in cubic feet mean velocity area of cross section 



per second in feet per second of pipe or channel in square feet. 



These formulae apply to openings in the sides of vessels, to 

 rivers, and to all other channels, as well as to pipes. According 

 to Hawksley, the formula for the delivery of water in pipes when 



G Number of gallons delivered per hour. 



L Length of pipe in yards. 



H Head of water in feet. 



D Diameter of pipe in inches. 



The theoretical velocity in feet per second is 8'O25\/Head of 



water in feet. 



A running spring or a stream delivers about as much water 

 as a pipe having the same area would discharge without extra 

 pressure, and it is worth while to note that a 



