142 ON THE ARTIFICIAL MODES 



ed down from the roofs of houses should not be turned 

 to account ; soiled as it is by this operation, it would but 

 be the better calculated for the nourishment of plants ; 

 and it might easily be collected into a reservoir, instead 

 of being carried off, as it usually is, by the common sewer. 



It is singular that we should have first learnt artificial 

 modes of watering from the Moors of Spain ; their labors 

 in that department were very extensive. Near Alicant 

 they constructed a wall between two hills in order to re- 

 tain the water which flowed through the valley, for the 

 purpose of irrigating the adjacent country. This wall, 

 which is still in existence, is only twenty-four feet in 

 length at the base, this being the breadth of the valley ; 

 but the hills receding as they rise, it is two hundred and 

 sixty feet long at the top, and sixty-seven feet in depth ; 

 which is much more than is required to withstand the 

 force of the waters it confines ; but the Moors were not 

 versed in the laws of hydraulics. 



There are various modes of irrigation : the inundations 

 are sometimes flowing, sometimes stagnant ; sometimes 

 stransitory, at other times permanent, according to the 

 nature of the culture. Of the latter description are the 

 rice plantations : this plant requires such abundance of 

 water, that the inundation is drawn off only when the 

 grain begins to ripen. 



Emily. I remember, in Lombardy, seeing the green 

 tops of the rice peeping through their watery bath, and 

 looking not very unlike the green scum which frequent- 

 ly covers pools of stagnant water. Nor does it appear to 

 be less pernicious ; for I have heard that the cultivators 

 of these rice fields are often afflicted with a frightful cuta- 

 neous disease, which terminates frequently in madness 

 and self-destruction. 



Mrs. B. The cultivation of rice is certainly not a 

 healthy employment, owing to the stagnant waters in 

 which it is raised ; but the disease to which you allude, 

 called the Pelagra, is supposed to proceed from feeding 

 on maize, or Indian corn, improperly prepared. The ori- 



789. What does Mrs. B. say of the rain water which falls on the roofs 

 of houses'? 790. From what was learnt the artificial modes of water- 

 ing! 791. What account is given of a wall constructed for this pur- 

 pose near Alicantl 792. What are the various modes of irrigation. 

 793. What does Emily say she has seen in Lombardyl 794. From 

 what proceeds the disease called Pelagra 1 



