INDEX. 231 

 TABLES. 



PAGE 



1. Decimals of a foot reduced to inclies 89 



2. Areas of tile in square feet , 137 



3. Head in inches per 100 feet reduced to feet per 100 feet and feet 



per mile 137 



4. Contents of tile in one foot of length 137 



5. Cubic feet per second which must be discharged from a drain to 



relieve one acre of land of various depths of water in 24 hours. 138 



6. Limit of size of tile to grade and length 142 



7. Excavation tables 170 



ILLUSTRATIONS. 



Figure i. Section showing effect of clay subsoil upon natural drain- 

 age 21 



2 . Heaving of wet soils 33 



3 . Line of saturation between tile drains 39 



4. Natural system 43 



5 . Grouping system 44 



6 . Gridiron system 45 



7 . Double-main system 45 



8 . Single-line system 46 



9 . Water-line in retentive clay soils 48 



10. Self-reading rod 54 



11 . Levelling 56 



12. Topography from central base line. , 63 



13 . Topography by contours 69 



14. Guide-stakes and hubs 72 



15 . Profile of Main A 78 



16. Taking compass bearings 80 



17. Obtaining meridian by equal shadows of the sun. 82 



18 . Angle and drop for tile drain 88 



19. Effect of drains on open soils 90 



20. Drainage of a 40-acre field , 92 



21 . Platting compass bearings , 97 



22. Drainage plan for a farm of 160 acres of level land 99 



23. Conventional signs used to represent topography 100 



^4. Grading by gauge and line 104 



Four-inch lateral drain facing 104 



25 . Grading by sight-line and target 105 



