OF WATERING PLANTS. 141 



in order that the water may the more easily penetrate to 

 the roots of the grass. 



Emily. The trenches are, I suppose, left open in or- 

 der that the water may derive the benefit of exposure to 

 the air ? 



Mrs. B. They are sometimes buried in the soil, and 

 at others left open. The first have the advantage of econ- 

 omising the soil, as the ground above them may be cul- 

 tivated ; loss is also prevented by evaporation ; yet I 

 prefer the open trenches, both on account of exposure 

 to the air and as affording facility for repairs, which are 

 often required. 



3dly. Watering by irrigation consists in conveying 

 the fluid through small channels similar to those used for 

 watering by filtration, but which are made, at pleasure, to 

 overflow the adjacent ground. In order to accomplish 

 this, it is necessary to be furnished with an ample supply 

 of water ; if it can be obtained from a superior elevation 

 the operation is greatly facilitated. When, on the con- 

 trary, it is necessary to raise it from rivers or wells, vari- 

 ous mechanical means may be resorted to. The current 

 of a river may be used to turn a wheel furnished with small 

 buckets, which, during one revolution of the wheel, fill 

 with water, raise it, and pour it into the reservoir prepared 

 to supply the rivulets of irrigation : when there is no 

 current, horses may be employed to turn the wheel. 



The hydraulic ram is another mode of raising water. 

 M. De Candolle mentioned one, which, put in motion 

 by a fall of water of twenty feet, raises a body of eight 

 cubic feet per minute to the height of one hundred and 

 sixty feet. 



Emily. I should think a steam-engine would afford 

 the most effectual means of raising water ; is it not used 

 for this purpose ? 



Mrs. B. Very frequently, for draining mines ; but it 

 would, I conceive, be too expensive a mode of raising 

 water for the purpose of agriculture ; at least, I never 

 heard of it being so applied. 



It is to be regretted that the rain water which is wash- 



784. What does Mrs. B. say of the two kinds of trenqhes used for 

 filtration! 785. In what does watering by filtration consist! 786. 

 How may water be raised from a river for filtration! 787. What ia 

 the mode of raising it mentioned by Candolle! 788. Why may not 

 the steam engine be used! 



