662 



PRACTICE OF AGRICULTURE. 



Part III. 



nature before floating, it is not necessary that it should be thrown up into high beds, but 

 merely as much inclined as will give the water a current. 



4103. Inclined planes are absolutely necessary for the purpose of irrigation^ To form 

 these between straight and parallel lines, it is necessary to dig away land where it is too 

 high, and move it to those places where it is too low, to make such an uniformity of sur- 

 face. The new made ground will of course settle in hollows proportioned to the depth 

 of loose matter which has been recently put together, but this settlement will not take 

 place until the new soil has been completely soaked and dried again ; therefore these de- 

 fects cannot be remedied before the second or third year of watering : it will then require 

 more skill to manage a water meadow for the three or four first years, than it can after- 

 wards. 



4104. Properly to construct a water meadow is much more difficult than is commonly 

 imagined. It is no easy task to give an irregular surface that regular yet various figure 

 which shall be fit for the overflowing of water. It is very necessary for the operator to 

 have just ideas of levels, lines, and angles ; a knowledge of superficial forms will not be 

 suflftcient; accurate notions of solid 529 



geometry (obtained from theory or prac- 

 tice) are absolutely necessary to put 

 such a surface into the form proper for 

 the reception of water without the trou- 

 ble and expense of doing much of the 

 work twice over. {Obs. on Irrigation, 



4105. jis an example of irrigating a 

 meadow from both sides of a river we 

 take the following case from Bosweil's 

 treatise. From the upper part of the 

 grounds, two main drains (fg. 529 a, a) 

 are formed at right angles to the river, 

 one running north the other south, 

 across the meadow, to within about six 

 yards of the fence ditches which sur- 

 ro.und it (6), and are used, for tail 

 drains : by means of these fence ditches the water is discharged into the river. A wear 

 erected across the river forces the water into either of the main drains, which is 

 done by shutting the other wear close. When there is not water enough, or it is not 

 convenient to water both parts of the meadow at once, by shutting close one of the 

 wears, the current is forced into that main whose wear is open, thence to be conveyed 

 through the trenches over the panes, to water that side of the meadow ; then by shutting 

 that, and opening the other, the opposite main is filled, and by means of the trenches 

 that side of the meadow is watered in the same manner ; and lastly, by shutting thera 

 both, and opening the river wear, the water flows in its usual course, and the land on both 

 sides is laid dry. From the main drains (a, a) the water flows along the highest part, or 

 crowns of the ridges in the trenches (c), and is carried ofi'to the tail drains by the trench 

 drains (rf). 



4106. As an example of an irregular surface watered from one side of a river, we shall 

 have recourse to the same author. There is a wear {fg. 530 e) erected across the river, 



and another across the head- 

 main (cr), from which proceed 

 three main and branch trenches 

 {g, g, g, and/, f), which 

 water the whole meadow. 

 There is a tail drain [b) for 

 carrying off the whole of the 

 water by means of the drain 

 trenches (d, d). The water 

 having thus passed over the 

 field, is -returned to the river 

 by the tail drain, already men- 

 tioned. When it is desired to 

 withhold the water, the wear of 

 the head main (a) is shut, and 

 that of the river (e) opened. 

 It will be observed, that in this 

 design there are branch trenches 

 {f* f)> ^^^ various gutters [h, A), taken out of the ends of some of the trenches, to carry 



