150 



By an inch of rain is understood as much rain as would form a 

 sheet of water one inch deep over the surface of the ground, if none 

 of it soaked into the soil or ran off. 



An inch of rain falling on a roof will be after the rate of a little 

 more than half a gallon to the square foot. 



As the slope of the roof makes no difference, a house roof will, 

 when an inch of rain falls, collect a half gallon of water for every 

 square foot of area the house stands upon. 



So if a house is 40 feet long and 30 feet wide, the catchment area 

 will be 1,200 square feet, and an inch of rain will supply to a cistern 

 600 gallons, allowing some 15 gallons for waste and evaporation. 



If there is 20 inches of rain-fall during the year, then with 

 proper spouting and cistern room, the above mentioned roof or area 

 would furnish during the year 12,000 gallons of water. 



An inch of rain over an acre of 4,840 square yards being 22,622 

 gallons to the acre, it is a matter of some interest to get at the 

 approximate quantity required for irrigating. 



As I find that usually, even in a dry season, after 2 inches of rain 

 have fallen, the land can be ploughed, I have suggested that 50,000 

 (fifty thousand) gallons be accepted as an estimate, the quantity 

 required for irrigating an acre of land once. 



Of course more or less water will be required according to the 

 nature or staple of the soil, its dryness and powers of absorption. 

 But still it is well to have a definite or approximate standard of 

 measurement as to the quantity of water required, to be delivered by 

 a pipe or furrow, or, it may be pumped for irrigation. 



In Spain the regulation quantity of water for one irrigation is 

 2| inches. This would be 52,210 gallons per acre. 



It has been found in practice that one good watering is much 

 better than two or three light ones. For unless the water soaks some 

 way into the ground, it does not enable the crop to feed on the plant 

 food in the soil. If only a little below the surface is kept moist, the 

 roots of the plants will be encouraged to grow near the surface and 

 suffer from the heat and drought, instead of penetrating deep into 

 the soil and sub-soil. 



Measuring the delivery of water as to quantity supplied in a 

 given time, has been a question of some consideration, enquiry, and 

 experiment. 



