[415] 



SCIENTIFIC MANUAL. 



129 



point. The poles, after being adjusted to each other as ac- 

 curately as possible, should be covered with pine straw, or 

 some similar material, well packed down, to prevent fine 

 earth from passing between the poles into the duct. 



These poles, if kept constantly wet, will last twenty 

 years, but if alternately wet and dry, they decay very rap- 

 idly, but will even then maintain their integrity, and make 

 an effective drain for eight or ten years. 



Trough Drains ', where lumber is very cheap and accessi- 

 ble, answer a good purpose without foot planks, on 

 clay bottoms, or with them on soft or sandy bottoms. 



Strips one inch thick, and half of them three, and the 

 others four inches wide, nailed together, so as to form a 

 trough, which, inverted in the bottom of the ditch, forms 

 a cheap and effective drain. If the bottom of the ditch is 

 firm clay, these may rest upon the soil ; if the bottom is 

 sandy, they should rest upon a foot-plank, laid in the bot- 

 tom of the ditch. 



/ 



The figures 17 and 18 represent such a drain with and 

 without the loot-plank. 



The planks should be all of the same 

 length, but put together so that one 

 p'ank of each, 

 trough shall lap 

 six inces over that 

 on the opposite 

 side of the next. 

 (See fig. 19.) If 

 foot - planks are 



Fig. 17. 



Fig. 18. 



Fig. 19. used, the joints of the 



troughs should be placed over the centres of the former. 



Rock^drains are expensive, unless the rock is on the sur- 

 face and convenient to the proposed drain. Surface rocks 

 10 



