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a number of plants in the State with a capacity of as much as 2,500 gallons of water per minute. Such a plant, if worked to its full capacity, will give a stream equal to 5.57 second-feet. Allowing one-third for loss by seepage and evaporation, there is left 3.7 second-feet. The usual duty of water is estimated at 100 acres to the second-foot, but in new irrigation districts it very often amounts to only half as much. Even with this low estimate there should be more than 180 acres irrigated from the plant. Such a plant, it is estimated by H. M. Wilson, can be erected for $5,000; this will give a cost of $28 per acre irrigated.

For estimating the quantity of water used in irrigation, various units of measurement are employed. For bodies of standing water the cubic foot, or, where that is too small a unit, the "acre-foot" is used. The latter is the quantity of water that will cover an acre of ground 1 foot deep, or 43,560 cubic feet. The gallon is also very largely used for stationary bodies of water and for pumping plants, especially those for municipal supply. In considering flowing water some unit must be used which expresses the capacity of the stream in a given period of time. That most commonly used is the second-foot, or the number of cubic feet of water which flow by in a second of time. The "miners' inch," so generally quoted in California and Colorado, is not used in this State. In the following table are given some convertible units of measurement:

The most important element of climate in its relation to the present discussion is precipitation. In Texas the rainfall is greatest in the eastern portion of the State and decreases steadily toward the west. This decrease is at the rate of about 4 inches every 60 miles, being about 50 inches in the extreme east and 9 inches at El Paso. The