DRAINAGE. 



107 



shoe," etc., but it Is not proposed, here, to discuss their compara- 

 tive merits. Experience, in both public and private works, in 



Fig- 37- — Position of Workman and Use of Finishing Scoop. 



this country, and the cumulative testimony of English and French 

 engineers, have demonstrated that the only tile which it is eco- 

 nomical to use, are the best that can be found ; and that the 





Fig 3S. — Sighting by the Boning Rods. 



\_A and C are theboning-rods. B is the plumb-rod. A, B, C, is the line of sight (7 feet above the 

 grade). 7; y, is the line of the bottom of the drain, which will be correct when the plumb-rod, 

 standing upon any point of it, has the top of its cross-head in the line of sight, A. B, C] 



best, thus far invented — much the best, is the " pipe and collar," 

 (Fig. 39,) — or round tiles ; and these are unhesitatingly recom- 

 mended for use in all cases. Round tiles of small sizes should 

 not be laid without collars, as the ability to use these with them 

 constitutes their chief advantage. They hold them perfectly in 

 place, prevent the rattling in of loose dirt in laying, and give twice 

 the space for the entrance of water at the joints. A chief ad- 

 vantage of the larger sizes is, that they may be laid on any side 

 and thus made to fit closely, while the shrinking of the top of the 

 sole tiles (from more rapid drying in manufacture) makes it ne- 



